using QuestionsApi.Models;
using QuestionsApi.Services;
using Xunit;

namespace QuestionsApi.Tests;

public sealed class DailyMissionPolicyTests
{
    private static readonly DateTime Now = new(2026, 8, 1, 12, 0, 0, DateTimeKind.Utc);

    [Fact]
    public void DueReviewsArePrioritizedAndCappedAtTen()
    {
        var candidates = DailyMissionStore.BuildCandidates(Dashboard(17), Questions(), Now);
        Assert.Equal(DailyMissionTypes.DueReviews, candidates[0].Type);
        Assert.Equal(10, candidates[0].Target);
    }

    [Fact]
    public void NoReviewsFallsBackToCoverageGaps()
    {
        var candidates = DailyMissionStore.BuildCandidates(Dashboard(0), Questions(), Now);
        Assert.DoesNotContain(candidates, value => value.Type == DailyMissionTypes.DueReviews);
        Assert.True(candidates.Count >= 3);
        Assert.Contains(candidates.Take(3), value => value.Type == DailyMissionTypes.DifficultyFourCorrect);
        Assert.All(candidates.Where(value => value.Type == DailyMissionTypes.WeakSystemCorrect),
            value => Assert.Equal(3, value.Target));
    }

    [Fact]
    public void HardMissionRequiresThreeEligiblePublishedQuestions()
    {
        var questions = Questions();
        questions.RemoveAll(value => value.Step3System == Step3SystemCatalog.All[1] && value.Difficulty >= 4);
        var candidates = DailyMissionStore.BuildCandidates(Dashboard(0), questions, Now);
        Assert.DoesNotContain(candidates, value => value.Type == DailyMissionTypes.DifficultyFourCorrect
            && value.Step3System == Step3SystemCatalog.All[1]);
    }

    [Fact]
    public void QuestionProgressRequiresCorrectEligibleActivityAfterMissionStart()
    {
        var system = Step3SystemCatalog.All[0];
        var mission = new DailyMission
        {
            Type = DailyMissionTypes.DifficultyFourCorrect, Step3System = system, StartsUtc = Now
        };
        var question = new Question { Step3System = system, Difficulty = 4 };
        Assert.True(DailyMissionStore.QualifiesQuestion(mission,
            new QuestionAttempt { IsCorrect = true, CreatedUtc = Now }, question));
        Assert.False(DailyMissionStore.QualifiesQuestion(mission,
            new QuestionAttempt { IsCorrect = false, CreatedUtc = Now }, question));
        Assert.False(DailyMissionStore.QualifiesQuestion(mission,
            new QuestionAttempt { IsCorrect = true, IsSkip = true, CreatedUtc = Now }, question));
        Assert.False(DailyMissionStore.QualifiesQuestion(mission,
            new QuestionAttempt { IsCorrect = true, CreatedUtc = Now.AddSeconds(-1) }, question));
        question.Difficulty = 3;
        Assert.False(DailyMissionStore.QualifiesQuestion(mission,
            new QuestionAttempt { IsCorrect = true, CreatedUtc = Now }, question));
    }

    private static DashboardResponse Dashboard(int pending) => new()
    {
        MissedQuestionCount = pending,
        Systems = Step3SystemCatalog.All.Take(4).Select((system, index) => new DashboardSystemPerformance
        {
            System = system, MasteryState = index == 0 ? MasteryStates.Unseen : MasteryStates.Learning,
            MasteryScore = index * 10, DistinctQuestions = index, Difficulty4PlusSuccessful = index
        }).ToList()
    };

    private static List<Question> Questions() => Step3SystemCatalog.All.Take(4)
        .SelectMany(system => Enumerable.Range(0, 6).Select(index => new Question
        {
            ExternalId = $"{system}-{index}", Step3System = system, Difficulty = index < 3 ? 4 : 2,
            IsPublished = true
        })).ToList();
}