using ErrorOr;
using Microsoft.EntityFrameworkCore;
using Musify.Application.Configuration;
using Musify.Application.Contracts;
using Musify.Application.Shared;
using Musify.Domain.Entities;
using Musify.Domain.ValueObjects;

namespace Musify.Application.Services;

public sealed class UploadIntentValidator(
    IDatabase database,
    IStorageService storageService,
    UploadIntentConfiguration config)
{
    public async Task<ErrorOr<Success>> CheckQuotaAsync(
        long userId,
        long requiredBytes,
        int requiredIntentCount,
        CancellationToken cancellationToken)
    {
        var now = DateTime.UtcNow;
        var pictureDefault = config.DefaultExpectedPictureSizeBytes;
        var audioDefault = config.DefaultExpectedAudioSizeBytes;

        var active = await database.UploadIntents
            .AsNoTracking()
            .Where(intent => intent.UserId == userId && intent.Status == UploadIntentStatus.Issued && intent.ExpiresAt > now)
            .GroupBy(_ => 1)
            .Select(group => new
            {
                Count = group.Count(),
                Bytes = group.Sum(intent => intent.ExpectedSizeBytes
                    ?? (intent.Purpose == UploadIntentPurpose.TrackAudio ? audioDefault : pictureDefault))
            })
            .SingleOrDefaultAsync(cancellationToken);

        if ((active?.Count ?? 0) + requiredIntentCount > config.MaxActiveUploadIntentsPerUser)
            return Error.Validation(description: "Upload intent limit exceeded. Wait for existing uploads to complete or expire.");

        if ((active?.Bytes ?? 0) + requiredBytes > config.MaxActiveUploadBytesPerUser)
            return Error.Validation(description: "Upload byte quota exceeded. Wait for existing uploads to complete or expire.");

        return Result.Success;
    }

    public async Task<ErrorOr<UploadIntent>> ValidateAndLoadAsync(
        Guid intentId,
        long userId,
        UploadIntentPurpose purpose,
        CancellationToken cancellationToken)
    {
        var intent = await database.UploadIntents
            .FirstOrDefaultAsync(i => i.Id == intentId, cancellationToken);

        if (intent == null || intent.UserId != userId)
            return AppErrors.NotFound("UploadIntent", intentId);

        if (intent.Purpose != purpose)
            return Error.Validation(description: "Upload intent was issued for a different purpose.");

        if (intent.IsConsumed)
            return AppErrors.Conflict("UploadIntent.Consumed", "Upload intent has already been consumed.");

        if (intent.IsExpiredAt(DateTime.UtcNow))
            return Error.Validation(description: "Upload intent has expired.");

        var metadata = await storageService.HeadObjectAsync(intent.Bucket, intent.Key, cancellationToken);
        if (metadata == null)
            return Error.NotFound("UploadIntent.ObjectMissing", "Uploaded object not found in storage. Upload the file first.");

        if (metadata.ContentLength > config.MaxUploadBytes)
            return Error.Validation(description: $"Uploaded file exceeds the maximum allowed size of {config.MaxUploadBytes} bytes.");

        return intent;
    }
}