using LiteDB;
using LehrerApp.Core.Models;

namespace LehrerApp.Data;

/// <summary>
/// Zentrale Datenbankverbindung. Einmalig als Singleton registrieren.
/// Eine Instanz = eine .db Datei = ein Nutzer.
/// </summary>
public class LiteDbContext : IDisposable
{
    private readonly LiteDatabase _db;

    public LiteDbContext(string databasePath)
    {
        // WAL-Modus für bessere Performance bei Concurrent Reads
        var connectionString = new ConnectionString(databasePath)
        {
            Connection = ConnectionType.Shared,
        };

        _db = new LiteDatabase(connectionString);
        EnsureIndexes();
    }

    // ── Collections ──────────────────────────────────────────────────────────

    public ILiteCollection<Student> Students =>
        _db.GetCollection<Student>("students");

    public ILiteCollection<LearningGroup> Groups =>
        _db.GetCollection<LearningGroup>("groups");

    public ILiteCollection<Enrollment> Enrollments =>
        _db.GetCollection<Enrollment>("enrollments");

    public ILiteCollection<Exam> Exams =>
        _db.GetCollection<Exam>("exams");

    public ILiteCollection<ExamResult> ExamResults =>
        _db.GetCollection<ExamResult>("exam_results");

    public ILiteCollection<Grade> Grades =>
        _db.GetCollection<Grade>("grades");

    public ILiteCollection<Unit> Units =>
        _db.GetCollection<Unit>("units");

    public ILiteCollection<Lesson> Lessons =>
        _db.GetCollection<Lesson>("lessons");

    public ILiteCollection<Documentation> Documentation =>
        _db.GetCollection<Documentation>("documentation");

    public ILiteCollection<WorkTask> Tasks =>
        _db.GetCollection<WorkTask>("tasks");

    public ILiteCollection<TimeEntry> TimeEntries =>
        _db.GetCollection<TimeEntry>("time_entries");

    // ── Transaktionen ─────────────────────────────────────────────────────────

    public T Transaction<T>(Func<T> action) => _db.BeginTrans() ? action() : action();

    public void Checkpoint() => _db.Checkpoint();

    // ── Backup ───────────────────────────────────────────────────────────────

    public void BackupTo(string targetPath)
    {
        _db.Checkpoint();
        File.Copy(_db.UserVersion.ToString(), targetPath, overwrite: true);
    }

    // ── Indizes ──────────────────────────────────────────────────────────────

    private void EnsureIndexes()
    {
        Students.EnsureIndex(x => x.LastName);
        Students.EnsureIndex(x => x.IsActive);

        Groups.EnsureIndex(x => x.SchoolYear);
        Groups.EnsureIndex(x => x.Type);

        Enrollments.EnsureIndex(x => x.StudentId);
        Enrollments.EnsureIndex(x => x.GroupId);
        Enrollments.EnsureIndex(x => x.SchoolYear);

        Exams.EnsureIndex(x => x.GroupId);
        Exams.EnsureIndex(x => x.Date);
        Exams.EnsureIndex(x => x.Status);

        ExamResults.EnsureIndex(x => x.ExamId);
        ExamResults.EnsureIndex(x => x.StudentId);

        Grades.EnsureIndex(x => x.StudentId);
        Grades.EnsureIndex(x => x.GroupId);

        Units.EnsureIndex(x => x.GroupId);
        Units.EnsureIndex(x => x.Status);

        Lessons.EnsureIndex(x => x.UnitId);
        Lessons.EnsureIndex(x => x.GroupId);
        Lessons.EnsureIndex(x => x.Date);

        Documentation.EnsureIndex(x => x.StudentId);
        Documentation.EnsureIndex(x => x.Type);

        Tasks.EnsureIndex(x => x.Status);
        Tasks.EnsureIndex(x => x.DueDate);

        TimeEntries.EnsureIndex(x => x.Date);
        TimeEntries.EnsureIndex(x => x.TaskId);
    }

    public void Dispose() => _db.Dispose();
}