using Microsoft.EntityFrameworkCore;
using Tiku.Application.Catalog;
using Tiku.Application.QuestionBanks;
using Tiku.Domain.Common;
using Tiku.Domain.Content;
using Tiku.Domain.QuestionBanks;
using Tiku.Infrastructure.Persistence;

namespace Tiku.Infrastructure.QuestionBanks;

public sealed class QuestionBankQueryService(TikuDbContext dbContext) : IQuestionBankQueryService
{
    private const int DefaultQuestionLimit = 200;
    private const int MaxQuestionLimit = 500;
    private const int DefaultBankLimit = 100;
    private const int MaxBankLimit = 500;

    public async Task<CatalogList<QuestionBankCatalogItem>> GetQuestionBanksAsync(
        QuestionBankFilter filter,
        CancellationToken cancellationToken = default)
    {
        var query = dbContext.QuestionBanks
            .AsNoTracking()
            .Where(bank =>
                bank.TenantId == filter.TenantId &&
                bank.Status == QuestionBankStatus.Active);

        if (filter.RegionId.HasValue)
        {
            query = query.Where(bank => bank.RegionId == filter.RegionId.Value || bank.RegionId == null);
        }

        query = ApplyKeyword(query, filter.Keyword);

        var items = await query
            .OrderBy(bank => bank.Name)
            .ThenBy(bank => bank.CreatedAt)
            .Take(ResolveLimit(filter.Limit, DefaultBankLimit, MaxBankLimit))
            .Select(bank => new QuestionBankCatalogItem(
                bank.Id,
                bank.RegionId,
                bank.Name,
                bank.SourceScope,
                bank.Status,
                bank.Metadata))
            .ToArrayAsync(cancellationToken);

        return new CatalogList<QuestionBankCatalogItem>(items);
    }

    public async Task<CatalogList<QuestionCatalogItem>> GetQuestionsAsync(
        QuestionBankFilter filter,
        CancellationToken cancellationToken = default)
    {
        var questions = ApplyQuestionFilters(BaseQuestionQuery(), filter)
            .OrderByDescending(question => question.CreatedAt)
            .Take(ResolveLimit(filter.Limit, DefaultQuestionLimit, MaxQuestionLimit));

        var items = await ProjectQuestions(questions)
            .ToArrayAsync(cancellationToken);

        return new CatalogList<QuestionCatalogItem>(items);
    }

    public async Task<QuestionCatalogItem> GetQuestionAsync(
        QuestionBankFilter filter,
        CancellationToken cancellationToken = default)
    {
        if (!filter.QuestionId.HasValue)
        {
            throw new QuestionBankRequiredFieldException("questionId is required.");
        }

        var questions = ApplyQuestionFilters(BaseQuestionQuery(), filter)
            .Where(question => question.Id == filter.QuestionId.Value);

        var question = await ProjectQuestions(questions)
            .SingleOrDefaultAsync(cancellationToken);

        return question ?? throw new QuestionBankNotFoundException("Question was not found.");
    }

    public async Task<CatalogList<QuestionVersionCatalogItem>> GetQuestionVersionsAsync(
        QuestionBankFilter filter,
        CancellationToken cancellationToken = default)
    {
        if (!filter.QuestionId.HasValue)
        {
            throw new QuestionBankRequiredFieldException("questionId is required.");
        }

        var questionExists = await dbContext.Questions
            .AsNoTracking()
            .AnyAsync(
                question =>
                    question.TenantId == filter.TenantId &&
                    question.Id == filter.QuestionId.Value &&
                    question.Status == QuestionStatus.Published,
                cancellationToken);

        if (!questionExists)
        {
            throw new QuestionBankNotFoundException("Question was not found.");
        }

        var items = await dbContext.QuestionVersions
            .AsNoTracking()
            .Where(version =>
                version.TenantId == filter.TenantId &&
                version.QuestionId == filter.QuestionId.Value)
            .OrderByDescending(version => version.VersionNo)
            .Select(version => new QuestionVersionCatalogItem(
                version.Id,
                version.QuestionId,
                version.VersionNo,
                version.Content,
                version.Options,
                version.CorrectOptionIndex,
                version.CorrectOptionIndices,
                version.AnswerText,
                version.Explanation,
                version.SubQuestions,
                version.CodeLang,
                version.CodeTemplate,
                version.CreatedAt))
            .ToArrayAsync(cancellationToken);

        return new CatalogList<QuestionVersionCatalogItem>(items);
    }

    private IQueryable<Question> BaseQuestionQuery()
    {
        return dbContext.Questions
            .AsNoTracking()
            .Where(question => question.Status == QuestionStatus.Published);
    }

    private IQueryable<Question> ApplyQuestionFilters(
        IQueryable<Question> query,
        QuestionBankFilter filter)
    {
        query = query.Where(question => question.TenantId == filter.TenantId);

        if (filter.QuestionBankId.HasValue)
        {
            query = query.Where(question => question.QuestionBankId == filter.QuestionBankId.Value);
        }

        if (filter.SubjectId.HasValue)
        {
            query = query.Where(question => question.SubjectId == filter.SubjectId.Value);
        }

        if (filter.CategoryId.HasValue)
        {
            query = query.Where(question => question.CategoryId == filter.CategoryId.Value);
        }

        if (filter.NodeId.HasValue)
        {
            query = query.Where(question => question.NodeId == filter.NodeId.Value);
        }

        if (filter.EntryId.HasValue)
        {
            query = query.Where(question => question.EntryId == filter.EntryId.Value);
        }

        if (filter.ContentNodeId.HasValue)
        {
            query = query.Where(question => question.ContentNodeId == filter.ContentNodeId.Value);
        }

        if (filter.CollectionId.HasValue)
        {
            query = query.Where(question =>
                question.PrimaryCollectionId == filter.CollectionId.Value ||
                dbContext.QuestionCollectionItems.Any(item =>
                    item.TenantId == question.TenantId &&
                    item.QuestionId == question.Id &&
                    item.CollectionId == filter.CollectionId.Value));
        }

        if (filter.QuestionIds?.Count > 0)
        {
            query = query.Where(question => filter.QuestionIds.Contains(question.Id));
        }

        if (!string.IsNullOrWhiteSpace(filter.Type))
        {
            var type = filter.Type.Trim();
            query = query.Where(question => question.Type == type);
        }

        if (!string.IsNullOrWhiteSpace(filter.Keyword))
        {
            var keyword = filter.Keyword.Trim();
            query = query.Where(question =>
                question.Type.Contains(keyword) ||
                (question.TypeLabel != null && question.TypeLabel.Contains(keyword)) ||
                dbContext.QuestionVersions.Any(version =>
                    version.TenantId == question.TenantId &&
                    version.QuestionId == question.Id &&
                    version.Id == question.CurrentVersionId &&
                    version.Content != null &&
                    version.Content.Contains(keyword)));
        }

        return query;
    }

    private static IQueryable<T> ApplyKeyword<T>(IQueryable<T> query, string? keyword)
        where T : class
    {
        if (string.IsNullOrWhiteSpace(keyword))
        {
            return query;
        }

        var trimmed = keyword.Trim();
        return query.Where(entity => EF.Property<string>(entity, nameof(QuestionBank.Name)).Contains(trimmed));
    }

    private IQueryable<QuestionCatalogItem> ProjectQuestions(IQueryable<Question> questions)
    {
        var emptyOptions = JsonDefaults.Array();
        var emptyCorrectOptionIndices = JsonDefaults.Array();
        var emptySubQuestions = JsonDefaults.Array();
        return
            from question in questions
            join version in dbContext.QuestionVersions.AsNoTracking()
                on new { question.TenantId, QuestionId = question.Id, VersionId = question.CurrentVersionId }
                equals new { version.TenantId, version.QuestionId, VersionId = (Guid?)version.Id }
                into versions
            from version in versions.DefaultIfEmpty()
            select new QuestionCatalogItem(
                question.Id,
                question.QuestionBankId,
                question.SubjectId,
                question.CategoryId,
                question.NodeId,
                question.EntryId,
                question.ContentNodeId,
                question.PrimaryCollectionId,
                question.LegacyId,
                question.LegacySubjectId,
                question.LegacyCategoryId,
                question.LegacyNodeId,
                question.Type,
                question.TypeLabel,
                question.Difficulty,
                question.Tags,
                question.ExamMarkers,
                question.MediaUrl,
                question.HasVideoExplanation,
                question.Status,
                version == null ? null : version.Id,
                version == null ? null : version.VersionNo,
                version == null ? null : version.Content,
                version == null ? emptyOptions : version.Options,
                version == null ? null : version.CorrectOptionIndex,
                version == null ? emptyCorrectOptionIndices : version.CorrectOptionIndices,
                version == null ? null : version.AnswerText,
                version == null ? null : version.Explanation,
                version == null ? emptySubQuestions : version.SubQuestions,
                version == null ? null : version.CodeLang,
                version == null ? null : version.CodeTemplate);
    }

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

public sealed class QuestionBankRequiredFieldException(string message) : Exception(message);

public sealed class QuestionBankNotFoundException(string message) : Exception(message);