package pagination

import (
	"strconv"

	apperrors "veza-backend-api/internal/errors"

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

const (
	DefaultPageSize = 20
	MaxPageSize     = 100
)

// Params holds parsed pagination parameters
type Params struct {
	Page  int
	Limit int
}

// Offset returns the offset for SQL queries (0-based)
func (p Params) Offset() int {
	if p.Page < 1 {
		return 0
	}
	return (p.Page - 1) * p.Limit
}

// PaginationMeta is the standard pagination object in responses
// Format: {"page": 1, "limit": 20, "total": 150, "total_pages": 8}
type PaginationMeta struct {
	Page       int   `json:"page"`
	Limit      int   `json:"limit"`
	Total      int64 `json:"total"`
	TotalPages int   `json:"total_pages"`
}

// ParseParams extracts page and limit from query string
// Uses ?page=1&limit=20. Returns default page=1, limit=20. Max limit=100.
// Empty or invalid values default to page=1, limit=20.
// Returns an AppError if validation fails (explicit page < 1 or limit > 100).
func ParseParams(c *gin.Context) (Params, *apperrors.AppError) {
	pageStr := c.DefaultQuery("page", "1")
	limitStr := c.DefaultQuery("limit", strconv.Itoa(DefaultPageSize))

	page, _ := strconv.Atoi(pageStr)
	limit, _ := strconv.Atoi(limitStr)

	if page < 1 {
		page = 1
	}
	if limit < 1 {
		limit = DefaultPageSize
	}
	if limit > MaxPageSize {
		return Params{}, apperrors.NewValidationError("pagination: limit must be between 1 and 100")
	}

	return Params{Page: page, Limit: limit}, nil
}

// ParseParamsLenient parses params with silent normalization (for backward compat)
// Invalid values are set to defaults. Use ParseParams for strict validation.
func ParseParamsLenient(c *gin.Context) Params {
	page, _ := strconv.Atoi(c.DefaultQuery("page", "1"))
	limit, _ := strconv.Atoi(c.DefaultQuery("limit", strconv.Itoa(DefaultPageSize)))
	if page < 1 {
		page = 1
	}
	if limit < 1 {
		limit = DefaultPageSize
	}
	if limit > MaxPageSize {
		limit = MaxPageSize
	}
	return Params{Page: page, Limit: limit}
}

// BuildMeta constructs PaginationMeta from page, limit, total
func BuildMeta(page, limit int, total int64) PaginationMeta {
	totalPages := 1
	if limit > 0 && total > 0 {
		totalPages = int((total + int64(limit) - 1) / int64(limit))
		if totalPages < 1 {
			totalPages = 1
		}
	}
	return PaginationMeta{
		Page:       page,
		Limit:      limit,
		Total:      total,
		TotalPages: totalPages,
	}
}