using System.Net.Http.Json;
using LehrerApp.Core.Interfaces;
using LehrerApp.Core.Models;
using LehrerApp.Core.Services;

namespace LehrerApp.Sync;

/// <summary>
/// Exportiert einen lesbaren Snapshot der lokalen LiteDB
/// und pusht ihn zur API – wo er für die WebApp abrufbar ist.
///
/// Wird automatisch nach jedem Sync-Zyklus ausgeführt
/// und kann manuell angestoßen werden.
/// </summary>
public class ReadableSnapshotService
{
    private readonly HttpClient _http;
    private readonly IStudentRepository _students;
    private readonly IGroupRepository _groups;
    private readonly IEnrollmentRepository _enrollments;
    private readonly IExamRepository _exams;
    private readonly IExamResultRepository _examResults;
    private readonly IGradeRepository _grades;
    private readonly IUnitRepository _units;
    private readonly ILessonRepository _lessons;
    private readonly IWorkTaskRepository _tasks;
    private readonly SchoolYearService _schoolYear;
    private readonly string _deviceId;

    public event Action<string>? StatusChanged;

    public ReadableSnapshotService(
        HttpClient http,
        IStudentRepository students,
        IGroupRepository groups,
        IEnrollmentRepository enrollments,
        IExamRepository exams,
        IExamResultRepository examResults,
        IGradeRepository grades,
        IUnitRepository units,
        ILessonRepository lessons,
        IWorkTaskRepository tasks,
        SchoolYearService schoolYear,
        string deviceId)
    {
        _http = http;
        _students = students;
        _groups = groups;
        _enrollments = enrollments;
        _exams = exams;
        _examResults = examResults;
        _grades = grades;
        _units = units;
        _lessons = lessons;
        _tasks = tasks;
        _schoolYear = schoolYear;
        _deviceId = deviceId;
    }

    // ── Export ────────────────────────────────────────────────────────────────

    public async Task<bool> ExportAndPushAsync(
        CancellationToken ct = default)
    {
        StatusChanged?.Invoke("Snapshot wird erstellt…");

        try
        {
            var snapshot = BuildSnapshot();

            StatusChanged?.Invoke("Snapshot wird übertragen…");
            var response = await _http.PostAsJsonAsync(
                "/api/snapshot/readable", snapshot, ct);

            if (!response.IsSuccessStatusCode)
            {
                StatusChanged?.Invoke(
                    $"Übertragung fehlgeschlagen: {response.StatusCode}");
                return false;
            }

            StatusChanged?.Invoke(
                $"Snapshot übertragen – {snapshot.Meta.StudentCount} Schüler, " +
                $"{snapshot.Meta.GroupCount} Gruppen");
            return true;
        }
        catch (Exception ex)
        {
            StatusChanged?.Invoke($"Fehler: {ex.Message}");
            return false;
        }
    }

    // ── Snapshot aufbauen ─────────────────────────────────────────────────────

    private ReadableSnapshot BuildSnapshot()
    {
        var schoolYear = _schoolYear.CurrentSchoolYear();
        var groups = _groups.GetBySchoolYear(schoolYear);
        var groupIds = groups.Select(g => g.Id).ToHashSet();

        var students = _students.GetAll();
        var enrollments = groups
            .SelectMany(g => _enrollments.GetByGroupAndYear(g.Id, schoolYear))
            .ToList();

        var exams = groupIds
            .SelectMany(gid => _exams.GetByGroup(gid))
            .ToList();

        var examResults = exams
            .SelectMany(e => _examResults.GetByExam(e.Id))
            .ToList();

        var grades = groupIds
            .SelectMany(gid => _grades.GetByGroup(gid))
            .ToList();

        var units = groupIds
            .SelectMany(gid => _units.GetByGroup(gid))
            .ToList();

        var lessons = units
            .SelectMany(u => _lessons.GetByUnit(u.Id))
            .ToList();

        var tasks = _tasks.GetAll()
            .Where(t => t.Status != WorkTaskStatus.Done)
            .ToList();

        var snapshot = new ReadableSnapshot
        {
            SchoolYear   = schoolYear,
            Students     = students,
            Groups       = groups,
            Enrollments  = enrollments,
            Exams        = exams,
            ExamResults  = examResults,
            Grades       = grades,
            Units        = units,
            Lessons      = lessons,
            Tasks        = tasks,
            Meta = new SnapshotMeta
            {
                StudentCount      = students.Count,
                GroupCount        = groups.Count,
                ExamCount         = exams.Count,
                ExportedByDevice  = _deviceId,
                OldestData        = DateTime.UtcNow.AddYears(-1), // vereinfacht
            },
        };

        return snapshot;
    }
}