using Ludarium.Domain;

namespace Ludarium.Application;

public sealed class SnapshotComparer : ISnapshotComparer
{
    public IReadOnlyList<SnapshotChange> Compare(IntegritySnapshot before, IntegritySnapshot after)
    {
        var changes = new List<SnapshotChange>();
        var beforeByArtifact = before.Items.ToDictionary(x => x.ArtifactId);
        var afterByArtifact = after.Items.ToDictionary(x => x.ArtifactId);
        foreach (var oldItem in before.Items)
        {
            if (afterByArtifact.TryGetValue(oldItem.ArtifactId, out var current))
            {
                if (!oldItem.Sha256.Equals(current.Sha256, StringComparison.OrdinalIgnoreCase))
                    changes.Add(new(SnapshotChangeKind.ContentChanged, oldItem, current, "The artifact identity is retained but its verified SHA-256 changed."));
                else if (!oldItem.RelativePath.Equals(current.RelativePath, StringComparison.OrdinalIgnoreCase) || oldItem.LibraryId != current.LibraryId)
                    changes.Add(new(SnapshotChangeKind.Moved, oldItem, current, "Verified content retained its artifact identity at a new location."));
                else changes.Add(new(SnapshotChangeKind.Unchanged, oldItem, current, "Path and verified content are unchanged."));
            }
            else changes.Add(new(SnapshotChangeKind.Removed, oldItem, null, "The artifact is absent from the later available-root snapshot."));
        }
        foreach (var current in after.Items.Where(x => !beforeByArtifact.ContainsKey(x.ArtifactId)))
            changes.Add(new(SnapshotChangeKind.Added, null, current, "A new artifact appears in the later snapshot."));
        return changes.OrderBy(x => x.Kind).ThenBy(x => x.After?.RelativePath ?? x.Before?.RelativePath, StringComparer.OrdinalIgnoreCase).ToArray();
    }
}