/**
 * session_state.js
 * 放在 assets/ 目錄，Dash 自動載入。
 */
(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(state) {
        try { sessionStorage.setItem(STORE_KEY, JSON.stringify(state)); }
        catch (e) {}
    }

    function getPathname() { return window.location.pathname || "/"; }

    function getPageState() {
        var s = loadState(); var p = getPathname();
        if (!s[p]) s[p] = {};
        return { state: s, page: p, ps: s[p] };
    }

    function save(key, value) {
        var r = getPageState();
        r.ps[key] = value;
        r.state[r.page] = r.ps;
        saveState(r.state);
    }

    // ── 從 id 字串取得 key ────────────────────────────────────────────────

    function parseId(idStr) {
        try { return JSON.parse(idStr); }
        catch (e) { return null; }
    }

    // ── 快照目前頁面所有狀態 ──────────────────────────────────────────────

    function snapshotState() {
        var r = getPageState();
        var ps = r.ps;

        // 1. 填空題輸入值
        if (!ps.quiz_inputs) ps.quiz_inputs = {};
        document.querySelectorAll("[id]").forEach(function (el) {
            var parsed = parseId(el.id);
            if (!parsed || parsed.type !== "quiz-input") return;
            var inp = el.querySelector("input");
            if (inp) ps.quiz_inputs[parsed.qid] = inp.value || "";
        });

        // 2. 選擇題已選中的按鈕（找 data-active 或 aria-pressed 的按鈕）
        if (!ps.quiz_choice) ps.quiz_choice = {};
        document.querySelectorAll("[id]").forEach(function (el) {
            var parsed = parseId(el.id);
            if (!parsed || parsed.type !== "quiz-feedback-choice") return;
            // feedback 有內容代表已作答
            if (el.textContent && el.textContent.trim()) {
                ps.quiz_choice[parsed.qid] = {
                    children: el.textContent.trim(),
                    color: el.getAttribute("data-color") || ""
                };
            }
        });

        // 3. 解法展開狀態
        if (!ps.solutions) ps.solutions = {};
        document.querySelectorAll("button[id]").forEach(function (btn) {
            var parsed = parseId(btn.id);
            if (!parsed || parsed.type !== "solution-toggle") return;
            var key = parsed.key;
            // 找對應的 collapse 元素，判斷是否展開
            var collapseEl = document.querySelector(
                '[id=\'{"key":"' + key + '","type":"solution-collapse"}\'],' +
                '[id=\'{"type":"solution-collapse","key":"' + key + '"}\']'
            );
            if (collapseEl) {
                ps.solutions[key] = collapseEl.offsetHeight > 10;
            }
        });

        r.state[r.page] = ps;
        saveState(r.state);
    }

    // ── 恢復狀態 ──────────────────────────────────────────────────────────

    var _restoring = false;

    function restoreState() {
        var r = getPageState();
        var ps = r.ps;
        _restoring = true;

        // 1. 恢復 section
        if (ps.section) {
            var secBtn = document.querySelector('[data-sid="' + ps.section + '"]');
            if (secBtn) secBtn.click();
        }

        // 2. 恢復填空題輸入值
        var inputs = ps.quiz_inputs || {};
        Object.keys(inputs).forEach(function (qid) {
            var val = inputs[qid];
            if (!val) return;
            var el = document.querySelector('[id=\'{"qid":"' + qid + '","type":"quiz-input"}\'],' +
                '[id=\'{"type":"quiz-input","qid":"' + qid + '"}\']');
            if (!el) return;
            var inp = el.querySelector("input");
            if (!inp) return;
            var setter = Object.getOwnPropertyDescriptor(window.HTMLInputElement.prototype, "value").set;
            setter.call(inp, val);
            inp.dispatchEvent(new Event("input", { bubbles: true }));
        });

        // 3. 恢復解法展開（點擊 toggle 按鈕）
        var solutions = ps.solutions || {};
        Object.keys(solutions).forEach(function (key) {
            if (!solutions[key]) return;
            var btn = document.querySelector(
                '[id=\'{"key":"' + key + '","type":"solution-toggle"}\'],' +
                '[id=\'{"type":"solution-toggle","key":"' + key + '"}\']'
            );
            if (btn) btn.click();
        });

        setTimeout(function () { _restoring = false; }, 600);
    }

    // ── 監聽 section 按鈕點擊 ────────────────────────────────────────────

    var _secListened = new Set();

    function attachSectionListeners() {
        document.querySelectorAll("[data-sid]").forEach(function (btn) {
            var sid = btn.getAttribute("data-sid");
            if (_secListened.has(sid)) return;
            _secListened.add(sid);
            btn.addEventListener("click", function () {
                if (_restoring) return;
                save("section", sid);
            });
        });
    }

    // ── 定時快照（每 2 秒存一次目前狀態）────────────────────────────────

    function startAutoSnapshot() {
        setInterval(function () {
            if (!_restoring) snapshotState();
        }, 2000);
    }

    // ── 監聽 URL 變化 ─────────────────────────────────────────────────────

    var _lastPathname = null;
    var _restoreTimer = null;

    function checkPathname() {
        var cur = getPathname();
        if (cur !== _lastPathname) {
            _lastPathname = cur;
            _secListened.clear();
            clearTimeout(_restoreTimer);
            _restoreTimer = setTimeout(function () {
                attachSectionListeners();
                restoreState();
            }, 1000);
        } else {
            attachSectionListeners();
        }
    }

    // ── 初始化 ────────────────────────────────────────────────────────────

    var _mutTimer = null;
    var observer = new MutationObserver(function () {
        clearTimeout(_mutTimer);
        _mutTimer = setTimeout(checkPathname, 150);
    });

    function init() {
        _lastPathname = getPathname();
        observer.observe(document.body, { childList: true, subtree: true });
        startAutoSnapshot();
        setTimeout(function () {
            attachSectionListeners();
            restoreState();
        }, 1200);
    }

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

})();