using System.Collections.Concurrent;
using System.Net.Http.Json;
using System.Security.Cryptography;
using System.Text.Json;
using Tiku.Api.Contracts;
using Tiku.Domain.Identity;
using Tiku.Domain.Tenancy;

namespace Tiku.IntegrationTests.Api;

internal sealed record TestAuthenticationTokens(string AccessToken, string RefreshToken);

internal static class AuthenticationTestClientExtensions
{
    private static readonly ConcurrentDictionary<string, string> AuthenticatorKeys = new(StringComparer.Ordinal);

    public static async Task<TestAuthenticationTokens> LoginAsTenantAsync(
        this HttpClient client,
        Guid tenantId,
        string identifier,
        string password = PasswordTestUserExtensions.TestPassword)
    {
        SetTenantHeader(client, tenantId);
        var response = await client.PostAsJsonAsync(
            "/api/auth/login/password",
            new PasswordLoginDto
            {
                Realm = AuthRealm.Tenant,
                TenantCode = tenantId.ToString("N"),
                Identifier = identifier,
                Password = password
            });

        return await client.CompleteTenantAuthenticationAsync(response, tenantId, identifier);
    }

    public static async Task<TestAuthenticationTokens> CompleteTenantAuthenticationAsync(
        this HttpClient client,
        HttpResponseMessage response,
        Guid tenantId,
        string authenticatorCacheKey)
    {
        SetTenantHeader(client, tenantId);
        using var authentication = await ReadSuccessfulJsonAsync(response);
        var root = authentication.RootElement;
        var status = root.GetProperty("status").GetString();

        if (string.Equals(status, "authenticated", StringComparison.OrdinalIgnoreCase))
        {
            return ReadTokens(root.GetProperty("user").GetProperty("tokens"));
        }

        var challengeToken = root.GetProperty("challengeToken").GetString()
            ?? throw new InvalidOperationException("Authentication challenge did not contain a challenge token.");
        var keyId = $"{tenantId:N}:{authenticatorCacheKey}";

        if (string.Equals(status, "mfa_enrollment_required", StringComparison.OrdinalIgnoreCase))
        {
            var setupResponse = await client.PostAsJsonAsync(
                "/api/auth/mfa/totp/setup",
                new MfaChallengeDto { ChallengeToken = challengeToken });
            using var setup = await ReadSuccessfulJsonAsync(setupResponse);
            var sharedKey = setup.RootElement.GetProperty("sharedKey").GetString()
                ?? throw new InvalidOperationException("MFA setup did not return a shared key.");
            AuthenticatorKeys[keyId] = sharedKey;

            var confirmResponse = await client.PostAsJsonAsync(
                "/api/auth/mfa/totp/confirm",
                new MfaChallengeDto
                {
                    ChallengeToken = challengeToken,
                    Code = GenerateTotp(sharedKey)
                });
            using var confirmation = await ReadSuccessfulJsonAsync(confirmResponse);
            return ReadTokens(
                confirmation.RootElement
                    .GetProperty("authentication")
                    .GetProperty("user")
                    .GetProperty("tokens"));
        }

        if (string.Equals(status, "mfa_required", StringComparison.OrdinalIgnoreCase) &&
            AuthenticatorKeys.TryGetValue(keyId, out var existingKey))
        {
            var verifyResponse = await client.PostAsJsonAsync(
                "/api/auth/mfa/totp/verify",
                new MfaChallengeDto
                {
                    ChallengeToken = challengeToken,
                    Code = GenerateTotp(existingKey)
                });
            using var verification = await ReadSuccessfulJsonAsync(verifyResponse);
            return ReadTokens(verification.RootElement.GetProperty("user").GetProperty("tokens"));
        }

        throw new InvalidOperationException($"Unsupported test authentication status '{status}'.");
    }

    public static void UseAccessToken(this HttpClient client, TestAuthenticationTokens tokens)
    {
        client.DefaultRequestHeaders.Authorization = new("Bearer", tokens.AccessToken);
    }

    private static void SetTenantHeader(HttpClient client, Guid tenantId)
    {
        client.DefaultRequestHeaders.Remove("x-tenant-code");
        client.DefaultRequestHeaders.Add("x-tenant-code", tenantId.ToString("N"));
    }

    private static async Task<JsonDocument> ReadSuccessfulJsonAsync(HttpResponseMessage response)
    {
        var body = await response.Content.ReadAsStringAsync();
        if (!response.IsSuccessStatusCode)
        {
            throw new HttpRequestException(
                $"Authentication request failed with {(int)response.StatusCode} ({response.StatusCode}): {body}");
        }

        return JsonDocument.Parse(body);
    }

    private static TestAuthenticationTokens ReadTokens(JsonElement tokens)
    {
        var accessToken = tokens.GetProperty("accessToken").GetString()
            ?? throw new InvalidOperationException("Authentication response did not contain an access token.");
        var refreshToken = tokens.GetProperty("refreshToken").GetString()
            ?? throw new InvalidOperationException("Authentication response did not contain a refresh token.");
        return new TestAuthenticationTokens(accessToken, refreshToken);
    }

    internal static string GenerateTotp(string sharedKey)
    {
        var secret = DecodeBase32(sharedKey);
        var counter = DateTimeOffset.UtcNow.ToUnixTimeSeconds() / 30;
        Span<byte> counterBytes = stackalloc byte[8];
        for (var index = counterBytes.Length - 1; index >= 0; index--)
        {
            counterBytes[index] = (byte)(counter & 0xff);
            counter >>= 8;
        }

        var hash = HMACSHA1.HashData(secret, counterBytes);
        var offset = hash[^1] & 0x0f;
        var binaryCode = ((hash[offset] & 0x7f) << 24) |
                         (hash[offset + 1] << 16) |
                         (hash[offset + 2] << 8) |
                         hash[offset + 3];
        return (binaryCode % 1_000_000).ToString("D6", System.Globalization.CultureInfo.InvariantCulture);
    }

    private static byte[] DecodeBase32(string value)
    {
        var normalized = value.Replace(" ", string.Empty, StringComparison.Ordinal)
            .TrimEnd('=')
            .ToUpperInvariant();
        var output = new byte[normalized.Length * 5 / 8];
        var buffer = 0;
        var bitsInBuffer = 0;
        var outputIndex = 0;

        foreach (var character in normalized)
        {
            var digit = character switch
            {
                >= 'A' and <= 'Z' => character - 'A',
                >= '2' and <= '7' => character - '2' + 26,
                _ => throw new FormatException("Authenticator shared key is not valid Base32.")
            };
            buffer = (buffer << 5) | digit;
            bitsInBuffer += 5;
            if (bitsInBuffer < 8)
            {
                continue;
            }

            output[outputIndex++] = (byte)(buffer >> (bitsInBuffer - 8));
            bitsInBuffer -= 8;
            buffer &= (1 << bitsInBuffer) - 1;
        }

        return output;
    }
}