import { type Readable } from './readable.ts';
import mime from 'mime/lite.js';
import fs from 'fs';
import path from 'path';
import { uint8FromBufLike } from '@dfinity/agent';

export class ReadablePath implements Readable {
  private readonly _path: string;
  private readonly _size: number;
  private _fd?: number;

  protected constructor(path: string, size: number) {
    this._path = path;
    this._size = size;
  }

  public get fileName(): string {
    return path.basename(this._path);
  }

  public get contentType(): string {
    return mime.getType(this.fileName) ?? 'application/octet-stream';
  }

  public get length(): number {
    return this._size;
  }

  static async create(path: string): Promise<ReadablePath> {
    return new Promise<ReadablePath>((resolve, reject) => {
      fs.stat(path, (err, stats) => {
        if (err) {
          reject(err);
          return;
        }
        resolve(new ReadablePath(path, stats.size));
      });
    });
  }

  public async open(): Promise<void> {
    return new Promise<void>((resolve, reject) => {
      if (this._fd !== undefined) {
        reject('File is already open');
        return;
      }
      fs.open(this._path, (err, fd) => {
        if (err) {
          reject(err);
          return;
        }
        this._fd = fd;
        resolve();
      });
    });
  }

  public async close(): Promise<void> {
    return new Promise<void>((resolve, reject) => {
      if (this._fd === undefined) {
        reject('No open file handle found');
        return;
      }
      fs.close(this._fd, err => {
        if (err) {
          reject(err);
          return;
        }
        resolve();
      });
    });
  }

  public async slice(start: number, end: number): Promise<Uint8Array> {
    return new Promise<Uint8Array>((resolve, reject) => {
      if (this._fd === undefined) {
        reject('No open file handle found');
        return;
      }
      const buffer = Buffer.alloc(end - start);
      fs.read(this._fd, uint8FromBufLike(buffer), 0, end - start, start, (err: unknown) => {
        if (err) {
          reject(err);
          return;
        }
        resolve(new Uint8Array(buffer));
      });
    });
  }
}