import axios, { AxiosError } from 'axios';
import qs from 'qs';

export interface TokenStore {
  saveToken(serviceId: string, account: string, token: any): Promise<boolean>;
  getToken(serviceId: string, account: string): Promise<any>;
  deleteToken(serviceId: string, account: string): Promise<boolean>;
}

export interface OAuth2Config {
  grantType: 'client_credentials' | 'password';
  accessTokenUrl: string;
  clientId?: string;
  clientSecret?: string;
  username?: string;
  password?: string;
  scope?: string;
  credentialsPlacement?: 'header' | 'body';
}

interface RequestConfig {
  headers: {
    'Content-Type': string;
    'Authorization'?: string;
  };
}

interface ClientCredentialsData {
  grant_type: string;
  scope: string;
  client_id?: string;
  client_secret?: string;
}

interface PasswordGrantData {
  grant_type: string;
  username: string;
  password: string;
  scope: string;
  client_id?: string;
  client_secret?: string;
}

/**
 * Fetches an OAuth2 token using client credentials grant
 */
const fetchTokenClientCredentials = async (oauth2Config: OAuth2Config) => {
  const {
    accessTokenUrl,
    clientId,
    clientSecret,
    scope,
    credentialsPlacement = 'header'
  } = oauth2Config;

  if (!accessTokenUrl || !clientId) {
    throw new Error('Missing required OAuth2 parameters');
  }

  const data: ClientCredentialsData = {
    grant_type: 'client_credentials',
    scope: scope || ''
  };

  const config: RequestConfig = {
    headers: {
      'Content-Type': 'application/x-www-form-urlencoded'
    }
  };

  // Handle credentials placement
  if (credentialsPlacement === 'header') {
    config.headers['Authorization'] = `Basic ${Buffer.from(`${clientId}:${clientSecret || ''}`).toString('base64')}`;
  } else {
    // Credentials in body
    data.client_id = clientId;
    if (clientSecret) {
      data.client_secret = clientSecret;
    }
  }

  try {
    const response = await axios.post(accessTokenUrl, qs.stringify(data), config);
    return response.data;
  } catch (error) {
    if (error instanceof Error) {
      console.error('CLIENT_CREDENTIALS: Error fetching OAuth2 token:', error.message);
    }
    throw error;
  }
};

/**
 * Fetches an OAuth2 token using password grant
 */
const fetchTokenPassword = async (oauth2Config: OAuth2Config) => {
  const {
    accessTokenUrl,
    clientId,
    clientSecret,
    username,
    password,
    scope,
    credentialsPlacement = 'header'
  } = oauth2Config;

  if (!accessTokenUrl || !username || !password) {
    throw new Error('Missing required OAuth2 parameters for password grant');
  }

  const data: PasswordGrantData = {
    grant_type: 'password',
    username,
    password,
    scope: scope || ''
  };

  const config: RequestConfig = {
    headers: {
      'Content-Type': 'application/x-www-form-urlencoded'
    }
  };

  // Handle credentials placement
  if (credentialsPlacement === 'header' && clientId) {
    config.headers['Authorization'] = `Basic ${Buffer.from(`${clientId}:${clientSecret || ''}`).toString('base64')}`;
  } else if (clientId) {
    // Credentials in body
    data.client_id = clientId;
    if (clientSecret) {
      data.client_secret = clientSecret;
    }
  }

  try {
    const response = await axios.post(accessTokenUrl, qs.stringify(data), config);
    return response.data;
  } catch (error) {
    if (error instanceof AxiosError && error.response) {
      console.error('PASSWORD_GRANT: Error fetching OAuth2 token:', error.message);
      console.error('Status:', error.response.status, 'Response:', error.response.data);
    } else if (error instanceof Error) {
      console.error('PASSWORD_GRANT: Error fetching OAuth2 token:', error.message);
    }
    throw error;
  }
};

/**
 * Manages OAuth2 token retrieval and storage
 */
export const getOAuth2Token = async (oauth2Config: OAuth2Config, tokenStore: TokenStore): Promise<string | null> => {
  const { grantType, clientId, accessTokenUrl } = oauth2Config;
  
  if (!grantType || !accessTokenUrl) {
    throw new Error('Missing required OAuth2 parameters: grantType or accessTokenUrl');
  }

  const serviceId = accessTokenUrl;
  const account = clientId || oauth2Config.username || 'default';

  // Check if we already have a token stored
  const existingToken = await tokenStore.getToken(serviceId, account);
  
  if (existingToken) {
    // Check if token is expired
    if (existingToken.expires_at && existingToken.expires_at > Date.now()) {
      return existingToken.access_token;
    }
  }

  // No valid token found, fetch a new one
  try {
    let tokenResponse;
    
    if (grantType === 'client_credentials') {
      tokenResponse = await fetchTokenClientCredentials(oauth2Config);
    } else if (grantType === 'password') {
      tokenResponse = await fetchTokenPassword(oauth2Config);
    } else {
      throw new Error(`Unsupported grant type: ${grantType}`);
    }
    
    // Calculate expiry time if expires_in is provided
    if (tokenResponse.expires_in) {
      tokenResponse.expires_at = Date.now() + tokenResponse.expires_in * 1000;
    }

    // Store the token
    await tokenStore.saveToken(serviceId, account, tokenResponse);
    
    return tokenResponse.access_token;
  } catch (error) {
    if (error instanceof Error) {
      console.error('Failed to get OAuth2 token:', error.message);
    }
    return null;
  }
};