import { access } from "node:fs/promises";
import { mkdir } from "node:fs/promises";
import { join } from "node:path";
import { execFile } from "node:child_process";
import { promisify } from "node:util";

const execFileAsync = promisify(execFile);

export type WorktreeContext = {
  repoRoot: string;
  worktreePath: string;
  branch: string;
};

async function pathExists(path: string): Promise<boolean> {
  try {
    await access(path);
    return true;
  } catch {
    return false;
  }
}

/** Reuse an existing worktree directory when present (crash resume without re-clone). */
export async function reuseWorktreeIfPresent(
  repoRoot: string,
  worktreePath: string,
  branch: string | null,
): Promise<WorktreeContext | null> {
  if (!(await pathExists(worktreePath))) {
    return null;
  }

  try {
    const { stdout } = await execFileAsync("git", ["rev-parse", "--show-toplevel"], {
      cwd: worktreePath,
    });
    if (stdout.trim() !== worktreePath && !(await pathExists(join(worktreePath, ".git")))) {
      return null;
    }
  } catch {
    return null;
  }

  let resolvedBranch = branch ?? "HEAD";
  if (!branch) {
    try {
      const { stdout } = await execFileAsync("git", ["rev-parse", "--abbrev-ref", "HEAD"], {
        cwd: worktreePath,
      });
      resolvedBranch = stdout.trim() || "HEAD";
    } catch {
      resolvedBranch = "HEAD";
    }
  }

  return { repoRoot, worktreePath, branch: resolvedBranch };
}

export async function ensureWorktree(
  repoRoot: string,
  worktreeBase: string,
  worktreeKey: string,
  branchSuffix: string,
  opts?: { needsWorktree?: boolean },
): Promise<WorktreeContext | null> {
  if (opts?.needsWorktree === false) {
    return null;
  }
  const branch = `worker/${branchSuffix}`.replace(/[^a-zA-Z0-9/_-]/g, "-");
  const worktreePath = join(worktreeBase, worktreeKey);
  await mkdir(worktreeBase, { recursive: true });

  const existing = await reuseWorktreeIfPresent(repoRoot, worktreePath, branch);
  if (existing) {
    return existing;
  }

  try {
    await execFileAsync("git", ["worktree", "add", "-B", branch, worktreePath], {
      cwd: repoRoot,
    });
  } catch {
    await execFileAsync("git", ["worktree", "add", worktreePath, branch], {
      cwd: repoRoot,
    });
  }

  return { repoRoot, worktreePath, branch };
}

export async function removeWorktree(repoRoot: string, worktreePath: string): Promise<void> {
  try {
    await execFileAsync("git", ["worktree", "remove", "--force", worktreePath], {
      cwd: repoRoot,
    });
  } catch {
    // Best-effort cleanup; operator can prune stale worktrees manually.
  }
}