// 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. Save (Ctrl+S) writes back via PUT
// when the file came from a server URL; FS-API and zip-virtual files
// are read-only for now (toolbar shows a hint).
//
// Toast UI Editor is loaded from mdedit's bundled vendor file in the
// browse build (see browse/build.sh). window.toastui is available
// synchronously when 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 }

    // Compute SHA-256 hex of a string for a quick "is this content
    // different from what was loaded?" check. Used to decide whether
    // the save button should be active. Not used for integrity.
    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;
    }

    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;
        }

        // Tear down any previous markdown instance (single-file model).
        dispose();

        // Read the file 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, dirty marker)     │
        //   ├──────────────────────────────────┤
        //   │ Toast UI editor                  │
        //   └──────────────────────────────────┘
        //
        // TOC pane is deferred — a near-term iteration can split this
        // into editor | toc once the simpler form is exercised.
        container.innerHTML = '';
        container.style.display = 'flex';
        container.style.flexDirection = 'column';

        var toolbar = document.createElement('div');
        toolbar.className = 'md-toolbar';
        toolbar.style.cssText = 'display:flex;align-items:center;gap:0.5rem;'
            + 'padding:0.35rem 0.75rem;background:var(--bg-secondary);'
            + 'border-bottom:1px solid var(--border);flex-shrink:0;';

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

        var dirty = document.createElement('span');
        dirty.style.cssText = 'color:var(--text-muted);font-size:0.85rem;';
        dirty.textContent = '';

        var status = document.createElement('span');
        status.style.cssText = 'flex:1;text-align:right;color:var(--text-muted);font-size:0.85rem;';

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

        var editorHost = document.createElement('div');
        editorHost.style.cssText = 'flex:1;min-height:0;overflow:hidden;';
        container.appendChild(editorHost);

        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 };

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

        editor.on('change', async function () {
            var current = editor.getMarkdown();
            var h = await hashContent(current);
            markDirty(h !== currentInstance.hash);
        });

        async function save() {
            if (!currentInstance.dirty) return;
            var content = editor.getMarkdown();
            // Read-only sources: zip-virtual, FS-API without write
            // permission. For now we only attempt PUT against server URLs;
            // FS-API saves can be wired in a later iteration via the
            // existing zddc-source polyfill.
            if (!node.url || window.app.state.source !== 'server') {
                status.textContent = 'Save not yet supported for this source.';
                return;
            }
            try {
                status.textContent = 'Saving…';
                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);
                }
                currentInstance.hash = await hashContent(content);
                markDirty(false);
                status.textContent = 'Saved ' + new Date().toLocaleTimeString();
            } catch (e) {
                status.textContent = 'Save failed: ' + (e.message || e);
            }
        }

        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.preventDefault();
                save();
            }
        });
    }

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