import * as vscode from "vscode";
import { randomBytes } from "crypto";

/**
 * The multi-line instruction input for "Ask Claude to Edit" — BOTH the selection
 * and the whole-document case. A small focused webview (a tall, resizable
 * textarea + Send) opened in a split pane BELOW the document — not a comment
 * thread, and not the top QuickInput (which is single-line only; VS Code has no
 * multi-line input at the command-palette location). For a selection edit the
 * document stays in the pane above with the selection still highlighted (VS
 * Code's inactive-selection style), so the user can see exactly what Claude will
 * edit; the caller has already captured the selection, so we never touch it.
 *
 * The split collapses when the input is submitted or cancelled, and focus is
 * handed back to the document so the collapsing split doesn't reveal the bottom
 * panel. `header` names the scope ("Ask Claude to Edit This Selection" /
 * "…This Document").
 *
 * The webview only collects text and posts it to the host — no SDK or secret
 * surface lives in it (INV-8/35); the sealed CSP allows no network. Because a
 * webview CAN read its own textarea, Cancel / Escape confirms ONLY when there is
 * text to lose (closing the tab is an explicit dismiss, no prompt). Resolves with
 * the typed instruction, or `undefined` if cancelled / closed / left empty.
 */
export async function promptEditInstruction(header: string): Promise<string | undefined> {
  // Remember the document editor we came from so we can hand focus back to it
  // when the input closes — otherwise, when the empty split group below collapses,
  // focus falls into the bottom panel (Output / Debug Console / …) and it pops
  // open. Restoring editor focus leaves whatever panel state the user had untouched.
  const source = vscode.window.activeTextEditor;
  // Open a split editor group BELOW the current one and host the input there, so
  // it sits under the document instead of covering it as a tab. The new group is
  // empty, so disposing the panel on submit/cancel leaves it empty and VS Code
  // collapses the split (the `workbench.editor.closeEmptyGroups` default). Falls
  // back to a tab in the active group if the split command is unavailable.
  try {
    await vscode.commands.executeCommand("workbench.action.newGroupBelow");
  } catch {
    /* no split — the panel opens as a tab in the active group instead */
  }
  return new Promise((resolve) => {
    const panel = vscode.window.createWebviewPanel(
      "cowriting.askClaudeInput",
      header,
      { viewColumn: vscode.ViewColumn.Active, preserveFocus: false },
      { enableScripts: true, retainContextWhenHidden: false },
    );

    let settled = false;
    const done = (value: string | undefined): void => {
      if (settled) return;
      settled = true;
      resolve(value);
      panel.dispose();
      // Hand focus back to the originating document so the collapsing split
      // doesn't leave focus in (and reveal) the bottom panel.
      if (source) {
        void vscode.window.showTextDocument(source.document, {
          viewColumn: source.viewColumn ?? vscode.ViewColumn.One,
          preserveFocus: false,
        });
      }
    };

    panel.webview.onDidReceiveMessage((m: { type?: string; text?: string }) => {
      const text = (m?.text ?? "").trim();
      if (m?.type === "submit") {
        done(text ? text : undefined);
      } else if (m?.type === "cancel") {
        // Confirm only if there's something to lose (we can read the textarea here).
        if (!text) {
          done(undefined);
          return;
        }
        void vscode.window
          .showWarningMessage("Discard your Ask-Claude instruction?", { modal: true }, "Discard")
          .then((pick) => {
            if (pick === "Discard") done(undefined);
            // else: leave the panel open so the operator can keep editing.
          });
      }
    });
    // Closing the tab is an explicit dismiss — cancel without a prompt.
    panel.onDidDispose(() => done(undefined));
    panel.webview.html = htmlFor(header);
  });
}

function escapeHtml(s: string): string {
  return s.replace(/[&<>"']/g, (c) => ({ "&": "&amp;", "<": "&lt;", ">": "&gt;", '"': "&quot;", "'": "&#39;" })[c]!);
}

function htmlFor(header: string): string {
  const nonce = randomBytes(16).toString("base64");
  // Sealed CSP: no network; inline style only; the one script is nonce-gated.
  const csp = `default-src 'none'; style-src 'unsafe-inline'; script-src 'nonce-${nonce}';`;
  const title = escapeHtml(header);
  return `<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <meta http-equiv="Content-Security-Policy" content="${csp}" />
  <title>${title}</title>
  <style>
    body { padding: 14px 16px; font-family: var(--vscode-font-family); color: var(--vscode-foreground); }
    h2 { font-size: 13px; font-weight: 600; margin: 0 0 10px; }
    textarea {
      width: 100%; min-height: 160px; resize: vertical; box-sizing: border-box;
      background: var(--vscode-input-background); color: var(--vscode-input-foreground);
      border: 1px solid var(--vscode-input-border, transparent); border-radius: 4px; padding: 8px;
      font-family: var(--vscode-editor-font-family); font-size: var(--vscode-editor-font-size); line-height: 1.4;
    }
    textarea::placeholder { color: var(--vscode-input-placeholderForeground); }
    textarea:focus { outline: 1px solid var(--vscode-focusBorder); border-color: var(--vscode-focusBorder); }
    .row { display: flex; justify-content: space-between; align-items: center; margin-top: 10px; gap: 12px; }
    .hint { color: var(--vscode-descriptionForeground); font-size: 12px; }
    button {
      background: var(--vscode-button-background); color: var(--vscode-button-foreground);
      border: none; padding: 6px 16px; border-radius: 4px; cursor: pointer; font-size: 13px;
    }
    button:hover { background: var(--vscode-button-hoverBackground); }
  </style>
</head>
<body>
  <h2>${title}</h2>
  <textarea id="inst" placeholder="e.g. tighten the intro, add a conclusion, and fix the heading levels" autofocus></textarea>
  <div class="row">
    <span class="hint">⌘↵ / Ctrl+↵ to send · Esc to cancel</span>
    <button id="send">Send to Claude</button>
  </div>
  <script nonce="${nonce}">
    const api = acquireVsCodeApi();
    const ta = document.getElementById('inst');
    const focus = () => ta.focus();
    focus();
    window.addEventListener('focus', focus);
    const submit = () => api.postMessage({ type: 'submit', text: ta.value });
    const cancel = () => api.postMessage({ type: 'cancel', text: ta.value });
    document.getElementById('send').addEventListener('click', submit);
    ta.addEventListener('keydown', (e) => {
      if ((e.metaKey || e.ctrlKey) && e.key === 'Enter') { e.preventDefault(); submit(); }
      else if (e.key === 'Escape') { e.preventDefault(); cancel(); }
    });
  </script>
</body>
</html>`;
}