package middleware

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"reflect"
	"strconv"
	"strings"
)

// ── Request Validation ────────────────────────────────────────────────────

type Validator struct {
	errors map[string][]string
}

func NewValidator() *Validator {
	return &Validator{errors: make(map[string][]string)}
}

func (v *Validator) AddError(field, message string) {
	v.errors[field] = append(v.errors[field], message)
}

func (v *Validator) HasErrors() bool {
	return len(v.errors) > 0
}

func (v *Validator) Errors() map[string][]string {
	return v.errors
}

func (v *Validator) ErrorResponse() map[string]interface{} {
	return map[string]interface{}{
		"error":   "validation failed",
		"details": v.errors,
	}
}

// ValidateString kontrollerar strängfält
func (v *Validator) ValidateString(field, value string, minLen, maxLen int, required bool) {
	if required && strings.TrimSpace(value) == "" {
		v.AddError(field, "is required")
		return
	}
	
	if value != "" {
		if len(value) < minLen {
			v.AddError(field, fmt.Sprintf("must be at least %d characters", minLen))
		}
		if len(value) > maxLen {
			v.AddError(field, fmt.Sprintf("must be at most %d characters", maxLen))
		}
	}
}

// ValidateEmail kontrollerar email
func (v *Validator) ValidateEmail(field, value string, required bool) {
	if required && strings.TrimSpace(value) == "" {
		v.AddError(field, "is required")
		return
	}
	
	if value != "" && !ValidateEmail(value) {
		v.AddError(field, "invalid email format")
	}
}

// ValidateUUID kontrollerar UUID
func (v *Validator) ValidateUUID(field, value string, required bool) {
	if required && strings.TrimSpace(value) == "" {
		v.AddError(field, "is required")
		return
	}
	
	if value != "" && !ValidateUUID(value) {
		v.AddError(field, "invalid UUID format")
	}
}

// ValidateInt kontrollerar heltal
func (v *Validator) ValidateInt(field string, value int, min, max int, required bool) {
	if required && value == 0 {
		v.AddError(field, "is required")
		return
	}
	
	if value != 0 {
		if value < min {
			v.AddError(field, fmt.Sprintf("must be at least %d", min))
		}
		if value > max {
			v.AddError(field, fmt.Sprintf("must be at most %d", max))
		}
	}
}

// ValidateFloat kontrollerar decimaltal
func (v *Validator) ValidateFloat(field string, value float64, min, max float64, required bool) {
	if required && value == 0 {
		v.AddError(field, "is required")
		return
	}
	
	if value != 0 {
		if value < min {
			v.AddError(field, fmt.Sprintf("must be at least %.2f", min))
		}
		if value > max {
			v.AddError(field, fmt.Sprintf("must be at most %.2f", max))
		}
	}
}

// ValidateEnum kontrollerar att värdet finns i tillåtna värden
func (v *Validator) ValidateEnum(field, value string, allowed []string, required bool) {
	if required && strings.TrimSpace(value) == "" {
		v.AddError(field, "is required")
		return
	}
	
	if value != "" {
		found := false
		for _, a := range allowed {
			if a == value {
				found = true
				break
			}
		}
		if !found {
			v.AddError(field, fmt.Sprintf("must be one of: %s", strings.Join(allowed, ", ")))
		}
	}
}

// ── Validation Middleware ─────────────────────────────────────────────────

// ValidateBody validerar request body mot en struct
func ValidateBody(dst interface{}) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			if r.Body == nil {
				http.Error(w, `{"error":"request body required"}`, http.StatusBadRequest)
				return
			}
			
			decoder := json.NewDecoder(r.Body)
			decoder.DisallowUnknownFields()
			
			if err := decoder.Decode(dst); err != nil {
				http.Error(w, fmt.Sprintf(`{"error":"invalid request body: %s"}`, err.Error()), http.StatusBadRequest)
				return
			}
			
			// Validera fält
			validator := NewValidator()
			validateStruct(validator, dst)
			
			if validator.HasErrors() {
				w.Header().Set("Content-Type", "application/json")
				w.WriteHeader(http.StatusBadRequest)
				json.NewEncoder(w).Encode(validator.ErrorResponse())
				return
			}
			
			// Spara validerad struct i context
			ctx := context.WithValue(r.Context(), "validated_body", dst)
			next.ServeHTTP(w, r.WithContext(ctx))
		})
	}
}

// validateStruct validerar en struct baserat på tags
func validateStruct(v *Validator, s interface{}) {
	val := reflect.ValueOf(s)
	if val.Kind() == reflect.Ptr {
		val = val.Elem()
	}
	
	typ := val.Type()
	for i := 0; i < val.NumField(); i++ {
		field := val.Field(i)
		fieldType := typ.Field(i)
		
		// Hämta validation tags
		tag := fieldType.Tag.Get("validate")
		if tag == "" {
			continue
		}
		
		// Parsa tag
		parts := strings.Split(tag, ",")
		required := false
		minLen := 0
		maxLen := 255
		
		for _, part := range parts {
			part = strings.TrimSpace(part)
			if part == "required" {
				required = true
			} else if strings.HasPrefix(part, "min=") {
				minLen, _ = strconv.Atoi(strings.TrimPrefix(part, "min="))
			} else if strings.HasPrefix(part, "max=") {
				maxLen, _ = strconv.Atoi(strings.TrimPrefix(part, "max="))
			}
		}
		
		// Validera baserat på typ
		switch field.Kind() {
		case reflect.String:
			v.ValidateString(fieldType.Name, field.String(), minLen, maxLen, required)
		case reflect.Int, reflect.Int64:
			v.ValidateInt(fieldType.Name, int(field.Int()), 0, 999999, required)
		case reflect.Float64:
			v.ValidateFloat(fieldType.Name, field.Float(), 0, 999999999, required)
		}
	}
}