using System.Net.Http.Headers;
using System.Text;
using System.Text.Json;

namespace Quorate.Oci;

public sealed class RegistryAuth
{
    internal RegistryAuth(string user, string password)
    {
        User = user;
        Password = password;
    }

    internal string User { get; }
    internal string Password { get; }

    public static RegistryAuth Load(string path, string registry)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(path);
        ArgumentException.ThrowIfNullOrWhiteSpace(registry);

        try
        {
            using FileStream stream = File.OpenRead(path);
            DockerConfigModel config = JsonSerializer.Deserialize(stream, OciJsonContext.Default.DockerConfigModel)
                ?? throw new InvalidDataException("Registry credential document is empty.");
            Dictionary<string, DockerAuthModel> auths = config.Auths
                ?? throw new InvalidDataException("Registry credential document has no auths.");

            if (!auths.TryGetValue(registry, out DockerAuthModel? entry) &&
                !auths.TryGetValue($"https://{registry}", out entry))
            {
                throw new InvalidDataException($"Registry credentials are unavailable for {registry}.");
            }

            string encoded = entry.Auth
                ?? throw new InvalidDataException("Registry credentials are invalid.");
            string decoded = Encoding.UTF8.GetString(Convert.FromBase64String(encoded));
            int separator = decoded.IndexOf(':', StringComparison.Ordinal);

            if (separator < 1)
            {
                throw new InvalidDataException("Registry credentials are invalid.");
            }

            return new RegistryAuth(decoded[..separator], decoded[(separator + 1)..]);
        }
        catch (Exception error) when (error is JsonException or FormatException)
        {
            throw new InvalidDataException("Registry credentials are invalid.", error);
        }
    }

    public override string ToString() => nameof(RegistryAuth);

    internal AuthenticationHeaderValue Basic() => new(
        "Basic",
        Convert.ToBase64String(Encoding.UTF8.GetBytes($"{User}:{Password}")));
}

internal sealed record BearerChallenge(Uri Realm, string? Service, string? Scope)
{
    public static BearerChallenge Parse(AuthenticationHeaderValue value)
    {
        if (!value.Scheme.Equals("Bearer", StringComparison.OrdinalIgnoreCase) ||
            string.IsNullOrWhiteSpace(value.Parameter))
        {
            throw new InvalidDataException("Registry bearer challenge is invalid.");
        }

        var values = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
        int offset = 0;
        string parameter = value.Parameter;

        while (offset < parameter.Length)
        {
            while (offset < parameter.Length && (parameter[offset] == ',' || char.IsWhiteSpace(parameter[offset])))
            {
                offset++;
            }

            int equals = parameter.IndexOf('=', offset);

            if (equals <= offset)
            {
                throw new InvalidDataException("Registry bearer challenge is invalid.");
            }

            string name = parameter[offset..equals].Trim();
            offset = equals + 1;

            if (offset >= parameter.Length || parameter[offset] != '"')
            {
                throw new InvalidDataException("Registry bearer challenge is invalid.");
            }

            int end = parameter.IndexOf('"', ++offset);

            if (end < 0)
            {
                throw new InvalidDataException("Registry bearer challenge is invalid.");
            }

            values.Add(name, parameter[offset..end]);
            offset = end + 1;
        }

        if (!values.TryGetValue("realm", out string? realmValue) ||
            !Uri.TryCreate(realmValue, UriKind.Absolute, out Uri? realm) ||
            realm.Scheme != Uri.UriSchemeHttps)
        {
            throw new InvalidDataException("Registry token endpoint must use HTTPS.");
        }

        values.TryGetValue("service", out string? service);
        values.TryGetValue("scope", out string? scope);
        return new BearerChallenge(realm, service, scope);
    }
}