package services

import (
	"context"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"fmt"
	"strings"
	"time"

	"veza-backend-api/internal/models"

	"github.com/google/uuid"
	"go.uber.org/zap"
	"gorm.io/gorm"
)

const apiKeyPrefix = "vza_"
const apiKeyPrefixLen = 8 // Display prefix length

// APIKeyService manages user API keys for developer portal
type APIKeyService struct {
	db     *gorm.DB
	logger *zap.Logger
}

// NewAPIKeyService creates a new APIKeyService
func NewAPIKeyService(db *gorm.DB, logger *zap.Logger) *APIKeyService {
	if logger == nil {
		logger = zap.NewNop()
	}
	return &APIKeyService{db: db, logger: logger}
}

// CreateAPIKeyRequest represents the request to create an API key
type CreateAPIKeyRequest struct {
	Name   string   `json:"name" binding:"required,max=100"`
	Scopes []string `json:"scopes"`
}

// APIKeyResponse represents an API key in API responses (no full key)
type APIKeyResponse struct {
	ID         string     `json:"id"`
	Name       string     `json:"name"`
	Prefix     string     `json:"prefix"`
	Scopes     []string   `json:"scopes"`
	LastUsedAt *time.Time `json:"last_used_at,omitempty"`
	ExpiresAt  *time.Time `json:"expires_at,omitempty"`
	CreatedAt  time.Time  `json:"created_at"`
}

// CreateAPIKeyResponse includes the full key only on creation (show once)
type CreateAPIKeyResponse struct {
	APIKeyResponse
	Key string `json:"key"` // Full key, only returned on create
}

func hashKey(key string) string {
	h := sha256.Sum256([]byte(key))
	return hex.EncodeToString(h[:])
}

// GenerateKey generates a new API key with vza_ prefix
func (s *APIKeyService) GenerateKey() (fullKey, prefix string, err error) {
	bytes := make([]byte, 24)
	if _, err := rand.Read(bytes); err != nil {
		return "", "", fmt.Errorf("failed to generate random bytes: %w", err)
	}
	secret := base64.URLEncoding.WithPadding(base64.NoPadding).EncodeToString(bytes)
	fullKey = apiKeyPrefix + secret
	prefix = fullKey
	if len(prefix) > apiKeyPrefixLen {
		prefix = prefix[:apiKeyPrefixLen] + "..."
	}
	return fullKey, prefix, nil
}

// Create creates a new API key for the user
func (s *APIKeyService) Create(ctx context.Context, userID uuid.UUID, req *CreateAPIKeyRequest) (*CreateAPIKeyResponse, error) {
	fullKey, prefix, err := s.GenerateKey()
	if err != nil {
		return nil, err
	}

	scopes := req.Scopes
	if len(scopes) == 0 {
		scopes = []string{"read"}
	}
	scopes = normalizeScopes(scopes)

	key := &models.APIKey{
		UserID:    userID,
		Name:      strings.TrimSpace(req.Name),
		Prefix:    prefix,
		HashedKey: hashKey(fullKey),
		Scopes:    scopes,
		CreatedAt: time.Now(),
	}

	if err := s.db.WithContext(ctx).Create(key).Error; err != nil {
		return nil, fmt.Errorf("failed to create API key: %w", err)
	}

	s.logger.Info("API key created",
		zap.String("user_id", userID.String()),
		zap.String("name", key.Name),
		zap.String("prefix", prefix))

	return &CreateAPIKeyResponse{
		APIKeyResponse: toResponse(key),
		Key:            fullKey,
	}, nil
}

// List returns all API keys for a user
func (s *APIKeyService) List(ctx context.Context, userID uuid.UUID) ([]APIKeyResponse, error) {
	var keys []models.APIKey
	if err := s.db.WithContext(ctx).Where("user_id = ?", userID).Order("created_at DESC").Find(&keys).Error; err != nil {
		return nil, err
	}
	res := make([]APIKeyResponse, len(keys))
	for i := range keys {
		res[i] = toResponse(&keys[i])
	}
	return res, nil
}

// Delete removes an API key
func (s *APIKeyService) Delete(ctx context.Context, userID, keyID uuid.UUID) error {
	result := s.db.WithContext(ctx).Where("id = ? AND user_id = ?", keyID, userID).Delete(&models.APIKey{})
	if result.Error != nil {
		return result.Error
	}
	if result.RowsAffected == 0 {
		return gorm.ErrRecordNotFound
	}
	return nil
}

// ValidateAPIKey validates an API key and returns the key record (for middleware)
func (s *APIKeyService) ValidateAPIKey(ctx context.Context, rawKey string) (*models.APIKey, error) {
	if !strings.HasPrefix(rawKey, apiKeyPrefix) {
		return nil, fmt.Errorf("invalid API key format")
	}
	hashed := hashKey(rawKey)

	var key models.APIKey
	if err := s.db.WithContext(ctx).Where("hashed_key = ?", hashed).First(&key).Error; err != nil {
		if err == gorm.ErrRecordNotFound {
			return nil, fmt.Errorf("invalid API key")
		}
		return nil, err
	}

	if key.ExpiresAt != nil && key.ExpiresAt.Before(time.Now()) {
		return nil, fmt.Errorf("API key expired")
	}

	// Update last_used_at (fire-and-forget, don't block)
	now := time.Now()
	go func() {
		_ = s.db.WithContext(context.Background()).Model(&models.APIKey{}).
			Where("id = ?", key.ID).Update("last_used_at", now).Error
	}()

	return &key, nil
}

// HasScope checks if the key has the required scope
func (s *APIKeyService) HasScope(key *models.APIKey, required string) bool {
	for _, s := range key.Scopes {
		if s == required || s == "admin" {
			return true
		}
	}
	return false
}

func normalizeScopes(scopes []string) []string {
	seen := make(map[string]bool)
	var out []string
	for _, s := range scopes {
		s = strings.ToLower(strings.TrimSpace(s))
		if s != "" && !seen[s] {
			seen[s] = true
			out = append(out, s)
		}
	}
	return out
}

func toResponse(k *models.APIKey) APIKeyResponse {
	return APIKeyResponse{
		ID:         k.ID.String(),
		Name:       k.Name,
		Prefix:     k.Prefix,
		Scopes:     k.Scopes,
		LastUsedAt: k.LastUsedAt,
		ExpiresAt:  k.ExpiresAt,
		CreatedAt:  k.CreatedAt,
	}
}