// Package validator provides validation utilities for API parameters
package validator

import (
	"errors"
	"fmt"
	"math"
	"time"
)

// Pagination constants
const (
	DefaultPageSize = 20
	MaxPageSize     = 100
	MinPageSize     = 1
)

// Amount constants
const (
	MinAmount = 0.01
	MaxAmount = 999999999999.99
)

// Date constants
const (
	MaxDateRangeDays = 366
	MaxFutureDays    = 365
)

// String length constants
const (
	MaxNameLength = 100
	MaxNoteLength = 500
)

// Validation errors
var (
	ErrPaginationLimitExceeded = errors.New("pagination limit exceeded maximum allowed value")
	ErrInvalidOffset           = errors.New("pagination offset cannot be negative")
	ErrAmountTooSmall          = errors.New("amount is below minimum allowed value")
	ErrAmountTooLarge          = errors.New("amount exceeds maximum allowed value")
	ErrDateRangeExceeded       = errors.New("date range exceeds maximum allowed days")
	ErrFutureDateExceeded      = errors.New("date exceeds maximum allowed future date")
	ErrEndDateBeforeStartDate  = errors.New("end date must be after start date")
	ErrNameTooLong             = errors.New("name exceeds maximum allowed length")
	ErrNoteTooLong             = errors.New("note exceeds maximum allowed length")
)

// ValidatePagination validates and normalizes pagination parameters
// Returns normalized offset and limit values
// Feature: api-interface-optimization
// Validates: Requirements 7.1, 7.2
func ValidatePagination(offset, limit int) (int, int) {
	// Normalize offset
	if offset < 0 {
		offset = 0
	}

	// Normalize limit
	if limit <= 0 {
		limit = DefaultPageSize
	}
	if limit > MaxPageSize {
		limit = MaxPageSize
	}

	return offset, limit
}

// ValidatePaginationStrict validates pagination parameters and returns error if invalid
// Feature: api-interface-optimization
// Validates: Requirements 7.1, 7.2, 7.3
func ValidatePaginationStrict(offset, limit int) error {
	if offset < 0 {
		return fmt.Errorf("%w: offset=%d", ErrInvalidOffset, offset)
	}
	if limit > MaxPageSize {
		return fmt.Errorf("%w: limit=%d, max=%d", ErrPaginationLimitExceeded, limit, MaxPageSize)
	}
	return nil
}

// ValidateAmount validates that an amount is within acceptable bounds
// Feature: api-interface-optimization
// Validates: Requirements 8.1, 8.2, 8.3
func ValidateAmount(amount float64) error {
	if amount < MinAmount {
		return fmt.Errorf("%w: amount=%.2f, min=%.2f", ErrAmountTooSmall, amount, MinAmount)
	}
	if amount > MaxAmount {
		return fmt.Errorf("%w: amount=%.2f, max=%.2f", ErrAmountTooLarge, amount, MaxAmount)
	}
	return nil
}

// RoundAmount rounds an amount to 2 decimal places
// Feature: api-interface-optimization
// Validates: Requirements 8.2
func RoundAmount(amount float64) float64 {
	return math.Round(amount*100) / 100
}

// ValidateDateRange validates that a date range is within acceptable bounds
// Feature: api-interface-optimization
// Validates: Requirements 9.1
func ValidateDateRange(startDate, endDate time.Time) error {
	if endDate.Before(startDate) {
		return ErrEndDateBeforeStartDate
	}

	days := int(endDate.Sub(startDate).Hours() / 24)
	if days > MaxDateRangeDays {
		return fmt.Errorf("%w: days=%d, max=%d", ErrDateRangeExceeded, days, MaxDateRangeDays)
	}

	return nil
}

// ValidateFutureDate validates that a date is not too far in the future
// Feature: api-interface-optimization
// Validates: Requirements 9.2
func ValidateFutureDate(date time.Time) error {
	maxFutureDate := time.Now().AddDate(0, 0, MaxFutureDays)
	if date.After(maxFutureDate) {
		return fmt.Errorf("%w: date=%s, max=%s", ErrFutureDateExceeded, date.Format("2006-01-02"), maxFutureDate.Format("2006-01-02"))
	}
	return nil
}

// ValidateStringLength validates that a string does not exceed the maximum length
// Feature: api-interface-optimization
// Validates: Requirements 10.1, 10.2
func ValidateStringLength(s string, maxLen int, fieldName string) error {
	if len(s) > maxLen {
		if fieldName == "name" {
			return fmt.Errorf("%w: length=%d, max=%d", ErrNameTooLong, len(s), maxLen)
		}
		if fieldName == "note" {
			return fmt.Errorf("%w: length=%d, max=%d", ErrNoteTooLong, len(s), maxLen)
		}
		return fmt.Errorf("%s exceeds maximum length: length=%d, max=%d", fieldName, len(s), maxLen)
	}
	return nil
}

// ValidateName validates a name field
// Feature: api-interface-optimization
// Validates: Requirements 10.1
func ValidateName(name string) error {
	return ValidateStringLength(name, MaxNameLength, "name")
}

// ValidateNote validates a note field
// Feature: api-interface-optimization
// Validates: Requirements 10.2
func ValidateNote(note string) error {
	return ValidateStringLength(note, MaxNoteLength, "note")
}