/**
 * question-core — pure logic shared by the terminal (blocking) and web
 * (dispatch) quiz/ask extensions. No pi imports, no UI: everything here is
 * deterministic and unit-testable.
 *
 * The WEB dispatch shape:
 *   1. Tool execute() validates + shuffles + resolves the correct answer,
 *      appends an `lh_question` custom entry (NOT in LLM context — safe to
 *      store correctAnswer/explanation there) and returns immediately.
 *   2. The agent ends its turn. The server pushes the question to the client.
 *   3. The learner answers; the server calls back into the extension bridge.
 *   4. The extension grades, appends `lh_question_answered` (gold-standard
 *      structured data for the extractor), and sends the graded answer into
 *      the session as a user message so the agent can continue.
 *
 * Because nothing blocks, a session can be exited and resumed mid-question:
 * the pending state lives in the session file itself (lh_question entries
 * with no matching lh_question_answered).
 */

// ─── shared types ───────────────────────────────────────────────────────────

export interface QuizOption {
	label: string;
	value: string;
	description?: string;
}

/** A real selected answer, in the order the options were displayed. */
export interface OptionAnswer {
	label: string;
	value: string;
	index: number; // 1-based display index
}

export type QuestionKind = "quiz" | "ask";
export type SelectMode = "single-select" | "multi-select";
export type QuestionMode = SelectMode | "text";

/** Full question data — stored in the `lh_question` custom entry. */
export interface QuestionData {
	id: string;
	kind: QuestionKind;
	question: string;
	context?: string;
	mode: QuestionMode;
	options: QuizOption[]; // display order (post-shuffle)
	// quiz only. NEVER send to the client before answering:
	correctIndices?: number[];
	explanation?: string;
	createdAt: string;
}

/** The learner's answer — full structured record, stored in `lh_question_answered`. */
export interface QuestionAnswerData {
	questionId: string;
	kind: QuestionKind;
	questionText: string;
	options?: { index: number; label: string }[]; // snapshot for rendering
	dontKnow: boolean;
	answers: OptionAnswer[];
	other?: string; // ask: "Other" free text
	text?: string; // ask: text-mode answer
	note?: string;
	correct?: boolean; // quiz only
	correctIndices?: number[]; // quiz only (rendering)
	explanation?: string; // quiz only (rendering)
	dismissed?: boolean;
	answeredAt: string;
}

/** Client-facing question payload — deliberately omits the answer. */
export interface ClientQuestion {
	id: string;
	kind: QuestionKind;
	question: string;
	context?: string;
	mode: QuestionMode;
	options: QuizOption[];
}

/** What the server passes to the bridge when the learner answers. */
export interface AnswerRequest {
	dontKnow?: boolean;
	values?: string[]; // option values
	other?: string; // ask "Other"
	text?: string; // ask text-mode
	note?: string;
}

export const QUESTION_ENTRY = "lh_question";
export const QUESTION_ANSWERED_ENTRY = "lh_question_answered";

// ─── options ────────────────────────────────────────────────────────────────

export function normalizeOptions(
	options: Array<{ label: string; value?: string; description?: string }> | undefined,
): QuizOption[] {
	const seen = new Set<string>();
	return (options || [])
		.map((option) => ({
			label: option.label.trim(),
			value: option.value?.trim() || option.label.trim(),
			description: option.description?.trim() || undefined,
		}))
		.filter((option) => {
			if (option.label.length === 0) return false;
			if (seen.has(option.value)) throw new Error(`duplicate option value "${option.value}"`);
			seen.add(option.value);
			return true;
		});
}

/** Fisher-Yates over a copy. correctAnswer is keyed by value, so display
 *  order can be shuffled safely before resolving indices. */
export function shuffleOptions(options: QuizOption[]): QuizOption[] {
	const out = [...options];
	for (let i = out.length - 1; i > 0; i--) {
		const j = Math.floor(Math.random() * (i + 1));
		const a = out[i]!;
		const b = out[j]!;
		out[i] = b;
		out[j] = a;
	}
	return out;
}

// ─── quiz grading ───────────────────────────────────────────────────────────

/** The harness sometimes delivers a multi-select correctAnswer array as a
 *  JSON-stringified string because the schema union lists String first. */
export function coerceCorrectAnswer(correctAnswer: string | string[]): string[] {
	if (Array.isArray(correctAnswer)) return correctAnswer;
	const trimmed = correctAnswer.trim();
	if (trimmed.startsWith("[") && trimmed.endsWith("]")) {
		try {
			const parsed = JSON.parse(trimmed);
			if (Array.isArray(parsed)) return parsed.map((v) => String(v));
		} catch {
			// not valid JSON — treat as a single literal value
		}
	}
	return [correctAnswer];
}

/** Resolve author-supplied value(s) to 1-based display indices. Keying by
 *  value (not position) makes a typo a hard error instead of a silent wrong
 *  grade. Must run AFTER shuffling. */
export function resolveCorrect(
	correctAnswer: string | string[] | undefined,
	options: QuizOption[],
): { indices: number[]; error?: string } {
	if (correctAnswer === undefined) return { indices: [], error: "correctAnswer is required" };
	const arr = coerceCorrectAnswer(correctAnswer);
	if (arr.length === 0) return { indices: [], error: "correctAnswer is required" };
	const byValue = new Map(options.map((o, i) => [o.value, i + 1]));
	const indices: number[] = [];
	for (const raw of arr) {
		const v = typeof raw === "string" ? raw.trim() : raw;
		const idx = byValue.get(v);
		if (idx === undefined) {
			const known = options.map((o) => `"${o.value}"`).join(", ");
			return { indices: [], error: `correctAnswer "${v}" does not match any option value (${known})` };
		}
		indices.push(idx);
	}
	return { indices: Array.from(new Set(indices)).sort((a, b) => a - b) };
}

/** Exact-set match: same number of selections, same indices. */
export function isCorrect(selectedIndices: number[], correctIndices: number[]): boolean {
	if (selectedIndices.length !== correctIndices.length) return false;
	const a = [...selectedIndices].sort((x, y) => x - y);
	const b = [...correctIndices].sort((x, y) => x - y);
	return a.every((v, i) => v === b[i]);
}

// ─── arming + answering ─────────────────────────────────────────────────────

export function makeId(): string {
	return `q_${Date.now().toString(36)}_${Math.random().toString(36).slice(2, 10)}`;
}

export function toClientQuestion(qd: QuestionData): ClientQuestion {
	return {
		id: qd.id,
		kind: qd.kind,
		question: qd.question,
		context: qd.context,
		mode: qd.mode,
		options: qd.options,
	};
}

function formatOptionRef(options: QuizOption[], index: number): string {
	const opt = options.find((o, i) => i + 1 === index);
	return `${index}. ${opt ? opt.label : "(unknown)"}`;
}

/**
 * Turn an AnswerRequest into the full answer record + the user message the
 * agent will see. Quiz answers are graded here; ask answers are not.
 */
export function buildAnswer(qd: QuestionData, req: AnswerRequest): QuestionAnswerData {
	const base: QuestionAnswerData = {
		questionId: qd.id,
		kind: qd.kind,
		questionText: qd.question,
		options: qd.options.map((o, i) => ({ index: i + 1, label: o.label })),
		dontKnow: req.dontKnow === true,
		answers: [],
		note: req.note?.trim() || undefined,
		answeredAt: new Date().toISOString(),
	};

	// resolve selected option values → OptionAnswer (in display order)
	if (req.values && req.values.length > 0) {
		const byValue = new Map(qd.options.map((o, i) => [o.value, { ...o, index: i + 1 }]));
		for (const v of req.values) {
			const opt = byValue.get(v);
			if (!opt) continue; // unknown value — ignore
			base.answers.push({ label: opt.label, value: opt.value, index: opt.index });
		}
		base.answers.sort((a, b) => a.index - b.index);
	}
	if (req.other?.trim()) base.other = req.other.trim();
	if (req.text?.trim()) base.text = req.text.trim();

	if (qd.kind === "quiz") {
		base.correctIndices = qd.correctIndices ?? [];
		base.explanation = qd.explanation;
		base.correct = base.dontKnow ? false : isCorrect(base.answers.map((a) => a.index), qd.correctIndices ?? []);
	}
	return base;
}

/** The user message that carries the answer into the agent's context. */
export function formatAnswerMessage(ad: QuestionAnswerData): string {
	const label = ad.kind === "quiz" ? "Quiz answer" : "Answer to your question";
	const head = `[${label}]`;
	const lines: string[] = [head];

	if (ad.dismissed) {
		lines.push("The learner dismissed this question without answering.");
		return lines.join("\n");
	}

	if (ad.kind === "quiz") {
		const correctStr = (ad.correctIndices ?? []).map((i) => formatOptionRefSnapshot(ad, i)).join(", ");
		if (ad.dontKnow) {
			lines.push(
				`The learner selected "I don't know" — they did NOT attempt an answer (a genuine knowledge gap, not a wrong guess).`,
			);
		} else {
			const verdict = ad.correct ? "CORRECT" : "INCORRECT";
			const selectedStr = ad.answers.map((a) => `${a.index}. ${a.label}`).join(", ");
			lines.push(`Selected: ${selectedStr || "(none)"}`);
			lines.push(`Result: ${verdict}`);
		}
		lines.push(`Correct: ${correctStr}`);
	} else {
		if (ad.text) {
			lines.push(`The learner answered: ${ad.text}`);
		} else if (ad.other) {
			lines.push(`The learner answered (Other): ${ad.other}`);
		} else if (ad.answers.length > 0) {
			const selectedStr = ad.answers.map((a) => `${a.index}. ${a.label}`).join(", ");
			lines.push(`Selected: ${selectedStr}`);
		} else {
			lines.push("(no answer)");
		}
	}

	if (ad.note) lines.push(`Note: ${ad.note}`);
	return lines.join("\n");
}

function formatOptionRefSnapshot(ad: QuestionAnswerData, index: number): string {
	const opt = (ad.options ?? []).find((o) => o.index === index);
	return `${index}. ${opt ? opt.label : "(unknown)"}`;
}

/**
 * Derive the pending (oldest unanswered) question from a session's entries.
 * Used on resume/backfill — pending state lives in the session file itself.
 */
export function findPendingQuestion(
	entries: Array<{ type: string; customType?: string; data?: unknown }>,
): ClientQuestion | null {
	const answered = new Set<string>();
	for (const e of entries) {
		if (e.type === "custom" && e.customType === QUESTION_ANSWERED_ENTRY) {
			const d = e.data as QuestionAnswerData | undefined;
			if (d?.questionId) answered.add(d.questionId);
		}
	}
	for (const e of entries) {
		if (e.type === "custom" && e.customType === QUESTION_ENTRY) {
			const d = e.data as QuestionData | undefined;
			if (d && !answered.has(d.id)) return toClientQuestion(d);
		}
	}
	return null;
}