using ErrorOr;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using Musify.Application.Configuration;
using Musify.Application.Contracts;
using Musify.Application.Pictures.Responses;
using Musify.Application.Shared;
using Musify.Domain.Entities;
using Musify.Domain.ValueObjects;

namespace Musify.Application.Services;

public sealed record UploadRequest(
    UploadIntentPurpose Purpose,
    PictureRoutes Routes,
    string FileType,
    string ContentType,
    long? ExpectedSizeBytes);

public sealed record IssuedUpload(
    Guid IntentId,
    string Key,
    string ObjectName,
    string ContentType,
    string UploadUrl);

/// <summary>Issues pre-signed upload URLs and the upload intents that track them, checking the user quota first.</summary>
public sealed class UploadIntentIssuer(
    IDatabase database,
    IStorageService storageService,
    UploadIntentValidator uploadIntentValidator,
    ApplicationStorageConfiguration storageConfiguration,
    UploadIntentConfiguration uploadIntentConfiguration,
    ILogger<UploadIntentIssuer> logger)
{
    public async Task<ErrorOr<IReadOnlyList<IssuedUpload>>> IssueAsync(
        long userId,
        IReadOnlyList<UploadRequest> requests,
        CancellationToken cancellationToken)
    {
        var userExists = await database.Users
            .AsNoTracking()
            .AnyAsync(user => user.Id == userId, cancellationToken);
        if (!userExists)
            return AppErrors.NotFound("User", userId);

        var planned = requests
            .Select(request =>
            {
                var objectName = $"{Guid.NewGuid()}.{request.FileType.TrimStart('.').ToLowerInvariant()}";
                var key = request.Routes.BuildTempPath(uploadIntentConfiguration.TempRootPrefix, userId, objectName);
                var size = request.ExpectedSizeBytes ?? DefaultSize(request.Purpose);
                return (Request: request, ObjectName: objectName, Key: key, Size: size);
            })
            .ToList();

        await using var transaction = await database.BeginTransactionAsync(
            System.Data.IsolationLevel.Serializable, cancellationToken);

        var quota = await uploadIntentValidator.CheckQuotaAsync(
            userId, planned.Sum(item => item.Size), planned.Count, cancellationToken);
        if (quota.IsError)
            return quota.Errors;

        var expiresIn = TimeSpan.FromSeconds(uploadIntentConfiguration.UploadUrlExpiresInSeconds);
        var expiresAt = DateTime.UtcNow + expiresIn;
        var issued = new List<IssuedUpload>(planned.Count);

        foreach (var item in planned)
        {
            var uploadUrl = await storageService.GetUploadUrlAsync(
                storageConfiguration.Bucket, item.Key, item.Request.ContentType, expiresIn, cancellationToken);

            var intent = new UploadIntent
            {
                UserId = userId,
                Bucket = storageConfiguration.Bucket,
                Key = item.Key,
                ObjectName = item.ObjectName,
                ContentType = item.Request.ContentType,
                ExpectedSizeBytes = item.Size,
                Purpose = item.Request.Purpose,
                ExpiresAt = expiresAt,
            };

            await database.UploadIntents.AddAsync(intent, cancellationToken);
            issued.Add(new IssuedUpload(intent.Id, item.Key, item.ObjectName, item.Request.ContentType, uploadUrl));
        }

        await database.SaveChangesAsync(cancellationToken);
        await transaction.CommitAsync(cancellationToken);

        logger.LogInformation("Issued {Count} upload intents for user {UserId} ({Purposes})",
            issued.Count, userId, string.Join('/', planned.Select(item => item.Request.Purpose)));

        return issued;
    }

    public async Task<ErrorOr<IssuedUpload>> IssueOneAsync(long userId, UploadRequest request, CancellationToken cancellationToken)
    {
        var issued = await IssueAsync(userId, [request], cancellationToken);
        return issued.IsError ? issued.Errors : issued.Value[0];
    }

    public async Task<ErrorOr<PictureUploadResponse>> IssuePictureAsync(
        long userId,
        UploadIntentPurpose purpose,
        IPictureOwnerConfiguration owner,
        string fileType,
        string contentType,
        long? expectedSizeBytes,
        CancellationToken cancellationToken)
    {
        var issued = await IssueOneAsync(
            userId, new UploadRequest(purpose, owner.Routes, fileType, contentType, expectedSizeBytes), cancellationToken);
        if (issued.IsError)
            return issued.Errors;

        return new PictureUploadResponse(
            issued.Value.IntentId,
            storageConfiguration.Bucket,
            issued.Value.Key,
            issued.Value.ObjectName,
            issued.Value.ContentType,
            uploadIntentConfiguration.UploadUrlExpiresInSeconds,
            issued.Value.UploadUrl);
    }

    private long DefaultSize(UploadIntentPurpose purpose) =>
        purpose == UploadIntentPurpose.TrackAudio
            ? uploadIntentConfiguration.DefaultExpectedAudioSizeBytes
            : uploadIntentConfiguration.DefaultExpectedPictureSizeBytes;
}