using LehrerApp.Core.Models;

namespace LehrerApp.Core.Services;

public sealed record CompetencyScore(
    double AchievedPoints, double MaxPoints, int EvidenceCount, int ParticipantCount)
{
    public double Percent => MaxPoints <= 0 ? 0 : AchievedPoints / MaxPoints * 100.0;
}

public sealed class CompetencyAnalysisItem
{
    public required string DomainName { get; init; }
    public required string DomainCode { get; init; }
    public required string Code { get; init; }
    public required string Description { get; init; }
    public int PlannedUnitCount { get; init; }
    public int TaughtUnitCount { get; init; }
    public int PlannedExamCount { get; init; }
    public int AssessedExamCount { get; init; }
    public CompetencyScore? GroupScore { get; init; }
    public IReadOnlyDictionary<Guid, CompetencyScore> StudentScores { get; init; } =
        new Dictionary<Guid, CompetencyScore>();
}

public sealed class CompetencyAnalysisService
{
    public List<CompetencyAnalysisItem> Analyze(
        IReadOnlyList<CompetencyDomain> catalog,
        IReadOnlyList<Unit> units,
        IReadOnlyList<Exam> exams,
        IReadOnlyList<ExamResult> results)
    {
        var builders = new List<ItemBuilder>();
        var byCode = new Dictionary<string, ItemBuilder>(StringComparer.OrdinalIgnoreCase);

        foreach (var domain in catalog.OrderBy(x => x.SortOrder))
        foreach (var item in domain.Items.OrderBy(x => x.SortOrder))
        {
            var builder = new ItemBuilder(domain.Name, domain.Code, item.Code, item.Description);
            builders.Add(builder);
            if (!string.IsNullOrWhiteSpace(item.Code)) byCode.TryAdd(item.Code.Trim(), builder);
        }

        ItemBuilder GetOrAdd(string rawCode)
        {
            var code = rawCode.Trim();
            if (byCode.TryGetValue(code, out var existing)) return existing;
            var added = new ItemBuilder("Nicht im Katalog", "", code,
                "Dieser Kompetenzcode wird noch verwendet, ist aber nicht im aktuellen Katalog enthalten.");
            byCode[code] = added;
            builders.Add(added);
            return added;
        }

        foreach (var unit in units)
        foreach (var code in NormalizeCodes(unit.Competencies))
        {
            var builder = GetOrAdd(code);
            if (unit.Status == UnitStatus.Planned) builder.PlannedUnits++;
            else builder.TaughtUnits++;
        }

        var resultsByExam = results.GroupBy(x => x.ExamId).ToDictionary(x => x.Key, x => x.ToList());
        foreach (var exam in exams)
        {
            var examCodes = NormalizeCodes(exam.Tasks.SelectMany(x => x.CompetencyCodes));
            foreach (var code in examCodes)
            {
                var builder = GetOrAdd(code);
                if (exam.Status == ExamStatus.Planned) builder.PlannedExams++;
                else builder.AssessedExams++;
            }

            if (exam.Status is ExamStatus.Planned or ExamStatus.Conducted
                || !resultsByExam.TryGetValue(exam.Id, out var examResults)) continue;

            foreach (var result in examResults.Where(x => !x.Absent))
            for (var taskIndex = 0; taskIndex < exam.Tasks.Count && taskIndex < result.Points.Count; taskIndex++)
            {
                var task = exam.Tasks[taskIndex];
                if (task.MaxPoints <= 0) continue;
                var achieved = Math.Clamp(result.Points[taskIndex], 0, task.MaxPoints);
                foreach (var code in NormalizeCodes(task.CompetencyCodes))
                    GetOrAdd(code).AddScore(result.StudentId, achieved, task.MaxPoints);
            }
        }

        return builders.Select(x => x.Build()).ToList();
    }

    private static bool HasCode(string? value) => !string.IsNullOrWhiteSpace(value);
    private static IEnumerable<string> NormalizeCodes(IEnumerable<string> codes) =>
        codes.Where(HasCode).Select(x => x.Trim()).Distinct(StringComparer.OrdinalIgnoreCase);

    private sealed class ItemBuilder(
        string domainName, string domainCode, string code, string description)
    {
        private readonly Dictionary<Guid, MutableScore> _scores = [];

        public int PlannedUnits { get; set; }
        public int TaughtUnits { get; set; }
        public int PlannedExams { get; set; }
        public int AssessedExams { get; set; }

        public void AddScore(Guid studentId, double achieved, double maximum)
        {
            if (!_scores.TryGetValue(studentId, out var score))
                _scores[studentId] = score = new MutableScore();
            score.Achieved += achieved;
            score.Maximum += maximum;
            score.EvidenceCount++;
        }

        public CompetencyAnalysisItem Build()
        {
            var studentScores = _scores.ToDictionary(x => x.Key, x => x.Value.ToScore(1));
            var achieved = _scores.Values.Sum(x => x.Achieved);
            var maximum = _scores.Values.Sum(x => x.Maximum);
            var evidence = _scores.Values.Sum(x => x.EvidenceCount);
            return new CompetencyAnalysisItem
            {
                DomainName = domainName,
                DomainCode = domainCode,
                Code = code,
                Description = description,
                PlannedUnitCount = PlannedUnits,
                TaughtUnitCount = TaughtUnits,
                PlannedExamCount = PlannedExams,
                AssessedExamCount = AssessedExams,
                GroupScore = maximum > 0
                    ? new CompetencyScore(achieved, maximum, evidence, _scores.Count)
                    : null,
                StudentScores = studentScores,
            };
        }
    }

    private sealed class MutableScore
    {
        public double Achieved { get; set; }
        public double Maximum { get; set; }
        public int EvidenceCount { get; set; }
        public CompetencyScore ToScore(int participantCount) =>
            new(Achieved, Maximum, EvidenceCount, participantCount);
    }
}