/**
 * Hoover — component.js
 *
 * Component wrapper: definePage, lifecycle hooks, state caching.
 *
 * definePage wraps a page definition into a renderer function compatible
 * with hoover's render engine. Handles reactive state creation, WS
 * subscription registration on mount, and cleanup on unmount.
 *
 * Usage:
 *   export default definePage({
 *       init() { return { data: null, loading: true, error: null }; },
 *       subscribe: ['*'],          // WS topics to subscribe to
 *       async load(state) { ... }, // called on mount
 *       render(state) { return [vnodes],
 *   });
 */

import { reactive } from './reactivity.js';
import { h } from './vdom.js';
import { _compExpandedCache } from './render.js';

/** Registry of mounted components: key → { state, subscriptions, loadAbort, entry, isLoading } */
const _mounted = new Map();

/** Check whether a state object belongs to a currently mounted component.
 * Used by websocket.js to skip auto-refresh for unmounted pages. */
export function isComponentStateMounted(state) {
    for (const entry of _mounted.values()) {
        if (entry.state === state) return true;
    }
    return false;
}

/** External subscribe function from websocket.js.
 * Set via setSubscribeFn() when the websocket module initializes.
 */
let _subscribeFn = null;

export function setSubscribeFn(fn) {
    _subscribeFn = fn;
}

/**
 * Define a page component.
 *
 * @param {object} def — Page definition
 * @param {function} def.init — Return initial state object
 * @param {string[]} [def.subscribe] — WS topics to subscribe to on mount
 * @param {function} def.load — Async function to load data into state
 * @param {function} def.render — Render function that returns vnodes
 * @returns {object} — Component renderer compatible with h('#comp', ...)
 */
export function definePage(def) {
    const state = reactive(def.init());

    const renderer = () => {
        return def.render(state);
    };

    renderer._pageDef = {
        state,
        subscribe: def.subscribe || [],
        load: def.load || null,
        onUnmount: def.onUnmount || null,
    };

    return renderer;
}

/**
 * Mount a page component. Called by the render engine when a #comp vnode
 * enters the tree for the first time.
 */
export function mountComponent(key, renderer) {
    const pd = renderer._pageDef;
    if (!pd) return;

    let entry = _mounted.get(key);

    if (entry) {
        // Re-mount of an already-mounted page: restart load with fresh AbortController
        if (entry.loadAbort) {
            entry.loadAbort.abort();
        }
        entry.requestId++;
        entry.loadAbort = null;
    } else {
        // Fresh mount
        entry = {
            state: pd.state,
            subscriptions: [],
            loadAbort: null,
            requestId: 0,
        };
        _mounted.set(key, entry);
    }

    // Clear error on re-mount; load() decides loading vs refreshing
    pd.state.error = null;

    // Fire load with fresh AbortController
    if (pd.load) {
        const abortController = new AbortController();
        entry.loadAbort = abortController;
        entry.requestId++;
        entry.isLoading = true;
        Promise.resolve()
            .then(() => pd.load(pd.state, abortController, entry))
            .finally(() => { entry.isLoading = false; });
    }

    // Register WS subscriptions (only on fresh mount)
    if (!entry.subscriptions.length && _subscribeFn && pd.subscribe.length) {
        for (const topic of pd.subscribe) {
            const unsub = _subscribeFn(renderer, topic, pd.load, pd.state);
            if (unsub) entry.subscriptions.push(unsub);
        }
    }
}

/**
 * Unmount a page component. Called by the render engine when a #comp vnode
 * is removed from the tree.
 */
export function unmountComponent(key, renderer) {
    const entry = _mounted.get(key);
    if (!entry) return;

    const pd = renderer._pageDef;

    // Cancel load
    if (entry.loadAbort) {
        entry.loadAbort.abort();
    }
    // Invalidate any in-flight callbacks
    entry.requestId++;

    // Unsubscribe from WS
    for (const unsub of entry.subscriptions) {
        try { unsub(); } catch (_) {}
    }

    // Fire custom onUnmount
    if (pd.onUnmount) {
        try { pd.onUnmount(entry.state); } catch (_) {}
    }

    _compExpandedCache.delete(key);
    _mounted.delete(key);
}

/**
 * Get the state of a mounted component.
 */
export function getComponentState(key) {
    const entry = _mounted.get(key);
    return entry ? entry.state : null;
}

/**
 * Create a component vnode that the render engine will wire up to lifecycle.
 */
export function hComp(renderer, key) {
    return h('#comp', { component: renderer, key }, []);
}