export type ViewerTheme = 'dark' | 'light' | undefined;

export interface PageOptions {
  /** webview.cspSource */
  cspSource: string;
  nonce: string;
  /** Forced diagram theme; undefined keeps the diagram's own choice. */
  theme: ViewerTheme;
  /** Location hash to restore (Archify keeps focus/route state there). */
  hash?: string;
  /** Opaque state handed to vscode.setState for panel restore. */
  state?: unknown;
  /** Banner shown on top of the diagram. */
  notice?: { text: string; kind: 'info' | 'warning' | 'error' };
}

export function makeNonce(): string {
  const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
  let nonce = '';
  for (let i = 0; i < 32; i += 1) nonce += chars.charAt(Math.floor(Math.random() * chars.length));
  return nonce;
}

export function escapeHtml(value: string): string {
  return value
    .replace(/&/g, '&amp;')
    .replace(/</g, '&lt;')
    .replace(/>/g, '&gt;')
    .replace(/"/g, '&quot;')
    .replace(/'/g, '&#39;');
}

/** JSON that is safe to embed inside an inline <script>. */
function scriptJson(value: unknown): string {
  return JSON.stringify(value ?? null)
    .replace(/</g, '\\u003c')
    .replace(/>/g, '\\u003e')
    .replace(/\u2028/g, '\\u2028')
    .replace(/\u2029/g, '\\u2029');
}

export function contentSecurityPolicy(cspSource: string, nonce: string): string {
  return [
    "default-src 'none'",
    `img-src ${cspSource} https: data: blob:`,
    `media-src ${cspSource} data: blob:`,
    `font-src ${cspSource} data:`,
    `style-src ${cspSource} 'unsafe-inline'`,
    `script-src 'nonce-${nonce}'`,
    'connect-src data: blob:',
    'worker-src blob:',
  ].join('; ');
}

/**
 * Runs before any page script: pins the theme, restores the hash, and
 * routes links, window.open and export downloads to the extension, since a
 * webview cannot navigate or download on its own.
 */
function bridgeScript(options: PageOptions): string {
  const config = { theme: options.theme, hash: options.hash, state: options.state, notice: options.notice };
  return `(function () {
  var config = ${scriptJson(config)};
  var vscode = acquireVsCodeApi();
  if (config.state) vscode.setState(config.state);
  if (config.theme) {
    try { localStorage.setItem('archify-theme', config.theme); } catch (_) {}
  }
  if (config.hash && !location.hash) {
    try { history.replaceState(null, '', config.hash); } catch (_) {}
  }
  window.addEventListener('hashchange', function () {
    if (config.state) vscode.setState(Object.assign({}, config.state, { hash: location.hash }));
    vscode.postMessage({ type: 'hash', hash: location.hash });
  });

  function post(message) { vscode.postMessage(message); }

  function saveBlobUrl(url, filename) {
    fetch(url).then(function (response) { return response.blob(); }).then(function (blob) {
      var reader = new FileReader();
      reader.onload = function () {
        var data = String(reader.result);
        post({ type: 'save', filename: filename || 'archify-export', base64: data.slice(data.indexOf(',') + 1) });
      };
      reader.readAsDataURL(blob);
    }).catch(function (error) {
      post({ type: 'error', message: 'Export failed: ' + (error && error.message || error) });
    });
  }

  document.addEventListener('click', function (event) {
    var target = event.target;
    var anchor = target && target.closest ? target.closest('a[href]') : null;
    if (!anchor) return;
    var href = anchor.getAttribute('href') || '';
    if (anchor.hasAttribute('download') && /^(blob|data):/i.test(anchor.href)) {
      event.preventDefault();
      saveBlobUrl(anchor.href, anchor.getAttribute('download'));
      return;
    }
    if (href.charAt(0) === '#') return;
    event.preventDefault();
    if (anchor.classList.contains('semantic-passport-source')) {
      var pathNode = anchor.querySelector('small');
      var match = /#L(\\d+)(?:-L(\\d+))?$/.exec(anchor.href);
      post({
        type: 'openSource',
        path: pathNode ? pathNode.textContent : '',
        line: match ? Number(match[1]) : undefined,
        endLine: match && match[2] ? Number(match[2]) : undefined,
        href: anchor.href
      });
      return;
    }
    if (/^(https?|mailto):/i.test(href)) post({ type: 'openExternal', href: href });
    else post({ type: 'openRelative', href: href });
  }, true);

  var nativeOpen = window.open;
  window.open = function (url) {
    if (typeof url === 'string' && /^(https?|mailto):/i.test(url)) {
      post({ type: 'openExternal', href: url });
      return null;
    }
    return nativeOpen ? nativeOpen.apply(window, arguments) : null;
  };

  function showNotice(notice) {
    var existing = document.getElementById('archify-vscode-notice');
    if (existing) existing.remove();
    if (!notice || !notice.text) return;
    var bar = document.createElement('div');
    bar.id = 'archify-vscode-notice';
    bar.setAttribute('role', notice.kind === 'error' ? 'alert' : 'status');
    bar.className = 'archify-vscode-notice archify-vscode-notice-' + notice.kind;
    var text = document.createElement('span');
    text.textContent = notice.text;
    var close = document.createElement('button');
    close.type = 'button';
    close.textContent = '\\u00d7';
    close.title = 'Dismiss';
    close.addEventListener('click', function () { bar.remove(); });
    bar.appendChild(text);
    bar.appendChild(close);
    (document.body || document.documentElement).appendChild(bar);
  }

  window.addEventListener('message', function (event) {
    var message = event.data || {};
    if (message.type === 'notice') showNotice(message.notice);
  });
  if (config.notice) {
    if (document.readyState === 'loading') {
      document.addEventListener('DOMContentLoaded', function () { showNotice(config.notice); });
    } else {
      showNotice(config.notice);
    }
  }
})();`;
}

const NOTICE_STYLE = `
.archify-vscode-notice {
  position: fixed; left: 12px; right: 12px; bottom: 12px; z-index: 2147483647;
  display: flex; gap: 12px; align-items: flex-start; justify-content: space-between;
  padding: 8px 12px; border-radius: 6px; font: 12px/1.45 var(--vscode-font-family, system-ui, sans-serif);
  color: var(--vscode-editorWidget-foreground, #ddd); background: var(--vscode-editorWidget-background, #252526);
  border: 1px solid var(--vscode-editorWidget-border, #454545); box-shadow: 0 4px 16px rgba(0,0,0,.35);
  white-space: pre-wrap;
}
.archify-vscode-notice-warning { border-left: 4px solid var(--vscode-editorWarning-foreground, #cca700); }
.archify-vscode-notice-error { border-left: 4px solid var(--vscode-editorError-foreground, #f14c4c); }
.archify-vscode-notice-info { border-left: 4px solid var(--vscode-editorInfo-foreground, #3794ff); }
.archify-vscode-notice button {
  background: none; border: 0; color: inherit; cursor: pointer; font-size: 16px; line-height: 1; padding: 0 2px;
}`;

/** Prepares Archify HTML for a VS Code webview. */
export function prepareDiagramHtml(html: string, options: PageOptions): string {
  const head =
    `<meta http-equiv="Content-Security-Policy" content="${escapeHtml(contentSecurityPolicy(options.cspSource, options.nonce))}">\n` +
    `<script nonce="${options.nonce}">${bridgeScript(options)}</script>\n` +
    `<style>${NOTICE_STYLE}</style>\n`;

  let page = html
    // Drop any CSP the file brings along; ours is the one that applies.
    .replace(/<meta\s+http-equiv=["']Content-Security-Policy["'][^>]*>/gi, '')
    // Allow the page's own inline scripts to run under the nonce policy.
    .replace(/<script\b(?![^>]*\bnonce=)/gi, `<script nonce="${options.nonce}"`);

  const headMatch = /<head\b[^>]*>/i.exec(page);
  if (headMatch) {
    const at = headMatch.index + headMatch[0].length;
    page = `${page.slice(0, at)}\n${head}${page.slice(at)}`;
  } else {
    page = `<!DOCTYPE html><html><head>${head}</head><body>${page}</body></html>`;
  }
  return page;
}

/** A small VS Code-styled page for loading and error states. */
export function messagePage(
  options: Pick<PageOptions, 'cspSource' | 'nonce' | 'state'>,
  title: string,
  body: string,
  detail?: string,
): string {
  return `<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="Content-Security-Policy" content="${escapeHtml(contentSecurityPolicy(options.cspSource, options.nonce))}">
<script nonce="${options.nonce}">(function () { var vscode = acquireVsCodeApi(); var state = ${scriptJson(options.state)}; if (state) vscode.setState(state); })();</script>
<style>
  body { font-family: var(--vscode-font-family); color: var(--vscode-foreground); background: var(--vscode-editor-background); padding: 24px 28px; }
  h2 { font-weight: 600; font-size: 15px; margin: 0 0 8px; }
  p { margin: 0 0 12px; color: var(--vscode-descriptionForeground); }
  pre { font-family: var(--vscode-editor-font-family); font-size: 12px; white-space: pre-wrap; word-break: break-word;
        background: var(--vscode-textCodeBlock-background); padding: 12px 14px; border-radius: 4px;
        border-left: 3px solid var(--vscode-editorError-foreground); }
</style>
</head>
<body>
<h2>${escapeHtml(title)}</h2>
<p>${escapeHtml(body)}</p>
${detail ? `<pre>${escapeHtml(detail)}</pre>` : ''}
</body>
</html>`;
}