import * as fs from 'fs';
import * as path from 'path';
import { TsPublishConfig } from '../mod_config/index.js';
import { FsHelpers } from '../mod_fs/index.js';

/**
 * TsUnpacker handles flattening of nested TypeScript output directories.
 *
 * When TypeScript compiles files that import from sibling directories,
 * it creates a nested structure like:
 *   dist_ts_core/ts_core/index.js
 *   dist_ts_core/ts_shared/helper.js
 *
 * This class flattens it to:
 *   dist_ts_core/index.js
 */
export class TsUnpacker {
  private sourceFolderName: string;
  private destDir: string;
  private cwd: string;
  private config: TsPublishConfig;

  constructor(sourceFolderName: string, destDir: string, cwd: string = process.cwd()) {
    this.sourceFolderName = sourceFolderName;
    this.destDir = destDir;
    this.cwd = cwd;
    this.config = new TsPublishConfig(path.join(cwd, sourceFolderName));
  }

  /**
   * Create an unpacker from a glob pattern
   * './ts_core/**\/*.ts' → sourceFolderName = 'ts_core'
   */
  public static fromGlobPattern(
    sourcePattern: string,
    destDir: string,
    cwd: string = process.cwd()
  ): TsUnpacker | null {
    const sourceFolderName = FsHelpers.extractSourceFolder(sourcePattern);
    if (!sourceFolderName) {
      return null;
    }
    return new TsUnpacker(sourceFolderName, destDir, cwd);
  }

  /**
   * Get the source folder name
   */
  public getSourceFolderName(): string {
    return this.sourceFolderName;
  }

  /**
   * Get the destination directory
   */
  public getDestDir(): string {
    return this.destDir;
  }

  /**
   * Check if unpacking should be performed based on tspublish.json config
   * Default is true if not specified
   */
  public async shouldUnpack(): Promise<boolean> {
    return this.config.shouldUnpack;
  }

  /**
   * Check if nested structure exists in the destination directory
   */
  public async detectNesting(): Promise<boolean> {
    const nestedPath = path.join(this.destDir, this.sourceFolderName);
    return FsHelpers.directoryExists(nestedPath);
  }

  /**
   * Get the path to the nested directory
   */
  public getNestedPath(): string {
    return path.join(this.destDir, this.sourceFolderName);
  }

  /**
   * Perform the unpack operation - flatten nested output directories.
   *
   * When TypeScript compiles files that import from sibling directories,
   * it creates a nested structure like dist_ts/ts/ with siblings like
   * dist_ts/ts_interfaces/. This method flattens by:
   * 1. Removing sibling directories (non-source folders)
   * 2. Moving contents of the nested source folder up to the dest dir
   * 3. Removing the now-empty nested source folder
   *
   * This approach never creates temporary sibling directories and never
   * removes the destination directory itself, avoiding filesystem race
   * conditions observed with the previous rename-rm-rename pattern.
   *
   * Returns true if unpacking was performed, false if skipped.
   */
  public async unpack(): Promise<boolean> {
    if (!(await this.shouldUnpack())) {
      return false;
    }

    if (!(await this.detectNesting())) {
      return false;
    }

    const nestedPath = this.getNestedPath();

    // Step 1: Remove sibling entries (everything in dest except the source folder)
    // Loop handles partial readdir results from signal-interrupted getdents64
    let destEntries = await fs.promises.readdir(this.destDir);
    while (destEntries.some(e => e !== this.sourceFolderName)) {
      for (const entry of destEntries) {
        if (entry !== this.sourceFolderName) {
          await fs.promises.rm(path.join(this.destDir, entry), { recursive: true, force: true });
        }
      }
      destEntries = await fs.promises.readdir(this.destDir);
    }

    // Step 2: Move all contents from nested dir up to dest dir
    // Loop handles partial readdir results from signal-interrupted getdents64
    let nestedEntries = await fs.promises.readdir(nestedPath);
    while (nestedEntries.length > 0) {
      for (const entry of nestedEntries) {
        await fs.promises.rename(
          path.join(nestedPath, entry),
          path.join(this.destDir, entry),
        );
      }
      nestedEntries = await fs.promises.readdir(nestedPath);
    }

    // Step 3: Remove the now-empty nested directory
    await fs.promises.rmdir(nestedPath);

    return true;
  }
}

/**
 * Convenience function to perform unpack operation
 * Can be used directly without instantiating the class
 */
export async function performUnpack(
  sourcePattern: string,
  destDir: string,
  cwd: string = process.cwd()
): Promise<boolean> {
  const unpacker = TsUnpacker.fromGlobPattern(sourcePattern, destDir, cwd);
  if (!unpacker) {
    return false;
  }
  return unpacker.unpack();
}