/**
 * session_state.js
 * 事件驅動版，不做定時掃描，只在互動時儲存。
 */
(function () {
    "use strict";

    var STORE_KEY = "dash_math_page_state";

    function loadState() {
        try { return JSON.parse(sessionStorage.getItem(STORE_KEY) || "{}"); }
        catch (e) { return {}; }
    }
    function saveState(s) {
        try { sessionStorage.setItem(STORE_KEY, JSON.stringify(s)); }
        catch (e) {}
    }
    function getPathname() { return window.location.pathname || "/"; }

    function saveProp(key, value) {
        var s = loadState(), p = getPathname();
        if (!s[p]) s[p] = {};
        s[p][key] = value;
        saveState(s);
    }
    function saveNested(group, key, value) {
        var s = loadState(), p = getPathname();
        if (!s[p]) s[p] = {};
        if (!s[p][group]) s[p][group] = {};
        s[p][group][key] = value;
        saveState(s);
    }
    function getPs() {
        var s = loadState(), p = getPathname();
        return s[p] || {};
    }

    // ── 恢復 ──────────────────────────────────────────────────────────────

    var _restoring = false;

    function restoreState() {
        var ps = getPs();
        _restoring = true;

        // Section
        if (ps.section) {
            var b = document.querySelector('[data-sid="' + ps.section + '"]');
            if (b) b.click();
        }

        // 填空題
        var inputs = ps.quiz_inputs || {};
        Object.keys(inputs).forEach(function (qid) {
            var val = inputs[qid];
            if (!val) return;
            // 用 querySelectorAll 找包含此 qid 的 input
            document.querySelectorAll("input").forEach(function (el) {
                var w = el.closest("[id]");
                if (!w || w.id.indexOf(qid) === -1 || w.id.indexOf("quiz-input") === -1) return;
                var setter = Object.getOwnPropertyDescriptor(window.HTMLInputElement.prototype, "value").set;
                setter.call(el, val);
                el.dispatchEvent(new Event("input", { bubbles: true }));
            });
        });

        // 解法展開
        var solutions = ps.solutions || {};
        Object.keys(solutions).forEach(function (key) {
            if (!solutions[key]) return;
            document.querySelectorAll("button").forEach(function (btn) {
                if (btn.id && btn.id.indexOf(key) > -1 && btn.id.indexOf("solution-toggle") > -1) {
                    btn.click();
                }
            });
        });

        setTimeout(function () { _restoring = false; }, 800);
    }

    // ── 掛載監聽 ─────────────────────────────────────────────────────────

    var _attached = new Set();

    function attachListeners() {
        // Section 按鈕
        document.querySelectorAll("[data-sid]").forEach(function (btn) {
            var sid = btn.getAttribute("data-sid");
            if (_attached.has("s:" + sid)) return;
            _attached.add("s:" + sid);
            btn.addEventListener("click", function () {
                if (!_restoring) saveProp("section", sid);
            });
        });

        // 填空題 input
        document.querySelectorAll("input").forEach(function (el) {
            if (_attached.has(el)) return;
            var w = el.closest("[id]");
            if (!w || !w.id || w.id.indexOf("quiz-input") === -1) return;
            var m = w.id.match(/"qid":"([^"]+)"/);
            if (!m) return;
            var qid = m[1];
            _attached.add(el);
            el.addEventListener("change", function () {
                if (!_restoring) saveNested("quiz_inputs", qid, el.value);
            });
        });

        // 解法 toggle 按鈕
        document.querySelectorAll("button").forEach(function (btn) {
            if (_attached.has(btn)) return;
            if (!btn.id || btn.id.indexOf("solution-toggle") === -1) return;
            var m = btn.id.match(/"key":"([^"]+)"/);
            if (!m) return;
            var key = m[1];
            _attached.add(btn);
            btn.addEventListener("click", function () {
                if (_restoring) return;
                // 延遲判斷是否展開
                setTimeout(function () {
                    var col = document.querySelector('[id*="' + key + '"][id*="solution-collapse"]');
                    var opened = col ? col.offsetHeight > 10 : false;
                    saveNested("solutions", key, opened);
                }, 400);
            });
        });
    }

    // ── 換頁偵測 ─────────────────────────────────────────────────────────

    var _lastPath = null, _timer = null;

    function checkPath() {
        var cur = getPathname();
        if (cur !== _lastPath) {
            _lastPath = cur;
            _attached.clear();
            clearTimeout(_timer);
            _timer = setTimeout(function () {
                attachListeners();
                restoreState();
            }, 900);
        } else {
            attachListeners();
        }
    }

    // MutationObserver：只做 debounce checkPath，不掃描整個 DOM
    var _mutTimer = null;
    var obs = new MutationObserver(function () {
        clearTimeout(_mutTimer);
        _mutTimer = setTimeout(checkPath, 200);
    });

    function init() {
        _lastPath = getPathname();
        obs.observe(document.body, { childList: true, subtree: false }); // subtree:false 減少觸發
        setTimeout(function () {
            attachListeners();
            restoreState();
        }, 1000);
    }

    if (document.readyState === "loading") {
        document.addEventListener("DOMContentLoaded", init);
    } else {
        init();
    }

})();