using System.Text.Json;

namespace StellaOps.Canonical.Json;

public static partial class CanonJson
{
    /// <summary>
    /// Canonicalizes an object with version marker for content-addressed hashing.
    /// The version marker is embedded as the first field in the canonical JSON,
    /// ensuring stable hashes even if canonicalization logic evolves.
    /// </summary>
    /// <typeparam name="T">The type to serialize.</typeparam>
    /// <param name="obj">The object to canonicalize.</param>
    /// <param name="version">Canonicalization version (default: Current).</param>
    /// <returns>UTF-8 encoded canonical JSON bytes with version marker.</returns>
    public static byte[] CanonicalizeVersioned<T>(T obj, string version = CanonVersion.Current)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(version);

        var json = JsonSerializer.SerializeToUtf8Bytes(obj, _defaultSerializerOptions);

        using var doc = JsonDocument.Parse(json);
        using var ms = new MemoryStream();
        using var writer = new Utf8JsonWriter(ms, _defaultWriterOptions);

        WriteElementVersioned(doc.RootElement, writer, version);
        writer.Flush();
        return ms.ToArray();
    }

    /// <summary>
    /// Canonicalizes an object with version marker using custom serializer options.
    /// </summary>
    /// <typeparam name="T">The type to serialize.</typeparam>
    /// <param name="obj">The object to canonicalize.</param>
    /// <param name="options">JSON serializer options to use for initial serialization.</param>
    /// <param name="version">Canonicalization version (default: Current).</param>
    /// <returns>UTF-8 encoded canonical JSON bytes with version marker.</returns>
    public static byte[] CanonicalizeVersioned<T>(T obj, JsonSerializerOptions options, string version = CanonVersion.Current)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(version);

        var json = JsonSerializer.SerializeToUtf8Bytes(obj, options);

        using var doc = JsonDocument.Parse(json);
        using var ms = new MemoryStream();
        using var writer = new Utf8JsonWriter(ms, CreateWriterOptions(options));

        WriteElementVersioned(doc.RootElement, writer, version);
        writer.Flush();
        return ms.ToArray();
    }

    private static void WriteElementVersioned(JsonElement el, Utf8JsonWriter w, string version)
    {
        if (el.ValueKind == JsonValueKind.Object)
        {
            w.WriteStartObject();

            // Write version marker first (underscore prefix ensures lexicographic first position)
            w.WriteString(CanonVersion.VersionFieldName, version);

            // Write remaining properties sorted
            foreach (var prop in el.EnumerateObject().OrderBy(p => p.Name, StringComparer.Ordinal))
            {
                if (string.Equals(prop.Name, CanonVersion.VersionFieldName, StringComparison.Ordinal))
                {
                    continue;
                }

                w.WritePropertyName(prop.Name);
                WriteElementSorted(prop.Value, w);
            }
            w.WriteEndObject();
        }
        else
        {
            // Non-object root: wrap in object with version marker
            w.WriteStartObject();
            w.WriteString(CanonVersion.VersionFieldName, version);
            w.WritePropertyName("_value");
            WriteElementSorted(el, w);
            w.WriteEndObject();
        }
    }
}