import * as fs from "fs";
import * as path from "path";
import * as vscode from "vscode";

/**
 * #54: `vscode.commands.executeCommand("undo")` is non-functional in some headless
 * `.vscode-test` instances (it does not restore the buffer), which false-fails
 * every undo-dependent E2E (#38, #40) and makes `main` E2E red there. This is a
 * RUNTIME probe: it performs a real edit-then-undo on a scratch buffer and reports
 * whether undo actually restored it. Undo-dependent suites gate on it — running
 * normally where undo works (real coverage), skipping with a loud warning where it
 * doesn't (no false red, no silent loss — the skip is logged). Memoized per run.
 */
let cached: boolean | undefined;

export async function undoWorks(): Promise<boolean> {
  if (cached !== undefined) return cached;
  const abs = path.join(process.env.E2E_WORKSPACE!, "docs/.undo-probe.md");
  fs.mkdirSync(path.dirname(abs), { recursive: true });
  fs.writeFileSync(abs, "undo probe baseline\n", "utf8");
  const doc = await vscode.workspace.openTextDocument(vscode.Uri.file(abs));
  await vscode.window.showTextDocument(doc);
  await new Promise((r) => setTimeout(r, 250));
  const edit = new vscode.WorkspaceEdit();
  edit.insert(doc.uri, doc.positionAt(doc.getText().length), "PROBE-EDIT-MARKER");
  await vscode.workspace.applyEdit(edit);
  await new Promise((r) => setTimeout(r, 250));
  if (!doc.getText().includes("PROBE-EDIT-MARKER")) {
    cached = false; // even the edit didn't take — treat as not undo-capable
    return cached;
  }
  await vscode.commands.executeCommand("undo");
  await new Promise((r) => setTimeout(r, 250));
  cached = !doc.getText().includes("PROBE-EDIT-MARKER"); // undo removed the marker → undo works
  return cached;
}

/** Loud, single-line reason logged when an undo suite skips (no silent loss — #54). */
export const UNDO_SKIP_REASON =
  "[E2E] SKIPPING undo-dependent suite — executeCommand('undo') is non-functional in this " +
  "VS Code test instance (see vscode-cowriting-plugin#54). These tests run where undo works.";