//! Per-file drafts and navigation. Accepted model/source history lives in Document.
use iced::widget::text_editor::Cursor;
use oa_core::{
    Id, language,
    source_project::{self, CompiledSourceProject, ProjectLimits, SourceBundle, SourceDiagnostic},
};
use std::collections::{BTreeMap, BTreeSet};

pub const LIMITS: ProjectLimits = ProjectLimits {
    max_files: 256,
    max_include_depth: 32,
    max_include_edges: 1024,
    model: language::ParseLimits {
        max_source_bytes: 64 * 1024 * 1024,
        max_graph_objects: 100_000,
        max_records: 250_000,
        max_step_references: 500_000,
    },
};

const DRAFT_HISTORY_BYTES: usize = 32 * 1024 * 1024;

#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
#[serde(deny_unknown_fields)]
pub struct RecoveryWorkspace {
    entry: String,
    active: String,
    files: BTreeMap<String, (String, String)>,
    reachable: BTreeSet<String>,
    applied: bool,
    new_path: String,
}

impl RecoveryWorkspace {
    /// Refresh only accepted clean buffers. Dirty baselines and invalid/unapplied
    /// workspaces are authored recovery data, not migration input.
    pub(crate) fn upgrade_clean_buffers(&mut self, old: &SourceBundle, new: &SourceBundle) {
        if !self.applied || self.entry != old.entry {
            return;
        }
        for (path, (text, baseline)) in &mut self.files {
            if text == baseline
                && old.files.get(path) == Some(text)
                && let Some(upgraded) = new.files.get(path)
            {
                *text = upgraded.clone();
                *baseline = upgraded.clone();
            }
        }
    }
    /// Check the same bounds before replacing a checkpoint and before restoring it.
    pub(crate) fn validate(&self) -> Result<(), String> {
        if self.files.len() > LIMITS.max_files
            || !self.files.contains_key(&self.entry)
            || !self.files.contains_key(&self.active)
            || !self.reachable.contains(&self.entry)
            || self.reachable.len() > LIMITS.max_include_edges + 1
        {
            return Err("Recovery has an invalid file count, entry or active file.".into());
        }
        if self.files.values().fold(0usize, |bytes, (text, base)| {
            bytes.saturating_add(text.len()).saturating_add(base.len())
        }) > LIMITS.model.max_source_bytes.saturating_mul(2)
        {
            return Err("Recovery source buffers exceed the size limit.".into());
        }
        for path in self.files.keys().chain(self.reachable.iter()) {
            // A recovery buffer is never a filesystem path to open implicitly.
            if path.starts_with('/')
                || path.contains('\\')
                || path.contains(':')
                || path
                    .split('/')
                    .any(|part| part == ".." || part == "." || part.is_empty())
            {
                return Err("Recovery contains an unsafe source path.".into());
            }
        }
        Ok(())
    }
}

pub struct Buffer {
    pub text: String,
    baseline: String,
    pub cursor: Cursor,
    past: Vec<String>,
    future: Vec<String>,
    generation: u64,
}

impl Buffer {
    fn new(text: String) -> Self {
        Self {
            baseline: text.clone(),
            text,
            cursor: Cursor {
                position: iced::widget::text_editor::Position { line: 0, column: 0 },
                selection: None,
            },
            past: Vec::new(),
            future: Vec::new(),
            generation: 0,
        }
    }
    pub fn dirty(&self) -> bool {
        self.text != self.baseline
    }
    pub fn generation(&self) -> u64 {
        self.generation
    }
}

pub struct Workspace {
    session: Id,
    revision: u64,
    pub entry: String,
    pub active: String,
    pub files: BTreeMap<String, Buffer>,
    pub reachable: BTreeSet<String>,
    pub new_path: String,
    /// An invalid Open retains the accepted model but has no applied source yet.
    pub applied: bool,
}

impl Workspace {
    /// Ephemeral editor identity, never a model identity or recovery payload.
    pub fn session(&self) -> Id {
        self.session
    }
    pub fn revision(&self) -> u64 {
        self.revision
    }
    fn advance(&mut self) -> u64 {
        if let Some(revision) = self.revision.checked_add(1) {
            self.revision = revision;
        } else {
            self.reset_navigation_session();
        }
        self.revision
    }
    /// A changed filesystem root must not reuse queued navigation from Save As.
    pub fn reset_navigation_session(&mut self) {
        self.session = Id::new_v4();
        self.revision = 0;
        for buffer in self.files.values_mut() {
            buffer.generation = 0;
        }
    }
    pub fn set_reachable(&mut self, reachable: BTreeSet<String>) {
        if self.reachable != reachable {
            self.advance();
            self.reachable = reachable;
        }
    }
    pub fn recovery_snapshot(&self) -> RecoveryWorkspace {
        RecoveryWorkspace {
            entry: self.entry.clone(),
            active: self.active.clone(),
            files: self
                .files
                .iter()
                .map(|(path, buffer)| {
                    (path.clone(), (buffer.text.clone(), buffer.baseline.clone()))
                })
                .collect(),
            reachable: self.reachable.clone(),
            applied: self.applied,
            new_path: self.new_path.clone(),
        }
    }
    pub fn from_recovery(saved: RecoveryWorkspace) -> Result<Self, String> {
        saved.validate()?;
        Ok(Self {
            session: Id::new_v4(),
            revision: 0,
            entry: saved.entry,
            active: saved.active,
            files: saved
                .files
                .into_iter()
                .map(|(path, (text, baseline))| {
                    let mut buffer = Buffer::new(text);
                    buffer.baseline = baseline;
                    (path, buffer)
                })
                .collect(),
            reachable: saved.reachable,
            applied: saved.applied,
            new_path: saved.new_path,
        })
    }
    pub fn new(bundle: &SourceBundle, applied: bool) -> Self {
        Self {
            session: Id::new_v4(),
            revision: 0,
            entry: bundle.entry.clone(),
            active: bundle.entry.clone(),
            files: bundle
                .files
                .iter()
                .map(|(p, t)| (p.clone(), Buffer::new(t.clone())))
                .collect(),
            reachable: bundle.files.keys().cloned().collect(),
            new_path: String::new(),
            applied,
        }
    }
    pub fn text(&self) -> &str {
        self.files.get(&self.active).map_or("", |b| b.text.as_str())
    }
    pub fn dirty(&self) -> bool {
        !self.applied || self.has_edits()
    }
    pub fn has_edits(&self) -> bool {
        self.files.values().any(Buffer::dirty)
    }
    pub fn detached_dirty(&self) -> bool {
        self.files
            .iter()
            .any(|(p, b)| !self.reachable.contains(p) && b.dirty())
    }
    pub fn bundle(&self) -> SourceBundle {
        SourceBundle {
            entry: self.entry.clone(),
            files: self
                .files
                .iter()
                .map(|(p, b)| (p.clone(), b.text.clone()))
                .collect(),
        }
    }
    pub fn edit(&mut self, text: String, cursor: Cursor) {
        let changed = self.files.get(&self.active).is_none_or(|b| b.text != text);
        let generation = if changed {
            self.advance()
        } else {
            self.revision
        };
        let buffer = self
            .files
            .entry(self.active.clone())
            .or_insert_with(|| Buffer::new(String::new()));
        buffer.cursor = cursor;
        if changed {
            buffer.generation = generation;
        }
        if text != buffer.text {
            buffer.past.push(std::mem::replace(&mut buffer.text, text));
            if buffer.past.len() > 100 {
                buffer.past.remove(0);
            }
            buffer.future.clear();
            self.trim_history(DRAFT_HISTORY_BYTES);
        }
    }
    // Bound all file histories together. Evict the oldest/furthest snapshot
    // from the largest history first; current text and baselines are retained.
    fn trim_history(&mut self, budget: usize) {
        loop {
            let histories: Vec<_> = self
                .files
                .iter()
                .flat_map(|(path, buffer)| {
                    [(&buffer.past, false), (&buffer.future, true)]
                        .into_iter()
                        .filter(|(history, _)| !history.is_empty())
                        .map(move |(history, future)| {
                            (
                                path.clone(),
                                future,
                                history.iter().map(String::len).sum::<usize>(),
                            )
                        })
                })
                .collect();
            if histories.iter().map(|(_, _, bytes)| bytes).sum::<usize>() <= budget {
                break;
            }
            let Some((path, future, _)) = histories.into_iter().max_by_key(|(_, _, bytes)| *bytes)
            else {
                break;
            };
            let buffer = self.files.get_mut(&path).unwrap();
            if future {
                buffer.future.remove(0);
            } else {
                buffer.past.remove(0);
            }
        }
    }
    pub fn switch(&mut self, path: &str, cursor: Cursor) -> bool {
        if path == self.active || !self.files.contains_key(path) {
            return false;
        }
        if let Some(buffer) = self.files.get_mut(&self.active) {
            buffer.cursor = cursor;
        }
        self.active = path.into();
        true
    }
    pub fn undo(&mut self, redo: bool) -> bool {
        let Some(buffer) = self.files.get_mut(&self.active) else {
            return false;
        };
        let value = if redo {
            buffer.future.pop()
        } else {
            buffer.past.pop()
        };
        let Some(value) = value else {
            return false;
        };
        let previous = std::mem::replace(&mut buffer.text, value);
        if redo {
            buffer.past.push(previous);
        } else {
            buffer.future.push(previous);
        }
        let generation = self.advance();
        self.files.get_mut(&self.active).unwrap().generation = generation;
        self.trim_history(DRAFT_HISTORY_BYTES);
        true
    }
    pub fn revert_active(&mut self) {
        if let Some((baseline, cursor)) = self
            .files
            .get(&self.active)
            .map(|b| (b.baseline.clone(), b.cursor))
        {
            self.edit(baseline, cursor);
        }
    }
    pub fn accept(&mut self, bundle: &SourceBundle) {
        let generation = self.advance();
        if self.entry != bundle.entry
            && !bundle.files.contains_key(&self.entry)
            && self.files.get(&self.entry).is_some_and(|b| !b.dirty())
        {
            self.files.remove(&self.entry);
        }
        self.entry = bundle.entry.clone();
        self.reachable = bundle.files.keys().cloned().collect();
        for (path, text) in &bundle.files {
            let cursor = self.files.get(path).map(|b| b.cursor);
            let previous_generation = self
                .files
                .get(path)
                .filter(|b| b.text == *text)
                .map(|b| b.generation);
            let mut buffer = Buffer::new(text.clone());
            buffer.generation = previous_generation.unwrap_or(generation);
            if let Some(cursor) = cursor {
                buffer.cursor = cursor;
            }
            self.files.insert(path.clone(), buffer);
        }
        if !self.files.contains_key(&self.active) {
            self.active = self.entry.clone();
        }
        self.applied = true;
    }
    pub fn discovered(&mut self, bundle: &SourceBundle, reachable: BTreeSet<String>) {
        let changed = self.reachable != reachable
            || bundle
                .files
                .keys()
                .any(|path| !self.files.contains_key(path));
        let generation = if changed {
            self.advance()
        } else {
            self.revision
        };
        for (path, text) in &bundle.files {
            self.files.entry(path.clone()).or_insert_with(|| {
                let mut buffer = Buffer::new(text.clone());
                buffer.generation = generation;
                buffer
            });
        }
        self.reachable = reachable;
    }
    pub fn discard_detached(&mut self, path: &str) -> bool {
        if self.reachable.contains(path) || self.files.get(path).is_none_or(Buffer::dirty) {
            return false;
        }
        self.advance();
        self.files.remove(path);
        if self.active == path {
            self.active = self.entry.clone();
        }
        true
    }
}

/// Follow only explicitly reachable documents. Disconnected buffers remain in
/// Workspace, while the compiler deliberately rejects extras in its input.
pub fn reachable(bundle: &SourceBundle) -> Result<SourceBundle, Vec<SourceDiagnostic>> {
    let mut included = BTreeSet::new();
    let mut todo = vec![(bundle.entry.clone(), 0usize)];
    let mut edges = 0usize;
    while let Some((path, depth)) = todo.pop() {
        if !included.insert(path.clone()) {
            continue;
        }
        if depth > LIMITS.max_include_depth || included.len() > LIMITS.max_files {
            // The compiler supplies its normative admission diagnostic.
            return source_project::compile_bundle(bundle, LIMITS).map(|c| c.bundle);
        }
        let Some(text) = bundle.files.get(&path) else {
            return source_project::compile_bundle(bundle, LIMITS).map(|c| c.bundle);
        };
        let includes = source_project::inspect_includes(&path, text, path == bundle.entry, LIMITS)?;
        edges = edges.saturating_add(includes.len());
        if edges > LIMITS.max_include_edges {
            return source_project::compile_bundle(bundle, LIMITS).map(|c| c.bundle);
        }
        todo.extend(
            includes
                .into_iter()
                .map(|include| (include.target, depth + 1)),
        );
    }
    Ok(SourceBundle {
        entry: bundle.entry.clone(),
        files: bundle
            .files
            .iter()
            .filter(|(p, _)| included.contains(*p))
            .map(|(p, t)| (p.clone(), t.clone()))
            .collect(),
    })
}

pub fn compile(bundle: &SourceBundle) -> Result<CompiledSourceProject, Vec<SourceDiagnostic>> {
    source_project::compile_bundle(&reachable(bundle)?, LIMITS)
}

pub fn lint(bundle: &SourceBundle) -> Vec<SourceDiagnostic> {
    match reachable(bundle) {
        Ok(bundle) => source_project::lint_bundle(&bundle, LIMITS),
        Err(diagnostics) => diagnostics,
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use oa_core::Project;

    #[test]
    fn fresh_session_cannot_reuse_a_retained_buffer_generation() {
        let bundle = SourceBundle {
            entry: "main.arcadia".into(),
            files: BTreeMap::from([
                ("main.arcadia".into(), "first".into()),
                ("other.arcadia".into(), "other".into()),
            ]),
        };
        let mut workspace = Workspace::new(&bundle, true);
        let cursor = workspace.files["main.arcadia"].cursor;
        workspace.edit("second".into(), cursor);
        workspace.reset_navigation_session();
        let before = workspace.files["main.arcadia"].generation();
        workspace.edit("third".into(), cursor);
        assert_ne!(workspace.files["main.arcadia"].generation(), before);
        workspace.switch("other.arcadia", cursor);
        workspace.revision = u64::MAX;
        workspace.edit("changed other".into(), cursor);
        let after_wrap = workspace.files["main.arcadia"].generation();
        workspace.switch("main.arcadia", cursor);
        workspace.edit("fourth".into(), cursor);
        assert_ne!(workspace.files["main.arcadia"].generation(), after_wrap);
        assert!(workspace.undo(false));
        assert_eq!(workspace.text(), "third");
    }

    #[test]
    fn navigation_versions_distinguish_reopened_recovered_and_changed_drafts() {
        let bundle = SourceBundle {
            entry: "project.arcadia".into(),
            files: BTreeMap::from([
                ("project.arcadia".into(), "entry\r\n".into()),
                ("part.arcadia".into(), "雨 draft\r\n".into()),
            ]),
        };
        let mut workspace = Workspace::new(&bundle, true);
        let reopened = Workspace::new(&bundle, true);
        let recovered = Workspace::from_recovery(workspace.recovery_snapshot()).unwrap();
        assert_ne!(workspace.session(), reopened.session());
        assert_ne!(workspace.session(), recovered.session());
        assert_eq!(workspace.bundle(), recovered.bundle());
        let saved = serde_json::to_value(workspace.recovery_snapshot()).unwrap();
        assert!(saved.get("session").is_none() && saved.get("revision").is_none());

        let cursor = Cursor {
            position: iced::widget::text_editor::Position { line: 0, column: 3 },
            selection: None,
        };
        let revision = workspace.revision();
        workspace.edit(workspace.text().into(), cursor);
        assert_eq!(
            workspace.revision(),
            revision,
            "selection is not a text change"
        );
        workspace.switch("part.arcadia", cursor);
        assert_eq!(
            workspace.revision(),
            revision,
            "switching retains the snapshot"
        );
        let untouched = workspace.files["project.arcadia"].generation();
        workspace.edit("雨 unfinished !\r\n".into(), cursor);
        let edited = workspace.files["part.arcadia"].generation();
        assert!(workspace.revision() > revision);
        assert_eq!(workspace.files["project.arcadia"].generation(), untouched);
        assert!(workspace.undo(false));
        assert_eq!(workspace.bundle(), bundle);
        assert!(workspace.files["part.arcadia"].generation() > edited);
        assert!(workspace.undo(true));
        assert_eq!(workspace.text(), "雨 unfinished !\r\n");
        let previous_session = workspace.session();
        let previous_text = workspace.bundle();
        workspace.reset_navigation_session();
        assert_ne!(workspace.session(), previous_session);
        assert_eq!(workspace.bundle(), previous_text);
        assert!(
            workspace.undo(false),
            "session reset preserves text history"
        );
    }

    #[test]
    fn navigation_scope_changes_invalidate_without_changing_unchanged_positions() {
        let bundle = SourceBundle {
            entry: "project.arcadia".into(),
            files: BTreeMap::from([
                ("project.arcadia".into(), "entry".into()),
                ("part.arcadia".into(), "part".into()),
            ]),
        };
        let mut workspace = Workspace::new(&bundle, true);
        let entry_generation = workspace.files[&bundle.entry].generation();
        let initial_revision = workspace.revision();
        workspace.set_reachable(BTreeSet::from([bundle.entry.clone()]));
        assert!(workspace.revision() > initial_revision);
        let membership_revision = workspace.revision();
        workspace.set_reachable(workspace.reachable.clone());
        assert_eq!(workspace.revision(), membership_revision);
        assert!(workspace.discard_detached("part.arcadia"));
        assert!(workspace.revision() > membership_revision);
        let closed_revision = workspace.revision();
        workspace.discovered(&bundle, BTreeSet::from([bundle.entry.clone()]));
        assert!(workspace.revision() > closed_revision);
        assert_eq!(
            workspace.files[&bundle.entry].generation(),
            entry_generation
        );
        assert!(workspace.files["part.arcadia"].generation() > closed_revision);
        let discovered_revision = workspace.revision();
        workspace.discovered(&bundle, workspace.reachable.clone());
        assert_eq!(workspace.revision(), discovered_revision);
        workspace.accept(&bundle);
        assert!(
            workspace.revision() > discovered_revision,
            "validation evidence changed"
        );
        assert_eq!(
            workspace.files[&bundle.entry].generation(),
            entry_generation
        );
        assert_eq!(workspace.bundle(), bundle);
    }

    #[test]
    fn navigation_revision_wrap_cannot_reuse_an_old_workspace_key() {
        let bundle = SourceBundle {
            entry: "project.arcadia".into(),
            files: BTreeMap::from([("project.arcadia".into(), "original".into())]),
        };
        let mut workspace = Workspace::new(&bundle, true);
        workspace.revision = u64::MAX;
        let before = workspace.session();
        let cursor = workspace.files[&bundle.entry].cursor;
        workspace.edit("changed".into(), cursor);
        assert_ne!(workspace.session(), before);
        assert_eq!(workspace.revision(), 0);
        assert!(workspace.undo(false));
        assert_eq!(workspace.bundle(), bundle);
    }
    #[test]
    fn draft_history_budget_covers_inactive_files_without_discarding_drafts() {
        let bundle = SourceBundle {
            entry: "project.arcadia".into(),
            files: BTreeMap::from([
                ("project.arcadia".into(), "entry baseline".into()),
                ("part.arcadia".into(), "part baseline".into()),
            ]),
        };
        let mut workspace = Workspace::new(&bundle, true);
        for buffer in workspace.files.values_mut() {
            buffer.past = vec!["old".repeat(20), "recent".repeat(10)];
            buffer.future = vec!["future".repeat(10)];
            buffer.text = "unfinished draft".into();
        }
        workspace.trim_history(130);
        assert!(
            workspace
                .files
                .values()
                .map(|b| b
                    .past
                    .iter()
                    .chain(&b.future)
                    .map(String::len)
                    .sum::<usize>())
                .sum::<usize>()
                <= 130
        );
        for (path, buffer) in &workspace.files {
            assert_eq!(buffer.text, "unfinished draft");
            assert_eq!(buffer.baseline, bundle.files[path]);
            assert!(buffer.dirty());
        }
    }

    #[test]
    fn switching_retains_invalid_drafts_and_independent_history() {
        let mut bundle = source_project::format_bundle(&Project::demo());
        let fragment = bundle
            .files
            .keys()
            .find(|p| **p != bundle.entry)
            .unwrap()
            .clone();
        let original = bundle.files[&fragment].clone();
        let mut workspace = Workspace::new(&bundle, true);
        let cursor = Cursor {
            position: iced::widget::text_editor::Position { line: 0, column: 0 },
            selection: None,
        };
        workspace.switch(&fragment, cursor);
        workspace.edit("? invalid".into(), cursor);
        workspace.switch(&bundle.entry, cursor);
        assert!(workspace.dirty());
        assert!(compile(&workspace.bundle()).is_err());
        workspace.switch(&fragment, cursor);
        assert_eq!(workspace.text(), "? invalid");
        assert!(workspace.undo(false));
        assert_eq!(workspace.text(), original);
        assert!(!workspace.dirty());
        bundle
            .files
            .insert("detached.arcadia".into(), "? parked".into());
        workspace.discovered(&bundle, workspace.reachable.clone());
        assert!(compile(&workspace.bundle()).is_ok());
        assert!(workspace.discard_detached("detached.arcadia"));
    }
}