import { type Active, type ActiveProps } from '$libs/reactive';
import { watch } from 'runed';
import type { ActiveDom } from '$adom';
import type { EngineMotion } from '$motion';
import type { PresenceGroup, PresenceMember, PresencePhase, PresenceRole } from './presence-group';

// ── Types ────────────────────────────────────────────────────────────────────

export interface PresenceOptions extends ActiveProps<{ open: boolean; ref: HTMLElement | null }> {
	dom: ActiveDom;
	/** Called after open/close animation completes. Receives the current open state. */
	onComplete?: (open: boolean) => void;
	/** When false, skips animation waiting — unmounts immediately on close. @default true */
	enabled?: boolean;
	/**
	 * The motion runtime (`uix.motion` / `soma.motion`). When present, the cycle
	 * runs `motion.run(node, phase)` and awaits its `finished` ALONGSIDE
	 * `getAnimations()` — so a JS preset (a `spring`, invisible to
	 * `getAnimations()`) still gates the unmount. CSS presets settle immediately
	 * (their generated CSS is awaited via `getAnimations()`). The component passes
	 * `this.soma.motion`; the engine reads the node's `data-animation-style`.
	 */
	motion?: EngineMotion;
	/**
	 * Presence-coordination group (RFC: eidos/MOTION_SERVICE_RFC.md §7). When
	 * present, this surface CEDES its enter timing to the group: it mounts and
	 * waits to be released instead of self-driving (the group sequences releases
	 * per the morfo's `animation.children.{enter,exit}` and aggregates `finished`).
	 * Absent (the common case) ⇒ this `Presence` is an island, exactly as before.
	 */
	group?: PresenceGroup;
	/**
	 * Role within the group. The parent/coordinating surface is `'owner'`; nested
	 * surfaces are `'child'` (the default). Only the owner triggers the group's
	 * coordinated enter; children mount and wait to be released.
	 */
	groupRole?: PresenceRole;
}

export type TransitionStatus = 'starting' | 'ending' | undefined;

// ── Presence ─────────────────────────────────────────────────────────────────

/**
 * Animation-aware presence manager.
 *
 * Lifecycle:
 *
 * OPENING:
 *   open=true → shouldRender=true + transitionStatus='starting'
 *   → next rAF: transitionStatus=undefined (removes data-starting-style, triggers CSS transition)
 *   → getAnimations().finished → onComplete(true)
 *
 * CLOSING:
 *   open=false → transitionStatus='ending' (element stays in DOM!)
 *   → getAnimations().finished
 *   → shouldRender=false + transitionStatus=undefined → onComplete(false)
 */
export class Presence implements PresenceMember {
	readonly opts: PresenceOptions;

	shouldRender = $state(false);
	transitionStatus = $state<TransitionStatus>(undefined);

	private runId = 0;
	private frameIds = new Set<number>();
	/** Run id captured when a grouped surface mounts and waits to be released (RFC §7). */
	private pendingRunId = 0;
	/** Deregister callback from the coordination group, if any. */
	private deregister: (() => void) | undefined;

	constructor(opts: PresenceOptions) {
		this.opts = opts;
		this.shouldRender = opts.open.current;

		// RFC §7.1: cede to a coordination group if one is in scope. Register now
		// (synchronously, in the provider's init) and deregister on teardown so the
		// group's member set tracks mount/unmount. No group ⇒ island (below).
		if (opts.group) {
			this.deregister = opts.group.register(this);
			$effect(() => () => this.deregister?.());
		}

		watch(
			() => opts.open.current,
			(isOpen) => {
				if (isOpen) {
					this.handleOpen();
				} else {
					this.handleClose();
				}
			}
		);
	}

	/** Whether the element should be in the DOM. Use in template: `{#if presence.isPresent}` */
	readonly isPresent = $derived.by(() => this.shouldRender);

	/** Data attrs to spread onto the element for CSS transition support. */
	readonly transitionAttrs = $derived.by(() => {
		if (this.transitionStatus === 'starting') return { 'data-starting-style': '' } as const;
		if (this.transitionStatus === 'ending') return { 'data-ending-style': '' } as const;
		return {} as const;
	});

	// ── Open ─────────────────────────────────────────────────────────────────

	private handleOpen() {
		// Grouped surface: cede the release timing to the group (RFC §7). The
		// island path below is unchanged.
		if (this.opts.group) {
			this.handleOpenGrouped();
			return;
		}

		this.cleanup();
		this.shouldRender = true;
		this.transitionStatus = 'starting';

		const runId = ++this.runId;

		// Remove data-starting-style on next frame to trigger CSS transition
		this.requestFrame(() => {
			if (runId !== this.runId) return;
			this.transitionStatus = undefined;

			// Start any JS-driven motion, then wait for CSS + JS to complete.
			const extra = this.startMotion('enter');
			this.waitForAnimations(runId, extra, () => {
				this.opts.onComplete?.(true);
			});
		});
	}

	// ── Close ────────────────────────────────────────────────────────────────

	private handleClose() {
		// Grouped surface: cede the exit to the group, which coordinates the tree's
		// exit and unmounts after (DOM retention §8.1). The island path is unchanged.
		if (this.opts.group) {
			this.handleCloseGrouped();
			return;
		}

		this.cleanup();

		const enabled = this.opts.enabled ?? true;
		if (!enabled) {
			this.shouldRender = false;
			this.transitionStatus = undefined;
			this.opts.onComplete?.(false);
			return;
		}

		this.transitionStatus = 'ending';

		const runId = ++this.runId;

		// Start any JS-driven exit motion, then wait for CSS + JS, then unmount.
		const extra = this.startMotion('exit');
		this.waitForAnimations(runId, extra, () => {
			if (runId !== this.runId) return;
			this.shouldRender = false;
			this.transitionStatus = undefined;
			this.opts.onComplete?.(false);
		});
	}

	// ── Grouped lifecycle (RFC §7) — only active when `opts.group` is set ──────

	/**
	 * Grouped ENTER: mount immediately, then WAIT to be released by the group.
	 * Only the owner triggers the group's coordinated enter; children mount and
	 * stay in `data-starting-style` until the group calls `release('enter')`.
	 */
	private handleOpenGrouped() {
		this.cleanup();
		this.shouldRender = true;
		this.transitionStatus = 'starting';
		this.pendingRunId = ++this.runId;

		if (this.role === 'owner') this.opts.group?.requestEnter();
	}

	/**
	 * Grouped EXIT: cede to the group (RFC §8.1). Mark `ending` and WAIT — the
	 * group runs the tree's exit in `when` order and calls `unmount()` here only
	 * after the whole exit settles (DOM retention). Only the owner triggers it.
	 */
	private handleCloseGrouped() {
		this.cleanup();
		const enabled = this.opts.enabled ?? true;
		if (!enabled) {
			this.unmount();
			return;
		}
		// Stay in the OPEN visual state (no `data-ending-style` yet) until the group
		// RELEASES this surface. That is what makes `when: 'after'` exit the children
		// before the owner — and the owner stay visibly intact while its children
		// leave — instead of everyone's exit animation firing at once. `release`
		// stamps `ending` when our turn comes (RFC §8.1).
		this.pendingRunId = ++this.runId;

		if (this.role === 'owner') this.opts.group?.requestExit();
	}

	/** This surface's role within its group (`PresenceMember`). */
	get role(): PresenceRole {
		return this.opts.groupRole ?? 'child';
	}

	/**
	 * Release this surface's motion for the phase — the group calls this in
	 * coordinated order (`PresenceMember`). Removes `data-starting-style` on enter,
	 * starts the JS motion, and resolves when this surface's own animation finishes
	 * (CSS via `getAnimations()` + any JS `finished`). The visual stagger is CSS
	 * (eidos); soma only awaits.
	 */
	release(phase: PresencePhase): Promise<void> {
		const runId = this.pendingRunId;
		return new Promise<void>((resolve) => {
			this.requestFrame(() => {
				if (runId !== this.runId) {
					resolve();
					return;
				}
				// Enter: drop `starting` → the CSS transition plays. Exit: stamp
				// `ending` NOW (not at close) so the surface holds its open state until
				// the group reaches it, giving `when: 'after'` its sequencing (§8.1).
				if (phase === 'enter') this.transitionStatus = undefined;
				else this.transitionStatus = 'ending';
				const extra = this.startMotion(phase);
				this.waitForAnimations(runId, extra, () => {
					if (phase === 'enter') this.opts.onComplete?.(true);
					resolve();
				});
			});
		});
	}

	/**
	 * Tear down after the group's coordinated exit settles (`PresenceMember`, RFC
	 * §8.1). Mirrors the island unmount: drop the surface and notify. The group
	 * calls this once the whole tree's exit has aggregated — never before, so the
	 * owner's DOM (and any retained subtree) survives the children's exit.
	 */
	unmount(): void {
		this.shouldRender = false;
		this.transitionStatus = undefined;
		this.opts.onComplete?.(false);
	}

	/**
	 * Cancel in-flight motion (interruption — RFC §8.3, M4). `cleanup()` bumps the
	 * runId so the in-flight async tail (frames, `waitForAnimations`) becomes a
	 * no-op, and `motion.cancel(node)` stops any JS-driven run so a reversal does
	 * not stack a second animation on the node (CSS presets are untracked → no-op;
	 * the reversed CSS transition continues from its current value). The group calls
	 * this on every member when a reversal supersedes the in-flight phase.
	 */
	cancel(): void {
		this.cleanup();
		const node = this.opts.ref.current;
		if (node) this.opts.motion?.cancel(node);
	}

	// ── Animation waiting ────────────────────────────────────────────────────

	/** Start the JS-driven motion for this phase, if a `motion` engine is wired. */
	private startMotion(phase: 'enter' | 'exit'): Promise<void> | undefined {
		const node = this.opts.ref.current;
		if (!node) return undefined;
		return this.opts.motion?.run(node, phase)?.finished;
	}

	private waitForAnimations(
		runId: number,
		extra: Promise<void> | undefined,
		onDone: () => void
	) {
		// getAnimations() needs a frame to see the active animations
		this.requestFrame(() => {
			if (runId !== this.runId) return;

			const node = this.opts.ref.current;
			if (!node) {
				onDone();
				return;
			}

			// CSS animations (via getAnimations) + any JS-driven `finished`. A spring
			// is invisible to getAnimations(), so its `finished` joins the wait here.
			const finishers: Promise<unknown>[] = node.getAnimations().map((a) => a.finished);
			if (extra) finishers.push(extra);
			if (finishers.length === 0) {
				onDone();
				return;
			}

			Promise.all(finishers)
				.then(() => {
					if (runId !== this.runId) return;
					onDone();
				})
				.catch(() => {
					// An awaited animation was CANCELLED (its `.finished` rejects).
					// This is not only rapid toggling (stale runId → no-op below): a
					// visual exit animation can be interrupted WITHOUT a state change —
					// e.g. sema unstamps the `data-event-*` that drives the close
					// `dismiss-fade` when its hold ends BEFORE the animation's own
					// duration, cancelling it. A cancelled exit MUST still finalize the
					// lifecycle; otherwise a closed overlay stays mounted forever and
					// its FocusScope traps focus (no block can be focused to type).
					// Stale runs are filtered by the runId guard, exactly as in `then`.
					if (runId !== this.runId) return;
					onDone();
				});
		});
	}

	// ── Cleanup ──────────────────────────────────────────────────────────────

	private requestFrame(callback: () => void) {
		const frame = this.opts.dom.requestFrame(() => {
			this.frameIds.delete(frame);
			callback();
		}, this.opts.ref.current);
		this.frameIds.add(frame);
	}

	private cleanup() {
		this.runId++;
		for (const frame of this.frameIds) {
			this.opts.dom.cancelFrame(frame, this.opts.ref.current);
		}
		this.frameIds.clear();
	}
}