using System.Collections.Concurrent;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json.Nodes;

namespace JJServiceManagerRelay;

/// <summary>비밀번호 해시, 토큰, 코드 만들기</summary>
public static class Secrets
{
    private const int Iterations = 210_000;

    public static string HashPassword(string password)
    {
        var salt = RandomNumberGenerator.GetBytes(16);
        var hash = Rfc2898DeriveBytes.Pbkdf2(password, salt, Iterations, HashAlgorithmName.SHA256, 32);
        return $"pbkdf2-sha256${Iterations}${Convert.ToBase64String(salt)}${Convert.ToBase64String(hash)}";
    }

    public static bool VerifyPassword(string password, string stored)
    {
        try
        {
            var p = stored.Split('$');
            if (p.Length != 4 || p[0] != "pbkdf2-sha256") return false;
            int iter = int.Parse(p[1]);
            var salt = Convert.FromBase64String(p[2]);
            var expect = Convert.FromBase64String(p[3]);
            var got = Rfc2898DeriveBytes.Pbkdf2(password ?? "", salt, iter, HashAlgorithmName.SHA256, expect.Length);
            return CryptographicOperations.FixedTimeEquals(got, expect);
        }
        catch
        {
            return false;
        }
    }

    /// <summary>비교용 비밀번호를 늘 계산해서 "없는 아이디"도 같은 시간이 걸리게</summary>
    public static readonly string DummyHash = HashPassword(Guid.NewGuid().ToString());

    public static string NewToken() => Base64Url(RandomNumberGenerator.GetBytes(32));

    public static byte[] Sha256(string s) => SHA256.HashData(Encoding.UTF8.GetBytes(s ?? ""));

    /// <summary>등록 코드: XXXX-XXXX (헷갈리는 글자 O/0/I/1 제외)</summary>
    public static string NewCode()
    {
        const string chars = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789";
        var sb = new StringBuilder();
        for (int i = 0; i < 8; i++)
        {
            if (i == 4) sb.Append('-');
            sb.Append(chars[RandomNumberGenerator.GetInt32(chars.Length)]);
        }
        return sb.ToString();
    }

    /// <summary>입력한 코드 정리 (대소문자·공백·하이픈 무시)</summary>
    public static string NormalizeCode(string code)
    {
        var s = new string((code ?? "").ToUpperInvariant().Where(char.IsLetterOrDigit).ToArray());
        return s.Length == 8 ? s[..4] + "-" + s[4..] : s;
    }

    public static string Base64Url(byte[] b) => Convert.ToBase64String(b).TrimEnd('=').Replace('+', '-').Replace('/', '_');

    public static byte[] FromBase64Url(string s)
    {
        s = s.Replace('-', '+').Replace('_', '/');
        switch (s.Length % 4) { case 2: s += "=="; break; case 3: s += "="; break; }
        return Convert.FromBase64String(s);
    }
}

/// <summary>권한 티켓 서명 (ECDSA P-256). 대상 PC가 서버 공개키로 확인한다.</summary>
public sealed class TicketSigner
{
    private readonly ECDsa _key;
    public string PublicKeyBase64 { get; }

    public TicketSigner(string pkcs8Base64)
    {
        _key = ECDsa.Create();
        _key.ImportPkcs8PrivateKey(Convert.FromBase64String(pkcs8Base64), out _);
        PublicKeyBase64 = Convert.ToBase64String(_key.ExportSubjectPublicKeyInfo());
    }

    public static string NewPrivateKey()
    {
        using var k = ECDsa.Create(ECCurve.NamedCurves.nistP256);
        return Convert.ToBase64String(k.ExportPkcs8PrivateKey());
    }

    /// <summary>티켓 = base64url(JSON) + "." + base64url(서명)</summary>
    public string Sign(JsonObject payload)
    {
        var body = Encoding.UTF8.GetBytes(payload.ToJsonString());
        var sig = _key.SignData(body, HashAlgorithmName.SHA256, DSASignatureFormat.IeeeP1363FixedFieldConcatenation);
        return Secrets.Base64Url(body) + "." + Secrets.Base64Url(sig);
    }
}

/// <summary>로그인·등록 실패 제한: 5분 동안 10번 넘게 틀리면 15분 거부</summary>
public sealed class Throttle
{
    private readonly ConcurrentDictionary<string, List<DateTime>> _fails = new();
    private readonly ConcurrentDictionary<string, DateTime> _blocked = new();
    private static readonly TimeSpan Window = TimeSpan.FromMinutes(5);
    private static readonly TimeSpan Block = TimeSpan.FromMinutes(15);
    private const int MaxFails = 10;

    public bool IsBlocked(params string[] keys)
    {
        var now = DateTime.UtcNow;
        foreach (var k in keys)
        {
            if (k == null) continue;
            if (_blocked.TryGetValue(k, out var until))
            {
                if (until > now) return true;
                _blocked.TryRemove(k, out _);
            }
        }
        return false;
    }

    public void Fail(params string[] keys)
    {
        var now = DateTime.UtcNow;
        foreach (var k in keys)
        {
            if (k == null) continue;
            var list = _fails.GetOrAdd(k, _ => new List<DateTime>());
            lock (list)
            {
                list.Add(now);
                list.RemoveAll(t => now - t > Window);
                if (list.Count > MaxFails)
                {
                    _blocked[k] = now + Block;
                    list.Clear();
                }
            }
        }
    }

    public void Success(params string[] keys)
    {
        foreach (var k in keys)
            if (k != null) _fails.TryRemove(k, out _);
    }
}