// Package validation provides validation utilities for the KnowFoolery application.
package validation

import (
	"fmt"
	"reflect"
	"strings"
	"unicode"

	"github.com/go-playground/validator/v10"

	"knowfoolery/backend/shared/domain/errors"
)

// Validator wraps the go-playground validator with custom validations.
type Validator struct {
	validate *validator.Validate
}

// NewValidator creates a new Validator with custom validations registered.
func NewValidator() *Validator {
	v := validator.New()

	// Use JSON tag names in error messages
	v.RegisterTagNameFunc(func(fld reflect.StructField) string {
		name := strings.SplitN(fld.Tag.Get("json"), ",", 2)[0]
		if name == "-" {
			return ""
		}
		return name
	})

	// Register custom validations
	err := v.RegisterValidation("alphanum_space", validateAlphanumSpace)
	if err != nil {
		panic(err)
	}
	err = v.RegisterValidation("no_html", validateNoHTML)
	if err != nil {
		panic(err)
	}
	err = v.RegisterValidation("safe_text", validateSafeText)
	if err != nil {
		panic(err)
	}
	err = v.RegisterValidation("player_name", validatePlayerName)
	if err != nil {
		panic(err)
	}

	return &Validator{validate: v}
}

// Validate validates a struct and returns a domain error if validation fails.
func (v *Validator) Validate(s interface{}) error {
	err := v.validate.Struct(s)
	if err == nil {
		return nil
	}

	validationErrors, ok := err.(validator.ValidationErrors)
	if !ok {
		return errors.Wrap(errors.CodeValidationFailed, "validation failed", err)
	}

	messages := make([]string, 0, len(validationErrors))
	for _, e := range validationErrors {
		messages = append(messages, formatValidationError(e))
	}

	return errors.Wrap(
		errors.CodeValidationFailed,
		strings.Join(messages, "; "),
		nil,
	)
}

// ValidateVar validates a single variable.
func (v *Validator) ValidateVar(field interface{}, tag string) error {
	err := v.validate.Var(field, tag)
	if err == nil {
		return nil
	}

	return errors.Wrap(errors.CodeValidationFailed, "validation failed", err)
}

// formatValidationError formats a single validation error into a readable message.
func formatValidationError(e validator.FieldError) string {
	field := e.Field()

	switch e.Tag() {
	case "required":
		return fmt.Sprintf("%s is required", field)
	case "min":
		return fmt.Sprintf("%s must be at least %s characters", field, e.Param())
	case "max":
		return fmt.Sprintf("%s must be at most %s characters", field, e.Param())
	case "email":
		return fmt.Sprintf("%s must be a valid email", field)
	case "alphanum":
		return fmt.Sprintf("%s must contain only alphanumeric characters", field)
	case "alphanum_space":
		return fmt.Sprintf("%s must contain only alphanumeric characters and spaces", field)
	case "player_name":
		return fmt.Sprintf("%s must be a valid player name (2-50 chars, alphanumeric with spaces)", field)
	case "oneof":
		return fmt.Sprintf("%s must be one of: %s", field, e.Param())
	case "gte":
		return fmt.Sprintf("%s must be greater than or equal to %s", field, e.Param())
	case "lte":
		return fmt.Sprintf("%s must be less than or equal to %s", field, e.Param())
	case "uuid":
		return fmt.Sprintf("%s must be a valid UUID", field)
	default:
		return fmt.Sprintf("%s is invalid", field)
	}
}

// Custom validation functions

// validateAlphanumSpace validates that a string contains only alphanumeric characters and spaces.
func validateAlphanumSpace(fl validator.FieldLevel) bool {
	str := fl.Field().String()
	for _, r := range str {
		if !unicode.IsLetter(r) && !unicode.IsNumber(r) && !unicode.IsSpace(r) && r != '-' && r != '_' && r != '.' {
			return false
		}
	}
	return true
}

// validateNoHTML validates that a string contains no HTML tags.
func validateNoHTML(fl validator.FieldLevel) bool {
	str := fl.Field().String()
	return !strings.Contains(str, "<") && !strings.Contains(str, ">")
}

// validateSafeText validates that a string contains no potentially dangerous patterns.
func validateSafeText(fl validator.FieldLevel) bool {
	str := strings.ToLower(fl.Field().String())
	dangerousPatterns := []string{
		"javascript:",
		"data:",
		"vbscript:",
		"<script",
		"</script",
	}

	for _, pattern := range dangerousPatterns {
		if strings.Contains(str, pattern) {
			return false
		}
	}
	return true
}

// validatePlayerName validates a player name format.
func validatePlayerName(fl validator.FieldLevel) bool {
	str := fl.Field().String()

	// Length check
	if len(str) < 2 || len(str) > 50 {
		return false
	}

	// Character validation
	for _, r := range str {
		if !unicode.IsLetter(r) && !unicode.IsNumber(r) && !unicode.IsSpace(r) && r != '-' && r != '_' && r != '.' {
			return false
		}
	}

	return true
}

// Common validation tags for reuse
const (
	TagRequired     = "required"
	TagPlayerName   = "required,player_name"
	TagEmail        = "required,email"
	TagUUID         = "required,uuid"
	TagOptionalUUID = "omitempty,uuid"
)