using System.Text.Json;
using System.Text.Json.Serialization;

namespace Metin2Launcher.Runtime;

/// <summary>
/// In-memory representation of a runtime key bundle delivered alongside an
/// m2pack release. The launcher never decrypts or opens .m2p archives itself;
/// it merely parses the key bundle produced by the release tool and passes it
/// through to the game executable via one of the <see cref="IRuntimeKeyDelivery"/>
/// mechanisms.
///
/// File layout (runtime-key.json, placed next to the manifest by the release
/// tool, never signed independently — its integrity comes from the signed
/// manifest that references it):
/// <code>
/// {
///   "key_id": "2026.04.14-1",
///   "master_key_hex": "&lt;64 hex chars&gt;",
///   "sign_pubkey_hex": "&lt;64 hex chars&gt;"
/// }
/// </code>
/// </summary>
public sealed class RuntimeKey
{
    [JsonPropertyName("key_id")]
    public string KeyId { get; set; } = "";

    [JsonPropertyName("master_key_hex")]
    public string MasterKeyHex { get; set; } = "";

    [JsonPropertyName("sign_pubkey_hex")]
    public string SignPubkeyHex { get; set; } = "";

    private static readonly JsonSerializerOptions _opts = new()
    {
        PropertyNameCaseInsensitive = false,
    };

    /// <summary>Parses a runtime-key.json blob. Throws on malformed or incomplete data.</summary>
    public static RuntimeKey Parse(ReadOnlySpan<byte> raw)
    {
        var rk = JsonSerializer.Deserialize<RuntimeKey>(raw, _opts)
                 ?? throw new InvalidDataException("runtime-key deserialized to null");
        Validate(rk);
        return rk;
    }

    public static RuntimeKey Load(string path)
    {
        var bytes = File.ReadAllBytes(path);
        return Parse(bytes);
    }

    private static void Validate(RuntimeKey rk)
    {
        if (string.IsNullOrWhiteSpace(rk.KeyId))
            throw new InvalidDataException("runtime-key missing 'key_id'");
        if (!IsHex(rk.MasterKeyHex, 64))
            throw new InvalidDataException("runtime-key 'master_key_hex' must be 64 hex chars");
        if (!IsHex(rk.SignPubkeyHex, 64))
            throw new InvalidDataException("runtime-key 'sign_pubkey_hex' must be 64 hex chars");
    }

    private static bool IsHex(string s, int expectedLen)
    {
        if (s is null || s.Length != expectedLen) return false;
        for (int i = 0; i < s.Length; i++)
        {
            char c = s[i];
            bool ok = (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F');
            if (!ok) return false;
        }
        return true;
    }
}