import { execSync } from 'child_process';
import * as fs from 'fs';
import * as os from 'os';
import * as path from 'path';
import * as uuid from 'uuid';

/*
 * Checkout a copy of a git directory, from a specified commit/branch, to a temp location.
 * This can be used to compare the current state of the directory to another commit.
 * Ful paths from the git root are preserved in the temp checkout.
 *
 * @param localDir  A local directory path. Can be absolute or relative. Must be in a git repo.
 * @param branch    A branch or commit directory to use for the checkout.
 */
export class GitCheckoutTmp {
  private _gitRoot: string | undefined;
  private _tmpDir: string | undefined;

  public checkout(localDir: string, branch: string): void {
    this._gitRoot = findGitRoot(localDir);
    const gitRelDir = path
      .relative(this._gitRoot, localDir)
      .replace(/\\/g, '/');
    if (!gitRelDir) {
      throw `localDir for checkout cannot be the git root!`;
    }
    this._tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), uuid.v4()));
    try {
      execSync(
        `git -C ${this._gitRoot} --work-tree=${this._tmpDir} checkout ${branch} -- ${gitRelDir}`,
      );
    } catch (e) {
      this.cleanUp();
      throw e;
    }
  }

  /*
   * Location of the temp directory. Root directory of the checked out files.
   */
  public get tmpDir(): string | undefined {
    return this._tmpDir;
  }

  /*
   * Location of the git root dir. Root directory of the original files.
   */
  public get gitRoot(): string | undefined {
    return this._gitRoot;
  }

  /*
   * Clean up temp files. This will remove the temp directory if it exists.
   */
  public cleanUp(): void {
    try {
      if (this._tmpDir !== undefined) {
        fs.rmdirSync(this._tmpDir, { recursive: true });
      }
    } catch (e) {
      console.error(`Failed to clean up tmp dir ${this._tmpDir}: ${e}`);
    }
    this._gitRoot = undefined;
    this._tmpDir = undefined;
  }
}

/*
 * Finds the git root directory for a local path (relative or absolute).
 */
export function findGitRoot(dir: string): string {
  return execSync(`git -C ${dir} rev-parse --show-toplevel`).toString().trim();
}