using Microsoft.EntityFrameworkCore;
using System.Text.Json;
using Tiku.Application.Learning;
using Tiku.Domain.Common;
using Tiku.Domain.Content;
using Tiku.Domain.Learning;
using Tiku.Domain.QuestionBanks;
using Tiku.Infrastructure.Persistence;

namespace Tiku.Infrastructure.Learning;

public sealed class LearningActivityService(TikuDbContext dbContext) : ILearningActivityService
{
    private const int DefaultLimit = 100;
    private const int MaxLimit = 500;

    public async Task<AnswerRecordItem> SubmitAnswerAsync(
        LearningActor actor,
        SubmitAnswerCommand command,
        CancellationToken cancellationToken = default)
    {
        var question = await dbContext.Questions
            .AsNoTracking()
            .Where(item =>
                item.TenantId == actor.TenantId &&
                item.Id == command.QuestionId &&
                item.Status == QuestionStatus.Published)
            .Select(item => new
            {
                item.Id,
                item.CurrentVersionId
            })
            .SingleOrDefaultAsync(cancellationToken);

        if (question is null)
        {
            throw new LearningResourceNotFoundException("question_not_found", "Question was not found.");
        }

        if (command.PracticeSessionId.HasValue)
        {
            var sessionExists = await dbContext.PracticeSessions.AnyAsync(
                session =>
                    session.TenantId == actor.TenantId &&
                    session.UserId == actor.UserId &&
                    session.Id == command.PracticeSessionId.Value,
                cancellationToken);

            if (!sessionExists)
            {
                throw new LearningResourceNotFoundException("practice_session_not_found", "Practice session was not found.");
            }
        }

        var now = DateTimeOffset.UtcNow;
        var record = new AnswerRecord
        {
            TenantId = actor.TenantId,
            UserId = actor.UserId,
            QuestionId = question.Id,
            QuestionVersionId = question.CurrentVersionId,
            PracticeSessionId = command.PracticeSessionId,
            SelectedOptions = JsonSerializer.SerializeToElement(command.SelectedOptions ?? []),
            AnswerText = command.AnswerText,
            IsCorrect = command.SelfJudgedCorrect,
            AnsweredAt = now,
            CreatedAt = now
        };
        dbContext.AnswerRecords.Add(record);

        if (command.SelfJudgedCorrect == false)
        {
            var wrongQuestion = await dbContext.WrongQuestions.FindAsync(
                [actor.TenantId, actor.UserId, question.Id],
                cancellationToken);

            if (wrongQuestion is null)
            {
                dbContext.WrongQuestions.Add(new WrongQuestion
                {
                    TenantId = actor.TenantId,
                    UserId = actor.UserId,
                    QuestionId = question.Id,
                    WrongCount = 1,
                    LastWrongAt = now
                });
            }
            else
            {
                wrongQuestion.WrongCount++;
                wrongQuestion.LastWrongAt = now;
                wrongQuestion.ResolvedAt = null;
            }
        }

        await dbContext.SaveChangesAsync(cancellationToken);
        return ToItem(record);
    }

    public async Task<LearningList<FavoriteQuestionItem>> GetFavoriteQuestionsAsync(
        LearningActor actor,
        LearningLimitFilter filter,
        CancellationToken cancellationToken = default)
    {
        var items = await dbContext.FavoriteQuestions
            .AsNoTracking()
            .Where(item =>
                item.TenantId == actor.TenantId &&
                item.UserId == actor.UserId)
            .OrderByDescending(item => item.CreatedAt)
            .Take(ResolveLimit(filter.Limit))
            .Select(item => new FavoriteQuestionItem(
                item.QuestionId,
                item.Source,
                item.CreatedAt))
            .ToArrayAsync(cancellationToken);

        return new LearningList<FavoriteQuestionItem>(items);
    }

    public async Task<LearningActionResult> ToggleFavoriteQuestionAsync(
        LearningActor actor,
        QuestionActionCommand command,
        CancellationToken cancellationToken = default)
    {
        await EnsureQuestionExistsAsync(actor.TenantId, command.QuestionId, cancellationToken);

        var favorite = command.Favorite ?? true;
        var item = await dbContext.FavoriteQuestions.FindAsync(
            [actor.TenantId, actor.UserId, command.QuestionId],
            cancellationToken);

        if (favorite)
        {
            if (item is null)
            {
                dbContext.FavoriteQuestions.Add(new FavoriteQuestion
                {
                    TenantId = actor.TenantId,
                    UserId = actor.UserId,
                    QuestionId = command.QuestionId,
                    Source = "api",
                    CreatedAt = DateTimeOffset.UtcNow
                });
            }
        }
        else if (item is not null)
        {
            dbContext.FavoriteQuestions.Remove(item);
        }

        await dbContext.SaveChangesAsync(cancellationToken);
        return new LearningActionResult(true, favorite);
    }

    public async Task<LearningList<WrongQuestionItem>> GetWrongQuestionsAsync(
        LearningActor actor,
        LearningLimitFilter filter,
        CancellationToken cancellationToken = default)
    {
        var query = dbContext.WrongQuestions
            .AsNoTracking()
            .Where(item =>
                item.TenantId == actor.TenantId &&
                item.UserId == actor.UserId);

        if (!string.Equals(filter.Status, "all", StringComparison.OrdinalIgnoreCase))
        {
            query = query.Where(item => item.ResolvedAt == null);
        }

        var items = await query
            .OrderByDescending(item => item.LastWrongAt)
            .Take(ResolveLimit(filter.Limit))
            .Select(item => new WrongQuestionItem(
                item.QuestionId,
                item.WrongCount,
                item.LastWrongAt,
                item.ResolvedAt))
            .ToArrayAsync(cancellationToken);

        return new LearningList<WrongQuestionItem>(items);
    }

    public async Task<LearningActionResult> ResolveWrongQuestionAsync(
        LearningActor actor,
        QuestionActionCommand command,
        CancellationToken cancellationToken = default)
    {
        var item = await dbContext.WrongQuestions.FindAsync(
            [actor.TenantId, actor.UserId, command.QuestionId],
            cancellationToken);

        if (item is null)
        {
            throw new LearningResourceNotFoundException("wrong_question_not_found", "Wrong question was not found.");
        }

        item.ResolvedAt = DateTimeOffset.UtcNow;
        await dbContext.SaveChangesAsync(cancellationToken);
        return new LearningActionResult(true);
    }

    public async Task<LearningList<WordProgressItem>> GetWordProgressAsync(
        LearningActor actor,
        LearningLimitFilter filter,
        CancellationToken cancellationToken = default)
    {
        var query = dbContext.UserWordProgress
            .AsNoTracking()
            .Where(item =>
                item.TenantId == actor.TenantId &&
                item.UserId == actor.UserId);

        if (filter.UnitId.HasValue)
        {
            query = query.Where(item => dbContext.VocabularyWords.Any(word =>
                word.TenantId == actor.TenantId &&
                word.Id == item.WordId &&
                word.UnitId == filter.UnitId.Value));
        }

        if (TryParseWordProgressStatus(filter.Status, out var status))
        {
            query = query.Where(item => item.Status == status);
        }

        var items = await query
            .OrderBy(item => item.NextReviewAt == null)
            .ThenBy(item => item.NextReviewAt)
            .ThenByDescending(item => item.UpdatedAt)
            .Take(ResolveLimit(filter.Limit))
            .Select(item => new WordProgressItem(
                item.WordId,
                item.Status,
                item.CorrectCount,
                item.WrongCount,
                item.LastReviewAt,
                item.NextReviewAt,
                item.ReviewCount,
                item.CorrectStreak,
                item.LastResult,
                item.DueLevel,
                item.Metadata))
            .ToArrayAsync(cancellationToken);

        return new LearningList<WordProgressItem>(items);
    }

    public async Task<WordProgressItem> UpdateWordProgressAsync(
        LearningActor actor,
        WordProgressCommand command,
        CancellationToken cancellationToken = default)
    {
        await EnsureWordExistsAsync(actor.TenantId, command.WordId, cancellationToken);

        var now = DateTimeOffset.UtcNow;
        var item = await dbContext.UserWordProgress
            .SingleOrDefaultAsync(
                progress =>
                    progress.TenantId == actor.TenantId &&
                    progress.UserId == actor.UserId &&
                    progress.WordId == command.WordId,
                cancellationToken);

        if (item is null)
        {
            item = new UserWordProgress
            {
                TenantId = actor.TenantId,
                UserId = actor.UserId,
                WordId = command.WordId
            };
            dbContext.UserWordProgress.Add(item);
        }

        if (TryParseWordProgressStatus(command.Status, out var status))
        {
            item.Status = status;
        }
        else if (string.IsNullOrWhiteSpace(command.Status))
        {
            item.Status = WordProgressStatus.Learning;
        }
        else
        {
            throw new LearningValidationException("invalid_word_status", "Word progress status is invalid.");
        }

        var correctDelta = command.CorrectDelta ?? 0;
        var wrongDelta = command.WrongDelta ?? 0;
        item.CorrectCount += correctDelta;
        item.WrongCount += wrongDelta;
        item.ReviewCount += correctDelta + wrongDelta;
        item.CorrectStreak = wrongDelta > 0
            ? 0
            : item.CorrectStreak + correctDelta;
        item.LastResult = wrongDelta > 0
            ? WordReviewResult.Wrong
            : correctDelta > 0
                ? WordReviewResult.Correct
                : item.LastResult;
        item.LastReviewAt = correctDelta + wrongDelta > 0 ? now : item.LastReviewAt;
        item.NextReviewAt = command.NextReviewAt ?? item.NextReviewAt;
        item.DueLevel = item.Status == WordProgressStatus.Mastered
            ? WordDueLevel.Mastered
            : item.WrongCount > 0 && item.CorrectStreak == 0
                ? WordDueLevel.Again
                : item.DueLevel;

        await dbContext.SaveChangesAsync(cancellationToken);
        return ToItem(item);
    }

    public async Task<LearningList<FavoriteWordItem>> GetFavoriteWordsAsync(
        LearningActor actor,
        LearningLimitFilter filter,
        CancellationToken cancellationToken = default)
    {
        var query = dbContext.UserWordFavorites
            .AsNoTracking()
            .Where(item =>
                item.TenantId == actor.TenantId &&
                item.UserId == actor.UserId);

        if (filter.UnitId.HasValue)
        {
            query = query.Where(item => dbContext.VocabularyWords.Any(word =>
                word.TenantId == actor.TenantId &&
                word.Id == item.WordId &&
                word.UnitId == filter.UnitId.Value));
        }

        var items = await query
            .OrderByDescending(item => item.FavoritedAt ?? item.CreatedAt)
            .Take(ResolveLimit(filter.Limit))
            .Select(item => new FavoriteWordItem(
                item.WordId,
                item.Note,
                item.FavoritedAt))
            .ToArrayAsync(cancellationToken);

        return new LearningList<FavoriteWordItem>(items);
    }

    public async Task<LearningActionResult> ToggleFavoriteWordAsync(
        LearningActor actor,
        FavoriteWordCommand command,
        CancellationToken cancellationToken = default)
    {
        await EnsureWordExistsAsync(actor.TenantId, command.WordId, cancellationToken);

        var favorite = command.Favorite ?? true;
        var item = await dbContext.UserWordFavorites
            .SingleOrDefaultAsync(
                favoriteWord =>
                    favoriteWord.TenantId == actor.TenantId &&
                    favoriteWord.UserId == actor.UserId &&
                    favoriteWord.WordId == command.WordId,
                cancellationToken);

        if (favorite)
        {
            if (item is null)
            {
                item = new UserWordFavorite
                {
                    TenantId = actor.TenantId,
                    UserId = actor.UserId,
                    WordId = command.WordId
                };
                dbContext.UserWordFavorites.Add(item);
            }

            item.Note = command.Note ?? item.Note;
            item.FavoritedAt ??= DateTimeOffset.UtcNow;
        }
        else if (item is not null)
        {
            dbContext.UserWordFavorites.Remove(item);
        }

        await dbContext.SaveChangesAsync(cancellationToken);
        return new LearningActionResult(true, favorite);
    }

    public async Task<PracticeSessionItem> CreatePracticeSessionAsync(
        LearningActor actor,
        PracticeSessionCommand command,
        CancellationToken cancellationToken = default)
    {
        var assembly = await BuildPracticeAssemblyAsync(actor.TenantId, command, cancellationToken);
        var questionIds = await CollectQuestionIdsAsync(actor, assembly, cancellationToken);
        if (questionIds.Count == 0)
        {
            throw new LearningValidationException("no_practice_questions", "No published questions are available for this practice target.");
        }

        var now = DateTimeOffset.UtcNow;
        var session = new PracticeSession
        {
            TenantId = actor.TenantId,
            UserId = actor.UserId,
            Mode = assembly.Mode,
            TargetType = assembly.TargetType,
            TargetId = assembly.TargetId,
            BlueprintId = assembly.BlueprintId,
            CollectionId = assembly.CollectionId,
            EntryId = assembly.EntryId,
            ContentNodeId = assembly.ContentNodeId,
            QuestionIds = JsonSerializer.SerializeToElement(questionIds),
            QuestionCount = questionIds.Count,
            DurationMinutes = assembly.DurationMinutes,
            TotalScore = assembly.TotalScore,
            ExpiresAt = assembly.DurationMinutes.HasValue
                ? now.AddMinutes(assembly.DurationMinutes.Value)
                : null,
            AccessMode = PracticeAccessMode.Free,
            ConsumedFreeQuota = questionIds.Count,
            AccessSnapshot = JsonSerializer.SerializeToElement(new
            {
                strategy = "v1_free",
                requestedCount = assembly.QuestionLimit,
                grantedCount = questionIds.Count
            }),
            Metadata = command.Metadata.ValueKind is JsonValueKind.Undefined
                ? JsonDefaults.Object()
                : command.Metadata
        };
        dbContext.PracticeSessions.Add(session);
        dbContext.PracticeAccessEvents.Add(new PracticeAccessEvent
        {
            TenantId = actor.TenantId,
            UserId = actor.UserId,
            PracticeSessionId = session.Id,
            EventType = PracticeAccessEventType.SessionCreated,
            AccessMode = PracticeAccessEventMode.Free,
            RequestedCount = assembly.QuestionLimit,
            GrantedCount = questionIds.Count,
            ConsumedFreeQuota = questionIds.Count,
            Metadata = session.AccessSnapshot
        });

        await dbContext.SaveChangesAsync(cancellationToken);
        return ToItem(session);
    }

    public async Task<PracticeSessionDetailItem> GetPracticeSessionDetailAsync(
        LearningActor actor,
        PracticeSessionFilter filter,
        CancellationToken cancellationToken = default)
    {
        var session = await GetPracticeSessionAsync(actor, filter.PracticeSessionId, cancellationToken);
        var questionIds = ReadGuidArray(session.QuestionIds);
        var questions = await dbContext.Questions
            .AsNoTracking()
            .Where(question =>
                question.TenantId == actor.TenantId &&
                questionIds.Contains(question.Id))
            .GroupJoin(
                dbContext.QuestionVersions.AsNoTracking(),
                question => new { question.TenantId, QuestionId = question.Id, VersionId = question.CurrentVersionId },
                version => new { version.TenantId, version.QuestionId, VersionId = (Guid?)version.Id },
                (question, versions) => new { question, version = versions.FirstOrDefault() })
            .Select(row => new PracticeSessionQuestionItem(
                row.question.Id,
                row.question.Type,
                row.question.TypeLabel,
                row.question.Difficulty,
                row.question.Tags,
                row.version == null ? null : row.version.Id,
                row.version == null ? null : row.version.Content,
                row.version == null ? JsonDefaults.Array() : row.version.Options,
                row.version == null ? null : row.version.Explanation))
            .ToArrayAsync(cancellationToken);
        var questionById = questions.ToDictionary(question => question.Id);
        var orderedQuestions = questionIds
            .Where(questionById.ContainsKey)
            .Select(questionId => questionById[questionId])
            .ToArray();

        var answers = await dbContext.AnswerRecords
            .AsNoTracking()
            .Where(answer =>
                answer.TenantId == actor.TenantId &&
                answer.UserId == actor.UserId &&
                answer.PracticeSessionId == session.Id &&
                answer.QuestionId != null)
            .ToArrayAsync(cancellationToken);
        var answersByQuestion = answers
            .GroupBy(answer => answer.QuestionId!.Value)
            .ToDictionary(
                group => group.Key,
                group => ToItem(group.OrderByDescending(answer => answer.AnsweredAt).First()));

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

    public async Task<PracticeSessionReportItem> SubmitPracticeSessionAsync(
        LearningActor actor,
        PracticeSessionFilter filter,
        CancellationToken cancellationToken = default)
    {
        var session = await GetPracticeSessionAsync(actor, filter.PracticeSessionId, cancellationToken);
        var existing = await dbContext.PracticeSessionReports
            .AsNoTracking()
            .SingleOrDefaultAsync(
                report =>
                    report.TenantId == actor.TenantId &&
                    report.PracticeSessionId == session.Id,
                cancellationToken);
        if (existing is not null)
        {
            return ToItem(existing);
        }

        var report = await BuildPracticeSessionReportAsync(actor, session, cancellationToken);
        session.FinishedAt ??= report.SubmittedAt;
        await dbContext.SaveChangesAsync(cancellationToken);
        return ToItem(report);
    }

    public async Task<PracticeSessionReportItem> GetPracticeSessionReportAsync(
        LearningActor actor,
        PracticeSessionFilter filter,
        CancellationToken cancellationToken = default)
    {
        if (!filter.PracticeSessionId.HasValue)
        {
            throw new LearningValidationException("practice_session_id_required", "Practice session id is required.");
        }

        var report = await dbContext.PracticeSessionReports
            .AsNoTracking()
            .SingleOrDefaultAsync(
                item =>
                    item.TenantId == actor.TenantId &&
                    item.UserId == actor.UserId &&
                    item.PracticeSessionId == filter.PracticeSessionId.Value,
                cancellationToken);

        if (report is null)
        {
            throw new LearningResourceNotFoundException("practice_report_not_found", "Practice session report was not found.");
        }

        return ToItem(report);
    }

    public async Task<LearningList<PracticeSessionReportItem>> GetPracticeReportsAsync(
        LearningActor actor,
        PracticeSessionFilter filter,
        CancellationToken cancellationToken = default)
    {
        var query = dbContext.PracticeSessionReports
            .AsNoTracking()
            .Where(report =>
                report.TenantId == actor.TenantId &&
                report.UserId == actor.UserId);

        if (filter.BlueprintId.HasValue)
        {
            query = query.Where(report => report.BlueprintId == filter.BlueprintId.Value);
        }

        if (!string.IsNullOrWhiteSpace(filter.Mode))
        {
            query = query.Where(report => report.Mode == filter.Mode.Trim());
        }

        var items = await query
            .OrderByDescending(report => report.SubmittedAt)
            .Take(ResolveLimit(filter.Limit))
            .ToArrayAsync(cancellationToken);

        return new LearningList<PracticeSessionReportItem>(items.Select(ToItem).ToArray());
    }

    public async Task<LearningList<PracticeHistoryItem>> GetPracticeHistoryAsync(
        LearningActor actor,
        PracticeSessionFilter filter,
        CancellationToken cancellationToken = default)
    {
        var query = dbContext.PracticeSessions
            .AsNoTracking()
            .Where(session =>
                session.TenantId == actor.TenantId &&
                session.UserId == actor.UserId);

        if (!string.IsNullOrWhiteSpace(filter.Mode))
        {
            query = query.Where(session => session.Mode == filter.Mode.Trim());
        }

        var rows = await query
            .GroupJoin(
                dbContext.PracticeSessionReports.AsNoTracking(),
                session => new { session.TenantId, PracticeSessionId = session.Id },
                report => new { report.TenantId, report.PracticeSessionId },
                (session, reports) => new { session, report = reports.FirstOrDefault() })
            .OrderByDescending(row => row.session.FinishedAt ?? row.session.StartedAt)
            .Take(ResolveLimit(filter.Limit))
            .ToArrayAsync(cancellationToken);
        var now = DateTimeOffset.UtcNow;
        var items = rows
            .Select(row => new PracticeHistoryItem(
                row.session.Id,
                row.session.Mode,
                row.session.TargetType,
                row.session.TargetId,
                row.session.BlueprintId,
                row.session.CollectionId,
                row.session.EntryId,
                row.session.ContentNodeId,
                row.session.QuestionCount,
                row.report?.AnsweredCount ?? 0,
                row.report?.CorrectCount ?? 0,
                row.report?.WrongCount ?? 0,
                row.session.StartedAt,
                row.session.FinishedAt,
                row.session.ExpiresAt,
                PracticeSessionStatus(row.session, now),
                row.report?.Id,
                row.report?.Score,
                row.report?.TotalScore,
                row.report?.Accuracy))
            .Where(item => string.IsNullOrWhiteSpace(filter.Status) || item.Status == filter.Status.Trim())
            .ToArray();

        return new LearningList<PracticeHistoryItem>(items);
    }

    private async Task<PracticeAssembly> BuildPracticeAssemblyAsync(
        Guid tenantId,
        PracticeSessionCommand command,
        CancellationToken cancellationToken)
    {
        var mode = NormalizeMode(command.Mode);
        var assembly = new PracticeAssembly(
            mode,
            command.TargetType,
            command.TargetId,
            command.BlueprintId,
            command.CollectionId,
            command.EntryId,
            command.ContentNodeId,
            Math.Clamp(command.QuestionLimit ?? 100, 1, MaxLimit),
            command.DurationMinutes,
            command.TotalScore);

        if (!command.BlueprintId.HasValue)
        {
            return assembly;
        }

        var blueprint = await dbContext.PracticeBlueprints
            .AsNoTracking()
            .SingleOrDefaultAsync(
                item =>
                    item.TenantId == tenantId &&
                    item.Id == command.BlueprintId.Value &&
                    item.Status == ContentStatus.Active,
                cancellationToken);

        if (blueprint is null)
        {
            throw new LearningResourceNotFoundException("practice_blueprint_not_found", "Practice blueprint was not found.");
        }

        return assembly with
        {
            Mode = NormalizeMode(blueprint.Mode.ToString()),
            TargetType = command.TargetType ?? "blueprint",
            TargetId = command.TargetId ?? blueprint.Id,
            CollectionId = command.CollectionId ?? blueprint.CollectionId,
            EntryId = command.EntryId ?? blueprint.EntryId,
            ContentNodeId = command.ContentNodeId ?? blueprint.NodeId,
            QuestionLimit = Math.Clamp(command.QuestionLimit ?? blueprint.QuestionLimit ?? 100, 1, MaxLimit),
            DurationMinutes = command.DurationMinutes ?? blueprint.DurationMinutes,
            TotalScore = command.TotalScore ?? blueprint.TotalScore
        };
    }

    private async Task<List<Guid>> CollectQuestionIdsAsync(
        LearningActor actor,
        PracticeAssembly assembly,
        CancellationToken cancellationToken)
    {
        if (assembly.Mode == "wrong_review")
        {
            return await dbContext.WrongQuestions
                .AsNoTracking()
                .Where(item =>
                    item.TenantId == actor.TenantId &&
                    item.UserId == actor.UserId &&
                    item.ResolvedAt == null)
                .Join(
                    dbContext.Questions.AsNoTracking(),
                    item => new { item.TenantId, item.QuestionId },
                    question => new { question.TenantId, QuestionId = question.Id },
                    (item, question) => new { item, question })
                .Where(row => row.question.Status == QuestionStatus.Published)
                .OrderByDescending(row => row.item.WrongCount)
                .ThenBy(row => row.item.LastWrongAt)
                .Take(assembly.QuestionLimit)
                .Select(row => row.question.Id)
                .ToListAsync(cancellationToken);
        }

        if (assembly.Mode == "favorite_review")
        {
            return await dbContext.FavoriteQuestions
                .AsNoTracking()
                .Where(item =>
                    item.TenantId == actor.TenantId &&
                    item.UserId == actor.UserId)
                .Join(
                    dbContext.Questions.AsNoTracking(),
                    item => new { item.TenantId, item.QuestionId },
                    question => new { question.TenantId, QuestionId = question.Id },
                    (item, question) => new { item, question })
                .Where(row => row.question.Status == QuestionStatus.Published)
                .OrderByDescending(row => row.item.CreatedAt)
                .Take(assembly.QuestionLimit)
                .Select(row => row.question.Id)
                .ToListAsync(cancellationToken);
        }

        if (assembly.CollectionId.HasValue)
        {
            return await dbContext.QuestionCollectionItems
                .AsNoTracking()
                .Where(item =>
                    item.TenantId == actor.TenantId &&
                    item.CollectionId == assembly.CollectionId.Value)
                .Join(
                    dbContext.Questions.AsNoTracking(),
                    item => new { item.TenantId, item.QuestionId },
                    question => new { question.TenantId, QuestionId = question.Id },
                    (item, question) => new { item, question })
                .Where(row => row.question.Status == QuestionStatus.Published)
                .OrderBy(row => row.item.SortOrder)
                .ThenBy(row => row.question.CreatedAt)
                .Take(assembly.QuestionLimit)
                .Select(row => row.question.Id)
                .ToListAsync(cancellationToken);
        }

        var query = dbContext.Questions
            .AsNoTracking()
            .Where(question =>
                question.TenantId == actor.TenantId &&
                question.Status == QuestionStatus.Published);

        if (assembly.ContentNodeId.HasValue)
        {
            query = query.Where(question => question.ContentNodeId == assembly.ContentNodeId.Value);
        }
        else if (assembly.EntryId.HasValue)
        {
            query = query.Where(question => question.EntryId == assembly.EntryId.Value);
        }
        else if (assembly.TargetId.HasValue && !string.IsNullOrWhiteSpace(assembly.TargetType))
        {
            query = ApplyLegacyTargetFilter(query, assembly.TargetType, assembly.TargetId.Value);
        }
        else
        {
            throw new LearningValidationException("practice_target_required", "Practice target is required.");
        }

        return await query
            .OrderBy(question => question.CreatedAt)
            .Take(assembly.QuestionLimit)
            .Select(question => question.Id)
            .ToListAsync(cancellationToken);
    }

    private static IQueryable<Question> ApplyLegacyTargetFilter(
        IQueryable<Question> query,
        string? targetType,
        Guid targetId)
    {
        return NormalizeEnumValue(targetType) switch
        {
            "subject" => query.Where(question => question.SubjectId == targetId),
            "category" => query.Where(question => question.CategoryId == targetId),
            "node" => query.Where(question => question.NodeId == targetId),
            "questionbank" => query.Where(question => question.QuestionBankId == targetId),
            "contentnode" => query.Where(question => question.ContentNodeId == targetId),
            "entry" => query.Where(question => question.EntryId == targetId),
            _ => query.Where(_ => false)
        };
    }

    private async Task<PracticeSession> GetPracticeSessionAsync(
        LearningActor actor,
        Guid? practiceSessionId,
        CancellationToken cancellationToken)
    {
        if (!practiceSessionId.HasValue)
        {
            throw new LearningValidationException("practice_session_id_required", "Practice session id is required.");
        }

        var session = await dbContext.PracticeSessions
            .SingleOrDefaultAsync(
                item =>
                    item.TenantId == actor.TenantId &&
                    item.UserId == actor.UserId &&
                    item.Id == practiceSessionId.Value,
                cancellationToken);

        if (session is null)
        {
            throw new LearningResourceNotFoundException("practice_session_not_found", "Practice session was not found.");
        }

        return session;
    }

    private async Task<PracticeSessionReport> BuildPracticeSessionReportAsync(
        LearningActor actor,
        PracticeSession session,
        CancellationToken cancellationToken)
    {
        var questionIds = ReadGuidArray(session.QuestionIds);
        if (questionIds.Count == 0)
        {
            throw new LearningValidationException("practice_session_empty", "Practice session has no question snapshot.");
        }

        var answers = await dbContext.AnswerRecords
            .AsNoTracking()
            .Where(answer =>
                answer.TenantId == actor.TenantId &&
                answer.UserId == actor.UserId &&
                answer.PracticeSessionId == session.Id &&
                answer.QuestionId != null)
            .ToArrayAsync(cancellationToken);
        var latestAnswers = answers
            .GroupBy(answer => answer.QuestionId!.Value)
            .ToDictionary(
                group => group.Key,
                group => group.OrderByDescending(answer => answer.AnsweredAt).First());
        var totalQuestions = questionIds.Count;
        var answeredCount = questionIds.Count(latestAnswers.ContainsKey);
        var correctCount = questionIds.Count(questionId =>
            latestAnswers.TryGetValue(questionId, out var answer) &&
            answer.IsCorrect == true);
        var wrongCount = questionIds.Count(questionId =>
            latestAnswers.TryGetValue(questionId, out var answer) &&
            answer.IsCorrect != true);
        var unansweredCount = Math.Max(0, totalQuestions - answeredCount);
        var totalScore = session.TotalScore ?? totalQuestions;
        var scorePerQuestion = totalQuestions == 0 ? 0 : totalScore / totalQuestions;
        var score = Math.Round(correctCount * scorePerQuestion, 2);
        var accuracy = totalQuestions == 0 ? 0 : Math.Round((decimal)correctCount / totalQuestions, 4);
        var submittedAt = DateTimeOffset.UtcNow;
        var durationSeconds = Math.Max(0, (int)(submittedAt - session.StartedAt).TotalSeconds);
        var wrongQuestionIds = questionIds
            .Where(questionId =>
                latestAnswers.TryGetValue(questionId, out var answer) &&
                answer.IsCorrect != true)
            .ToArray();
        var questionResults = questionIds
            .Select(questionId =>
            {
                latestAnswers.TryGetValue(questionId, out var answer);
                return new
                {
                    questionId,
                    answered = answer is not null,
                    isCorrect = answer?.IsCorrect,
                    score = answer?.IsCorrect == true ? scorePerQuestion : 0,
                    totalScore = scorePerQuestion,
                    answeredAt = answer?.AnsweredAt
                };
            })
            .ToArray();
        var sectionStats = new[]
        {
            new
            {
                key = "default",
                title = "默认",
                questionCount = totalQuestions,
                answeredCount,
                correctCount,
                wrongCount,
                unansweredCount,
                score,
                totalScore,
                accuracy,
                sortOrder = 0
            }
        };

        var report = new PracticeSessionReport
        {
            TenantId = actor.TenantId,
            UserId = actor.UserId,
            PracticeSessionId = session.Id,
            BlueprintId = session.BlueprintId,
            CollectionId = session.CollectionId,
            Mode = session.Mode,
            TotalQuestions = totalQuestions,
            AnsweredCount = answeredCount,
            CorrectCount = correctCount,
            WrongCount = wrongCount,
            UnansweredCount = unansweredCount,
            Score = score,
            TotalScore = totalScore,
            Accuracy = accuracy,
            DurationSeconds = durationSeconds,
            StartedAt = session.StartedAt,
            SubmittedAt = submittedAt,
            SectionStats = JsonSerializer.SerializeToElement(sectionStats),
            QuestionResults = JsonSerializer.SerializeToElement(questionResults),
            WrongQuestionIds = JsonSerializer.SerializeToElement(wrongQuestionIds),
            Metadata = JsonSerializer.SerializeToElement(new
            {
                scoringVersion = 1,
                scorePerQuestion
            })
        };
        dbContext.PracticeSessionReports.Add(report);
        dbContext.PracticeSessionReportSections.Add(new PracticeSessionReportSection
        {
            TenantId = actor.TenantId,
            ReportId = report.Id,
            PracticeSessionId = session.Id,
            SectionKey = "default",
            SectionName = "默认",
            QuestionCount = totalQuestions,
            AnsweredCount = answeredCount,
            CorrectCount = correctCount,
            WrongCount = wrongCount,
            UnansweredCount = unansweredCount,
            Score = score,
            TotalScore = totalScore,
            Accuracy = accuracy,
            SortOrder = 0
        });

        return report;
    }

    private async Task EnsureQuestionExistsAsync(
        Guid tenantId,
        Guid questionId,
        CancellationToken cancellationToken)
    {
        var exists = await dbContext.Questions.AnyAsync(
            question =>
                question.TenantId == tenantId &&
                question.Id == questionId &&
                question.Status == QuestionStatus.Published,
            cancellationToken);

        if (!exists)
        {
            throw new LearningResourceNotFoundException("question_not_found", "Question was not found.");
        }
    }

    private async Task EnsureWordExistsAsync(
        Guid tenantId,
        Guid wordId,
        CancellationToken cancellationToken)
    {
        var exists = await dbContext.VocabularyWords.AnyAsync(
            word =>
                word.TenantId == tenantId &&
                word.Id == wordId &&
                word.IsActive,
            cancellationToken);

        if (!exists)
        {
            throw new LearningResourceNotFoundException("word_not_found", "Word was not found.");
        }
    }

    private static AnswerRecordItem ToItem(AnswerRecord record)
    {
        return new AnswerRecordItem(
            record.Id,
            record.QuestionId!.Value,
            record.QuestionVersionId,
            record.PracticeSessionId,
            record.SelectedOptions,
            record.AnswerText,
            record.IsCorrect,
            record.AnsweredAt);
    }

    private static WordProgressItem ToItem(UserWordProgress item)
    {
        return new WordProgressItem(
            item.WordId,
            item.Status,
            item.CorrectCount,
            item.WrongCount,
            item.LastReviewAt,
            item.NextReviewAt,
            item.ReviewCount,
            item.CorrectStreak,
            item.LastResult,
            item.DueLevel,
            item.Metadata);
    }

    private static PracticeSessionItem ToItem(PracticeSession item)
    {
        return new PracticeSessionItem(
            item.Id,
            item.Mode,
            item.TargetType,
            item.TargetId,
            item.BlueprintId,
            item.CollectionId,
            item.EntryId,
            item.ContentNodeId,
            item.QuestionIds,
            item.QuestionCount,
            item.DurationMinutes,
            item.TotalScore,
            item.AccessMode,
            item.AccessEntitlementId,
            item.ConsumedFreeQuota,
            item.AccessSnapshot,
            item.StartedAt,
            item.FinishedAt,
            item.ExpiresAt,
            item.Metadata,
            PracticeSessionStatus(item, DateTimeOffset.UtcNow));
    }

    private static PracticeSessionReportItem ToItem(PracticeSessionReport item)
    {
        return new PracticeSessionReportItem(
            item.Id,
            item.PracticeSessionId,
            item.BlueprintId,
            item.CollectionId,
            item.Mode,
            item.TotalQuestions,
            item.AnsweredCount,
            item.CorrectCount,
            item.WrongCount,
            item.UnansweredCount,
            item.Score,
            item.TotalScore,
            item.Accuracy,
            item.DurationSeconds,
            item.StartedAt,
            item.SubmittedAt,
            item.SectionStats,
            item.QuestionResults,
            item.WrongQuestionIds,
            item.Metadata);
    }

    private static List<Guid> ReadGuidArray(JsonElement value)
    {
        if (value.ValueKind is not JsonValueKind.Array)
        {
            return [];
        }

        return value.EnumerateArray()
            .Select(item => item.ValueKind == JsonValueKind.String && Guid.TryParse(item.GetString(), out var id)
                ? (Guid?)id
                : null)
            .Where(id => id.HasValue)
            .Select(id => id!.Value)
            .ToList();
    }

    private static string PracticeSessionStatus(PracticeSession session, DateTimeOffset now)
    {
        if (session.FinishedAt.HasValue)
        {
            return "finished";
        }

        if (session.ExpiresAt.HasValue && session.ExpiresAt.Value <= now)
        {
            return "expired";
        }

        return "active";
    }

    private static string NormalizeMode(string? mode)
    {
        return NormalizeEnumValue(mode) switch
        {
            "sequential" => "sequential",
            "random" => "random",
            "mockexam" => "mock_exam",
            "paper" => "paper",
            "wrongreview" => "wrong_review",
            "favoritereview" => "favorite_review",
            _ => "chapter"
        };
    }

    private static bool TryParseWordProgressStatus(string? value, out WordProgressStatus status)
    {
        return Enum.TryParse(NormalizeEnumValue(value), ignoreCase: true, out status);
    }

    private static int ResolveLimit(int? limit)
    {
        return Math.Clamp(limit ?? DefaultLimit, 1, MaxLimit);
    }

    private static string? NormalizeEnumValue(string? value)
    {
        return string.IsNullOrWhiteSpace(value)
            ? null
            : value.Replace("_", string.Empty, StringComparison.Ordinal)
                .Replace("-", string.Empty, StringComparison.Ordinal);
    }

    private sealed record PracticeAssembly(
        string Mode,
        string? TargetType,
        Guid? TargetId,
        Guid? BlueprintId,
        Guid? CollectionId,
        Guid? EntryId,
        Guid? ContentNodeId,
        int QuestionLimit,
        int? DurationMinutes,
        decimal? TotalScore);
}

public class LearningException(string code, string message) : Exception(message)
{
    public string Code { get; } = code;
}

public sealed class LearningResourceNotFoundException(string code, string message) : LearningException(code, message);

public sealed class LearningValidationException(string code, string message) : LearningException(code, message);