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 : IDisposable
{
    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;

    public void Dispose() => spelunk.Dispose();

    [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 ARefusedCode_IsSaidInSpelunksOwnWords()
    {
        spelunk.Status = HttpStatusCode.BadRequest;
        spelunk.ProblemDetail = "The code is wrong, used or expired. Sign in again from the app.";

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

        refusal.Message.ShouldContain("used or expired");
    }

    [Fact]
    public async Task ATokenThatIsNotAnAppSignIns_IsRefused()
    {
        // Spelunk reads a bearer token by its prefix: without this one it is an API key or a JWT to it, and an
        // answer carrying one is not Spelunk's app sign-in.
        spelunk.IssuedToken = "spelunk_0123456789abcdefghijklmnopqrstuvwxyzABCDEFG";

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

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

    [Fact]
    public async Task ABrowserThatWillNotOpen_IsSaid()
    {
        browser.Failure = new InvalidOperationException("No browser is installed.");

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

        refusal.Message.ShouldContain("No browser is installed.");
        spelunk.Bodies.ShouldBeEmpty();
    }

    [Fact]
    public async Task APhoneBrowserClosedWithoutAnAnswer_IsSaid_AsTheReasonThePhoneGave()
    {
        // What AndroidRedirectCallback.Abandon fails the wait with when the app comes back with no redirect.
        browser.Callback.Failure = new OidcException("Sign-in was cancelled: the browser closed without signing you in.");

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

        refusal.Message.ShouldContain("browser closed without signing you in");
        spelunk.Bodies.ShouldBeEmpty();
    }

    [Fact]
    public async Task ABrowserThatNeverComesBack_TimesOut_AndSaysSo()
    {
        browser.Callback.Never = true;

        var accounts = new SpelunkAccounts(new HttpClient(spelunk), browser, _ => browser.Callback, TimeProvider.System, "work laptop")
        {
            BrowserTimeout = TimeSpan.FromMilliseconds(50),
        };
        var refusal = await Should.ThrowAsync<SpelunkSignInException>(() => accounts.SignInAsync(ApiBase, Token));

        refusal.Message.ShouldContain("in time");
    }

    [Fact]
    public async Task ClosingTheDialog_CancelsTheSignIn_AndRedeemsNothing()
    {
        browser.Callback.Never = true;
        using var closed = CancellationTokenSource.CreateLinkedTokenSource(Token);
        closed.CancelAfter(TimeSpan.FromMilliseconds(50));

        await Should.ThrowAsync<OperationCanceledException>(() => Accounts().SignInAsync(ApiBase, closed.Token));

        spelunk.Bodies.ShouldBeEmpty();
    }

    [Fact]
    public async Task APhonesRedirect_IsSentExactlyAsSpelunkAllowsIt_BothTimes()
    {
        // Spelunk matches an app-scheme redirect byte for byte, at authorize and again at the token request.
        browser.Callback.RedirectUri = new Uri("dev.dodotech.dodossh:/callback");

        await Accounts().SignInAsync(ApiBase, Token);

        Query(browser.Opened.ShouldHaveSingleItem())["redirect_uri"].ShouldBe("dev.dodotech.dodossh:/callback");
        using var sent = JsonDocument.Parse(spelunk.Bodies.ShouldHaveSingleItem());
        sent.RootElement.GetProperty("redirectUri").GetString().ShouldBe("dev.dodotech.dodossh:/callback");
    }

    [Fact]
    public async Task OnADesktop_TheBrowserComesBackToALoopbackLiteral_AndTheListenerTakesOneAnswer()
    {
        // The real listener, and a "browser" that follows Spelunk's redirect the way a browser would. Spelunk
        // allows plain HTTP to a loopback IP literal only - never localhost - on any port.
        var following = new FollowingBrowser();
        var accounts = new SpelunkAccounts(new HttpClient(spelunk), following, deviceName: "work laptop");

        var signIn = await accounts.SignInAsync(ApiBase, Token);

        var redirect = new Uri(Query(following.Opened.ShouldHaveSingleItem())["redirect_uri"]);
        redirect.Scheme.ShouldBe("http");
        redirect.Host.ShouldBe("127.0.0.1");
        redirect.AbsolutePath.ShouldBe("/callback");
        (await following.Page).ShouldContain("return to DodoSSH");
        signIn.Token.ShouldBe(IssuedToken);

        // Closed once it has its answer: nothing is listening there any more.
        await Should.ThrowAsync<HttpRequestException>(() => following.Http.GetAsync(redirect, Token));
    }

    [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);
    }

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

        // A damaged record whose address is no longer one a sign-in could have come from is forgotten unsent.
        await accounts.SignOutAsync(signIn with { ApiBase = "http://spelunk.example.com" }, Token);

        spelunk.Others.ShouldBeEmpty();
    }

    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 };

        /// <summary>What opening the browser throws, or null when it opens.</summary>
        internal Exception? Failure { get; set; }

        public Task OpenAsync(Uri url, CancellationToken cancellationToken)
        {
            if (Failure is { } failure)
            {
                throw failure;
            }

            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; }

        /// <summary>What the wait fails with, or null when it answers.</summary>
        internal Exception? Failure { get; set; }

        /// <summary>Whether the browser never comes back, so only a cancellation ends the wait.</summary>
        internal bool Never { get; set; }

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

        public async Task<CallbackResult> WaitForCallbackAsync(string completionHtml, CancellationToken cancellationToken)
        {
            if (Never)
            {
                await Task.Delay(Timeout.Infinite, cancellationToken);
            }

            return Failure is { } failure
                ? throw failure
                : Result ?? throw new InvalidOperationException("The browser was never opened.");
        }

        public void Dispose()
        {
        }
    }

    /// <summary>
    /// A browser that does what Spelunk's consent page ends with: goes to the redirect URI with a code and the
    /// state it was opened with.
    /// </summary>
    private sealed class FollowingBrowser : IBrowserLauncher
    {
        internal HttpClient Http { get; } = new() { Timeout = TimeSpan.FromSeconds(5) };

        internal List<Uri> Opened { get; } = [];

        /// <summary>The page the listener showed once the browser came back.</summary>
        internal Task<string> Page { get; private set; } = Task.FromResult(string.Empty);

        public async Task OpenAsync(Uri url, CancellationToken cancellationToken)
        {
            Opened.Add(url);
            var query = Query(url);

            // Not awaited by the sign-in, as a real browser is not: it is answered once the listener is waiting.
            var back = new Uri($"{query["redirect_uri"]}?code=the-code&state={Uri.EscapeDataString(query["state"])}");
            Page = Task.Run(() => Http.GetStringAsync(back, cancellationToken), cancellationToken);

            await Task.CompletedTask;
        }
    }

    /// <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;

        /// <summary>The detail of a refusal, as Spelunk's problem details carry it.</summary>
        internal string? ProblemDetail { get; set; }

        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" },
                        })
                        : JsonSerializer.Serialize(new { title = "Sign-in not accepted", detail = ProblemDetail }),
                    Encoding.UTF8,
                    "application/json"),
            };
        }
    }
}