using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json;

#if NETSTANDARD2_0
using Org.BouncyCastle.Crypto.Engines;
using Org.BouncyCastle.Crypto.Generators;
using Org.BouncyCastle.Crypto.Modes;
using Org.BouncyCastle.Crypto.Parameters;
#endif

namespace Deploymentcenter.Client;

public class LocalCacheData
{
    public int SchemaVersion { get; set; } = StateStore.CurrentSchemaVersion;
    public string ProductSlug { get; set; } = string.Empty;
    public string LicenseKey { get; set; } = string.Empty;
    public string HardwareId { get; set; } = string.Empty;
    public string Status { get; set; } = "invalid";
    public long IssuedAt { get; set; }

    /// <summary>Ablauf der Lizenz selbst (Unix-Zeit), 0 wenn unbefristet.</summary>
    public long ExpiresAt { get; set; }

    /// <summary>
    /// Ende der Offline-Gnadenfrist (Unix-Zeit). Getrennt von
    /// <see cref="ExpiresAt"/>, weil eine Lizenz bis 2040 laufen kann, die
    /// Frist ohne Serverkontakt aber nur ueber die vom Server gemeldeten
    /// cache_ttl_hours. Schema 2 kannte das Feld nicht; dort wird die Frist
    /// aus IssuedAt abgeleitet.
    /// </summary>
    public long CacheExpiresAt { get; set; }

    /// <summary>Vom Server gemeldete Gnadenfrist in Stunden.</summary>
    public int CacheTtlHours { get; set; }

    public long MaxSeenTime { get; set; }
    public string Checksum { get; set; } = string.Empty;
}

public static class StateStore
{
    private static readonly byte[] Magic = Encoding.UTF8.GetBytes("LLS2"); // 4 bytes: 0x4C, 0x4C, 0x53, 0x32

    /// <summary>Schema, das dieser Client schreibt.</summary>
    public const int CurrentSchemaVersion = 3;

    /// <summary>
    /// Schemata, die noch gelesen werden. Schema 2 hat keine getrennte
    /// Cache-Frist; ein Aufsteigen darf keinen Zwang zur Online-Pruefung
    /// ausloesen, nur weil das SDK aktualisiert wurde.
    /// </summary>
    private static readonly int[] SupportedSchemaVersions = { 2, 3 };

    public static LocalCacheData? Load(string productSlug, string hardwareId)
    {
        try
        {
            string dir = LicenseConfig.GetStorageDirectory(productSlug);
            string statePath = Path.Combine(dir, "state.dat");

            if (!File.Exists(statePath))
                return null;

            byte[] rawFileContent = File.ReadAllBytes(statePath);
            if (rawFileContent.Length == 0)
                return null;

            byte[] payloadBytes = rawFileContent;

            // Try DPAPI unwrap on Windows
            if (OperatingSystemHelpers.IsWindows())
            {
                try
                {
                    payloadBytes = ProtectedData.Unprotect(rawFileContent, null, DataProtectionScope.CurrentUser);
                }
                catch
                {
                    payloadBytes = rawFileContent;
                }
            }

            // Check LLS2 Magic Header
            if (payloadBytes.Length >= 4 + 12 + 16 && StartsWithMagic(payloadBytes, Magic))
            {
                byte[] key = DeriveKey(hardwareId, productSlug);
                byte[]? jsonBytes = DecryptAesGcmEnvelope(payloadBytes, key);
                if (jsonBytes == null)
                    return null; // Decryption/Auth failed -> Treat strictly as Cache Miss

                string jsonStr = Encoding.UTF8.GetString(jsonBytes);
                var data = JsonSerializer.Deserialize<LocalCacheData>(jsonStr);

                if (data == null || Array.IndexOf(SupportedSchemaVersions, data.SchemaVersion) < 0)
                    return null; // Incompatible schema -> Treat as Cache Miss

                if (!BelongsHere(data, productSlug, hardwareId))
                    return null;

                return data;
            }

            // Legacy Migration Check (non-LLS2 file)
            //
            // Vorher wurde hier beliebiges JSON nach LocalCacheData
            // deserialisiert und sofort im LLS2-Format zurueckgeschrieben.
            // Passte kein einziges Feld, entstand ein Standardobjekt, das die
            // urspruengliche Datei ueberschrieb. Da LicenseLabrador denselben
            // Pfad und Dateinamen verwendet - GetStorageDirectory beruecksichtigt
            // dafuer eigens LICENSELABRADOR_STORAGE_DIR - zerstoerte das den
            // fremden Cache still. Uebernommen wird jetzt nur, was sich als
            // Cache genau dieses Produkts auf genau dieser Maschine ausweist.
            try
            {
                string legacyJson = Encoding.UTF8.GetString(payloadBytes);

                // Ein Ueberbleibsel im Binaerformat ist kein JSON-Objekt.
                if (legacyJson.TrimStart().StartsWith("{", StringComparison.Ordinal))
                {
                    var legacyData = JsonSerializer.Deserialize<LocalCacheData>(legacyJson);

                    if (legacyData != null && BelongsHere(legacyData, productSlug, hardwareId))
                    {
                        legacyData.SchemaVersion = CurrentSchemaVersion;
                        Save(productSlug, hardwareId, legacyData);
                        return legacyData;
                    }
                }
            }
            catch (JsonException) { }

            return null;
        }
        catch
        {
            return null;
        }
    }

    /// <summary>
    /// Prueft, ob ein gelesener Cache tatsaechlich zu diesem Produkt gehoert.
    ///
    /// Fuer LLS2-Dateien ist die Hardware-Bindung bereits durch die
    /// Schluesselableitung gegeben - dort faellt die Entschluesselung sonst aus.
    /// Entscheidend ist der Produktbezug: ohne ihn wuerde eine fremde
    /// state.dat im selben Verzeichnis uebernommen und ueberschrieben.
    /// </summary>
    private static bool BelongsHere(LocalCacheData data, string productSlug, string hardwareId)
    {
        if (string.IsNullOrWhiteSpace(data.ProductSlug))
            return false;

        if (!string.Equals(data.ProductSlug, productSlug, StringComparison.OrdinalIgnoreCase))
            return false;

        // Ein Cache ohne Schluessel taugt zu nichts und ist meist ein
        // Standardobjekt aus einer Datei, die gar keine unsrige war.
        if (string.IsNullOrWhiteSpace(data.LicenseKey))
            return false;

        return true;
    }

    public static bool Save(string productSlug, string hardwareId, LocalCacheData cacheData)
    {
        try
        {
            cacheData.SchemaVersion = CurrentSchemaVersion;
            string dir = LicenseConfig.GetStorageDirectory(productSlug);
            Directory.CreateDirectory(dir);
            string statePath = Path.Combine(dir, "state.dat");

            string jsonStr = JsonSerializer.Serialize(cacheData);
            byte[] jsonBytes = Encoding.UTF8.GetBytes(jsonStr);

            byte[] key = DeriveKey(hardwareId, productSlug);
            byte[] envelopeBytes = EncryptAesGcmEnvelope(jsonBytes, key);

            byte[] finalFileBytes = envelopeBytes;

            // Wrap with DPAPI on Windows
            if (OperatingSystemHelpers.IsWindows())
            {
                try
                {
                    finalFileBytes = ProtectedData.Protect(envelopeBytes, null, DataProtectionScope.CurrentUser);
                }
                catch
                {
                    finalFileBytes = envelopeBytes;
                }
            }

            File.WriteAllBytes(statePath, finalFileBytes);
            SetUnixPermissions(statePath, "600");
            return true;
        }
        catch
        {
            return false;
        }
    }

    private static bool StartsWithMagic(byte[] data, byte[] magic)
    {
        if (data.Length < magic.Length) return false;
        for (int i = 0; i < magic.Length; i++)
        {
            if (data[i] != magic[i]) return false;
        }
        return true;
    }

    private static byte[] DeriveKey(string hardwareId, string productSlug)
    {
        string ikmStr = $"{hardwareId}:{productSlug}";
        byte[] ikm = Encoding.UTF8.GetBytes(ikmStr);
        byte[] salt = Encoding.UTF8.GetBytes("LicenseLabradorHKDFSaltV2");
        byte[] info = Encoding.UTF8.GetBytes("StateStoreEncryptionKey");

#if NET8_0_OR_GREATER
        return HKDF.DeriveKey(HashAlgorithmName.SHA256, ikm, 32, salt, info);
#else
        var hkdf = new HkdfBytesGenerator(new Org.BouncyCastle.Crypto.Digests.Sha256Digest());
        hkdf.Init(new HkdfParameters(ikm, salt, info));
        byte[] key = new byte[32];
        hkdf.GenerateBytes(key, 0, 32);
        return key;
#endif
    }

    private static byte[] EncryptAesGcmEnvelope(byte[] plaintext, byte[] key)
    {
        byte[] nonce = new byte[12];
        using (var rng = RandomNumberGenerator.Create())
        {
            rng.GetBytes(nonce);
        }

#if NET8_0_OR_GREATER
        byte[] ciphertext = new byte[plaintext.Length];
        byte[] tag = new byte[16];
        using (var aes = new AesGcm(key, 16))
        {
            aes.Encrypt(nonce, plaintext, ciphertext, tag);
        }

        byte[] envelope = new byte[4 + 12 + ciphertext.Length + 16];
        Buffer.BlockCopy(Magic, 0, envelope, 0, 4);
        Buffer.BlockCopy(nonce, 0, envelope, 4, 12);
        Buffer.BlockCopy(ciphertext, 0, envelope, 16, ciphertext.Length);
        Buffer.BlockCopy(tag, 0, envelope, 16 + ciphertext.Length, 16);
        return envelope;
#else
        var cipher = new GcmBlockCipher(new AesEngine());
        var parameters = new AeadParameters(new KeyParameter(key), 128, nonce);
        cipher.Init(true, parameters);

        byte[] output = new byte[cipher.GetOutputSize(plaintext.Length)];
        int len = cipher.ProcessBytes(plaintext, 0, plaintext.Length, output, 0);
        cipher.DoFinal(output, len);

        // output in BouncyCastle contains Ciphertext + 16-byte Tag
        int cipherLen = output.Length - 16;
        byte[] ciphertext = new byte[cipherLen];
        byte[] tag = new byte[16];
        Buffer.BlockCopy(output, 0, ciphertext, 0, cipherLen);
        Buffer.BlockCopy(output, cipherLen, tag, 0, 16);

        byte[] envelope = new byte[4 + 12 + ciphertext.Length + 16];
        Buffer.BlockCopy(Magic, 0, envelope, 0, 4);
        Buffer.BlockCopy(nonce, 0, envelope, 4, 12);
        Buffer.BlockCopy(ciphertext, 0, envelope, 16, ciphertext.Length);
        Buffer.BlockCopy(tag, 0, envelope, 16 + ciphertext.Length, 16);
        return envelope;
#endif
    }

    private static byte[]? DecryptAesGcmEnvelope(byte[] envelope, byte[] key)
    {
        try
        {
            if (envelope.Length < 4 + 12 + 16)
                return null;

            byte[] nonce = new byte[12];
            Buffer.BlockCopy(envelope, 4, nonce, 0, 12);

            int cipherLen = envelope.Length - 4 - 12 - 16;
            byte[] ciphertext = new byte[cipherLen];
            Buffer.BlockCopy(envelope, 16, ciphertext, 0, cipherLen);

            byte[] tag = new byte[16];
            Buffer.BlockCopy(envelope, 16 + cipherLen, tag, 0, 16);

#if NET8_0_OR_GREATER
            byte[] plaintext = new byte[cipherLen];
            using (var aes = new AesGcm(key, 16))
            {
                aes.Decrypt(nonce, ciphertext, tag, plaintext);
            }
            return plaintext;
#else
            var cipher = new GcmBlockCipher(new AesEngine());
            var parameters = new AeadParameters(new KeyParameter(key), 128, nonce);
            cipher.Init(false, parameters);

            byte[] input = new byte[ciphertext.Length + 16];
            Buffer.BlockCopy(ciphertext, 0, input, 0, ciphertext.Length);
            Buffer.BlockCopy(tag, 0, input, ciphertext.Length, 16);

            byte[] plaintext = new byte[cipher.GetOutputSize(input.Length)];
            int len = cipher.ProcessBytes(input, 0, input.Length, plaintext, 0);
            cipher.DoFinal(plaintext, len);

            return plaintext;
#endif
        }
        catch
        {
            return null; // Auth/Decryption failed
        }
    }

    private static void SetUnixPermissions(string filePath, string mode)
    {
        if (OperatingSystemHelpers.IsWindows())
            return;

#if NET8_0_OR_GREATER
        try
        {
            File.SetUnixFileMode(filePath, UnixFileMode.UserRead | UnixFileMode.UserWrite);
        }
        catch { }
#else
        try
        {
            var proc = System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo
            {
                FileName = "chmod",
                Arguments = $"{mode} \"{filePath}\"",
                UseShellExecute = false,
                CreateNoWindow = true
            });
            proc?.WaitForExit();
        }
        catch { }
#endif
    }
}