using System.Collections.ObjectModel;
using LehrerApp.Core.Models;

namespace LehrerApp.Core.Importing;

public sealed record ImportedStudentContact
{
    public string? Email { get; init; }
    public string? MobilePhone { get; init; }
    public string? Phone { get; init; }
    public string? Street { get; init; }
    public string? PostalCode { get; init; }
    public string? City { get; init; }

    public bool HasData => new[] { Email, MobilePhone, Phone, Street, PostalCode, City }
        .Any(value => !string.IsNullOrWhiteSpace(value));
}

/// <summary>Formatunabhängige Schülerdaten, die ein konkreter Handler erzeugt.</summary>
public sealed record ImportedStudent
{
    public required string FirstName { get; init; }
    public required string LastName { get; init; }
    public DateOnly? DateOfBirth { get; init; }
    public Gender? Gender { get; init; }
    public string? ExternalId { get; init; }
    public string? GroupName { get; init; }
    public ImportedStudentContact? Contact { get; init; }
    public string? SourceReference { get; init; }
}

public static class StudentImportFormats
{
    public static readonly ImportFormatId MasterDataCsv = new("student-master-data.csv");
    public static readonly ImportFormatId LessonStudentListCsv = new("lesson-student-list.csv");
    public static readonly ImportFormatId MarksPerLessonCsv = new("marks-per-lesson.csv");
}

public enum StudentImportResolutionKind { CreateNew, UseExisting, Skip }

public sealed record StudentImportResolution(
    StudentImportResolutionKind Kind,
    Guid? ExistingStudentId = null);

public sealed record StudentImportEntry(
    string Id,
    ImportedStudent Student,
    StudentImportResolution? AutomaticResolution,
    string? ConflictId,
    IReadOnlyList<string> FieldsToSupplement);

public sealed record StudentImportGroupAssignment(
    string SourceGroupName,
    Guid? AutomaticGroupId,
    string? ConflictId);

public sealed class StudentImportPreview
{
    public ImportFormatId FormatId { get; }
    public string FormatName { get; }
    public IReadOnlyList<StudentImportEntry> Entries { get; }
    public IReadOnlyList<ImportMessage> Messages { get; }
    public IReadOnlyList<ImportConflict> Conflicts { get; }
    public IReadOnlyList<StudentImportGroupAssignment> GroupAssignments { get; }
    public Guid? TargetGroupId { get; }
    internal string ExistingStudentsFingerprint { get; }
    internal string GroupStateFingerprint { get; }

    public bool CanApply =>
        Entries.Count > 0 && Messages.All(message => message.Severity != ImportMessageSeverity.Error);

    internal StudentImportPreview(
        ImportFormatId formatId,
        string formatName,
        IEnumerable<StudentImportEntry> entries,
        IEnumerable<ImportMessage> messages,
        IEnumerable<ImportConflict> conflicts,
        IEnumerable<StudentImportGroupAssignment> groupAssignments,
        Guid? targetGroupId,
        string existingStudentsFingerprint,
        string groupStateFingerprint)
    {
        FormatId = formatId;
        FormatName = formatName;
        Entries = ReadOnly(entries);
        Messages = ReadOnly(messages);
        Conflicts = ReadOnly(conflicts);
        GroupAssignments = ReadOnly(groupAssignments);
        TargetGroupId = targetGroupId;
        ExistingStudentsFingerprint = existingStudentsFingerprint;
        GroupStateFingerprint = groupStateFingerprint;
    }

    private static IReadOnlyList<T> ReadOnly<T>(IEnumerable<T> values) =>
        new ReadOnlyCollection<T>(values.ToList());
}

public sealed record StudentImportApplyResult(
    int CreatedStudents,
    int UpdatedStudents,
    int MatchedExistingStudents,
    int SkippedStudents,
    int CreatedMemberships,
    IReadOnlyList<Guid> CreatedStudentIds);