using Core.Models;

namespace Core.Services;

/// <summary>
/// Decides which parsed student notes should be created or updated.
/// Unchanged merges are omitted so a re-import does not write history.
/// </summary>
public static class StudentNotesImportPlan
{
    /// <summary>
    /// Builds persist actions from a parse result. Only matches with field changes are included.
    /// </summary>
    public static IReadOnlyList<StudentNotePersistAction> Create(
        StudentNotesImportResult parseResult,
        IReadOnlySet<int> studentIdsWithExistingNotes)
    {
        ArgumentNullException.ThrowIfNull(parseResult);
        ArgumentNullException.ThrowIfNull(studentIdsWithExistingNotes);

        List<StudentNotePersistAction> actions = [];
        foreach (var match in parseResult.Matches)
        {
            if (!match.Merge.Changed)
                continue;

            actions.Add(new StudentNotePersistAction
            {
                StudentId = match.Student.Id,
                Markdown = match.Merge.Markdown,
                Kind = studentIdsWithExistingNotes.Contains(match.Student.Id)
                    ? StudentNotePersistKind.Update
                    : StudentNotePersistKind.Create
            });
        }

        return actions;
    }
}

public enum StudentNotePersistKind
{
    Create,
    Update
}

public class StudentNotePersistAction
{
    public required int StudentId { get; init; }

    public required string Markdown { get; init; }

    public required StudentNotePersistKind Kind { get; init; }
}