using ErsatzTV.Core;
using ErsatzTV.Core.Domain;
using ErsatzTV.Infrastructure.Data;
using Microsoft.EntityFrameworkCore;

namespace ErsatzTV.Application.MediaCollections;

/// <summary>
///     Shared existence check for the id a rerun collection selects via <see cref="CollectionType" />
///     (see <c>RerunCollectionRequestMapping.ResolveSelection</c> in the API layer). Used by both
///     <see cref="CreateRerunCollectionHandler" /> and <see cref="UpdateRerunCollectionHandler" /> so
///     a bad/stale id fails validation (422) instead of persisting a dangling FK or 500ing at
///     SaveChanges.
/// </summary>
internal static class RerunCollectionSelectionValidation
{
    public static Task<Validation<BaseError, Unit>> SelectedEntityMustExist(
        TvContext dbContext,
        CollectionType collectionType,
        int? collectionId,
        int? multiCollectionId,
        int? smartCollectionId,
        int? mediaItemId,
        CancellationToken cancellationToken) =>
        collectionType switch
        {
            CollectionType.Collection => Exists(
                dbContext.Collections,
                collectionId,
                "Collection does not exist.",
                cancellationToken),
            CollectionType.MultiCollection => Exists(
                dbContext.MultiCollections,
                multiCollectionId,
                "Multi collection does not exist.",
                cancellationToken),
            CollectionType.SmartCollection => Exists(
                dbContext.SmartCollections,
                smartCollectionId,
                "Smart collection does not exist.",
                cancellationToken),
            CollectionType.TelevisionShow => Exists(
                dbContext.Shows,
                mediaItemId,
                "Show does not exist.",
                cancellationToken),
            CollectionType.TelevisionSeason => Exists(
                dbContext.Seasons,
                mediaItemId,
                "Season does not exist.",
                cancellationToken),
            CollectionType.Artist => Exists(
                dbContext.Artists,
                mediaItemId,
                "Artist does not exist.",
                cancellationToken),
            CollectionType.Movie => Exists(
                dbContext.Movies,
                mediaItemId,
                "Movie does not exist.",
                cancellationToken),
            CollectionType.Episode => Exists(
                dbContext.Episodes,
                mediaItemId,
                "Episode does not exist.",
                cancellationToken),
            CollectionType.MusicVideo => Exists(
                dbContext.MusicVideos,
                mediaItemId,
                "Music video does not exist.",
                cancellationToken),
            CollectionType.OtherVideo => Exists(
                dbContext.OtherVideos,
                mediaItemId,
                "Other video does not exist.",
                cancellationToken),
            CollectionType.Song => Exists(
                dbContext.Songs,
                mediaItemId,
                "Song does not exist.",
                cancellationToken),
            CollectionType.Image => Exists(
                dbContext.Images,
                mediaItemId,
                "Image does not exist.",
                cancellationToken),
            CollectionType.RemoteStream => Exists(
                dbContext.RemoteStreams,
                mediaItemId,
                "Remote stream does not exist.",
                cancellationToken),
            _ => Task.FromResult(
                Fail<BaseError, Unit>($"Unsupported collection type '{collectionType}' for a rerun collection."))
        };

    private static async Task<Validation<BaseError, Unit>> Exists<T>(
        DbSet<T> set,
        int? id,
        string errorMessage,
        CancellationToken cancellationToken)
        where T : class
    {
        // pure existence check — no tracking, nothing materialized into the save-path context
        if (id is null ||
            !await set.AnyAsync(e => EF.Property<int>(e, "Id") == id.Value, cancellationToken))
        {
            return Fail<BaseError, Unit>(errorMessage);
        }

        return Success<BaseError, Unit>(Unit.Default);
    }
}