tiku-backend.net/Tiku.Infrastructure/Learning/Answering/AnsweringService.cs

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

namespace Tiku.Infrastructure.Learning;

internal sealed class AnsweringService(LearningServiceDependencies dependencies)
    : LearningActivityServiceBase(dependencies), IAnsweringService
{
    public async Task<AnswerRecordItem> SubmitAnswerAsync(
        LearningActor actor,
        SubmitAnswerCommand command,
        CancellationToken cancellationToken = default)
    {
        if (string.IsNullOrWhiteSpace(command.IdempotencyKey))
            throw new LearningValidationException("idempotency_key_required", "An idempotency key is required.");
        if (command.SelectedOptionIndices?.Any(index => index < 0) == true)
            throw new LearningValidationException("selected_option_index_invalid",
                "Selected option indices must be zero-based non-negative values.");

        var idempotencyKey = command.IdempotencyKey.Trim();
        var now = DateTimeOffset.UtcNow;
        var sessionQuestion = await learningPersistence.PracticeSessionQuestions.SingleOrDefaultAsync(item =>
            item.TenantId == actor.TenantId && item.Id == command.SessionQuestionId, cancellationToken);

        if (sessionQuestion is null)
            throw new LearningResourceNotFoundException(
                "session_question_not_found",
                "An active practice session question was not found.");

        var session = await learningPersistence.PracticeSessions.SingleOrDefaultAsync(item =>
            item.TenantId == actor.TenantId &&
            item.UserId == actor.UserId &&
            item.Id == sessionQuestion.PracticeSessionId, cancellationToken);
        if (session is null)
            throw new LearningResourceNotFoundException("practice_session_not_found",
                "Practice session was not found.");
        await learningAccessService.EnsureStrongRevocationVersionAsync(
            actor, session.StrongRevocationVersion, cancellationToken);
        var deliveryVersion = await LoadDeliveryVersionAsync(actor.TenantId, sessionQuestion, cancellationToken);
        var revealedSolution = DefersSolutionUntilSubmission(session.Mode) ? null : ToSolutionItem(deliveryVersion);

        var requestHash = HashAnswer(command);
        var existingSubmission = await learningPersistence.AnswerSubmissionIdempotencies.AsNoTracking()
            .SingleOrDefaultAsync(
            item =>
                item.TenantId == actor.TenantId &&
                item.UserId == actor.UserId &&
                item.PracticeSessionId == session.Id &&
                item.IdempotencyKey == idempotencyKey,
            cancellationToken);
        if (existingSubmission is not null)
        {
            if (!string.Equals(existingSubmission.RequestHash, requestHash, StringComparison.Ordinal))
            {
                AnswerConflicts.Add(1);
                throw new LearningValidationException("idempotency_conflict",
                    "The idempotency key was used with a different request.");
            }

            IdempotencyReplays.Add(1);
            return await ReplayAsync(existingSubmission, revealedSolution, cancellationToken);
        }

        if (session.ExpiresAt.HasValue && session.ExpiresAt <= now)
        {
            session.Status = PracticeSessionStatus.Expired;
            session.Version++;
            await unitOfWork.SaveChangesAsync(cancellationToken);
            throw new LearningValidationException("practice_session_expired", "The practice session has expired.");
        }

        EnsureAnswerSessionState(session, command);
        var current = await learningPersistence.CurrentAnswers.SingleOrDefaultAsync(answer =>
            answer.TenantId == actor.TenantId &&
            answer.UserId == actor.UserId &&
            answer.PracticeSessionId == session.Id &&
            answer.SessionQuestionId == sessionQuestion.Id, cancellationToken);
        if (current is not null && command.ClientSequence <= current.ClientSequence)
            throw new LearningValidationException(
                "practice_client_sequence_conflict",
                "Client sequence must increase for a revised answer.");

        var selectedIndices = command.SelectedOptionIndices?.Distinct().Order().ToArray() ?? [];
        var score = sessionQuestion.Score ?? 1;
        QuestionGradingResult grading;
        try
        {
            grading = QuestionGrader.Grade(new QuestionGradingInput(
                deliveryVersion.QuestionType,
                deliveryVersion.CorrectOptionIndex,
                deliveryVersion.CorrectOptionIndices,
                deliveryVersion.AnswerText,
                sessionQuestion.GradingRulesSnapshot,
                selectedIndices,
                command.AnswerText,
                score));
        }
        catch (InvalidOperationException exception)
        {
            ScoringFailures.Add(1);
            logger.LogWarning(exception,
                "Question scoring failed for tenant {TenantId}, session {PracticeSessionId}, question {SessionQuestionId}",
                actor.TenantId, session.Id, sessionQuestion.Id);
            throw new LearningValidationException("question_grading_rule_invalid", exception.Message);
        }

        var record = new AnswerRecord
        {
            TenantId = actor.TenantId,
            UserId = actor.UserId,
            PracticeSessionId = sessionQuestion.PracticeSessionId,
            SessionQuestionId = sessionQuestion.Id,
            SelectedOptions = JsonSerializer.SerializeToElement(selectedIndices),
            AnswerText = command.AnswerText,
            IsCorrect = grading.IsCorrect,
            GradingStatus = grading.Status,
            AwardedScore = grading.AwardedScore,
            Revision = (current?.Revision ?? 0) + 1,
            ClientSequence = command.ClientSequence,
            IdempotencyKey = idempotencyKey,
            RequestHash = requestHash,
            AnsweredAt = now,
            CreatedAt = now
        };
        learningPersistence.AnswerRecords.Add(record);
        if (current is null)
        {
            current = new CurrentAnswer
            {
                TenantId = actor.TenantId,
                UserId = actor.UserId,
                PracticeSessionId = session.Id,
                SessionQuestionId = sessionQuestion.Id,
                AnswerRecordId = record.Id,
                Revision = record.Revision,
                ClientSequence = record.ClientSequence,
                UpdatedAt = now
            };
            learningPersistence.CurrentAnswers.Add(current);
        }
        else
        {
            current.AnswerRecordId = record.Id;
            current.Revision = record.Revision;
            current.ClientSequence = record.ClientSequence;
            current.Version++;
            current.UpdatedAt = now;
        }
        var response = ToItem(record, revealedSolution);
        learningPersistence.AnswerSubmissionIdempotencies.Add(new AnswerSubmissionIdempotency
        {
            TenantId = actor.TenantId,
            UserId = actor.UserId,
            PracticeSessionId = session.Id,
            IdempotencyKey = idempotencyKey,
            RequestHash = requestHash,
            AnswerRecordId = record.Id,
            ResponseSnapshot = JsonSerializer.SerializeToElement(response),
            CreatedAt = now
        });
        try
        {
            await unitOfWork.SaveChangesAsync(cancellationToken);
        }
        catch (DbUpdateConcurrencyException)
        {
            throw new LearningValidationException("practice_session_version_conflict",
                "The practice session changed. Reload it before answering.");
        }
        catch (DbUpdateException exception) when (
            exception.InnerException is PostgresException postgresException &&
            postgresException.SqlState == PostgresErrorCodes.UniqueViolation)
        {
            unitOfWork.ChangeTracker.Clear();
            var replay = await learningPersistence.AnswerSubmissionIdempotencies.AsNoTracking()
                .SingleOrDefaultAsync(item =>
                    item.TenantId == actor.TenantId &&
                    item.UserId == actor.UserId &&
                    item.PracticeSessionId == session.Id &&
                    item.IdempotencyKey == idempotencyKey, cancellationToken);
            if (replay is not null && string.Equals(replay.RequestHash, requestHash, StringComparison.Ordinal))
            {
                IdempotencyReplays.Add(1);
                return await ReplayAsync(replay, revealedSolution, cancellationToken);
            }

            AnswerConflicts.Add(1);
            throw new LearningValidationException("practice_answer_conflict",
                "The answer conflicted with another client operation.");
        }

        return response;
    }

    private async Task<AnswerRecordItem> ReplayAsync(
        AnswerSubmissionIdempotency submission,
        QuestionSolutionItem? revealedSolution,
        CancellationToken cancellationToken)
    {
        if (submission.ResponseSnapshot.ValueKind == JsonValueKind.Object &&
            (submission.ResponseSnapshot.TryGetProperty(nameof(AnswerRecordItem.Id), out _) ||
             submission.ResponseSnapshot.TryGetProperty("id", out _)))
            return submission.ResponseSnapshot.Deserialize<AnswerRecordItem>()
                   ?? throw new InvalidOperationException("The stored answer response is invalid.");

        var historicalRecord = await learningPersistence.AnswerRecords.AsNoTracking().SingleOrDefaultAsync(
            item => item.TenantId == submission.TenantId && item.Id == submission.AnswerRecordId,
            cancellationToken);
        return historicalRecord is null
            ? throw new InvalidOperationException("The idempotent answer record no longer exists.")
            : ToItem(historicalRecord, revealedSolution);
    }
}