// Pure routine metrics, shared by server services and UI. No db access.
// All timestamps are ISO strings; all math is done in ms then converted to days.
// Due dates anchor on UTC calendar days, not exact 24h intervals: a daily
// routine done yesterday is due today, whatever the time of day.

const DAY_MS = 24 * 60 * 60 * 1000;

/** Midnight UTC starting the calendar day containing ms. */
function startOfUtcDay(ms: number): number {
	const d = new Date(ms);
	return Date.UTC(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate());
}

export type RoutineStatus = 'ok' | 'due' | 'late' | 'veryLate';

export interface RoutineInput {
	id: number;
	version: number;
	name: string;
	frequencyDays: number;
	createdAt: string;
}

export interface CompletionInput {
	routineId: number;
	doneAt: string;
}

export interface RoutineState {
	id: number;
	version: number;
	name: string;
	frequencyDays: number;
	lastDoneAt: string | null;
	/** When the routine should next be done. */
	dueAt: string;
	/** Days past dueAt (0 if not yet due). */
	overdueDays: number;
	/** Time past due, in units of the routine's own frequency (0 if not due). */
	overdueRatio: number;
	status: RoutineStatus;
	/** 100 on schedule, 50 when a full period overdue, 0 at two periods, floor at 0. */
	health: number;
}

export function computeRoutineState(
	routine: RoutineInput,
	completions: CompletionInput[],
	now: number,
): RoutineState {
	const mine = completions
		.filter((c) => c.routineId === routine.id)
		.map((c) => Date.parse(c.doneAt));
	const lastDoneMs = mine.length > 0 ? Math.max(...mine) : null;
	const createdMs = Date.parse(routine.createdAt);
	const referenceMs =
		lastDoneMs ?? (Number.isFinite(createdMs) ? createdMs : now);
	const periodMs = routine.frequencyDays * DAY_MS;
	// Calendar-day anchor: the period starts at midnight of the reference day,
	// so any new calendar day past the frequency flips the routine to due.
	const dueMs = startOfUtcDay(referenceMs) + periodMs;
	const rawRatio = (now - dueMs) / periodMs;
	const overdueRatio = Math.max(0, rawRatio);
	// Buckets on overdue time in units of the routine's own frequency: due
	// until a full period is missed (a daily done yesterday is due today, not
	// late), late once an occurrence was skipped entirely, very late after two.
	// A routine that was never done is always at least due: there is
	// something to do, even right after creation.
	const status: RoutineStatus =
		rawRatio < 0 && lastDoneMs !== null
			? 'ok'
			: overdueRatio < 1
				? 'due'
				: overdueRatio < 2
					? 'late'
					: 'veryLate';

	return {
		id: routine.id,
		version: routine.version,
		name: routine.name,
		frequencyDays: routine.frequencyDays,
		lastDoneAt: lastDoneMs !== null ? new Date(lastDoneMs).toISOString() : null,
		dueAt: new Date(dueMs).toISOString(),
		overdueDays: Math.floor(overdueRatio * routine.frequencyDays),
		overdueRatio,
		status,
		health: Math.max(0, Math.round(100 - overdueRatio * 50)),
	};
}

/** Average health across routines; 100 when there is nothing to do. */
export function computeHealthScore(states: { health: number }[]): number {
	if (states.length === 0) return 100;
	const total = states.reduce((sum, s) => sum + s.health, 0);
	return Math.round(total / states.length);
}

export interface HealthPoint {
	/** Epoch ms of the sample. */
	at: number;
	/** Health (0-100) at that instant. */
	health: number;
}

/** Health at instant t given the reference anchor (creation or last completion). */
function healthAtPoint(refMs: number, periodMs: number, t: number): number {
	const dueMs = startOfUtcDay(refMs) + periodMs;
	const rawRatio = (t - dueMs) / periodMs;
	return Math.max(0, Math.round(100 - Math.max(0, rawRatio) * 50));
}

/**
 * Daily health samples from the routine's creation to now: 100 right after a
 * completion, then a linear decay to 0 once two full periods are overdue
 * (sawtooth).
 * Each sample anchors on the latest completion at or before it (or creation).
 * Uses the routine's current frequency across the whole history.
 */
export function computeHealthSeries(
	routine: RoutineInput,
	completions: CompletionInput[],
	now: number,
): HealthPoint[] {
	const createdMs = Date.parse(routine.createdAt);
	const startMs = Number.isFinite(createdMs) ? createdMs : now;
	const periodMs = routine.frequencyDays * DAY_MS;

	const completionMs = completions
		.filter((c) => c.routineId === routine.id)
		.map((c) => Date.parse(c.doneAt))
		.sort((a, b) => a - b);

	const points: HealthPoint[] = [];
	if (now <= startMs) {
		return [{ at: now, health: 100 }];
	}

	// Reference anchor: latest completion at-or-before the sampled instant.
	let refMs = startMs;
	let nextCompletion = 0;
	const sampleAt = (t: number): number => {
		while (
			nextCompletion < completionMs.length &&
			completionMs[nextCompletion] <= t
		) {
			refMs = completionMs[nextCompletion];
			nextCompletion++;
		}
		return healthAtPoint(refMs, periodMs, t);
	};

	for (let t = startMs; t <= now; t += DAY_MS) {
		points.push({ at: t, health: sampleAt(t) });
	}

	// Final unaligned sample so the curve ends at the present instant.
	if (points[points.length - 1].at < now) {
		points.push({ at: now, health: sampleAt(now) });
	}
	return points;
}

/**
 * Project health series: daily mean of per-routine health across the routines
 * alive that day (createdAt <= t). Same sawtooth as the per-routine series,
 * so the project curve ends at the current health score. Empty when no
 * routines.
 */
export function computeProjectHealthSeries(
	routines: RoutineInput[],
	completions: CompletionInput[],
	now: number,
): HealthPoint[] {
	if (routines.length === 0) return [];
	const ids = new Set(routines.map((r) => r.id));
	const completionsByRoutine = new Map<number, number[]>();
	for (const c of completions) {
		if (!ids.has(c.routineId)) continue;
		const t = Date.parse(c.doneAt);
		if (!Number.isFinite(t)) continue;
		completionsByRoutine.set(c.routineId, [
			...(completionsByRoutine.get(c.routineId) ?? []),
			t,
		]);
	}
	for (const times of completionsByRoutine.values())
		times.sort((a, b) => a - b);

	const createdOrNow = (r: RoutineInput): number => {
		const t = Date.parse(r.createdAt);
		return Number.isFinite(t) ? t : now;
	};
	// Mean per-routine health across the routines alive at t.
	const sampleAt = (t: number): number | null => {
		const alive = routines.filter((r) => Date.parse(r.createdAt) <= t);
		if (alive.length === 0) return null;
		const total = alive.reduce((sum, r) => {
			const doneAt = (completionsByRoutine.get(r.id) ?? []).filter(
				(d) => d <= t,
			);
			const anchor = doneAt.length > 0 ? Math.max(...doneAt) : createdOrNow(r);
			return sum + healthAtPoint(anchor, r.frequencyDays * DAY_MS, t);
		}, 0);
		return Math.round(total / alive.length);
	};

	const startMs = Math.min(...routines.map(createdOrNow));
	if (now <= startMs) return [{ at: now, health: 100 }];

	const points: HealthPoint[] = [];
	for (let t = startMs; t <= now; t += DAY_MS) {
		const health = sampleAt(t);
		if (health !== null) points.push({ at: t, health });
	}
	if (points.length === 0) return [{ at: now, health: 100 }];

	// Final unaligned sample so the curve ends at the present instant.
	if (points[points.length - 1].at < now) {
		points.push({ at: now, health: sampleAt(now) ?? 100 });
	}
	return points;
}

export function formatFrequency(days: number): string {
	if (days === 1) return 'chaque jour';
	if (days === 7) return 'chaque semaine';
	if (days === 30) return 'chaque mois';
	if (days === 365) return 'chaque année';
	return `tous les ${days} jours`;
}

const UNIT_DAYS: Record<string, number> = { d: 1, w: 7, m: 30, y: 365 };

/** Parses "1d | 2w | 3m | 1y" into days; returns null when invalid. */
export function parseIntervalToDays(input: string): number | null {
	const match = input
		.trim()
		.toLowerCase()
		.match(/^(\d+)([dwmy])$/);
	if (!match) return null;
	const days = Number(match[1]) * UNIT_DAYS[match[2]];
	return days >= 1 ? days : null;
}

export const STATUS_LABELS: Record<RoutineStatus, string> = {
	ok: 'À jour',
	due: 'À faire',
	late: 'En retard',
	veryLate: 'Très en retard',
};