// Package service provides business logic for the application
package service

import (
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"time"

	"accounting-app/internal/config"
	"accounting-app/internal/models"
	"accounting-app/internal/repository"
)

// GitHub OAuth errors
var (
	ErrGitHubOAuthFailed    = errors.New("github oauth authentication failed")
	ErrGitHubUserInfoFailed = errors.New("failed to get github user info")
)

// GitHubUser represents GitHub user information
type GitHubUser struct {
	ID        int64  `json:"id"`
	Login     string `json:"login"`
	Email     string `json:"email"`
	Name      string `json:"name"`
	AvatarURL string `json:"avatar_url"`
}

// GitHubTokenResponse represents GitHub OAuth token response
type GitHubTokenResponse struct {
	AccessToken string `json:"access_token"`
	TokenType   string `json:"token_type"`
	Scope       string `json:"scope"`
}

// GitHubOAuthService handles GitHub OAuth operations
// Feature: api-interface-optimization
// Validates: Requirements 13.1, 13.2, 13.3, 13.4, 13.5
type GitHubOAuthService struct {
	userRepo    *repository.UserRepository
	authService *AuthService
	cfg         *config.Config
	httpClient  *http.Client
}

// NewGitHubOAuthService creates a new GitHubOAuthService instance
func NewGitHubOAuthService(userRepo *repository.UserRepository, authService *AuthService, cfg *config.Config) *GitHubOAuthService {
	return &GitHubOAuthService{
		userRepo:    userRepo,
		authService: authService,
		cfg:         cfg,
		httpClient: &http.Client{
			Timeout: 30 * time.Second, // 澧炲姞瓒呮椂鏃堕棿
		},
	}
}

// GetAuthorizationURL returns the GitHub OAuth authorization URL
// Feature: api-interface-optimization
// Validates: Requirements 13.1
func (s *GitHubOAuthService) GetAuthorizationURL(state string) string {
	params := url.Values{}
	params.Set("client_id", s.cfg.GitHubClientID)
	params.Set("redirect_uri", s.cfg.GitHubRedirectURL)
	params.Set("scope", "user:email")
	params.Set("state", state)

	return fmt.Sprintf("https://github.com/login/oauth/authorize?%s", params.Encode())
}

// ExchangeCodeForToken exchanges authorization code for access token
// Feature: api-interface-optimization
// Validates: Requirements 13.2
func (s *GitHubOAuthService) ExchangeCodeForToken(code string) (*GitHubTokenResponse, error) {
	data := url.Values{}
	data.Set("client_id", s.cfg.GitHubClientID)
	data.Set("client_secret", s.cfg.GitHubClientSecret)
	data.Set("code", code)
	data.Set("redirect_uri", s.cfg.GitHubRedirectURL)

	req, err := http.NewRequest("POST", "https://github.com/login/oauth/access_token", strings.NewReader(data.Encode()))
	if err != nil {
		fmt.Printf("[GitHub] Failed to create request: %v\n", err)
		return nil, err
	}

	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	req.Header.Set("Accept", "application/json")

	fmt.Printf("[GitHub] Exchanging code for token...\n")
	resp, err := s.httpClient.Do(req)
	if err != nil {
		fmt.Printf("[GitHub] Request failed: %v\n", err)
		return nil, err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		fmt.Printf("[GitHub] Token exchange failed with status: %d\n", resp.StatusCode)
		return nil, ErrGitHubOAuthFailed
	}

	var tokenResp GitHubTokenResponse
	if err := json.NewDecoder(resp.Body).Decode(&tokenResp); err != nil {
		fmt.Printf("[GitHub] Failed to decode response: %v\n", err)
		return nil, err
	}

	if tokenResp.AccessToken == "" {
		fmt.Printf("[GitHub] No access token in response\n")
		return nil, ErrGitHubOAuthFailed
	}

	return &tokenResp, nil
}

// GetUserInfo retrieves GitHub user information using access token
// Feature: api-interface-optimization
// Validates: Requirements 13.3
func (s *GitHubOAuthService) GetUserInfo(accessToken string) (*GitHubUser, error) {
	req, err := http.NewRequest("GET", "https://api.github.com/user", nil)
	if err != nil {
		return nil, err
	}

	req.Header.Set("Authorization", "Bearer "+accessToken)
	req.Header.Set("Accept", "application/json")

	resp, err := s.httpClient.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return nil, ErrGitHubUserInfoFailed
	}

	var user GitHubUser
	if err := json.NewDecoder(resp.Body).Decode(&user); err != nil {
		return nil, err
	}

	// If email is not public, try to get it from emails endpoint
	if user.Email == "" {
		email, err := s.getUserEmail(accessToken)
		if err == nil {
			user.Email = email
		}
	}

	return &user, nil
}

// getUserEmail retrieves user's primary email from GitHub
func (s *GitHubOAuthService) getUserEmail(accessToken string) (string, error) {
	req, err := http.NewRequest("GET", "https://api.github.com/user/emails", nil)
	if err != nil {
		return "", err
	}

	req.Header.Set("Authorization", "Bearer "+accessToken)
	req.Header.Set("Accept", "application/json")

	resp, err := s.httpClient.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return "", ErrGitHubUserInfoFailed
	}

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return "", err
	}

	var emails []struct {
		Email    string `json:"email"`
		Primary  bool   `json:"primary"`
		Verified bool   `json:"verified"`
	}

	if err := json.Unmarshal(body, &emails); err != nil {
		return "", err
	}

	for _, e := range emails {
		if e.Primary && e.Verified {
			return e.Email, nil
		}
	}

	return "", nil
}

// HandleCallback processes GitHub OAuth callback
// Feature: api-interface-optimization
// Validates: Requirements 13.4, 13.5
func (s *GitHubOAuthService) HandleCallback(code string) (*models.User, *TokenPair, error) {
	// Exchange code for token
	tokenResp, err := s.ExchangeCodeForToken(code)
	if err != nil {
		return nil, nil, err
	}

	// Get GitHub user info
	githubUser, err := s.GetUserInfo(tokenResp.AccessToken)
	if err != nil {
		return nil, nil, err
	}

	// Check if user already exists with this GitHub account
	user, err := s.userRepo.GetByOAuthProvider("github", fmt.Sprintf("%d", githubUser.ID))
	if err == nil {
		// User exists, update token and return
		_ = s.userRepo.UpdateOAuthToken("github", fmt.Sprintf("%d", githubUser.ID), tokenResp.AccessToken)
		tokens, err := s.authService.generateTokenPair(user)
		if err != nil {
			return nil, nil, err
		}
		return user, tokens, nil
	}

	// Check if user exists with same email
	if githubUser.Email != "" {
		existingUser, err := s.userRepo.GetByEmail(githubUser.Email)
		if err == nil {
			// Link GitHub account to existing user
			oauth := &models.OAuthAccount{
				UserID:      existingUser.ID,
				Provider:    "github",
				ProviderID:  fmt.Sprintf("%d", githubUser.ID),
				AccessToken: tokenResp.AccessToken,
			}
			if err := s.userRepo.CreateOAuthAccount(oauth); err != nil {
				return nil, nil, err
			}
			tokens, err := s.authService.generateTokenPair(existingUser)
			if err != nil {
				return nil, nil, err
			}
			return existingUser, tokens, nil
		}
	}

	// Create new user
	username := githubUser.Login
	if githubUser.Name != "" {
		username = githubUser.Name
	}

	email := githubUser.Email
	if email == "" {
		email = fmt.Sprintf("%d@github.user", githubUser.ID)
	}

	newUser := &models.User{
		Email:    email,
		Username: username,
		Avatar:   githubUser.AvatarURL,
		IsActive: true,
	}

	if err := s.userRepo.Create(newUser); err != nil {
		return nil, nil, err
	}

	// Create OAuth account link
	oauth := &models.OAuthAccount{
		UserID:      newUser.ID,
		Provider:    "github",
		ProviderID:  fmt.Sprintf("%d", githubUser.ID),
		AccessToken: tokenResp.AccessToken,
	}
	if err := s.userRepo.CreateOAuthAccount(oauth); err != nil {
		return nil, nil, err
	}

	tokens, err := s.authService.generateTokenPair(newUser)
	if err != nil {
		return nil, nil, err
	}

	return newUser, tokens, nil
}