import { readFileSync, writeFileSync, existsSync, mkdirSync } from 'fs';
import { dirname } from 'path';

export interface AccountLink {
  githubUserId: string;
  githubLogin: string;
  huggingfaceUsername: string;
  huggingfaceAccessToken?: string;
  linkedAt: string;
  lastUpdated: string;
}

export interface AccountLinksData {
  links: AccountLink[];
  metadata: {
    version: string;
    createdAt: string;
    lastModified: string;
  };
}

export class AccountLinkingService {
  private filePath: string;

  constructor() {
    this.filePath = process.env.ACCOUNT_LINKS_FILE || '/tmp/account-links.json';
    this.ensureFileExists();
  }

  private ensureFileExists(): void {
    const dir = dirname(this.filePath);
    
    // Create directory if it doesn't exist
    if (!existsSync(dir)) {
      mkdirSync(dir, { recursive: true });
    }

    // Create file if it doesn't exist
    if (!existsSync(this.filePath)) {
      const initialData: AccountLinksData = {
        links: [],
        metadata: {
          version: '1.0.0',
          createdAt: new Date().toISOString(),
          lastModified: new Date().toISOString(),
        },
      };
      this.writeData(initialData);
    }
  }

  private readData(): AccountLinksData {
    try {
      const content = readFileSync(this.filePath, 'utf-8');
      return JSON.parse(content);
    } catch (error) {
      console.error('Error reading account links file:', error);
      // Return default structure if file is corrupted
      return {
        links: [],
        metadata: {
          version: '1.0.0',
          createdAt: new Date().toISOString(),
          lastModified: new Date().toISOString(),
        },
      };
    }
  }

  private writeData(data: AccountLinksData): void {
    try {
      data.metadata.lastModified = new Date().toISOString();
      writeFileSync(this.filePath, JSON.stringify(data, null, 2), 'utf-8');
    } catch (error) {
      console.error('Error writing account links file:', error);
      throw new Error('Failed to save account links');
    }
  }

  /**
   * Create a new account link
   */
  createLink(githubUserId: string, githubLogin: string, huggingfaceUsername: string, huggingfaceAccessToken?: string): AccountLink {
    const data = this.readData();
    const now = new Date().toISOString();

    // Check for existing links
    const existingGithubLink = data.links.find(link => link.githubUserId === githubUserId);
    const existingHfLink = data.links.find(link => link.huggingfaceUsername === huggingfaceUsername);

    if (existingGithubLink) {
      throw new Error(`GitHub user ${githubLogin} is already linked to HuggingFace user ${existingGithubLink.huggingfaceUsername}`);
    }

    if (existingHfLink) {
      throw new Error(`HuggingFace user ${huggingfaceUsername} is already linked to GitHub user ${existingHfLink.githubLogin}`);
    }

    const newLink: AccountLink = {
      githubUserId,
      githubLogin,
      huggingfaceUsername,
      huggingfaceAccessToken,
      linkedAt: now,
      lastUpdated: now,
    };

    data.links.push(newLink);
    this.writeData(data);

    console.log(`✅ Created account link: ${githubLogin} ↔ ${huggingfaceUsername}`);
    return newLink;
  }

  /**
   * Find account link by GitHub user
   */
  findByGitHubUser(githubUserId: string): AccountLink | null {
    const data = this.readData();
    return data.links.find(link => link.githubUserId === githubUserId) || null;
  }

  /**
   * Find account link by HuggingFace user
   */
  findByHuggingFaceUser(huggingfaceUsername: string): AccountLink | null {
    const data = this.readData();
    return data.links.find(link => link.huggingfaceUsername === huggingfaceUsername) || null;
  }

  /**
   * Update an existing account link
   */
  updateLink(githubUserId: string, updates: Partial<Omit<AccountLink, 'githubUserId' | 'linkedAt'>>): AccountLink {
    const data = this.readData();
    const linkIndex = data.links.findIndex(link => link.githubUserId === githubUserId);

    if (linkIndex === -1) {
      throw new Error(`No account link found for GitHub user ID: ${githubUserId}`);
    }

    const existingLink = data.links[linkIndex];
    const updatedLink: AccountLink = {
      ...existingLink,
      ...updates,
      lastUpdated: new Date().toISOString(),
    };

    data.links[linkIndex] = updatedLink;
    this.writeData(data);

    console.log(`✅ Updated account link for GitHub user: ${existingLink.githubLogin}`);
    return updatedLink;
  }
  
  /**
   * Update HuggingFace access token for an existing account link
   */
  updateAccessToken(githubUserId: string, accessToken: string): AccountLink {
    return this.updateLink(githubUserId, { huggingfaceAccessToken: accessToken });
  }

  /**
   * Remove an account link
   */
  removeLink(githubUserId: string): boolean {
    const data = this.readData();
    const initialLength = data.links.length;
    
    data.links = data.links.filter(link => link.githubUserId !== githubUserId);
    
    if (data.links.length < initialLength) {
      this.writeData(data);
      console.log(`✅ Removed account link for GitHub user ID: ${githubUserId}`);
      return true;
    }

    return false;
  }

  /**
   * Get all account links
   */
  getAllLinks(): AccountLink[] {
    const data = this.readData();
    return data.links;
  }

  /**
   * Get linking statistics
   */
  getStats(): { totalLinks: number; lastModified: string } {
    const data = this.readData();
    return {
      totalLinks: data.links.length,
      lastModified: data.metadata.lastModified,
    };
  }

  /**
   * Check if accounts can be linked (no conflicts)
   */
  canLink(githubUserId: string, huggingfaceUsername: string): { canLink: boolean; reason?: string } {
    const data = this.readData();
    
    const existingGithubLink = data.links.find(link => link.githubUserId === githubUserId);
    if (existingGithubLink) {
      return {
        canLink: false,
        reason: `GitHub account is already linked to HuggingFace user: ${existingGithubLink.huggingfaceUsername}`,
      };
    }

    const existingHfLink = data.links.find(link => link.huggingfaceUsername === huggingfaceUsername);
    if (existingHfLink) {
      return {
        canLink: false,
        reason: `HuggingFace account is already linked to GitHub user: ${existingHfLink.githubLogin}`,
      };
    }

    return { canLink: true };
  }
}

// Singleton instance
export const accountLinkingService = new AccountLinkingService();