//! Readable behavioral projections. Selection edits the same typed records as text.
use crate::{
    app::{App, Choice, Message},
    style,
    views::{action, heading, label, short},
};
use iced::{
    Color, Element, Fill, Point, Rectangle, Renderer, Size, Theme, mouse,
    widget::{
        Action, button,
        canvas::{self, Frame, Path, Stroke, Text},
        column, container, pick_list, row, scrollable, text,
    },
};
use oa_core::*;
use std::collections::BTreeMap;
pub(crate) mod scenario;
pub(crate) mod state_canvas;
pub(crate) mod state_edit;
pub(crate) mod state_menu;
pub(crate) mod state_view;
pub(crate) mod states;
pub(crate) mod topology;
#[derive(Debug, Clone)]
pub enum Event {
    Topology(topology::Event),
    Scenario(scenario::Event),
    States(states::Event),
    Submit,
}
impl Event {
    pub fn starts_form(&self) -> bool {
        matches!(
            self,
            Self::Topology(topology::Event::Start(..))
                | Self::Scenario(scenario::Event::Start(..))
                | Self::States(states::Event::Start(..) | states::Event::Edit(..))
        )
    }
    pub fn is_submit(&self) -> bool {
        matches!(
            self,
            Self::Submit
                | Self::Topology(topology::Event::Submit)
                | Self::Scenario(scenario::Event::Submit)
                | Self::States(states::Event::Submit)
        )
    }
}
#[derive(Default)]
pub struct State {
    pub active_owner: Option<Id>,
    pub diagram: state_view::State,
    topology: topology::State,
    pub(crate) scenario: scenario::State,
    states: states::State,
}
const PENDING_DRAFT: &str = "Apply or cancel the current behavior form before starting another.";
impl State {
    pub fn has_pending(&self) -> bool {
        self.pending_owner().is_some()
    }

    pub fn pending_owner(&self) -> Option<Id> {
        self.topology
            .pending_owner()
            .or_else(|| self.scenario.pending_owner())
            .or_else(|| self.states.pending_owner())
    }

    /// Prepare the active form without discarding inputs. The caller must execute
    /// this exact command and acknowledge only a successful document transaction.
    pub fn prepare_pending(&self, p: &Project) -> Result<Option<Command>, String> {
        if self.topology.pending_owner().is_some() {
            self.topology.prepare_pending(p).map(Some)
        } else if self.scenario.pending_owner().is_some() {
            self.scenario.prepare_pending(p).map(Some)
        } else if self.states.pending_owner().is_some() {
            self.states.prepare_pending(p).map(Some)
        } else {
            Ok(None)
        }
    }

    /// Clear the active form after its prepared command commits successfully.
    /// Rejected commands must leave the form available for repair and retry.
    pub fn acknowledge_commit(&mut self) {
        self.topology.acknowledge_commit();
        self.scenario.acknowledge_commit();
        self.states.acknowledge_commit();
    }

    pub fn update(&mut self, p: &Project, event: Event) -> Result<Option<Command>, String> {
        if self.has_pending()
            && matches!(
                &event,
                Event::Topology(topology::Event::Start(..))
                    | Event::Scenario(scenario::Event::Start(..))
                    | Event::States(states::Event::Start(..) | states::Event::Edit(..))
            )
        {
            return Err(PENDING_DRAFT.into());
        }
        let cancels_pending = match &event {
            Event::Topology(topology::Event::Cancel) => self.topology.pending_owner().is_some(),
            Event::Scenario(scenario::Event::Cancel) => self.scenario.pending_owner().is_some(),
            Event::States(states::Event::Cancel) => self.states.pending_owner().is_some(),
            _ => false,
        };
        if cancels_pending {
            self.acknowledge_commit();
            return Ok(None);
        }
        match event {
            Event::Topology(event) => self.topology.update(p, event),
            Event::Scenario(event) => self.scenario.update(p, event),
            Event::States(event) => self.states.update(p, event),
            Event::Submit => self
                .prepare_pending(p)?
                .map(Some)
                .ok_or_else(|| "Choose a behavior modeling tool.".into()),
        }
    }
}

pub fn view(app: &App) -> Element<'_, Message> {
    let p = app.project();
    let choices = p
        .elements
        .values()
        .filter(|e| {
            e.layer() == app.layer && (e.kind().is_sequence() || e.kind() == Kind::StateMachine)
        })
        .map(|e| Choice {
            id: e.id,
            label: format!("{} · {}", e.kind(), e.name),
        })
        .collect::<Vec<_>>();
    let owner = selected_owner(app);
    let selected = owner
        .and_then(|id| choices.iter().find(|c| c.id == id))
        .or(choices.first())
        .cloned();
    let mut out = column![heading("Behavior & scenarios", "Follow exchanges and operating conditions. Select a message, state or transition to edit it.")].spacing(14);
    let Some(selected) = selected else {
        return out.push(label("Start with a Process, Scenario or State machine using Create element. Add occurrences or regions inside it to describe behavior.")).padding(24).into();
    };
    let e = &p.elements[&selected.id];
    if e.kind() == Kind::StateMachine {
        out = column![text("States & modes").size(20)].spacing(8);
    }
    out = out.push(
        pick_list(choices, Some(selected), Message::BehaviorOwner)
            .width(Fill)
            .text_size(13)
            .padding(10),
    );
    if matches!(e.kind(), Kind::Process | Kind::FunctionalChain) {
        return topology::view(app, e.id, out);
    }
    if e.kind() == Kind::Scenario {
        return scenario::view(app, e.id, out);
    }
    state_view::view(app, e.id, out)
}

pub fn selected_owner(app: &App) -> Option<Id> {
    let valid = |id: &Id| {
        app.project().elements.get(id).is_some_and(|e| {
            e.layer() == app.layer && (e.kind().is_sequence() || e.kind() == Kind::StateMachine)
        })
    };
    app.behavior
        .pending_owner()
        .or(app.behavior.active_owner.filter(valid))
        .or_else(|| selected_behavior(app.project(), app.selected).filter(valid))
        .or_else(|| app.project().elements.keys().find(|id| valid(id)).copied())
}
/// Mirror the core's legacy-versus-explicit process interpretation. Existing
/// exchange-only lists still describe ordered paths until explicitly migrated.
fn uses_explicit_topology(p: &Project, owner: Id) -> bool {
    let Some(e) = p.elements.get(&owner) else {
        return false;
    };
    if !matches!(e.kind(), Kind::Process | Kind::FunctionalChain) {
        return false;
    }
    p.relations.values().any(|r| {
        r.kind() == RelationKind::SequenceLink
            && p.elements.get(&r.source()).and_then(|e| e.parent) == Some(owner)
            && p.elements.get(&r.target()).and_then(|e| e.parent) == Some(owner)
    }) || e.steps().into_iter().flatten().any(|id| {
        matches!(
            p.elements.get(id).and_then(|e| e.shared()),
            Some(SharedBody::Occurrence {
                body: OccurrenceBody::Action { .. }
                    | OccurrenceBody::Control { .. }
                    | OccurrenceBody::SequenceReference { .. },
                ..
            })
        )
    })
}
pub fn selected_behavior(p: &Project, selected: Id) -> Option<Id> {
    let mut current = Some(
        p.relations
            .get(&selected)
            .filter(|r| {
                matches!(
                    r.kind(),
                    RelationKind::StateTransition | RelationKind::SequenceLink
                )
            })
            .map(|r| r.source())
            .unwrap_or(selected),
    );
    while let Some(id) = current {
        let e = p.elements.get(&id)?;
        if e.kind().is_sequence() || e.kind() == Kind::StateMachine {
            return Some(id);
        }
        current = e.parent;
    }
    None
}
fn in_machine(p: &Project, id: Id, machine: Id) -> bool {
    let mut current = Some(id);
    while let Some(id) = current {
        if id == machine {
            return true;
        }
        current = p.elements.get(&id).and_then(|e| e.parent);
    }
    false
}

struct BoxItem {
    id: Id,
    rect: Rectangle,
    title: String,
    detail: String,
    marker: Option<Kind>,
}
struct Line {
    id: Id,
    points: Vec<Point>,
    label: String,
    label_at: Point,
    dashed: bool,
}
struct Scene {
    boxes: Vec<BoxItem>,
    lines: Vec<Line>,
    size: Size,
    selected: Id,
    scale: f32,
    interaction: Option<(scenario::Context, scenario::CanvasTool, bool)>,
    lanes: BTreeMap<Id, f32>,
    slots: Vec<SequenceSlot>,
    rows: BTreeMap<Id, (Id, f32)>,
    open_calls: Vec<Point>,
}
struct SequenceSlot {
    slot: scenario::Slot,
    y: f32,
    label: String,
}
#[derive(Default)]
struct SequenceInput {
    context: Option<scenario::Context>,
    tool: scenario::CanvasTool,
    pointer: Option<Point>,
    source: Option<(Id, scenario::Slot)>,
    press: Option<SequencePress>,
}
#[derive(Clone, Copy)]
enum SequencePress {
    Message {
        source: Id,
        slot: scenario::Slot,
        start: Point,
        first: bool,
        moved: bool,
    },
    Reorder {
        occurrence: Id,
        parent: Id,
        start: Point,
        moved: bool,
    },
}
impl SequenceInput {
    fn cancel(&mut self) {
        self.source = None;
        self.press = None;
    }
}
impl Scene {
    fn sequence(p: &Project, owner: Id, selected: Id) -> Self {
        let mut scene = Self {
            scale: 1.,
            boxes: vec![],
            lines: vec![],
            size: Size::new(700., 200.),
            selected,
            interaction: None,
            lanes: BTreeMap::new(),
            slots: vec![],
            rows: BTreeMap::new(),
            open_calls: vec![],
        };
        let mut lanes = p
            .children(owner)
            .filter(|e| e.kind() == Kind::Lifeline)
            .map(|e| {
                (
                    e.id,
                    e.name.clone(),
                    match e.shared() {
                        Some(SharedBody::Lifeline {
                            represented: Some(id),
                        }) => p.named(*id).to_owned(),
                        _ => "Unassigned participant".into(),
                    },
                )
            })
            .collect::<Vec<_>>();
        let scenario = p.elements[&owner].kind() == Kind::Scenario;
        if !scenario {
            fn endpoints(p: &Project, steps: &[Id], ids: &mut Vec<Id>) {
                for id in steps {
                    if let Some(SharedBody::Occurrence { body, .. }) =
                        p.elements.get(id).and_then(|e| e.shared())
                    {
                        match body {
                            OccurrenceBody::Exchange {
                                exchange: Some(id), ..
                            } => {
                                if let Some(r) = p.relations.get(id) {
                                    for endpoint in [r.source(), r.target()] {
                                        if !ids.contains(&endpoint) {
                                            ids.push(endpoint);
                                        }
                                    }
                                }
                            }
                            OccurrenceBody::Fragment { branches, .. } => {
                                endpoints(p, branches, ids)
                            }
                            OccurrenceBody::Branch { occurrences, .. } => {
                                endpoints(p, occurrences, ids)
                            }
                            _ => {}
                        }
                    }
                }
            }
            let mut ids = vec![];
            endpoints(p, p.elements[&owner].steps().unwrap_or(&vec![]), &mut ids);
            lanes = ids
                .into_iter()
                .map(|id| {
                    (
                        id,
                        p.named(id).to_owned(),
                        p.elements
                            .get(&id)
                            .map(|e| e.kind().label())
                            .unwrap_or("Endpoint")
                            .into(),
                    )
                })
                .collect();
        }
        let lane_x = lanes
            .iter()
            .enumerate()
            .map(|(i, (id, ..))| (*id, 160. + i as f32 * 240.))
            .collect::<BTreeMap<_, _>>();
        scene.size.width = (lanes.len() as f32 * 240. + 80.).max(680.);
        if scenario {
            scene.lanes = lane_x
                .iter()
                .filter(|(id, _)| {
                    matches!(
                        p.elements.get(id).and_then(|e| e.shared()),
                        Some(SharedBody::Lifeline {
                            represented: Some(_)
                        })
                    )
                })
                .map(|(id, x)| (*id, *x))
                .collect();
        }
        let mut y = if scenario { 148. } else { 120. };
        scene.occurrences(p, owner, scenario, &lane_x, &mut y, 0);
        if scenario {
            for (&id, &(_, top)) in &scene.rows {
                let Some(SharedBody::Occurrence {
                    body:
                        OccurrenceBody::Exchange {
                            message_kind: MessageKind::Call,
                            receiver: Some(receiver),
                            ..
                        },
                    ..
                }) = p.elements[&id].shared()
                else {
                    continue;
                };
                let Some(x) = lane_x.get(receiver) else {
                    continue;
                };
                let ends: Vec<_> = scene.rows.iter().filter_map(|(reply, (_, y))| {
                    matches!(p.elements[reply].shared(), Some(SharedBody::Occurrence { body: OccurrenceBody::Exchange {
                        message_kind: MessageKind::Reply, reply_to: Some(call), .. }, .. }) if *call == id && *y > top).then_some(*y)
                }).collect();
                let bottom = ends
                    .iter()
                    .copied()
                    .max_by(f32::total_cmp)
                    .unwrap_or(top + 26.);
                scene.boxes.push(BoxItem {
                    id,
                    rect: Rectangle::new(Point::new(*x - 4., top), Size::new(8., bottom - top)),
                    title: String::new(),
                    detail: String::new(),
                    marker: None,
                });
                if ends.is_empty() {
                    scene.open_calls.push(Point::new(*x + 8., bottom - 7.));
                }
                for end in ends {
                    scene.boxes.push(BoxItem {
                        id,
                        rect: Rectangle::new(Point::new(*x - 7., end - 1.), Size::new(14., 2.)),
                        title: String::new(),
                        detail: String::new(),
                        marker: None,
                    });
                }
            }
        }
        scene.size.height = (y + 45.).max(210.);
        for (id, name, detail) in lanes {
            let x = lane_x[&id];
            scene.lines.insert(
                0,
                Line {
                    id,
                    points: vec![Point::new(x, 85.), Point::new(x, scene.size.height - 20.)],
                    label: String::new(),
                    label_at: Point::ORIGIN,
                    dashed: false,
                },
            );
            scene.boxes.push(BoxItem {
                id,
                rect: Rectangle::new(Point::new(x - 102., 15.), Size::new(204., 70.)),
                title: name,
                detail,
                marker: None,
            });
        }
        scene
    }
    fn occurrences(
        &mut self,
        p: &Project,
        owner: Id,
        scenario: bool,
        lanes: &BTreeMap<Id, f32>,
        y: &mut f32,
        depth: usize,
    ) {
        let steps = p
            .elements
            .get(&owner)
            .and_then(|e| {
                e.steps().map(Vec::as_slice).or_else(|| {
                    if let Some(SharedBody::Occurrence {
                        body: OccurrenceBody::Fragment { branches, .. },
                        ..
                    }) = e.shared()
                    {
                        Some(branches.as_slice())
                    } else {
                        None
                    }
                })
            })
            .unwrap_or(&[]);
        let ordered = p.elements.get(&owner).and_then(|e| e.steps()).is_some();
        for (index, id) in steps.iter().enumerate() {
            let Some(e) = p.elements.get(id) else {
                continue;
            };
            let Some(SharedBody::Occurrence { body, .. }) = e.shared() else {
                continue;
            };
            if ordered {
                let slot = scenario::Slot {
                    parent: owner,
                    before: Some(*id),
                };
                self.slots.push(SequenceSlot {
                    slot,
                    y: *y - 42.,
                    label: scenario::slot_label(p, slot),
                });
                self.rows.insert(*id, (owner, *y));
            }
            match body {
                OccurrenceBody::Fragment { operator, .. } => {
                    let top = *y;
                    *y += 55.;
                    self.occurrences(p, *id, scenario, lanes, y, depth + 1);
                    let rect = Rectangle::new(
                        Point::new(18. + depth as f32 * 10., top),
                        Size::new(
                            self.size.width - 36. - depth as f32 * 20.,
                            (*y - top).max(95.),
                        ),
                    );
                    self.boxes.insert(
                        0,
                        BoxItem {
                            id: *id,
                            rect,
                            title: format!("{operator:?} · {}", e.name),
                            detail: String::new(),
                            marker: Some(Kind::Occurrence),
                        },
                    );
                    *y += if scenario { 64. } else { 20. };
                }
                OccurrenceBody::Branch { guard, .. } => {
                    self.boxes.push(BoxItem {
                        id: *id,
                        rect: Rectangle::new(
                            Point::new(36. + depth as f32 * 10., *y),
                            Size::new(self.size.width - 85. - depth as f32 * 20., 43.),
                        ),
                        title: format!(
                            "[{}]",
                            if guard.is_empty() {
                                "guard not specified"
                            } else {
                                guard
                            }
                        ),
                        detail: String::new(),
                        marker: Some(Kind::Occurrence),
                    });
                    *y += if scenario { 90. } else { 62. };
                    self.occurrences(p, *id, scenario, lanes, y, depth + 1);
                }
                OccurrenceBody::Exchange {
                    exchange,
                    sender,
                    receiver,
                    message_kind,
                    ..
                } => {
                    let r = exchange.and_then(|id| p.relations.get(&id));
                    let source = if scenario {
                        *sender
                    } else {
                        r.map(|r| r.source())
                    };
                    let target = if scenario {
                        if matches!(message_kind, MessageKind::Timer { .. }) {
                            *sender
                        } else {
                            *receiver
                        }
                    } else {
                        r.map(|r| r.target())
                    };
                    if let (Some(a), Some(b)) = (
                        source.and_then(|id| lanes.get(&id)),
                        target.and_then(|id| lanes.get(&id)),
                    ) {
                        let points = if a == b {
                            vec![
                                Point::new(*a, *y),
                                Point::new(a + 75., *y),
                                Point::new(a + 75., *y + 24.),
                                Point::new(*a, *y + 24.),
                            ]
                        } else {
                            vec![Point::new(*a, *y), Point::new(*b, *y)]
                        };
                        let kind = if !scenario {
                            ""
                        } else {
                            match message_kind {
                                MessageKind::Asynchronous => "signal · ",
                                MessageKind::Call => "call · ",
                                MessageKind::Reply => "reply · ",
                                MessageKind::Create => "create · ",
                                MessageKind::Delete => "delete · ",
                                MessageKind::Timer { .. } => "timer · ",
                            }
                        };
                        let message_label = if let MessageKind::Timer { expression } = message_kind
                        {
                            expression.as_str()
                        } else {
                            r.map(|r| r.name.as_str()).unwrap_or(&e.name)
                        };
                        self.lines.push(Line {
                            id: *id,
                            points,
                            label: format!("{}. {kind}{}", index + 1, message_label),
                            label_at: Point::new(a.min(*b) + 12., *y - 26.),
                            dashed: matches!(message_kind, MessageKind::Reply),
                        });
                    } else {
                        self.boxes.push(BoxItem {
                            id: *id,
                            rect: Rectangle::new(
                                Point::new(65., *y - 20.),
                                Size::new(self.size.width - 130., 65.),
                            ),
                            title: e.name.clone(),
                            detail: "Choose an exchange and its lifelines in Properties".into(),
                            marker: None,
                        });
                    }
                    *y += 92.;
                }
                OccurrenceBody::Action { action, lifeline }
                | OccurrenceBody::State {
                    state: action,
                    lifeline,
                } => {
                    let x = lifeline
                        .and_then(|id| lanes.get(&id))
                        .copied()
                        .unwrap_or(180.);
                    self.boxes.push(BoxItem {
                        id: *id,
                        rect: Rectangle::new(Point::new(x - 110., *y - 20.), Size::new(220., 70.)),
                        title: e.name.clone(),
                        detail: action
                            .map(|id| p.named(id).to_owned())
                            .unwrap_or("Choose observed behavior".into()),
                        marker: None,
                    });
                    *y += 95.;
                }
                OccurrenceBody::Control { kind } => {
                    self.boxes.push(BoxItem {
                        id: *id,
                        rect: Rectangle::new(Point::new(65., *y - 20.), Size::new(240., 70.)),
                        title: format!("{kind:?} · {}", e.name),
                        detail: "Contextual process control".into(),
                        marker: None,
                    });
                    *y += 95.;
                }
                OccurrenceBody::SequenceReference { sequence } => {
                    self.boxes.push(BoxItem {
                        id: *id,
                        rect: Rectangle::new(Point::new(65., *y - 20.), Size::new(280., 70.)),
                        title: e.name.clone(),
                        detail: sequence
                            .map(|id| format!("Use {}", p.named(id)))
                            .unwrap_or("Choose a reusable process or chain".into()),
                        marker: None,
                    });
                    *y += 95.;
                }
                OccurrenceBody::ScenarioUse { scenario, bindings } => {
                    self.boxes.push(BoxItem {
                        id: *id,
                        rect: Rectangle::new(
                            Point::new(65., *y - 20.),
                            Size::new(self.size.width - 130., 70.),
                        ),
                        title: format!("ref · {}", e.name),
                        detail: scenario
                            .map(|id| {
                                format!(
                                    "{} · {} explicit lifeline bindings",
                                    p.named(id),
                                    bindings.len()
                                )
                            })
                            .unwrap_or("Choose a scenario".into()),
                        marker: Some(Kind::Occurrence),
                    });
                    *y += 95.;
                }
            }
        }
        if ordered {
            let slot = scenario::Slot {
                parent: owner,
                before: None,
            };
            self.slots.push(SequenceSlot {
                slot,
                y: *y - 42.,
                label: scenario::slot_label(p, slot),
            });
        }
    }
    fn slot_at(&self, point: Point, parent: Option<Id>) -> Option<&SequenceSlot> {
        self.slots
            .iter()
            .min_by(|a, b| (a.y - point.y).abs().total_cmp(&(b.y - point.y).abs()))
            .filter(|slot| parent.is_none_or(|id| id == slot.slot.parent))
    }
    fn lane_at(&self, point: Point) -> Option<Id> {
        if let Some(header) = self
            .boxes
            .iter()
            .find(|b| self.lanes.contains_key(&b.id) && b.rect.contains(point))
        {
            return Some(header.id);
        }
        self.lanes
            .iter()
            .filter(|(_, x)| (**x - point.x).abs() < 12. / self.scale)
            .min_by(|a, b| (a.1 - point.x).abs().total_cmp(&(b.1 - point.x).abs()))
            .map(|(id, _)| *id)
    }
    fn reorder_handle(&self) -> Option<Rectangle> {
        let (_, y) = self.rows.get(&self.selected)?;
        Some(Rectangle::new(
            Point::new(6., *y - 12.),
            Size::new(22., 24.),
        ))
    }
    fn hit(&self, point: Point) -> Option<Id> {
        self.boxes
            .iter()
            .rev()
            .find(|b| {
                !b.title.is_empty()
                    && b.rect.contains(point)
                    && (b.marker != Some(Kind::Occurrence) || point.y < b.rect.y + 38.)
            })
            .map(|b| b.id)
            .or_else(|| {
                self.lines
                    .iter()
                    .find(|line| {
                        !line.label.is_empty()
                            && (Rectangle::new(
                                line.label_at,
                                Size::new(
                                    (line.label.chars().count() as f32 * 6.8 + 8.).min(225.),
                                    25.,
                                ),
                            )
                            .contains(point)
                                || line.points.windows(2).any(|p| {
                                    crate::diagram::distance_to_segment(point, p[0], p[1])
                                        < 8. / self.scale
                                }))
                    })
                    .map(|line| line.id)
            })
            .or_else(|| {
                self.boxes
                    .iter()
                    .rev()
                    .find(|b| b.rect.contains(point) && b.title.is_empty())
                    .map(|b| b.id)
            })
            .or_else(|| self.lane_at(point))
            .or_else(|| {
                self.lines
                    .iter()
                    .find(|line| {
                        line.label.is_empty()
                            && line.points.windows(2).any(|p| {
                                crate::diagram::distance_to_segment(point, p[0], p[1])
                                    < 8. / self.scale
                            })
                    })
                    .map(|line| line.id)
            })
    }
}
impl canvas::Program<Message> for Scene {
    type State = SequenceInput;
    fn update(
        &self,
        state: &mut SequenceInput,
        event: &canvas::Event,
        bounds: Rectangle,
        cursor: mouse::Cursor,
    ) -> Option<Action<Message>> {
        use scenario::{CanvasEvent, CanvasTool};
        let (context, tool, editable) = self
            .interaction
            .map_or((None, CanvasTool::Select, false), |(c, t, e)| {
                (Some(c), t, e)
            });
        if state.context != context || state.tool != tool {
            state.cancel();
            state.pointer = None;
            state.context = context;
            state.tool = tool;
        }
        if !editable {
            state.cancel();
        }
        // Scrollable marks a pointer outside its visible viewport unavailable,
        // even when it lies inside the full (scrolled) canvas rectangle.
        let visible = cursor.position().is_some();
        if !visible
            && matches!(
                event,
                canvas::Event::Mouse(mouse::Event::ButtonReleased(mouse::Button::Left))
            )
        {
            state.cancel();
            return Some(Action::request_redraw());
        }
        let cursor = match event {
            canvas::Event::Mouse(mouse::Event::CursorMoved { position }) => {
                state.pointer = Some(*position);
                if let Some(press) = &mut state.press {
                    match press {
                        SequencePress::Message { start, moved, .. }
                        | SequencePress::Reorder { start, moved, .. } => {
                            *moved |= position.distance(*start) >= 3.
                        }
                    }
                }
                mouse::Cursor::Available(*position)
            }
            canvas::Event::Mouse(mouse::Event::CursorLeft)
            | canvas::Event::Window(iced::window::Event::Unfocused) => {
                state.cancel();
                state.pointer = None;
                return Some(Action::request_redraw());
            }
            canvas::Event::Mouse(
                mouse::Event::ButtonPressed(_) | mouse::Event::ButtonReleased(_),
            ) => state.pointer.map_or(cursor, mouse::Cursor::Available),
            canvas::Event::Window(iced::window::Event::RedrawRequested(_)) => {
                state.pointer = cursor.position();
                cursor
            }
            canvas::Event::Keyboard(iced::keyboard::Event::KeyPressed {
                key: iced::keyboard::Key::Named(iced::keyboard::key::Named::Escape),
                ..
            }) if state.source.is_some() || state.press.is_some() => {
                state.cancel();
                return Some(Action::request_redraw().and_capture());
            }
            _ => cursor,
        };
        let world = cursor
            .position_in(bounds)
            .map(|p| Point::new(p.x / self.scale, p.y / self.scale));
        match event {
            canvas::Event::Mouse(mouse::Event::ButtonPressed(mouse::Button::Left)) => {
                if !visible {
                    return None;
                }
                let point = world?;
                if let Some(context) = context {
                    if !editable {
                        return None;
                    }
                    if let CanvasTool::Message(_) = tool {
                        let first = state.source.is_none();
                        let (source, slot) = state.source.or_else(|| {
                            Some((self.lane_at(point)?, self.slot_at(point, None)?.slot))
                        })?;
                        state.source = Some((source, slot));
                        state.press = Some(SequencePress::Message {
                            source,
                            slot,
                            start: cursor.position()?,
                            first,
                            moved: false,
                        });
                        return Some(Action::request_redraw().and_capture());
                    }
                    if self.reorder_handle().is_some_and(|r| r.contains(point)) {
                        state.press = Some(SequencePress::Reorder {
                            occurrence: self.selected,
                            parent: self.rows[&self.selected].0,
                            start: cursor.position()?,
                            moved: false,
                        });
                        return Some(Action::request_redraw().and_capture());
                    }
                    return self.hit(point).map(|id| {
                        Action::publish(Message::ScenarioCanvas(CanvasEvent::Select(context, id)))
                            .and_capture()
                    });
                }
                self.hit(point)
                    .map(|id| Action::publish(Message::Select(id)).and_capture())
            }
            canvas::Event::Mouse(mouse::Event::ButtonReleased(mouse::Button::Left)) => {
                let press = state.press.take()?;
                let context = context?;
                match press {
                    SequencePress::Message { source, slot, .. }
                        if tool == CanvasTool::Message(scenario::MessageStyle::Timer)
                            && world.is_some() =>
                    {
                        state.cancel();
                        return Some(
                            Action::publish(Message::ScenarioCanvas(CanvasEvent::Begin {
                                context,
                                slot,
                                sender: source,
                                receiver: source,
                                style: scenario::MessageStyle::Timer,
                            }))
                            .and_capture(),
                        );
                    }
                    SequencePress::Message {
                        source,
                        slot,
                        first,
                        moved,
                        ..
                    } if moved || !first => {
                        if let Some(receiver) = world.and_then(|p| self.lane_at(p)) {
                            let CanvasTool::Message(style) = tool else {
                                return None;
                            };
                            state.cancel();
                            return Some(
                                Action::publish(Message::ScenarioCanvas(CanvasEvent::Begin {
                                    context,
                                    slot,
                                    sender: source,
                                    receiver,
                                    style,
                                }))
                                .and_capture(),
                            );
                        }
                    }
                    SequencePress::Reorder {
                        occurrence,
                        parent,
                        moved: true,
                        ..
                    } => {
                        if let Some(slot) = world.and_then(|p| self.slot_at(p, Some(parent))) {
                            return Some(
                                Action::publish(Message::ScenarioCanvas(CanvasEvent::Reorder {
                                    context,
                                    occurrence,
                                    slot: slot.slot,
                                }))
                                .and_capture(),
                            );
                        }
                    }
                    _ => {}
                }
                Some(Action::request_redraw().and_capture())
            }
            canvas::Event::Mouse(mouse::Event::CursorMoved { .. }) if context.is_some() => {
                Some(Action::request_redraw())
            }
            _ => None,
        }
    }
    fn draw(
        &self,
        state: &SequenceInput,
        renderer: &Renderer,
        _: &Theme,
        bounds: Rectangle,
        cursor: mouse::Cursor,
    ) -> Vec<canvas::Geometry> {
        let mut f = Frame::new(renderer, bounds.size());
        f.fill_rectangle(Point::ORIGIN, bounds.size(), Color::WHITE);
        f.scale(self.scale);
        for b in &self.boxes {
            let outline = matches!(
                b.marker,
                Some(Kind::Region | Kind::StateMachine | Kind::Occurrence)
            );
            let color = if b.id == self.selected {
                style::TEAL
            } else {
                style::LINE
            };
            if outline {
                f.stroke(
                    &Path::rectangle(b.rect.position(), b.rect.size()),
                    Stroke::default().with_color(color),
                );
            } else {
                let path = Path::rounded_rectangle(b.rect.position(), b.rect.size(), 8.into());
                f.fill(&path, Color::from_rgb8(243, 248, 248));
                f.stroke(
                    &path,
                    Stroke::default()
                        .with_color(color)
                        .with_width(if b.id == self.selected { 2.5 } else { 1. }),
                );
            }
        }
        for l in &self.lines {
            let color = if l.id == self.selected {
                style::TEAL
            } else {
                style::MUTED
            };
            f.stroke(
                &Path::new(|p| {
                    p.move_to(l.points[0]);
                    for point in &l.points[1..] {
                        p.line_to(*point);
                    }
                }),
                Stroke {
                    line_dash: canvas::LineDash {
                        segments: if l.dashed { &[6., 4.] } else { &[] },
                        offset: 0,
                    },
                    ..Stroke::default()
                        .with_color(color)
                        .with_width(if l.id == self.selected { 2.5 } else { 1.2 })
                },
            );
            if !l.label.is_empty() {
                let end = l.points[l.points.len() - 1];
                let prev = l.points[l.points.len() - 2];
                let delta = end - prev;
                let len = (delta.x * delta.x + delta.y * delta.y).sqrt().max(1.);
                let d = delta / len;
                f.stroke(
                    &Path::new(|p| {
                        p.move_to(end - d * 9. + iced::Vector::new(-d.y, d.x) * 4.);
                        p.line_to(end);
                        p.line_to(end - d * 9. - iced::Vector::new(-d.y, d.x) * 4.);
                    }),
                    Stroke::default().with_color(color),
                );
                f.fill_rectangle(
                    l.label_at,
                    Size::new((l.label.chars().count() as f32 * 6.8 + 8.).min(225.), 22.),
                    Color::WHITE,
                );
                f.fill_text(Text {
                    content: short(&l.label, 32),
                    position: l.label_at,
                    color,
                    size: 12.into(),
                    ..Default::default()
                });
            }
        }
        for b in &self.boxes {
            f.fill_text(Text {
                content: short(&b.title, ((b.rect.width - 25.) / 7.) as usize),
                position: Point::new(b.rect.x + 12., b.rect.y + 12.),
                size: 13.into(),
                color: if b.id == self.selected {
                    style::TEAL
                } else {
                    style::INK
                },
                ..Default::default()
            });
            if !b.detail.is_empty() {
                f.fill_text(Text {
                    content: short(&b.detail, ((b.rect.width - 25.) / 6.) as usize),
                    position: Point::new(b.rect.x + 12., b.rect.y + 39.),
                    size: 11.into(),
                    color: style::MUTED,
                    ..Default::default()
                });
            }
        }
        for point in &self.open_calls {
            f.fill_text(Text {
                content: "…".into(),
                position: *point,
                size: 11.into(),
                color: style::MUTED,
                ..Default::default()
            });
        }
        if let Some((context, tool, true)) = self.interaction {
            let active = state.context == Some(context) && state.tool == tool;
            let point = cursor
                .position_in(bounds)
                .map(|p| Point::new(p.x / self.scale, p.y / self.scale));
            let source = active.then_some(state.source).flatten();
            let reorder = active.then_some(state.press).flatten().and_then(|press| {
                if let SequencePress::Reorder { parent, .. } = press {
                    Some(parent)
                } else {
                    None
                }
            });
            if tool == scenario::CanvasTool::Select
                && let Some(handle) = self.reorder_handle()
            {
                f.fill_rectangle(handle.position(), handle.size(), style::TEAL);
                f.fill_text(Text {
                    content: "↕".into(),
                    position: handle.position() + iced::Vector::new(5., 2.),
                    size: 16.into(),
                    color: Color::WHITE,
                    ..Default::default()
                });
            }
            let slot = if let Some((_, slot)) = source {
                self.slots.iter().find(|s| s.slot == slot)
            } else if matches!(tool, scenario::CanvasTool::Message(_)) || reorder.is_some() {
                point.and_then(|p| self.slot_at(p, reorder))
            } else {
                None
            };
            if let Some(slot) = slot {
                f.stroke(
                    &Path::line(
                        Point::new(32., slot.y),
                        Point::new(self.size.width - 24., slot.y),
                    ),
                    Stroke::default().with_color(style::TEAL).with_width(1.5),
                );
                f.fill_rectangle(
                    Point::new(34., slot.y - 20.),
                    Size::new((self.size.width - 70.).min(650.), 19.),
                    Color::WHITE,
                );
                f.fill_text(Text {
                    content: short(&format!("Insert: {}", slot.label), 88),
                    position: Point::new(38., slot.y - 19.),
                    size: 11.into(),
                    color: style::TEAL,
                    ..Default::default()
                });
                if let Some((source, _)) = source
                    && let Some(x) = self.lanes.get(&source)
                    && let Some(point) = point
                {
                    let to = self
                        .lane_at(point)
                        .and_then(|id| self.lanes.get(&id))
                        .copied()
                        .unwrap_or(point.x);
                    f.stroke(
                        &Path::line(Point::new(*x, slot.y), Point::new(to, slot.y)),
                        Stroke::default().with_color(style::TEAL).with_width(3.),
                    );
                    f.fill(&Path::circle(Point::new(to, slot.y), 5.), style::TEAL);
                }
            }
        }
        vec![f.into_geometry()]
    }
    fn mouse_interaction(
        &self,
        _: &SequenceInput,
        bounds: Rectangle,
        cursor: mouse::Cursor,
    ) -> mouse::Interaction {
        if cursor.is_over(bounds) {
            mouse::Interaction::Pointer
        } else {
            mouse::Interaction::default()
        }
    }
}

#[cfg(test)]
mod direct_canvas_tests {
    use super::*;
    use scenario::{CanvasEvent, CanvasTool, MessageStyle};
    fn scene() -> (scenario::direct_tests::Fixture, Scene) {
        let f = scenario::direct_tests::fixture();
        let mut scene = Scene::sequence(&f.project, f.owner, f.call);
        scene.interaction = Some((
            scenario::direct_tests::context(f.owner),
            CanvasTool::Message(MessageStyle::CallReply),
            true,
        ));
        (f, scene)
    }
    fn send(
        scene: &Scene,
        state: &mut SequenceInput,
        event: mouse::Event,
        final_cursor: Point,
        bounds: Rectangle,
    ) -> Option<CanvasEvent> {
        canvas::Program::update(
            scene,
            state,
            &canvas::Event::Mouse(event),
            bounds,
            mouse::Cursor::Available(final_cursor),
        )
        .and_then(|action| action.into_inner().0)
        .and_then(|message| {
            if let Message::ScenarioCanvas(event) = message {
                Some(event)
            } else {
                None
            }
        })
    }
    #[test]
    fn direct_drag_and_click_click_use_ordered_sources_and_publish_once() {
        for drag in [false, true] {
            let (f, scene) = scene();
            let mut state = SequenceInput::default();
            let bounds = Rectangle::new(Point::new(30., 50.), scene.size);
            let a = Point::new(
                bounds.x + scene.lanes[&f.sender],
                bounds.y + scene.slots[0].y,
            );
            let b = Point::new(bounds.x + scene.lanes[&f.receiver], a.y);
            send(
                &scene,
                &mut state,
                mouse::Event::CursorMoved { position: a },
                b,
                bounds,
            );
            assert!(
                send(
                    &scene,
                    &mut state,
                    mouse::Event::ButtonPressed(mouse::Button::Left),
                    b,
                    bounds
                )
                .is_none()
            );
            if !drag {
                assert!(
                    send(
                        &scene,
                        &mut state,
                        mouse::Event::ButtonReleased(mouse::Button::Left),
                        b,
                        bounds
                    )
                    .is_none()
                );
                assert_eq!(state.source.unwrap().0, f.sender);
            }
            send(
                &scene,
                &mut state,
                mouse::Event::CursorMoved { position: b },
                b,
                bounds,
            );
            if !drag {
                send(
                    &scene,
                    &mut state,
                    mouse::Event::ButtonPressed(mouse::Button::Left),
                    b,
                    bounds,
                );
            }
            let result = send(
                &scene,
                &mut state,
                mouse::Event::ButtonReleased(mouse::Button::Left),
                b,
                bounds,
            );
            assert!(
                matches!(result, Some(CanvasEvent::Begin { sender, receiver, slot, .. }) if sender == f.sender && receiver == f.receiver && slot.before == Some(f.call))
            );
            assert!(
                send(
                    &scene,
                    &mut state,
                    mouse::Event::ButtonReleased(mouse::Button::Left),
                    b,
                    bounds
                )
                .is_none()
            );
            assert!(state.source.is_none() && state.press.is_none());
        }
    }
    #[test]
    fn direct_scroll_origin_changes_do_not_create_motion_and_unavailable_release_cancels() {
        let (f, scene) = scene();
        let mut state = SequenceInput::default();
        let bounds = Rectangle::new(Point::new(20., 70.), scene.size);
        let at = Point::new(
            bounds.x + scene.lanes[&f.sender],
            bounds.y + scene.slots[0].y,
        );
        send(
            &scene,
            &mut state,
            mouse::Event::CursorMoved { position: at },
            at,
            bounds,
        );
        send(
            &scene,
            &mut state,
            mouse::Event::ButtonPressed(mouse::Button::Left),
            at,
            bounds,
        );
        let shifted = Rectangle::new(
            bounds.position() - iced::Vector::new(15., 32.),
            bounds.size(),
        );
        assert!(
            send(
                &scene,
                &mut state,
                mouse::Event::ButtonReleased(mouse::Button::Left),
                at,
                shifted
            )
            .is_none()
        );
        assert!(
            state.source.is_some(),
            "stationary first click only arms its source"
        );
        canvas::Program::update(
            &scene,
            &mut state,
            &canvas::Event::Mouse(mouse::Event::ButtonReleased(mouse::Button::Left)),
            shifted,
            mouse::Cursor::Unavailable,
        );
        assert!(state.source.is_none());
    }
    #[test]
    fn direct_context_escape_unfocus_and_pending_form_cancel_gestures() {
        for cancellation in 0..5 {
            let (f, mut scene) = scene();
            let mut state = SequenceInput::default();
            let bounds = Rectangle::new(Point::ORIGIN, scene.size);
            let a = Point::new(scene.lanes[&f.sender], scene.slots[0].y);
            let b = Point::new(scene.lanes[&f.receiver], a.y);
            send(
                &scene,
                &mut state,
                mouse::Event::CursorMoved { position: a },
                a,
                bounds,
            );
            send(
                &scene,
                &mut state,
                mouse::Event::ButtonPressed(mouse::Button::Left),
                a,
                bounds,
            );
            send(
                &scene,
                &mut state,
                mouse::Event::CursorMoved { position: b },
                b,
                bounds,
            );
            match cancellation {
                0 => {
                    scene.interaction.as_mut().unwrap().0.revision += 1;
                }
                1 => {
                    scene.interaction.as_mut().unwrap().1 = CanvasTool::Select;
                }
                2 => {
                    scene.interaction.as_mut().unwrap().2 = false;
                }
                3 => {
                    canvas::Program::update(
                        &scene,
                        &mut state,
                        &canvas::Event::Window(iced::window::Event::Unfocused),
                        bounds,
                        mouse::Cursor::Unavailable,
                    );
                }
                _ => {
                    canvas::Program::update(
                        &scene,
                        &mut state,
                        &canvas::Event::Keyboard(iced::keyboard::Event::KeyPressed {
                            key: iced::keyboard::Key::Named(iced::keyboard::key::Named::Escape),
                            modified_key: iced::keyboard::Key::Named(
                                iced::keyboard::key::Named::Escape,
                            ),
                            physical_key: iced::keyboard::key::Physical::Code(
                                iced::keyboard::key::Code::Escape,
                            ),
                            location: iced::keyboard::Location::Standard,
                            modifiers: iced::keyboard::Modifiers::empty(),
                            text: None,
                            repeat: false,
                        }),
                        bounds,
                        mouse::Cursor::Available(b),
                    );
                }
            }
            assert!(
                send(
                    &scene,
                    &mut state,
                    mouse::Event::ButtonReleased(mouse::Button::Left),
                    b,
                    bounds
                )
                .is_none()
            );
            assert!(state.press.is_none() && state.source.is_none());
        }
    }
    #[test]
    fn direct_selected_handle_reorders_and_hits_keep_semantic_identity() {
        let (f, mut scene) = scene();
        scene.interaction.as_mut().unwrap().1 = CanvasTool::Select;
        let bounds = Rectangle::new(Point::ORIGIN, scene.size);
        let header = scene
            .boxes
            .iter()
            .find(|b| b.id == f.sender)
            .unwrap()
            .rect
            .center();
        assert_eq!(scene.hit(header), Some(f.sender));
        assert_eq!(
            scene.hit(Point::new(scene.lanes[&f.sender], scene.size.height - 28.)),
            Some(f.sender)
        );
        let line = scene.lines.iter().find(|line| line.id == f.reply).unwrap();
        assert_eq!(
            scene.hit(line.label_at + iced::Vector::new(4., 4.)),
            Some(f.reply)
        );
        let mut state = SequenceInput::default();
        let start = scene.reorder_handle().unwrap().center();
        let end = Point::new(start.x, scene.slots.last().unwrap().y);
        send(
            &scene,
            &mut state,
            mouse::Event::CursorMoved { position: start },
            start,
            bounds,
        );
        send(
            &scene,
            &mut state,
            mouse::Event::ButtonPressed(mouse::Button::Left),
            start,
            bounds,
        );
        send(
            &scene,
            &mut state,
            mouse::Event::CursorMoved { position: end },
            end,
            bounds,
        );
        assert!(
            matches!(send(&scene, &mut state, mouse::Event::ButtonReleased(mouse::Button::Left), end, bounds), Some(CanvasEvent::Reorder { occurrence, slot, .. }) if occurrence == f.call && slot.parent == f.owner && slot.before.is_none())
        );
    }
    #[test]
    fn direct_execution_span_ends_at_its_correlated_reply_and_marks_an_open_call() {
        let (f, scene) = scene();
        let bar = scene
            .boxes
            .iter()
            .find(|b| b.id == f.call && b.rect.width == 8.)
            .unwrap();
        assert_eq!(bar.rect.y + bar.rect.height, scene.rows[&f.reply].1);
        assert!(scene.open_calls.is_empty());
        let p = execute_batch(&f.project, &[Command::Delete(f.reply)]).unwrap();
        let scene = Scene::sequence(&p, f.owner, f.call);
        assert_eq!(scene.open_calls.len(), 1);
        assert_eq!(
            scene
                .boxes
                .iter()
                .find(|b| b.id == f.call && b.rect.width == 8.)
                .unwrap()
                .rect
                .height,
            26.
        );
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::document::{Document, DocumentError};
    use oa_core::source_project::{self, ProjectLimits};

    #[test]
    fn one_behavior_form_survives_start_edit_and_unrelated_cancel_until_commit() {
        let p = Project::demo();
        let owner = |kind| p.elements.values().find(|e| e.kind() == kind).unwrap().id;
        let process = owner(Kind::Process);
        let scenario = owner(Kind::Scenario);
        let machine = owner(Kind::StateMachine);
        let transition = p
            .relations
            .values()
            .find(|r| r.kind() == RelationKind::StateTransition)
            .unwrap()
            .id;
        let starts = [
            Event::Topology(topology::Event::Start(
                process,
                topology::Tool::Control,
                None,
            )),
            Event::Scenario(scenario::Event::Start(scenario, scenario::Tool::Fragment)),
            Event::States(states::Event::Start(machine, states::Tool::Region, machine)),
        ];
        let names = [
            Event::Topology(topology::Event::Name("Keep this draft".into())),
            Event::Scenario(scenario::Event::Name("Keep this draft".into())),
            Event::States(states::Event::Name("Keep this draft".into())),
        ];
        let cancels = [
            Event::Topology(topology::Event::Cancel),
            Event::Scenario(scenario::Event::Cancel),
            Event::States(states::Event::Cancel),
        ];
        for (index, expected_owner) in [process, scenario, machine].into_iter().enumerate() {
            let mut state = State::default();
            assert!(!state.has_pending());
            assert!(state.prepare_pending(&p).unwrap().is_none());
            state.update(&p, starts[index].clone()).unwrap();
            state.update(&p, names[index].clone()).unwrap();
            if index == 1 {
                state
                    .update(
                        &p,
                        Event::Scenario(scenario::Event::Expression("approved".into())),
                    )
                    .unwrap();
            }
            assert_eq!(state.pending_owner(), Some(expected_owner));
            for replacement in starts
                .iter()
                .cloned()
                .chain([Event::States(states::Event::Edit(transition))])
            {
                assert_eq!(state.update(&p, replacement).unwrap_err(), PENDING_DRAFT);
                assert_eq!(state.pending_owner(), Some(expected_owner));
            }
            state.update(&p, cancels[(index + 1) % 3].clone()).unwrap();
            assert!(state.has_pending(), "Another editor's cancel is stale");
            let command = state.update(&p, Event::Submit).unwrap().unwrap();
            assert!(state.has_pending(), "Preparation must retain the form");
            let expected = execute_batch(&p, std::slice::from_ref(&command)).unwrap();
            assert!(expected.elements.values().any(|e| {
                !p.elements.contains_key(&e.id)
                    && e.name == "Keep this draft"
                    && e.parent == Some(expected_owner)
            }));
            let mut document = Document::from_project(p.clone(), ProjectLimits::default()).unwrap();
            document.execute(command).unwrap();
            assert_eq!(document.project(), &expected);
            state.acknowledge_commit();
            assert!(!state.has_pending());
            assert!(state.prepare_pending(document.project()).unwrap().is_none());
            assert_eq!(document.revision(), 1);
            assert!(document.undo());
            assert_eq!(document.project(), &p);
            assert!(!document.can_undo());

            state.update(&p, starts[index].clone()).unwrap();
            state.update(&p, cancels[index].clone()).unwrap();
            assert!(!state.has_pending(), "Explicit cancel discards this form");
            state.update(&p, starts[(index + 1) % 3].clone()).unwrap();
        }
    }

    #[test]
    fn failed_document_commit_retains_typed_transition_and_time_event_for_repair() {
        let mut p = Project::empty();
        let owner = p
            .add_element(Kind::System, Layer::Sa, "System", None)
            .unwrap();
        let machine = p
            .add_element(Kind::StateMachine, Layer::Sa, "Modes", Some(owner))
            .unwrap();
        let region = p
            .add_element(Kind::Region, Layer::Sa, "Region", Some(machine))
            .unwrap();
        let source = p
            .add_element(Kind::State, Layer::Sa, "Ready", Some(region))
            .unwrap();
        let target = p
            .add_element(Kind::State, Layer::Sa, "Waiting", Some(region))
            .unwrap();
        let work = p
            .add_element(Kind::Function, Layer::Sa, "Monitor", None)
            .unwrap();
        let choice = |id| Choice {
            id,
            label: p.named(id).into(),
        };
        let mut state = State::default();
        for event in [
            states::Event::Start(machine, states::Tool::Transition, source),
            states::Event::Name("Transition".repeat(1024)),
            states::Event::Trigger(choice(work)),
            states::Event::Effect(choice(work)),
            states::Event::TriggerNotes("On a monitor result".into()),
            states::Event::Guard("connection unavailable".into()),
            states::Event::EffectNotes("Record the timeout".into()),
            states::Event::Timed(true),
            states::Event::TimeKind("At".into()),
            states::Event::Expression("12:30 UTC".into()),
        ] {
            state.update(&p, Event::States(event)).unwrap();
        }
        assert!(
            state.prepare_pending(&p).is_err(),
            "A target is still missing"
        );
        assert_eq!(state.pending_owner(), Some(machine));
        state
            .update(&p, Event::States(states::Event::Target(choice(target))))
            .unwrap();
        let command = state.prepare_pending(&p).unwrap().unwrap();
        let bundle = source_project::format_bundle(&p);
        let mut limits = ProjectLimits::default();
        limits.model.max_source_bytes =
            bundle.files.values().map(String::len).sum::<usize>() + 2000;
        let mut document = Document::from_bundle(bundle.clone(), limits).unwrap();
        assert!(matches!(
            document.execute(command),
            Err(DocumentError::Source(_))
        ));
        assert_eq!(document.project(), &p);
        assert_eq!(document.bundle(), &bundle);
        assert_eq!(document.revision(), 0);
        assert!(!document.can_undo());
        assert!(state.has_pending());

        state
            .update(
                &p,
                Event::States(states::Event::Name("Wait for recovery".into())),
            )
            .unwrap();
        let command = state.prepare_pending(&p).unwrap().unwrap();
        let Command::Batch(commands) = &command else {
            panic!("Expected one atomic transition batch")
        };
        assert_eq!(commands.len(), 2);
        let Command::CreateElement(event) = &commands[0] else {
            panic!("Expected a typed time event")
        };
        assert!(
            matches!(event.shared(), Some(SharedBody::Event { body: EventBody::Time { kind: TimeEventKind::At, expression } }) if expression == "12:30 UTC")
        );
        let Command::CreateRelation(relation) = &commands[1] else {
            panic!("Expected the transition")
        };
        let RelationBody::StateTransition {
            triggers,
            effects,
            trigger,
            guard,
            effect,
            ..
        } = &relation.body
        else {
            panic!()
        };
        assert_eq!(triggers, &[work, event.id]);
        assert_eq!(effects, &[work]);
        assert_eq!(trigger, "On a monitor result");
        assert_eq!(guard, "connection unavailable");
        assert_eq!(effect, "Record the timeout");
        let expected = execute_batch(&p, std::slice::from_ref(&command)).unwrap();
        document.execute(command).unwrap();
        assert_eq!(
            document.project(),
            &expected,
            "Commit the exact prepared identities"
        );
        state.acknowledge_commit();
        assert!(!state.has_pending());
        assert_eq!(document.revision(), 1);
        assert!(document.undo());
        assert_eq!(document.bundle(), &bundle);
        assert_eq!(document.project(), &p);
        assert!(!document.can_undo());
    }

    #[test]
    fn legacy_process_and_chain_keep_their_ordered_exchange_scene() {
        let p = Project::demo();
        let owners: Vec<_> = p
            .elements
            .values()
            .filter(|e| matches!(e.kind(), Kind::Process | Kind::FunctionalChain))
            .collect();
        assert!(owners.iter().any(|e| e.kind() == Kind::Process));
        assert!(owners.iter().any(|e| e.kind() == Kind::FunctionalChain));
        for owner in owners {
            assert!(!uses_explicit_topology(&p, owner.id));
            let expected: Vec<_> = owner
                .steps()
                .unwrap()
                .iter()
                .enumerate()
                .map(|(index, id)| {
                    let Some(SharedBody::Occurrence {
                        body:
                            OccurrenceBody::Exchange {
                                exchange: Some(exchange),
                                ..
                            },
                        ..
                    }) = p.elements[id].shared()
                    else {
                        panic!("Demo legacy sequence should contain exchange occurrences");
                    };
                    format!("{}. {}", index + 1, p.relations[exchange].name)
                })
                .collect();
            assert!(!expected.is_empty());
            let scene = Scene::sequence(&p, owner.id, owner.id);
            let actual: Vec<_> = scene
                .lines
                .iter()
                .filter(|line| !line.label.is_empty())
                .map(|line| line.label.clone())
                .collect();
            assert_eq!(
                actual, expected,
                "Legacy rendering must preserve the model's ordered exchange path"
            );
        }
    }
    #[test]
    fn selecting_state_transition_keeps_its_behavior_context() {
        let p = Project::demo();
        for r in p
            .relations
            .values()
            .filter(|r| r.kind() == RelationKind::StateTransition)
        {
            let machine = selected_behavior(&p, r.id).expect("Transition remains in its machine");
            assert_eq!(p.elements[&machine].kind(), Kind::StateMachine);
            assert!(in_machine(&p, r.source(), machine));
            assert!(in_machine(&p, r.target(), machine));
        }
    }
}