using System.Text;

namespace VoiceCat.Crypto;

public enum TofuStatus { FirstConnect, Matched, Mismatch }

public sealed class TofuStore
{
    private readonly string path;
    private readonly Dictionary<string, string> pins = new(StringComparer.Ordinal);

    public TofuStore(string path)
    {
        this.path = Path.GetFullPath(path);
        if (!File.Exists(this.path)) return;
        foreach (string line in File.ReadLines(this.path))
        {
            if (string.IsNullOrWhiteSpace(line) || line.StartsWith('#')) continue;
            string[] parts = line.Split((char[]?)null, StringSplitOptions.RemoveEmptyEntries);
            if (parts.Length != 2) throw new InvalidDataException("Malformed TOFU pin entry.");
            pins[parts[0]] = NormalizeFingerprint(parts[1]);
        }
    }

    public TofuStatus Check(string host, ushort port, string fingerprint)
    {
        string key = Endpoint(host, port);
        string normalized = NormalizeFingerprint(fingerprint);
        return !pins.TryGetValue(key, out var pin) ? TofuStatus.FirstConnect :
            pin == normalized ? TofuStatus.Matched : TofuStatus.Mismatch;
    }

    public void Pin(string host, ushort port, string fingerprint)
    {
        string key = Endpoint(host, port);
        string value = NormalizeFingerprint(fingerprint);
        var updated = new Dictionary<string, string>(pins, StringComparer.Ordinal) { [key] = value };
        Save(updated);
        pins[key] = value;
    }

    public void Remove(string host, ushort port)
    {
        string key = Endpoint(host, port);
        var updated = new Dictionary<string, string>(pins, StringComparer.Ordinal);
        updated.Remove(key);
        Save(updated);
        pins.Remove(key);
    }

    private void Save(Dictionary<string, string> updated)
    {
        string contents = string.Concat(updated.OrderBy(pair => pair.Key, StringComparer.Ordinal).Select(pair => $"{pair.Key} {pair.Value}\n"));
        PrivateFiles.Write(path, Encoding.UTF8.GetBytes(contents));
    }

    private static string Endpoint(string host, ushort port)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(host);
        if (host.Any(char.IsWhiteSpace)) throw new ArgumentException("Host cannot contain whitespace.", nameof(host));
        ArgumentOutOfRangeException.ThrowIfZero(port);
        return $"{host}:{port}";
    }

    private static string NormalizeFingerprint(string fingerprint)
    {
        ArgumentNullException.ThrowIfNull(fingerprint);
        if (fingerprint.Length != 64 || !fingerprint.All(Uri.IsHexDigit))
            throw new InvalidDataException("TLS certificate fingerprints must contain 64 hexadecimal characters.");
        return fingerprint.ToLowerInvariant();
    }
}