/**
 * Hoover — render.js
 *
 * Render engine: render(container, fn), container-level diffing,
 * batched re-render loop integration with reactivity.js.
 */

import { requestUpdate, setCommitFn } from './reactivity.js?v=9';
import {
    _vnodeDom, createDom, getDom, patchNode, sweepDom,
    setMountFn, setUnmountFn,
} from './vdom.js?v=9';
import { mountComponent, unmountComponent } from './component.js?v=9';

/** Container → previous root vnodes */
export const _renderSlots = new Map();

/** Container → render function */
export const _renderFns = new Map();

/** Component key → last normalized #comp output (for _vnodeDom preservation) */
export const _compExpandedCache = new Map();

/** Component key → renderer function (survives normalization that expands #comp) */
const _compRegistry = new Map();

/**
 * Set up lifecycle callback hooks from vdom.js.
 * Called once during render initialization.
 */
setMountFn((el) => {
    // Reserved for future DOM-level mount hooks
});

setUnmountFn((el) => {
    // Called during sweepDom for cleanup
});

/**
 * Commit callback: re-renders all registered containers in batch.
 * Set as the callback for reactivity.js's requestUpdate().
 */
function commitAll() {
    for (const container of _renderFns.keys()) {
        commit(container);
    }
}

setCommitFn(commitAll);

/**
 * Mount a render function onto a DOM container.
 *   - First call: create DOM from scratch, append to container
 *   - Subsequent calls: diff against previous VNodes, patch in place
 */
export function render(container, fn) {
    _renderFns.set(container, fn);
    commit(container);
}

/**
 * Evaluate render function, diff vs previous, commit to _renderSlots.
 */
function commit(container) {
    const fn = _renderFns.get(container);
    if (!fn) return;

    let result = fn();
    if (typeof result === 'function') result = result();
    const prev = _renderSlots.get(container);

    // Normalize: expand #comp vnodes and track lifecycle
    const vnodes = normalizeVNodesWithLifecycle(result, prev);

    if (!prev) {
        for (const v of vnodes) {
            const d = createDom(v);
            _vnodeDom.set(v, d);
            container.appendChild(d);
        }
    } else {
        diffContainer(container, prev, vnodes);
    }

    _renderSlots.set(container, vnodes);
}

/**
 * Normalize render output: filter nulls, expand #comp vnodes,
 * and manage component lifecycle based on key changes.
 */
function normalizeVNodesWithLifecycle(result, prevVnodes) {
    const oldEntries = [..._compRegistry.entries()].map(([key, renderer]) => ({ key, renderer }));
    const oldKeyMap = new Map(oldEntries.map(e => [e.key, e]));
    const newEntries = [];

    const normalized = normalizeRecursive(result, oldKeyMap, newEntries);

    for (const entry of oldEntries) {
        if (!newEntries.some(e => e.key === entry.key)) {
            unmountComponent(entry.key, entry.renderer);
        }
    }
    for (const entry of newEntries) {
        if (!oldKeyMap.has(entry.key)) {
            mountComponent(entry.key, entry.renderer);
        }
    }

    // Sync registry with current render (prevVnodes are normalized and lack #comp tags,
    // so collectCompEntries always returns [] after the first render)
    const newKeySet = new Set(newEntries.map(e => e.key));
    for (const [key] of _compRegistry) {
        if (!newKeySet.has(key)) _compRegistry.delete(key);
    }
    for (const entry of newEntries) {
        _compRegistry.set(entry.key, entry.renderer);
    }

    return normalized;
}

/**
 * Recursively normalize a value to a flat VNode array, expanding
 * #comp vnodes into their rendered content while tracking lifecycle.
 *
 * When prevCh is provided, preserves _vnodeDom entries so that diff
 * can locate existing DOM after normalization creates new vnode objects.
 */
function normalizeRecursive(result, oldKeyMap, newEntries, prevCh) {
    if (result == null) return [];
    if (Array.isArray(result)) {
        const flat = [];
        let idx = 0;
        for (const item of result) {
            flat.push(...normalizeRecursive(item, oldKeyMap, newEntries, prevCh && prevCh[idx]));
            idx++;
        }
        return flat;
    }

    const vnode = result;
    if (typeof vnode !== 'object') return [{ tag: '#text', text: String(vnode) }];
    if (vnode.tag === '#text') return [vnode];

    if (vnode.tag === '#comp') {
        const renderer = vnode.props?.component;
        const key = vnode.props?.key;
        if (key !== undefined) {
            const existing = newEntries.find(e => e.key === key);
            if (!existing) newEntries.push({ key, renderer });
        }
        if (renderer && typeof renderer === 'function') {
            const content = renderer();
            const prevExpanded = key !== undefined ? _compExpandedCache.get(key) : null;
            const result = normalizeRecursive(content, oldKeyMap, newEntries, prevExpanded);
            if (key !== undefined) _compExpandedCache.set(key, result);
            return result;
        }
        return normalizeRecursive([...(vnode.ch || [])], oldKeyMap, newEntries, prevCh);
    }

    const rawChildren = vnode.ch || [];
    const prevChildren = prevCh && prevCh.ch ? prevCh.ch : null;
    const children = [];
    for (let i = 0; i < rawChildren.length; i++) {
        const normalized = normalizeRecursive(rawChildren[i], oldKeyMap, newEntries, prevChildren && prevChildren[i]);
        children.push(...normalized);
    }

    const newVNode = { tag: vnode.tag, props: vnode.props, ch: children };

    // Preserve _vnodeDom entry: if the old vnode at this position had a
    // DOM association, transfer it to the new normalized vnode so diff
    // can locate existing DOM without creating duplicates.
    if (prevCh && _vnodeDom.has(prevCh)) {
        _vnodeDom.set(newVNode, _vnodeDom.get(prevCh));
    }

    return [newVNode];
}

/** Collect all #comp entries {key, renderer} from a vnode tree. */
function collectCompEntries(vnodes, entries) {
    for (const v of vnodes || []) {
        if (!v) continue;
        if (v.tag === '#comp') {
            const key = v.props?.key;
            const renderer = v.props?.component;
            if (key !== undefined) entries.push({ key, renderer });
        }
        if (v.ch) collectCompEntries(v.ch, entries);
    }
    return entries;
}

/**
 * Diff two VNode arrays inside a container, patching in place.
 *
 * Fix: anchor tracking ensures correct DOM insertion order.
 * Fix: _vnodeDom updated after every patch.
 */
function diffContainer(container, prev, vnodes) {
    const maxLen = Math.max(vnodes.length, prev.length);
    let lastDom = null;

    for (let i = 0; i < maxLen; i++) {
        const oldV = prev[i], newV = vnodes[i];

        if (!newV && oldV) {
            const d = getDom(oldV);
            if (d?.parentNode) {
                if (d.nodeType === Node.ELEMENT_NODE) sweepDom(d);
                d.parentNode.removeChild(d);
                lastDom = i > 0 ? getDom(prev[i - 1]) : null;
            }
            continue;
        }
        if (newV && !oldV) {
            const d = createDom(newV);
            _vnodeDom.set(newV, d);
            container.insertBefore(d, lastDom ? lastDom.nextSibling : null);
            lastDom = d;
            continue;
        }

        const oldDom = getDom(oldV);
        if (oldDom && oldV.tag === newV.tag) {
            patchNode(oldDom.nodeType === 1 ? oldDom.parentNode : container, oldV, newV, null);
            lastDom = getDom(newV);
        } else if (oldDom && !oldDom.parentNode) {
            // oldDom exists in _vnodeDom but detached from the tree
            if (oldDom.nodeType === Node.ELEMENT_NODE) sweepDom(oldDom);
            const nd = createDom(newV);
            _vnodeDom.set(newV, nd);
            container.insertBefore(nd, lastDom ? lastDom.nextSibling : null);
            lastDom = nd;
        } else if (oldDom && oldV.tag !== newV.tag) {
            // tag mismatch — replace old DOM with new
            if (oldDom.nodeType === Node.ELEMENT_NODE) sweepDom(oldDom);
            const nd = createDom(newV);
            _vnodeDom.set(newV, nd);
            oldDom.parentNode.replaceChild(nd, oldDom);
            lastDom = nd;
        } else {
            // oldDom is null — create and insert new DOM
            const nd = createDom(newV);
            _vnodeDom.set(newV, nd);
            container.insertBefore(nd, lastDom ? lastDom.nextSibling : null);
            lastDom = nd;
        }
    }
}