#!/usr/bin/env node

/**
 * Deploys the bundle-authoritative system prompt cover into the Pi agent directory.
 *
 * The cover is bundle-owned configuration: the repository copy under
 * `config/system-prompt-cover.md` is authoritative, and this helper synchronizes it to
 * `<agentDir>/SYSTEM_COVER.md`. There is no user-owned variant, so an existing file is
 * replaced atomically without keeping a backup.
 */

import { readFileSync, realpathSync } from "node:fs";
import { mkdir, open, rename, rm } from "node:fs/promises";
import { dirname, join } from "node:path";
import { fileURLToPath } from "node:url";

export const COVER_FILE_NAME = "SYSTEM_COVER.md";

const scriptPath = fileURLToPath(import.meta.url);
const bundleRoot = dirname(dirname(scriptPath));
export const BUNDLED_COVER_PATH = join(bundleRoot, "config", "system-prompt-cover.md");

/**
 * Resolve the Pi agent directory, mirroring Pi's own `getAgentDir()`.
 *
 * Implemented locally so this helper stays runnable from `install.sh` / `update.sh`
 * without loading the Pi runtime.
 *
 * @param {NodeJS.ProcessEnv} [env]
 * @param {string} homedir
 * @returns {string}
 */
export function resolveAgentDir(env = process.env, homedir) {
  const configured = env.PI_CODING_AGENT_DIR;
  if (configured) {
    return configured.startsWith("~/") ? join(homedir, configured.slice(2)) : configured;
  }
  return join(homedir, ".pi", "agent");
}

/**
 * Compare the bundle cover against the deployed copy and replace it when they differ.
 *
 * Returns `{ status }`:
 * - `current` — deployed copy already matches the bundle.
 * - `updated` — deployed copy was replaced.
 * - `created` — no deployed copy existed.
 *
 * Read or write failures throw so callers can report a real failure instead of
 * silently leaving a stale cover in place.
 *
 * @param {{ agentDir?: string, bundledCoverPath?: string }} options
 * @returns {Promise<{ status: "current" | "updated" | "created", targetPath: string }>}
 */
export async function deploySystemPromptCover({ agentDir, bundledCoverPath = BUNDLED_COVER_PATH } = {}) {
  if (!agentDir) {
    throw new Error("agentDir is required");
  }

  let bundledCover;
  try {
    bundledCover = readFileSync(bundledCoverPath, "utf8");
  } catch (error) {
    throw new Error(
      `cannot read bundled system prompt cover at ${bundledCoverPath}: ${
        error instanceof Error ? error.message : String(error)
      }`,
    );
  }

  const targetPath = join(agentDir, COVER_FILE_NAME);

  let existing;
  let existed = false;
  try {
    existing = readFileSync(targetPath, "utf8");
    existed = true;
  } catch (error) {
    if (error?.code !== "ENOENT") {
      throw new Error(
        `cannot read deployed system prompt cover at ${targetPath}: ${
          error instanceof Error ? error.message : String(error)
        }`,
      );
    }
  }

  if (existed && existing === bundledCover) {
    return { status: "current", targetPath };
  }

  await mkdir(agentDir, { recursive: true });
  const temporaryPath = join(
    agentDir,
    `.${COVER_FILE_NAME}.my-pi-${process.pid}-${Math.random().toString(16).slice(2)}.tmp`,
  );

  try {
    const handle = await open(temporaryPath, "wx", 0o644);
    try {
      await handle.writeFile(bundledCover, "utf8");
      await handle.sync();
    } finally {
      await handle.close();
    }
    await rename(temporaryPath, targetPath);
  } catch (error) {
    await rm(temporaryPath, { force: true }).catch(() => {});
    throw error;
  }

  return { status: existed ? "updated" : "created", targetPath };
}

function isMainModule() {
  if (!process.argv[1]) return false;
  try {
    return fileURLToPath(import.meta.url) === realpathSync(process.argv[1]);
  } catch {
    return false;
  }
}

async function main() {
  const agentDir = process.argv[2] || resolveAgentDir(process.env, process.env.HOME);
  const { status } = await deploySystemPromptCover({ agentDir });
  process.stdout.write(`${status}\n`);
}

if (isMainModule()) {
  main().catch((error) => {
    console.error(error instanceof Error ? error.message : String(error));
    process.exitCode = 1;
  });
}