Musify/backend/Core/Musify.Application/Shared/Pagination.cs

using Microsoft.EntityFrameworkCore;

namespace Musify.Application.Shared
{
    public record PageRequest(int PageNumber = 1, int PageSize = 20)
    {
        public const int MaxPageSize = 100;
    }

    public record PaginatedResponse<T>(
        IReadOnlyList<T> Items,
        int PageNumber,
        int PageSize,
        int PageCount,
        int TotalItemCount,
        bool HasNextPage,
        bool HasPreviousPage);

    public static class PaginationExtensions
    {
        /// <summary>Counts and pages the same (already filtered, ordered and projected) query.</summary>
        public static async Task<PaginatedResponse<T>> ToPaginatedAsync<T>(
            this IQueryable<T> query, PageRequest page, CancellationToken cancellationToken)
        {
            var pageNumber = Math.Max(page.PageNumber, 1);
            var pageSize = Math.Clamp(page.PageSize, 1, PageRequest.MaxPageSize);

            var totalCount = await query.CountAsync(cancellationToken);
            var items = await query
                .Skip((pageNumber - 1) * pageSize)
                .Take(pageSize)
                .ToListAsync(cancellationToken);

            var pageCount = (int)Math.Ceiling(totalCount / (double)pageSize);

            return new PaginatedResponse<T>(
                items,
                pageNumber,
                pageSize,
                pageCount,
                totalCount,
                HasNextPage: pageNumber < pageCount,
                HasPreviousPage: pageNumber > 1 && pageCount > 0);
        }
    }
}