package middleware

import (
	"github.com/gin-gonic/gin"
)

// CORSConfig holds the configuration for the CORS middleware
type CORSConfig struct {
	AllowedOrigins   []string
	AllowedMethods   []string
	AllowedHeaders   []string
	AllowCredentials bool
	MaxAge           int
}

// DefaultCORSConfig returns the default CORS configuration
func DefaultCORSConfig() *CORSConfig {
	return &CORSConfig{
		AllowedOrigins:   []string{"*"},
		AllowedMethods:   []string{"GET", "POST", "PUT", "DELETE", "OPTIONS", "PATCH"},
		AllowedHeaders:   []string{"Content-Type", "Authorization", "X-Requested-With", "Accept", "Origin"},
		AllowCredentials: false,
		MaxAge:           86400, // 24 hours
	}
}

// CORS returns a Gin middleware handler for CORS (Cross-Origin Resource Sharing)
func CORS() gin.HandlerFunc {
	return CORSWithConfig(DefaultCORSConfig())
}

// CORSWithConfig returns a Gin middleware handler for CORS with custom configuration
func CORSWithConfig(config *CORSConfig) gin.HandlerFunc {
	return func(c *gin.Context) {
		origin := c.GetHeader("Origin")
		
		// Check if the origin is allowed
		if len(config.AllowedOrigins) > 0 && config.AllowedOrigins[0] != "*" {
			allowed := false
			for _, allowedOrigin := range config.AllowedOrigins {
				if origin == allowedOrigin {
					allowed = true
					break
				}
			}
			if !allowed {
				c.AbortWithStatusJSON(403, gin.H{
					"error": "origin not allowed",
				})
				return
			}
		}
		
		// Set CORS headers
		if len(config.AllowedOrigins) > 0 {
			if config.AllowedOrigins[0] == "*" {
				c.Header("Access-Control-Allow-Origin", "*")
			} else {
				c.Header("Access-Control-Allow-Origin", origin)
			}
		}
		
		c.Header("Access-Control-Allow-Methods", joinStringSlice(config.AllowedMethods, ", "))
		c.Header("Access-Control-Allow-Headers", joinStringSlice(config.AllowedHeaders, ", "))
		
		if config.AllowCredentials {
			c.Header("Access-Control-Allow-Credentials", "true")
		}
		
		c.Header("Access-Control-Max-Age", stringFromInt(config.MaxAge))
		
		// Handle preflight requests
		if c.Request.Method == "OPTIONS" {
			c.AbortWithStatus(204)
			return
		}
		
		c.Next()
	}
}

// Helper function to join a slice of strings
func joinStringSlice(slice []string, sep string) string {
	if len(slice) == 0 {
		return ""
	}
	result := slice[0]
	for i := 1; i < len(slice); i++ {
		result += sep + slice[i]
	}
	return result
}

// Helper function to convert int to string
func stringFromInt(n int) string {
	if n == 0 {
		return ""
	}
	return string(rune('0'+n%10)) + stringFromInt(n/10)
}