import { execFile } from 'node:child_process';
import { mkdir, readFile, rename, writeFile } from 'node:fs/promises';
import { dirname } from 'node:path';
import { promisify } from 'node:util';
import { writeInventories } from './inventory.mjs';

const execFileAsync = promisify(execFile);
const BRANCH_PATTERN = /^(?!\/)(?!.*(?:\.\.|\/\/|@\{|\\))[A-Za-z0-9._/-]{1,200}$/;
const ZERO_SHA = /^0{40,64}$/;

export class DeploymentError extends Error {
  constructor(message, status = 409) {
    super(message);
    this.name = 'DeploymentError';
    this.status = status;
  }
}

export class GitService {
  constructor(config, { run = execFileAsync, now = () => new Date() } = {}) {
    this.config = config;
    this.run = run;
    this.now = now;
    this.queue = Promise.resolve();
    this.state = null;
  }

  async initialize() {
    await mkdir(dirname(this.config.statePath), { recursive: true });
    this.state = await this.#loadState();
    await this.#assertRepository();
    await this.#assertClean();
    if (!this.config.allowedBranches.includes(this.state.activeBranch)) {
      throw new Error(`Active branch ${this.state.activeBranch} is not allowed`);
    }
    await this.refreshInventory();
  }

  enqueue(operation) {
    const result = this.queue.then(operation, operation);
    this.queue = result.catch(() => undefined);
    return result;
  }

  async deployWebhook({ deliveryId, branch, after }) {
    return this.enqueue(async () => {
      if (!deliveryId || deliveryId.length > 128) {
        throw new DeploymentError('Invalid delivery ID', 400);
      }
      if (this.state.deliveries.includes(deliveryId)) {
        return { duplicate: true, ...this.publicStatus() };
      }
      if (branch !== this.state.activeBranch) {
        return { ignored: true, reason: 'inactive branch', ...this.publicStatus() };
      }
      if (ZERO_SHA.test(after)) {
        return { ignored: true, reason: 'deleted ref', ...this.publicStatus() };
      }

      const result = await this.#deploy({ branch, expectedCommit: after, allowUnrelated: false });
      this.state.deliveries = [...this.state.deliveries.slice(-199), deliveryId];
      await this.#saveState();
      return result;
    });
  }

  async deployAdmin({ requestId, branch, expectedCommit }) {
    return this.enqueue(async () => {
      if (this.state.adminRequests.includes(requestId)) {
        return { duplicate: true, ...this.publicStatus() };
      }
      const result = await this.#deploy({ branch, expectedCommit, allowUnrelated: branch !== this.state.activeBranch });
      this.state.activeBranch = branch;
      this.state.adminRequests = [...this.state.adminRequests.slice(-199), requestId];
      await this.#saveState();
      return result;
    });
  }

  async deploySync({ requestKey, expectedCommit }) {
    return this.enqueue(async () => {
      if (this.state.syncRequests.includes(requestKey)) {
        return { duplicate: true, ...this.publicStatus() };
      }
      const result = await this.#deploy({
        branch: this.state.activeBranch,
        expectedCommit,
        allowUnrelated: false,
      });
      this.state.syncRequests = [...this.state.syncRequests.slice(-199), requestKey];
      await this.#saveState();
      return result;
    });
  }

  async #deploy({ branch, expectedCommit, allowUnrelated }) {
    this.#validateBranch(branch);
    await this.#assertClean();
    const remoteRef = `refs/remotes/image-hook/${branch}`;
    await this.#git('fetch', '--no-tags', '--prune', this.config.remoteUrl, `+refs/heads/${branch}:${remoteRef}`);
    const target = await this.#gitText('rev-parse', '--verify', `${remoteRef}^{commit}`);
    if (expectedCommit && target !== expectedCommit) {
      throw new DeploymentError('Payload commit does not match remote branch tip');
    }

    const current = await this.#gitText('rev-parse', 'HEAD');
    if (!allowUnrelated && current !== target) {
      const ancestor = await this.#gitExit('merge-base', '--is-ancestor', current, target);
      if (ancestor !== 0) {
        throw new DeploymentError('Non-fast-forward deployment rejected');
      }
    }

    if (current !== target) {
      await this.#git('checkout', '--detach', target);
    }
    this.state.lastSuccess = {
      branch,
      commit: target,
      at: this.now().toISOString(),
    };
    this.state.lastError = null;
    const inventory = await this.refreshInventory(branch, target);
    await this.#saveState();
    return { changed: current !== target, inventoryAssets: inventory.assets.length, ...this.publicStatus() };
  }

  async refreshInventory(branch = this.state.activeBranch, commit) {
    const resolvedCommit = commit ?? await this.#gitText('rev-parse', 'HEAD');
    const output = await this.#gitRaw('ls-files', '-z', '--', 'game', 'icons');
    const paths = output.split('\0').filter(Boolean);
    return writeInventories({
      repositoryPath: this.config.repositoryPath,
      paths,
      branch,
      commit: resolvedCommit,
      publicBases: this.config.publicBases,
      generatedAt: this.now(),
    });
  }

  publicStatus() {
    return {
      activeBranch: this.state.activeBranch,
      lastSuccess: this.state.lastSuccess,
      lastError: this.state.lastError,
    };
  }

  async recordError(error) {
    this.state.lastError = { message: error.message, at: this.now().toISOString() };
    await this.#saveState();
  }

  #validateBranch(branch) {
    if (!BRANCH_PATTERN.test(branch) || !this.config.allowedBranches.includes(branch)) {
      throw new DeploymentError('Branch is not allowed', 400);
    }
  }

  async #assertRepository() {
    const inside = await this.#gitText('rev-parse', '--is-inside-work-tree');
    if (inside !== 'true') {
      throw new Error('IMAGE_REPOSITORY_PATH is not a Git worktree');
    }
  }

  async #assertClean() {
    const status = await this.#gitRaw('status', '--porcelain=v1', '--untracked-files=no');
    if (status.trim()) {
      throw new DeploymentError('Tracked worktree changes prevent deployment');
    }
  }

  async #loadState() {
    try {
      const saved = JSON.parse(await readFile(this.config.statePath, 'utf8'));
      return {
        activeBranch: saved.activeBranch ?? this.config.defaultBranch,
        deliveries: Array.isArray(saved.deliveries) ? saved.deliveries : [],
        adminRequests: Array.isArray(saved.adminRequests) ? saved.adminRequests : [],
        syncRequests: Array.isArray(saved.syncRequests) ? saved.syncRequests : [],
        lastSuccess: saved.lastSuccess ?? null,
        lastError: saved.lastError ?? null,
      };
    } catch (error) {
      if (error.code !== 'ENOENT') {
        throw error;
      }
      return {
        activeBranch: this.config.defaultBranch,
        deliveries: [],
        adminRequests: [],
        syncRequests: [],
        lastSuccess: null,
        lastError: null,
      };
    }
  }

  async #saveState() {
    const temporary = `${this.config.statePath}.tmp-${process.pid}`;
    await writeFile(temporary, JSON.stringify(this.state, null, 2), { encoding: 'utf8', mode: 0o600 });
    await rename(temporary, this.config.statePath);
  }

  async #git(...args) {
    await this.run('git', ['-C', this.config.repositoryPath, ...args], { maxBuffer: 16 * 1024 * 1024 });
  }

  async #gitRaw(...args) {
    const { stdout } = await this.run('git', ['-C', this.config.repositoryPath, ...args], {
      encoding: 'buffer',
      maxBuffer: 64 * 1024 * 1024,
    });
    return Buffer.isBuffer(stdout) ? stdout.toString('utf8') : stdout;
  }

  async #gitText(...args) {
    return (await this.#gitRaw(...args)).trim();
  }

  async #gitExit(...args) {
    try {
      await this.#git(...args);
      return 0;
    } catch (error) {
      return error.code ?? 1;
    }
  }
}