using System.Net;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using DodoSSH.Client.Auth;

namespace DodoSSH.Client.Session.Tests;

/// <summary>
/// Signing this device in to Spelunk, with the browser and the redirect stood in for and Spelunk's token
/// endpoint answered in-process: what is opened, what is checked when the browser comes back, what is sent for
/// the token, and what is refused.
/// </summary>
public sealed class SpelunkAccountsTests
{
    private const string ApiBase = "https://api.spelunk.example.com";

    private const string IssuedToken = "spelunkapp_0123456789abcdefghijklmnopqrstuvwxyzABCDEFG";

    private static readonly Guid SessionId = Guid.Parse("0192f0c8-eeee-7c3d-8e4f-5a6b7c8d9e0e");

    private readonly ScriptedBrowser browser = new();

    private readonly TokenEndpoint spelunk = new();

    private static CancellationToken Token => TestContext.Current.CancellationToken;

    [Fact]
    public async Task ASignIn_OpensSpelunksAuthorize_WithPkceAndThisDevice_AndRedeemsTheCode()
    {
        var signIn = await Accounts().SignInAsync(ApiBase + "/", Token);

        var opened = browser.Opened.ShouldHaveSingleItem();
        opened.GetLeftPart(UriPartial.Path).ShouldBe($"{ApiBase}/api/app-sign-in/authorize");
        var query = Query(opened);
        query["client_id"].ShouldBe("dodossh");
        query["response_type"].ShouldBe("code");
        query["code_challenge_method"].ShouldBe("S256");
        query["device_name"].ShouldBe("work laptop");
        query["redirect_uri"].ShouldBe(ScriptedCallback.Redirect);

        // The verifier sent for the token is the one the challenge was made from.
        using var sent = JsonDocument.Parse(spelunk.Bodies.ShouldHaveSingleItem());
        var verifier = sent.RootElement.GetProperty("codeVerifier").GetString()!;
        Base64Url(SHA256.HashData(Encoding.ASCII.GetBytes(verifier))).ShouldBe(query["code_challenge"]);
        sent.RootElement.GetProperty("code").GetString().ShouldBe("the-code");
        sent.RootElement.GetProperty("redirectUri").GetString().ShouldBe(ScriptedCallback.Redirect);
        sent.RootElement.GetProperty("clientId").GetString().ShouldBe("dodossh");

        signIn.ApiBase.ShouldBe(ApiBase);
        signIn.Token.ShouldBe(IssuedToken);
        signIn.SessionId.ShouldBe(SessionId);
        signIn.Email.ShouldBe("ops@example.com");
        signIn.ToString().ShouldNotContain(IssuedToken);
    }

    [Fact]
    public async Task AnAnswerToSomeOtherSignIn_IsIgnored()
    {
        browser.Answer = (_, _) => new Dictionary<string, string>(StringComparer.Ordinal) { ["code"] = "the-code", ["state"] = "not-this-one" };

        var refusal = await Should.ThrowAsync<SpelunkSignInException>(() => Accounts().SignInAsync(ApiBase, Token));

        refusal.Message.ShouldContain("different sign-in");
        spelunk.Bodies.ShouldBeEmpty("a code from another sign-in is never redeemed");
    }

    [Fact]
    public async Task SayingNoInTheBrowser_IsSaidAsACancel()
    {
        browser.Answer = (_, state) => new Dictionary<string, string>(StringComparer.Ordinal) { ["error"] = "access_denied", ["state"] = state };

        var refusal = await Should.ThrowAsync<SpelunkSignInException>(() => Accounts().SignInAsync(ApiBase, Token));

        refusal.Message.ShouldContain("cancelled in the browser");
        spelunk.Bodies.ShouldBeEmpty();
    }

    [Fact]
    public async Task ARefusedCode_IsSaid()
    {
        spelunk.Status = HttpStatusCode.BadRequest;

        var refusal = await Should.ThrowAsync<SpelunkSignInException>(() => Accounts().SignInAsync(ApiBase, Token));

        refusal.Message.ShouldContain("did not accept the sign-in");
    }

    [Fact]
    public async Task ATokenThatCouldNotBeAHeader_IsRefused()
    {
        spelunk.IssuedToken = "spelunkapp_with a space";

        var refusal = await Should.ThrowAsync<SpelunkSignInException>(() => Accounts().SignInAsync(ApiBase, Token));

        refusal.Message.ShouldContain("does not understand");
    }

    [Fact]
    public async Task AnAddressThatWouldSendTheSignInInClear_OpensNoBrowser()
    {
        var refusal = await Should.ThrowAsync<SpelunkSignInException>(
            () => Accounts().SignInAsync("http://api.spelunk.example.com", Token));

        refusal.Message.ShouldContain("https");
        browser.Opened.ShouldBeEmpty();
    }

    [Fact]
    public async Task SigningOut_TellsSpelunk_WithTheToken_AndNeverThrows()
    {
        var accounts = Accounts();
        var signIn = await accounts.SignInAsync(ApiBase, Token);

        await accounts.SignOutAsync(signIn, Token);

        var (method, uri, authorization) = spelunk.Others.ShouldHaveSingleItem();
        method.ShouldBe(HttpMethod.Delete);
        uri.ShouldBe(new Uri($"{ApiBase}/api/app-sign-in/session"));
        authorization.ShouldBe($"Bearer {IssuedToken}");

        spelunk.Unreachable = true;
        await accounts.SignOutAsync(signIn, Token);
    }

    private SpelunkAccounts Accounts() =>
        new(new HttpClient(spelunk), browser, _ => browser.Callback, TimeProvider.System, "work laptop");

    private static Dictionary<string, string> Query(Uri uri) =>
        uri.Query.TrimStart('?').Split('&')
            .Select(pair => pair.Split('=', 2))
            .ToDictionary(pair => pair[0], pair => Uri.UnescapeDataString(pair[1]), StringComparer.Ordinal);

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

    /// <summary>A browser that, opened at the authorize URL, comes straight back with what the test scripts.</summary>
    private sealed class ScriptedBrowser : IBrowserLauncher
    {
        internal List<Uri> Opened { get; } = [];

        internal ScriptedCallback Callback { get; } = new();

        /// <summary>The answer, from the authorize URL and the state it carried. A code and that state by default.</summary>
        internal Func<Uri, string, Dictionary<string, string>> Answer { get; set; } =
            (_, state) => new Dictionary<string, string>(StringComparer.Ordinal) { ["code"] = "the-code", ["state"] = state };

        public Task OpenAsync(Uri url, CancellationToken cancellationToken)
        {
            Opened.Add(url);
            Callback.Result = new CallbackResult(Answer(url, Query(url)["state"]));
            return Task.CompletedTask;
        }
    }

    private sealed class ScriptedCallback : IAuthorizationCallback
    {
        internal const string Redirect = "http://127.0.0.1:53682/callback";

        internal CallbackResult? Result { get; set; }

        public Uri RedirectUri { get; } = new(Redirect);

        public Task<CallbackResult> WaitForCallbackAsync(string completionHtml, CancellationToken cancellationToken) =>
            Task.FromResult(Result ?? throw new InvalidOperationException("The browser was never opened."));

        public void Dispose()
        {
        }
    }

    /// <summary>Spelunk's token and sign-out endpoints.</summary>
    private sealed class TokenEndpoint : HttpMessageHandler
    {
        internal List<string> Bodies { get; } = [];

        internal List<(HttpMethod Method, Uri Uri, string? Authorization)> Others { get; } = [];

        internal HttpStatusCode Status { get; set; } = HttpStatusCode.OK;

        internal string IssuedToken { get; set; } = SpelunkAccountsTests.IssuedToken;

        internal bool Unreachable { get; set; }

        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            if (Unreachable)
            {
                throw new HttpRequestException("Connection refused.");
            }

            if (request.Method != HttpMethod.Post)
            {
                Others.Add((request.Method, request.RequestUri!, request.Headers.Authorization?.ToString()));
                return new HttpResponseMessage(HttpStatusCode.NoContent);
            }

            Bodies.Add(await request.Content!.ReadAsStringAsync(cancellationToken));

            return new HttpResponseMessage(Status)
            {
                Content = new StringContent(
                    Status == HttpStatusCode.OK
                        ? JsonSerializer.Serialize(new
                        {
                            token = IssuedToken,
                            sessionId = SessionId,
                            user = new { id = Guid.CreateVersion7(), email = "ops@example.com", displayName = "Ops" },
                        })
                        : """{"title":"Sign-in not accepted"}""",
                    Encoding.UTF8,
                    "application/json"),
            };
        }
    }
}