servicetrade-toolbox-wmv/internal/utils/pagination.go

package utils

import (
	"math"
)

// Default pagination constants
const (
	DefaultPage     = 1
	DefaultPageSize = 5
	MaxPageSize     = 100
)

// PaginationInfo contains all the information needed for pagination
type PaginationInfo struct {
	TotalResults int
	TotalPages   int
	CurrentPage  int
	Limit        int
	StartIndex   int
	EndIndex     int
	StartPage    int
	EndPage      int
}

// CalculatePagination calculates pagination information based on total results, current page, and limit
func CalculatePagination(totalResults, currentPage, limit int) PaginationInfo {
	if currentPage < 1 {
		currentPage = 1
	}
	if limit < 1 {
		limit = DefaultPageSize
	}

	totalPages := int(math.Ceil(float64(totalResults) / float64(limit)))
	if totalPages < 1 {
		totalPages = 1
	}

	// Ensure current page is within bounds
	if currentPage > totalPages {
		currentPage = totalPages
	}

	startIndex := (currentPage - 1) * limit
	endIndex := startIndex + limit
	if endIndex > totalResults {
		endIndex = totalResults
	}

	// Calculate pagination range for display
	startPage := 1
	endPage := totalPages

	// Show up to 10 page numbers, centered around current page when possible
	if totalPages > 10 {
		if currentPage <= 5 {
			endPage = 10
		} else if currentPage >= totalPages-4 {
			startPage = totalPages - 9
		} else {
			startPage = currentPage - 4
			endPage = currentPage + 5
		}
	}

	return PaginationInfo{
		TotalResults: totalResults,
		TotalPages:   totalPages,
		CurrentPage:  currentPage,
		Limit:        limit,
		StartIndex:   startIndex + 1, // Convert to 1-based for display
		EndIndex:     endIndex,
		StartPage:    startPage,
		EndPage:      endPage,
	}
}

// GetPageResults extracts the results for the current page from a slice
func GetPageResults[T any](allResults []T, startIndex, endIndex int) []T {
	if startIndex >= len(allResults) {
		return []T{}
	}
	if endIndex > len(allResults) {
		endIndex = len(allResults)
	}
	return allResults[startIndex:endIndex]
}