using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using System.Text.Json;
using Tiku.Application.Content;
using Tiku.Application.Jobs;
using Tiku.Application.Security;
using Tiku.Application.Tenancy;
using Tiku.Domain.Commerce;
using Tiku.Domain.Common;
using Tiku.Domain.Content;
using Tiku.Domain.Operations;
using Tiku.Infrastructure.Persistence;

namespace Tiku.Infrastructure.Jobs;

internal sealed class BackgroundJobService(
    TikuDbContext dbContext,
    ITenantExecutionScope tenantExecutionScope,
    IFeatureAccessService featureAccessService,
    IBackgroundJobDispatcher backgroundJobDispatcher) : IBackgroundJobService
{
    private static readonly TimeSpan LeaseDuration = TimeSpan.FromMinutes(5);

    public async Task<BackgroundJobItem> EnqueueAsync(
        CreateBackgroundJobCommand command,
        CancellationToken cancellationToken = default)
    {
        var normalizedJobType = NormalizeJobType(command.JobType);
        if (!(await featureAccessService.EvaluateAsync(
                command.TenantId,
                ResolveRequiredFeature(normalizedJobType, command.Payload),
                FeatureAccessOperation.Write,
                cancellationToken)).Allowed)
        {
            throw new InvalidOperationException("Tenant feature entitlement does not allow this background job.");
        }
        var quotaMetric = ResolveQuotaMetric(normalizedJobType);
        var quotaConsumed = false;
        if (quotaMetric is not null)
        {
            var quota = (await featureAccessService.GetQuotaSummaryAsync(command.TenantId, cancellationToken))
                .SingleOrDefault(value => value.MetricCode == quotaMetric);
            if (quota is not null)
            {
                quotaConsumed = await featureAccessService.TryConsumeQuotaAsync(
                    command.TenantId, quotaMetric, 1, cancellationToken);
                if (!quotaConsumed)
                {
                    throw new FeatureAccessException("The background job quota has been exhausted.", "feature_quota_exhausted");
                }
            }
        }
        var job = new BackgroundJob
        {
            TenantId = command.TenantId,
            JobType = normalizedJobType,
            Payload = command.Payload,
            RunAfter = command.RunAfter,
            MaxRetries = Math.Clamp(command.MaxRetries, 0, 20)
        };
        dbContext.BackgroundJobs.Add(job);
        try
        {
            await dbContext.SaveChangesAsync(cancellationToken);
        }
        catch
        {
            if (quotaConsumed && quotaMetric is not null)
            {
                await featureAccessService.ReleaseQuotaAsync(command.TenantId, quotaMetric, 1, CancellationToken.None);
            }
            throw;
        }
        if (job.RunAfter is null && backgroundJobDispatcher.IsEnabled)
        {
            await backgroundJobDispatcher.DispatchAsync(
                job.Id,
                job.TenantId,
                job.JobType,
                job.Id.ToString("N"),
                cancellationToken);
        }
        return ToItem(job);
    }

    private static string? ResolveQuotaMetric(string jobType) => jobType switch
    {
        "content_import" => SaasQuotaMetricCatalog.ImportCount,
        "content_export" => SaasQuotaMetricCatalog.ExportCount,
        _ => null
    };

    public async Task<int> ProcessPendingAsync(
        string workerId,
        int batchSize,
        bool includeImmediateJobs = true,
        CancellationToken cancellationToken = default)
    {
        var now = DateTimeOffset.UtcNow;
        var leaseExpiresAt = now.Add(LeaseDuration);
        var claimedIds = await dbContext.Database.SqlQuery<Guid>($"""
                UPDATE background_jobs AS job
                SET status = 'processing',
                    locked_by = {workerId},
                    lock_expires_at = {leaseExpiresAt},
                    started_at = COALESCE(started_at, {now}),
                    updated_at = {now}
                WHERE job.id IN (
                    SELECT candidate.id
                    FROM background_jobs AS candidate
                    WHERE (
                        (candidate.status = 'pending' AND ({includeImmediateJobs} OR candidate.run_after IS NOT NULL) AND
                         (candidate.run_after IS NULL OR candidate.run_after <= {now})) OR
                        (candidate.status = 'processing' AND candidate.lock_expires_at <= {now})
                    )
                    ORDER BY candidate.created_at, candidate.id
                    FOR UPDATE SKIP LOCKED
                    LIMIT {Math.Clamp(batchSize, 1, 100)}
                )
                RETURNING job.id AS "Value"
                """)
            .ToArrayAsync(cancellationToken);

        var processed = 0;
        dbContext.ChangeTracker.Clear();
        foreach (var jobId in claimedIds)
        {
            cancellationToken.ThrowIfCancellationRequested();
            var job = await dbContext.BackgroundJobs.SingleAsync(value => value.Id == jobId, cancellationToken);
            if (await ProcessJobAsync(job, workerId, alreadyClaimed: true, cancellationToken)) processed++;
            dbContext.ChangeTracker.Clear();
        }

        return processed;
    }

    public async Task<bool> ProcessRequestedAsync(
        Guid jobId,
        Guid tenantId,
        string jobType,
        string workerId,
        CancellationToken cancellationToken = default)
    {
        var normalizedJobType = NormalizeJobType(jobType);
        var claimed = await dbContext.BackgroundJobs
            .Where(item => item.Id == jobId && item.TenantId == tenantId &&
                           item.JobType == normalizedJobType && item.Status == BackgroundJobStatus.Pending &&
                           item.RunAfter == null)
            .ExecuteUpdateAsync(setters => setters
                .SetProperty(item => item.Status, BackgroundJobStatus.Processing)
                .SetProperty(item => item.LockedBy, workerId)
                .SetProperty(item => item.LockExpiresAt, DateTimeOffset.UtcNow.Add(LeaseDuration))
                .SetProperty(item => item.StartedAt, DateTimeOffset.UtcNow), cancellationToken);
        if (claimed == 0)
        {
            return false;
        }

        dbContext.ChangeTracker.Clear();
        var job = await dbContext.BackgroundJobs.SingleOrDefaultAsync(
            item => item.Id == jobId && item.TenantId == tenantId,
            cancellationToken);
        if (job is null)
        {
            throw new InvalidOperationException("The requested background job does not exist in the target tenant.");
        }
        if (!string.Equals(job.JobType, normalizedJobType, StringComparison.Ordinal))
        {
            throw new InvalidOperationException("The requested background job type does not match the persisted job.");
        }
        return await ProcessJobAsync(job, workerId, alreadyClaimed: true, cancellationToken);
    }

    private async Task<bool> ProcessJobAsync(
        BackgroundJob job,
        string workerId,
        bool alreadyClaimed,
        CancellationToken cancellationToken)
    {
        if ((!alreadyClaimed && job.Status != BackgroundJobStatus.Pending) ||
            (alreadyClaimed && (job.Status != BackgroundJobStatus.Processing || job.LockedBy != workerId)))
        {
            return false;
        }
        if (!(await featureAccessService.EvaluateAsync(
                job.TenantId,
                ResolveRequiredFeature(job.JobType, job.Payload),
                FeatureAccessOperation.Write,
                cancellationToken)).Allowed)
        {
            await CompleteAsync(
                job,
                workerId,
                BackgroundJobStatus.Failed,
                JsonDefaults.Object(),
                "Tenant feature entitlement was revoked before job execution.",
                cancellationToken);
            return true;
        }

        if (!alreadyClaimed)
        {
            var now = DateTimeOffset.UtcNow;
            job.Status = BackgroundJobStatus.Processing;
            job.LockedBy = workerId;
            job.LockExpiresAt = now.Add(LeaseDuration);
            job.StartedAt = now;
            await dbContext.SaveChangesAsync(cancellationToken);
        }

        try
        {
            var result = await tenantExecutionScope.ExecuteAsync(
                new SystemScopeRequest(
                    job.TenantId, SystemScopeCallerType.Worker, workerId,
                    $"Background job {job.JobType}", job.Id.ToString("N")),
                (provider, token) => ProcessCoreAsync(provider, job, token),
                cancellationToken);
            job.Status = BackgroundJobStatus.Succeeded;
            job.CompletedAt = DateTimeOffset.UtcNow;
            job.LastError = null;
            job.Result = result;
        }
        catch (Exception exception) when (exception is not OperationCanceledException)
        {
            job.RetryCount++;
            job.LastError = exception.Message;
            job.Status = job.RetryCount > job.MaxRetries
                ? BackgroundJobStatus.Failed
                : BackgroundJobStatus.Pending;
            job.RunAfter = job.Status == BackgroundJobStatus.Pending
                ? DateTimeOffset.UtcNow.AddSeconds(Math.Min(300, 10 * job.RetryCount))
                : null;
        }
        finally
        {
            await CompleteAsync(job, workerId, job.Status, job.Result, job.LastError, cancellationToken);
        }

        return true;
    }

    private async Task CompleteAsync(
        BackgroundJob job,
        string workerId,
        BackgroundJobStatus status,
        JsonElement result,
        string? lastError,
        CancellationToken cancellationToken)
    {
        await dbContext.BackgroundJobs
            .Where(value => value.Id == job.Id && value.LockedBy == workerId)
            .ExecuteUpdateAsync(setters => setters
                .SetProperty(value => value.Status, status)
                .SetProperty(value => value.RetryCount, job.RetryCount)
                .SetProperty(value => value.RunAfter, job.RunAfter)
                .SetProperty(value => value.CompletedAt, job.CompletedAt)
                .SetProperty(value => value.LastError, lastError)
                .SetProperty(value => value.OutputAssetId, job.OutputAssetId)
                .SetProperty(value => value.Result, result)
                .SetProperty(value => value.LockedBy, (string?)null)
                .SetProperty(value => value.LockExpiresAt, (DateTimeOffset?)null),
                cancellationToken);
    }

    public async Task<IReadOnlyCollection<BackgroundJobItem>> ListAsync(
        Guid tenantId,
        string? jobType = null,
        int limit = 50,
        CancellationToken cancellationToken = default)
    {
        var query = dbContext.BackgroundJobs.AsNoTracking()
            .Where(job => job.TenantId == tenantId);
        if (!string.IsNullOrWhiteSpace(jobType))
        {
            var normalized = NormalizeJobType(jobType);
            query = query.Where(job => job.JobType == normalized);
        }

        var jobs = await query
            .OrderByDescending(job => job.CreatedAt)
            .Take(Math.Clamp(limit, 1, 200))
            .ToArrayAsync(cancellationToken);
        return jobs.Select(ToItem).ToArray();
    }

    private async Task<JsonElement> ProcessCoreAsync(
        IServiceProvider scopedProvider,
        BackgroundJob job,
        CancellationToken cancellationToken)
    {
        cancellationToken.ThrowIfCancellationRequested();
        var scopedDbContext = scopedProvider.GetRequiredService<TikuDbContext>();
        return job.JobType switch
        {
            "content_export" => await ProcessContentExportAsync(scopedDbContext, job, cancellationToken),
            "content_import" => await ProcessContentImportAsync(scopedProvider, job, cancellationToken),
            "asset_security_scan" => throw new NotSupportedException("asset_security_scan requires a configured scanner provider before it can write scan results."),
            "statistics_aggregation" => await ProcessStatisticsAggregationAsync(scopedProvider, scopedDbContext, job, cancellationToken),
            "commerce_reconciliation" => await ProcessCommerceReconciliationAsync(scopedDbContext, job, cancellationToken),
            "tenant_domain_recheck" => await ProcessTenantDomainRecheckAsync(scopedProvider, cancellationToken),
            _ => throw new InvalidOperationException($"Unsupported background job type '{job.JobType}'.")
        };
    }

    private static async Task<JsonElement> ProcessContentImportAsync(
        IServiceProvider scopedProvider,
        BackgroundJob job,
        CancellationToken cancellationToken)
    {
        var directContentService = scopedProvider.GetRequiredService<IDirectContentService>();
        var createdBy = GetJsonGuid(job.Payload, "createdBy") ?? Guid.Empty;
        if (createdBy == Guid.Empty)
        {
            throw new InvalidOperationException("content_import job requires createdBy.");
        }

        var command = new SimpleImportCommand(
            GetJsonString(job.Payload, "importType") ?? throw new InvalidOperationException("content_import job requires importType."),
            GetJsonString(job.Payload, "sourceFormat"),
            GetJsonString(job.Payload, "sourceName"),
            GetJsonGuid(job.Payload, "regionId"),
            GetJsonGuid(job.Payload, "entryId"),
            GetJsonGuid(job.Payload, "contentNodeId"),
            GetJsonGuid(job.Payload, "subjectId"),
            GetJsonGuid(job.Payload, "categoryId"),
            GetJsonGuid(job.Payload, "questionBankId"),
            GetJsonGuid(job.Payload, "collectionId"),
            GetJsonArray(job.Payload, "items"),
            false);
        var result = await directContentService.ExecuteImportAsync(
            new DirectContentActor(job.TenantId, createdBy),
            command,
            cancellationToken);
        return JsonSerializer.SerializeToElement(new
        {
            importJobId = result.Job.Id,
            result.Job.ImportType,
            result.Job.Status,
            result.Job.TotalCount,
            result.Job.InsertedCount,
            result.Job.UpdatedCount,
            result.Job.ErrorCount
        });
    }

    private async Task<JsonElement> ProcessContentExportAsync(
        TikuDbContext scopedDbContext,
        BackgroundJob job,
        CancellationToken cancellationToken)
    {
        var exportType = GetJsonString(job.Payload, "exportType") ?? "summary";
        var assetKey = $"background-jobs/{job.Id:N}/content-export.json";
        var asset = await scopedDbContext.ContentAssets.SingleOrDefaultAsync(
            item => item.TenantId == job.TenantId && item.AssetKey == assetKey,
            cancellationToken);
        if (asset is null)
        {
            asset = new ContentAsset
            {
                TenantId = job.TenantId,
                AssetKey = assetKey,
                AssetType = ContentAssetType.Document,
                StorageProvider = AssetStorageProvider.ExternalUrl,
                UploadStatus = AssetUploadStatus.Verified,
                SecurityScanStatus = AssetSecurityScanStatus.NotRequired,
                Source = "background_job"
            };
            scopedDbContext.ContentAssets.Add(asset);
        }

        var questionBankCount = await scopedDbContext.QuestionBanks.CountAsync(item => item.TenantId == job.TenantId, cancellationToken);
        var questionCount = await scopedDbContext.Questions.CountAsync(item => item.TenantId == job.TenantId, cancellationToken);
        var studentCount = await scopedDbContext.StudentProfiles.CountAsync(item => item.TenantId == job.TenantId, cancellationToken);
        asset.FileName = $"content-export-{DateTimeOffset.UtcNow:yyyyMMddHHmmss}.json";
        asset.Title = "Content export manifest";
        asset.Description = $"Generated content export manifest for {exportType}.";
        asset.ObjectKey = assetKey;
        asset.MimeType = "application/json";
        asset.Metadata = JsonSerializer.SerializeToElement(new
        {
            exportType,
            generatedAt = DateTimeOffset.UtcNow,
            questionBankCount,
            questionCount,
            studentCount,
            payload = job.Payload
        });
        await scopedDbContext.SaveChangesAsync(cancellationToken);
        job.OutputAssetId = asset.Id;
        return JsonSerializer.SerializeToElement(new
        {
            outputAssetId = asset.Id,
            asset.AssetKey,
            questionBankCount,
            questionCount,
            studentCount
        });
    }

    private async Task<JsonElement> ProcessCommerceReconciliationAsync(
        TikuDbContext scopedDbContext,
        BackgroundJob job,
        CancellationToken cancellationToken)
    {
        var provider = NormalizeProvider(GetJsonString(job.Payload, "provider"));
        var hasProviderConfig = await scopedDbContext.TenantExternalProviders.AnyAsync(
            item =>
                item.TenantId == job.TenantId &&
                item.Capability == Tiku.Domain.Tenancy.TenantExternalProviderCapability.Payment &&
                item.Provider == provider &&
                item.Status == Tiku.Domain.Tenancy.TenantExternalProviderStatus.Active,
            cancellationToken);
        if (!hasProviderConfig)
        {
            throw new InvalidOperationException($"Active payment provider '{provider}' is required for commerce reconciliation job.");
        }

        var billDate = GetJsonDateOnly(job.Payload, "billDate") ?? DateOnly.FromDateTime(DateTime.UtcNow.Date);
        var billType = GetJsonEnum(job.Payload, "billType", ReconciliationBillType.Combined);
        var sourceHash = $"background-job:{job.Id:N}";
        var batch = await scopedDbContext.CommerceReconciliationBatches.SingleOrDefaultAsync(
            item =>
                item.TenantId == job.TenantId &&
                item.Provider == provider &&
                item.Source == ReconciliationSource.ProviderDownload &&
                item.SourceHash == sourceHash,
            cancellationToken);
        if (batch is null)
        {
            batch = new CommerceReconciliationBatch
            {
                TenantId = job.TenantId,
                Provider = provider,
                BillDate = billDate,
                BillType = billType,
                Source = ReconciliationSource.ProviderDownload,
                SourceName = $"provider-bill:{provider}:{billDate:yyyyMMdd}",
                SourceHash = sourceHash,
                Status = ReconciliationBatchStatus.Pending,
                Metadata = JsonSerializer.SerializeToElement(new
                {
                    jobId = job.Id,
                    note = "Provider bill job created the reconciliation batch; provider download/parser is handled by a dedicated provider processor."
                })
            };
            scopedDbContext.CommerceReconciliationBatches.Add(batch);
            await scopedDbContext.SaveChangesAsync(cancellationToken);
        }

        return JsonSerializer.SerializeToElement(new
        {
            batchId = batch.Id,
            provider,
            billDate,
            billType = billType.ToString(),
            status = batch.Status.ToString()
        });
    }

    private static async Task<JsonElement> ProcessTenantDomainRecheckAsync(
        IServiceProvider scopedProvider,
        CancellationToken cancellationToken)
    {
        var lifecycleService = scopedProvider.GetRequiredService<ITenantDomainLifecycleService>();
        var processed = await lifecycleService.ProcessPendingAsync(cancellationToken);
        return JsonSerializer.SerializeToElement(new
        {
            processed
        });
    }

    private async Task<JsonElement> ProcessStatisticsAggregationAsync(
        IServiceProvider scopedProvider,
        TikuDbContext scopedDbContext,
        BackgroundJob job,
        CancellationToken cancellationToken)
    {
        var since = DateTimeOffset.UtcNow.AddDays(-7);
        var activeLearnerCount = await scopedDbContext.PracticeSessions
            .Where(item => item.TenantId == job.TenantId && item.StartedAt >= since)
            .Select(item => item.UserId)
            .Distinct()
            .CountAsync(cancellationToken);
        var paidOrderCount = await scopedDbContext.Orders
            .CountAsync(item => item.TenantId == job.TenantId && item.Status == OrderStatus.Paid, cancellationToken);
        var revenueCents = await scopedDbContext.Orders
            .Where(item => item.TenantId == job.TenantId &&
                           (item.Status == OrderStatus.Paid ||
                            item.Status == OrderStatus.PartiallyRefunded ||
                            item.Status == OrderStatus.Refunded))
            .SumAsync(item => item.AmountCents - item.RefundedAmountCents, cancellationToken);
        var quotaUsage = await scopedProvider.GetRequiredService<IFeatureUsageReconciliationService>()
            .ReconcileTenantAsync(
                new ReconcileFeatureUsageRequest(
                    job.TenantId,
                    SystemScopeCallerType.Worker,
                    nameof(BackgroundJobService),
                    "Reconcile tenant current feature usage during statistics aggregation",
                    $"feature-usage-{job.Id:N}"),
                cancellationToken);
        return JsonSerializer.SerializeToElement(new
        {
            since,
            activeLearnerCount,
            paidOrderCount,
            revenueCents,
            quotaUsage
        });
    }

    private static string NormalizeJobType(string jobType)
    {
        return jobType.Trim().ToLowerInvariant();
    }

    private static string ResolveRequiredFeature(string jobType, JsonElement payload) => jobType switch
    {
        "content_import" => SaasFeatureCatalog.ResolveContentImportFeature(GetJsonString(payload, "importType"))
            ?? throw new InvalidOperationException("Background content import type is not supported."),
        "content_export" or "asset_security_scan" => SaasFeatureCatalog.PrivateQuestionBank,
        "commerce_reconciliation" => SaasFeatureCatalog.StudentStore,
        "statistics_aggregation" or "tenant_domain_recheck" => SaasFeatureCatalog.CoreBackoffice,
        _ => SaasFeatureCatalog.CoreBackoffice
    };

    private static string NormalizeProvider(string? provider)
    {
        var normalized = (provider ?? string.Empty).Trim().ToLowerInvariant();
        return string.IsNullOrWhiteSpace(normalized)
            ? throw new InvalidOperationException("Background job provider is required.")
            : normalized;
    }

    private static string? GetJsonString(JsonElement element, string propertyName)
    {
        return element.ValueKind == JsonValueKind.Object &&
               element.TryGetProperty(propertyName, out var property) &&
               property.ValueKind == JsonValueKind.String
            ? property.GetString()
            : null;
    }

    private static Guid? GetJsonGuid(JsonElement element, string propertyName)
    {
        if (element.ValueKind != JsonValueKind.Object ||
            !element.TryGetProperty(propertyName, out var property))
        {
            return null;
        }

        return property.ValueKind == JsonValueKind.String && Guid.TryParse(property.GetString(), out var value)
            ? value
            : null;
    }

    private static IReadOnlyCollection<JsonElement> GetJsonArray(JsonElement element, string propertyName)
    {
        if (element.ValueKind != JsonValueKind.Object ||
            !element.TryGetProperty(propertyName, out var property) ||
            property.ValueKind != JsonValueKind.Array)
        {
            return [];
        }

        return property.EnumerateArray().Select(item => item.Clone()).ToArray();
    }

    private static DateOnly? GetJsonDateOnly(JsonElement element, string propertyName)
    {
        var value = GetJsonString(element, propertyName);
        return DateOnly.TryParse(value, out var parsed) ? parsed : null;
    }

    private static TEnum GetJsonEnum<TEnum>(JsonElement element, string propertyName, TEnum fallback)
        where TEnum : struct
    {
        var value = GetJsonString(element, propertyName);
        return Enum.TryParse<TEnum>(value, true, out var parsed) ? parsed : fallback;
    }

    private static BackgroundJobItem ToItem(BackgroundJob job)
    {
        return new BackgroundJobItem(
            job.Id,
            job.TenantId,
            job.JobType,
            job.Status,
            job.RetryCount,
            job.MaxRetries,
            job.RunAfter,
            job.StartedAt,
            job.CompletedAt,
            job.LastError,
            job.OutputAssetId,
            job.Result);
    }
}