const debug = require('debug')('awesome-wechat-sdk:api:common');

export class WechatAPIError extends Error {
  code: number;
}

export class AccessToken {
  readonly accessToken: string;
  readonly expireTime: number;
  constructor(token: {accessToken: string, expireTime: number}) {
    this.accessToken = token.accessToken;
    this.expireTime = token.expireTime;
  }
  isValid(): boolean {
    return !!this.accessToken && Date.now() < this.expireTime;
  }
  toJSON(): object {
    return {
      accessToken: this.accessToken,
      expireTime: this.expireTime
    };
  }
}

export default {
  async loadAccessToken(): Promise<AccessToken> {
    return this.store.accessToken;
  },
  async saveAccessToken(token: AccessToken): Promise<void> {
    this.store.accessToken = token;
  },
  registerAccessTokenHandler(handler: {loadAccessToken?: () => Promise<AccessToken>, saveAccessToken?: (token: AccessToken) => Promise<void>} = {}): void {
    if (handler.loadAccessToken) {
      this.loadAccessToken = handler.loadAccessToken;
    }
    if (handler.saveAccessToken) {
      this.saveAccessToken = handler.saveAccessToken;
    }
  },
  async _processWechatResponse(data: any): Promise<any> {
    debug('process response %j', data);
    if (data.errcode) {
      const err = new WechatAPIError(data.errmsg);
      err.name = 'WechatAPIError';
      err.code = data.errcode;
      if (data.errcode === 40001) {
        await this.saveAccessToken(new AccessToken({accessToken: null, expireTime: null}));
      }
      throw err;
    }

    return data;
  },
  async getAccessToken(): Promise<AccessToken> {
    const url = `${this.endpoint}/cgi-bin/token?grant_type=client_credential&appid=${this.appid}&secret=${this.appsecret}`;
    const response = await this.request(url, {dataType: 'json'});
    const data = await this._processWechatResponse(response.data);
    const expireTime = Date.now() + (data.expires_in - 10) * 1000;
    const token = new AccessToken({accessToken: data.access_token, expireTime});
    await this.saveAccessToken(token);
    return token;
  },
  async getLatestAccessToken(): Promise<AccessToken> {
    const token = await this.loadAccessToken();
    if (token && token.isValid()) {
      return token;
    } else {
      return await this.getAccessToken();
    }
  }
};