// preview-markdown.js — markdown plugin for the browse preview pane.
// Click a .md / .markdown file in the tree → instantiate Toast UI
// editor inside the right pane, alongside a TOC pane on the right.
// Save (Ctrl+S) writes back via:
//   - PUT to the file's server URL when in server mode, or
//   - FileSystemWritableFileStream when in FS-API mode (local folder
//     picker). Both paths set dirty=false + a status timestamp on
//     success.
// zip-virtual files are read-only — the save button stays disabled.
//
// Toast UI Editor is bundled (shared/vendor/toastui-editor-all.min.js)
// and is available synchronously as window.toastui by the time this
// module runs.
(function () {
    'use strict';

    if (!window.app || !window.app.modules) return;

    function escapeHtml(s) {
        return String(s).replace(/&/g, '&amp;').replace(/</g, '&lt;')
            .replace(/>/g, '&gt;').replace(/"/g, '&quot;');
    }

    var currentInstance = null; // { editor, container, dirty, node, hash, tocEl }

    // Compute SHA-256 hex of a string for a "is this content different
    // from what we loaded?" check. Used to enable/disable Save.
    async function hashContent(text) {
        if (!window.crypto || !window.crypto.subtle) return null;
        var enc = new TextEncoder().encode(text);
        var buf = await window.crypto.subtle.digest('SHA-256', enc);
        var bytes = new Uint8Array(buf);
        var hex = '';
        for (var i = 0; i < bytes.length; i++) {
            hex += bytes[i].toString(16).padStart(2, '0');
        }
        return hex;
    }

    function dispose() {
        if (currentInstance && currentInstance.editor) {
            try { currentInstance.editor.destroy(); } catch (_) { /* ignore */ }
        }
        currentInstance = null;
    }

    // ── TOC (table of contents) ─────────────────────────────────────────────
    //
    // Ported from mdedit/js/toc.js, condensed: parse markdown for ATX-style
    // headings, build a flat hierarchical list, click jumps the editor to
    // the heading's line. We track WYSIWYG vs markdown mode and route the
    // scroll behaviour to whichever pane is visible.

    function parseHeadings(content) {
        var headings = [];
        var lines = content.split('\n');
        for (var i = 0; i < lines.length; i++) {
            var m = lines[i].match(/^(#{1,6})\s+(.+)$/);
            if (!m) continue;
            var text = m[2].trim()
                .replace(/\\(.)/g, '$1')
                .replace(/\*\*(.*?)\*\*/g, '$1')
                .replace(/\*(.*?)\*/g, '$1')
                .replace(/`(.*?)`/g, '$1')
                .replace(/\[(.*?)\]\(.*?\)/g, '$1')
                .replace(/~~(.*?)~~/g, '$1')
                .trim();
            headings.push({ level: m[1].length, text: text, lineIndex: i });
        }
        return headings;
    }

    function scrollEditorToHeading(editor, heading) {
        try {
            var els = editor.getEditorElements();
            if (editor.isWysiwygMode && editor.isWysiwygMode()) {
                var ww = els.wwEditor;
                if (!ww) return;
                var hs = ww.querySelectorAll('h1, h2, h3, h4, h5, h6');
                for (var i = 0; i < hs.length; i++) {
                    if (hs[i].textContent.trim() === heading.text) {
                        var top = hs[i].getBoundingClientRect().top - ww.getBoundingClientRect().top;
                        ww.scrollTop = top - 10;
                        flashHeading(hs[i]);
                        return;
                    }
                }
            } else {
                var line = heading.lineIndex + 1;
                try { editor.setSelection([line, 1], [line, 1]); } catch (_) { /* ignore */ }
                var preview = els.mdPreview;
                if (!preview) return;
                var phs = preview.querySelectorAll('h1, h2, h3, h4, h5, h6');
                for (var j = 0; j < phs.length; j++) {
                    if (phs[j].textContent.trim() === heading.text) {
                        var ptop = phs[j].getBoundingClientRect().top - preview.getBoundingClientRect().top;
                        preview.scrollTop = ptop - 10;
                        flashHeading(phs[j]);
                        return;
                    }
                }
            }
        } catch (e) { /* swallow; click was best-effort */ }
    }

    function flashHeading(el) {
        if (!el) return;
        el.style.transition = 'background-color 0.3s ease';
        el.style.backgroundColor = 'var(--primary-light)';
        setTimeout(function () {
            el.style.backgroundColor = '';
            setTimeout(function () { el.style.transition = ''; }, 300);
        }, 1200);
    }

    function renderToc(tocEl, content, editor) {
        if (!tocEl) return;
        var headings = parseHeadings(content);
        if (!content.trim()) {
            tocEl.innerHTML = '<p class="toc-empty">Empty file.</p>';
            return;
        }
        if (headings.length === 0) {
            tocEl.innerHTML = '<p class="toc-empty">No headings.</p>';
            return;
        }
        // Build a flat ordered list; CSS handles the visual indent.
        var html = '<ul class="toc-list">';
        for (var i = 0; i < headings.length; i++) {
            var h = headings[i];
            html += '<li class="toc-item toc-level-' + h.level + '" data-line="' + h.lineIndex + '" data-text="' + escapeHtml(h.text) + '">'
                + '<a href="#" tabindex="0">' + escapeHtml(h.text) + '</a></li>';
        }
        html += '</ul>';
        tocEl.innerHTML = html;

        // One delegated click handler.
        tocEl.querySelectorAll('.toc-item').forEach(function (li) {
            li.addEventListener('click', function (e) {
                e.preventDefault();
                var idx = parseInt(li.dataset.line, 10);
                var text = li.dataset.text;
                scrollEditorToHeading(editor, { text: text, lineIndex: idx });
            });
        });
    }

    // Light debounce so TOC doesn't rebuild on every keystroke.
    function debounce(fn, ms) {
        var t;
        return function () {
            clearTimeout(t);
            var args = arguments, self = this;
            t = setTimeout(function () { fn.apply(self, args); }, ms);
        };
    }

    // ── Save (server + FS-API) ──────────────────────────────────────────────

    async function saveContent(node, content) {
        // FS-API mode: write via the local file handle.
        if (node.handle && typeof node.handle.createWritable === 'function') {
            var writable = await node.handle.createWritable();
            await writable.write(content);
            await writable.close();
            return;
        }
        // Server mode: PUT the new bytes.
        if (node.url && window.app.state.source === 'server') {
            var resp = await fetch(node.url, {
                method: 'PUT',
                headers: { 'Content-Type': 'text/markdown; charset=utf-8' },
                body: content,
                credentials: 'same-origin'
            });
            if (!resp.ok) {
                throw new Error('HTTP ' + resp.status);
            }
            return;
        }
        throw new Error('No write target for this file (read-only source).');
    }

    function canSave(node) {
        if (node.zipParentId != null) return false;
        if (node.handle && typeof node.handle.createWritable === 'function') return true;
        if (node.url && window.app.state.source === 'server') return true;
        return false;
    }

    // ── Mount ───────────────────────────────────────────────────────────────

    async function render(node, container, ctx) {
        if (typeof window.toastui === 'undefined') {
            container.innerHTML =
                '<div class="preview-empty" style="color:var(--danger)">'
                + 'Toast UI Editor isn\'t bundled in this build.</div>';
            return;
        }

        dispose();

        // Read content.
        var text;
        try {
            var buf = await ctx.getArrayBuffer(node);
            text = new TextDecoder('utf-8', { fatal: false }).decode(buf);
        } catch (e) {
            container.innerHTML =
                '<div class="preview-empty" style="color:var(--danger)">'
                + 'Could not read ' + escapeHtml(node.name) + ': '
                + escapeHtml(e.message || String(e)) + '</div>';
            return;
        }

        // Build the markdown plugin's DOM:
        //   ┌──────────────────────────────────────────────────┐
        //   │ toolbar (Save, ● modified, status, source hint)  │
        //   ├──────────────────────────────────┬───────────────┤
        //   │ editor (Toast UI)                │ TOC pane      │
        //   └──────────────────────────────────┴───────────────┘
        container.innerHTML = '';
        container.style.display = 'flex';
        container.style.flexDirection = 'column';

        var toolbar = document.createElement('div');
        toolbar.className = 'md-toolbar';

        var saveBtn = document.createElement('button');
        saveBtn.className = 'btn btn-sm btn-primary';
        saveBtn.type = 'button';
        saveBtn.textContent = 'Save';
        saveBtn.disabled = true;

        var dirty = document.createElement('span');
        dirty.className = 'md-toolbar__dirty';

        var status = document.createElement('span');
        status.className = 'md-toolbar__status';

        var sourceHint = document.createElement('span');
        sourceHint.className = 'md-toolbar__source';
        if (node.zipParentId != null) {
            sourceHint.textContent = 'read-only (inside zip)';
        } else if (node.handle) {
            sourceHint.textContent = 'local';
        } else if (node.url) {
            sourceHint.textContent = 'server';
        }

        toolbar.appendChild(saveBtn);
        toolbar.appendChild(dirty);
        toolbar.appendChild(status);
        toolbar.appendChild(sourceHint);
        container.appendChild(toolbar);

        var split = document.createElement('div');
        split.className = 'md-split';
        container.appendChild(split);

        var editorHost = document.createElement('div');
        editorHost.className = 'md-editor-host';
        split.appendChild(editorHost);

        var tocPane = document.createElement('div');
        tocPane.className = 'md-toc-pane';
        var tocHeader = document.createElement('div');
        tocHeader.className = 'md-toc-pane__header';
        tocHeader.textContent = 'Outline';
        var tocBody = document.createElement('div');
        tocBody.className = 'md-toc-pane__body';
        tocBody.innerHTML = '<p class="toc-empty">Loading…</p>';
        tocPane.appendChild(tocHeader);
        tocPane.appendChild(tocBody);
        split.appendChild(tocPane);

        var initialHash = await hashContent(text);
        var editor = new window.toastui.Editor({
            el: editorHost,
            height: '100%',
            initialEditType: 'markdown',
            previewStyle: 'vertical',
            initialValue: text,
            usageStatistics: false,
            toolbarItems: [
                ['heading', 'bold', 'italic', 'strike'],
                ['hr', 'quote'],
                ['ul', 'ol', 'task', 'indent', 'outdent'],
                ['table', 'image', 'link'],
                ['code', 'codeblock']
            ]
        });

        currentInstance = {
            editor: editor,
            container: container,
            dirty: false,
            node: node,
            hash: initialHash,
            tocEl: tocBody
        };

        var writable = canSave(node);
        if (!writable) {
            saveBtn.disabled = true;
            saveBtn.title = 'Save not available — read-only source.';
        }

        renderToc(tocBody, text, editor);

        function markDirty(isDirty) {
            currentInstance.dirty = isDirty;
            saveBtn.disabled = !isDirty || !writable;
            dirty.textContent = isDirty ? '● modified' : '';
        }

        var updateOnChange = debounce(async function () {
            var current = editor.getMarkdown();
            var h = await hashContent(current);
            markDirty(h !== currentInstance.hash);
            renderToc(tocBody, current, editor);
        }, 250);

        editor.on('change', updateOnChange);

        async function save() {
            if (!currentInstance.dirty || !writable) return;
            var content = editor.getMarkdown();
            try {
                status.textContent = 'Saving…';
                await saveContent(node, content);
                currentInstance.hash = await hashContent(content);
                markDirty(false);
                var now = new Date();
                status.textContent = 'Saved ' + now.toLocaleTimeString();
                if (window.zddc && window.zddc.toast) {
                    window.zddc.toast('Saved ' + node.name, 'success');
                }
            } catch (e) {
                status.textContent = 'Save failed: ' + (e.message || e);
                if (window.zddc && window.zddc.toast) {
                    window.zddc.toast('Save failed: ' + (e.message || e), 'error');
                }
            }
        }

        saveBtn.addEventListener('click', save);

        // Ctrl+S / Cmd+S inside the editor → save.
        container.addEventListener('keydown', function (e) {
            if ((e.ctrlKey || e.metaKey) && (e.key === 's' || e.key === 'S')) {
                e.preventDefault();
                save();
            }
        });
    }

    window.app.modules.markdown = {
        render: render,
        dispose: dispose
    };
})();