using System.Text.Json;
using Microsoft.EntityFrameworkCore;
using Npgsql;
using Tiku.Application.Learning;
using Tiku.Domain.Learning;

namespace Tiku.Infrastructure.Learning;

internal sealed class PracticeSessionService(
    LearningServiceDependencies dependencies,
    IV2PracticeSessionService v2PracticeSessionService)
    : LearningActivityServiceBase(dependencies), IPracticeSessionService
{
    public async Task<PracticeSessionItem> CreatePracticeSessionAsync(
        LearningActor actor,
        PracticeSessionCommand command,
        CancellationToken cancellationToken = default)
    {
        return await v2PracticeSessionService.CreateAsync(actor, command, cancellationToken);
    }

    public async Task<PracticeSessionDetailItem> GetPracticeSessionDetailAsync(
        LearningActor actor,
        PracticeSessionFilter filter,
        CancellationToken cancellationToken = default)
    {
        var session = await GetPracticeSessionAsync(actor, filter.PracticeSessionId, cancellationToken);
        await strongRevocationService.EnsureVersionAsync(
            actor, session.StrongRevocationVersion, cancellationToken);
        var orderedQuestions = await LoadSessionQuestionItemsAsync(
            actor.TenantId,
            session.Id,
            cancellationToken);

        var answers = await learningPersistence.AnswerRecords
            .AsNoTracking()
            .Where(answer =>
                answer.TenantId == actor.TenantId &&
                answer.UserId == actor.UserId &&
                answer.PracticeSessionId == session.Id &&
                learningPersistence.CurrentAnswers.Any(current =>
                    current.TenantId == answer.TenantId && current.AnswerRecordId == answer.Id))
            .ToArrayAsync(cancellationToken);
        var answersByQuestion = answers
            .GroupBy(answer => answer.SessionQuestionId)
            .ToDictionary(
                group => group.Key,
                group => ToItem(
                    group.OrderByDescending(answer => answer.Revision).First()));

        var revealAll = session.Status is PracticeSessionStatus.Submitted or PracticeSessionStatus.PendingReview;
        var revealAnswered = !DefersSolutionUntilSubmission(session.Mode);
        var revealQuestionIds = revealAll
            ? orderedQuestions.Select(item => item.SessionQuestionId).ToArray()
            : revealAnswered ? answersByQuestion.Keys.ToArray() : [];
        var solutions = revealQuestionIds.Length == 0
            ? new Dictionary<Guid, QuestionSolutionItem>()
            : await LoadSolutionsAsync(actor.TenantId, session.Id, revealQuestionIds, cancellationToken);

        return new PracticeSessionDetailItem(ToItem(session), orderedQuestions, answersByQuestion, solutions);
    }

    private async Task<Dictionary<Guid, QuestionSolutionItem>> LoadSolutionsAsync(
        Guid tenantId,
        Guid sessionId,
        IReadOnlyCollection<Guid> revealQuestionIds,
        CancellationToken cancellationToken)
    {
        var sessionQuestions = await learningPersistence.PracticeSessionQuestions.AsNoTracking()
                .Where(item => item.TenantId == tenantId &&
                               item.PracticeSessionId == sessionId &&
                               revealQuestionIds.Contains(item.Id))
                .ToArrayAsync(cancellationToken);
        return await v2PracticeSessionService.LoadSolutionsAsync(sessionQuestions, cancellationToken);
    }

    public async Task<PracticeSessionReportItem> SubmitPracticeSessionAsync(
        LearningActor actor,
        SubmitPracticeSessionCommand command,
        CancellationToken cancellationToken = default)
    {
        if (string.IsNullOrWhiteSpace(command.IdempotencyKey))
            throw new LearningValidationException("idempotency_key_required", "An idempotency key is required.");

        await using var transaction = await unitOfWork.Database.BeginTransactionAsync(cancellationToken);
        var submissionLockKey = $"practice-submit:{actor.TenantId:N}:{actor.UserId:N}:{command.PracticeSessionId:N}";
        await unitOfWork.Database.ExecuteSqlInterpolatedAsync(
            $"SELECT pg_advisory_xact_lock(hashtextextended({submissionLockKey}, 0))",
            cancellationToken);
        var session = await learningPersistence.PracticeSessions.SingleOrDefaultAsync(item =>
            item.TenantId == actor.TenantId &&
            item.UserId == actor.UserId &&
            item.Id == command.PracticeSessionId,
            cancellationToken) ?? throw new LearningResourceNotFoundException(
            "practice_session_not_found", "Practice session was not found.");
        await strongRevocationService.EnsureVersionAsync(
            actor, session.StrongRevocationVersion, cancellationToken);
        var requestHash = HashSubmission(command);
        var existingOperation = await learningPersistence.LearningOperationIdempotencies.AsNoTracking().SingleOrDefaultAsync(
            item =>
                item.TenantId == actor.TenantId &&
                item.UserId == actor.UserId &&
                item.PracticeSessionId == session.Id &&
                item.OperationType == "submit" &&
                item.IdempotencyKey == command.IdempotencyKey, cancellationToken);
        if (existingOperation is not null)
        {
            if (!string.Equals(existingOperation.RequestHash, requestHash, StringComparison.Ordinal))
            {
                SubmissionConflicts.Add(1);
                throw new LearningValidationException("idempotency_conflict",
                    "The idempotency key was used with a different request.");
            }

            IdempotencyReplays.Add(1);
            return existingOperation.ResponseSnapshot.Deserialize<PracticeSessionReportItem>()
                   ?? throw new InvalidOperationException("The stored report response is invalid.");
        }

        if (session.Status != PracticeSessionStatus.Active)
            throw new LearningValidationException("practice_session_not_active",
                "Only an active practice session can be submitted.");
        if (session.ExpiresAt.HasValue && session.ExpiresAt <= DateTimeOffset.UtcNow)
        {
            session.Status = PracticeSessionStatus.Expired;
            session.Version++;
            await unitOfWork.SaveChangesAsync(cancellationToken);
            await transaction.CommitAsync(cancellationToken);
            throw new LearningValidationException("practice_session_expired", "The practice session has expired.");
        }

        session.Status = PracticeSessionStatus.Scoring;
        session.Version++;
        var report = await BuildPracticeSessionReportAsync(actor, session, cancellationToken);
        session.Status = report.IsFinal ? PracticeSessionStatus.Submitted : PracticeSessionStatus.PendingReview;
        session.FinishedAt = report.SubmittedAt;
        session.Version++;
        var response = ToItem(report);
        learningPersistence.LearningOperationIdempotencies.Add(new LearningOperationIdempotency
        {
            TenantId = actor.TenantId,
            UserId = actor.UserId,
            PracticeSessionId = session.Id,
            OperationType = "submit",
            IdempotencyKey = command.IdempotencyKey.Trim(),
            RequestHash = requestHash,
            ResponseSnapshot = JsonSerializer.SerializeToElement(response),
            CompletedAt = report.SubmittedAt
        });
        try
        {
            await unitOfWork.SaveChangesAsync(cancellationToken);
            await transaction.CommitAsync(cancellationToken);
        }
        catch (DbUpdateConcurrencyException)
        {
            SubmissionConflicts.Add(1);
            throw new LearningValidationException("practice_session_version_conflict",
                "The practice session changed during submission.");
        }
        catch (DbUpdateException exception) when (exception.InnerException is NpgsqlException)
        {
            SubmissionConflicts.Add(1);
            throw new LearningValidationException("practice_submission_conflict",
                "The practice session was already submitted by another request.");
        }

        return response;
    }

}