using System.Net;
using System.Text;
using System.Text.Json;

namespace ClawdDotNet.Core.Deploymentcenter;

/// <summary>
/// The shared foundation for all Deploymentcenter modules (watchdog, error stream,
/// bug tracker, token provisioning).
///
/// <para>All JSON endpoints answer uniformly with an envelope —
/// <c>{"status":"success",…}</c> or <c>{"status":"error","error":{"code":…}}</c>. The
/// <c>code</c> is stable and meant for programs, the <c>message</c> for humans.
/// This class unpacks the envelope and turns an error into a
/// <see cref="DeploymentcenterException"/> with the code attached.</para>
///
/// <para><b>Exception:</b> the license endpoints deliberately do <em>not</em> carry this envelope
/// — there the field <c>status</c> holds the license state. They are
/// therefore not addressed through this class, but through <c>Deploymentcenter.Client</c>.</para>
/// </summary>
public sealed class DeploymentcenterApi : IDisposable
{
    private static readonly JsonSerializerOptions JsonOpts = new(JsonSerializerDefaults.Web);

    private readonly HttpClient _http;
    private readonly bool _ownsHttp;
    private readonly string _token;

    /// <summary>The base URL without a trailing slash.</summary>
    public string BaseUrl { get; }

    /// <param name="baseUrl">Base URL of the Deploymentcenter, for example <c>https://dc.mhdf.de</c>.</param>
    /// <param name="token">Token with the necessary rights. Sent as <c>Authorization: Bearer</c>.</param>
    /// <param name="httpClient">Only for tests — otherwise an own one with a timeout is created.</param>
    public DeploymentcenterApi(string baseUrl, string token, HttpClient? httpClient = null)
    {
        if (string.IsNullOrWhiteSpace(baseUrl))
            throw new ArgumentException("Deploymentcenter-URL fehlt.", nameof(baseUrl));

        // Over an unsecured connection the token would go in plain text. The only exception is
        // the own machine — there is no route there on which someone could
        // listen in, and a local test installation rarely has a certificate.
        if (!IsAcceptableUrl(baseUrl))
        {
            throw new ArgumentException(
                "Deploymentcenter-URL muss mit https:// beginnen (Ausnahme: localhost).",
                nameof(baseUrl));
        }

        BaseUrl = baseUrl.TrimEnd('/');
        _token = token ?? throw new ArgumentNullException(nameof(token));

        _ownsHttp = httpClient is null;
        _http = httpClient ?? new HttpClient { Timeout = TimeSpan.FromSeconds(10) };
    }

    private static bool IsAcceptableUrl(string url)
    {
        if (!Uri.TryCreate(url, UriKind.Absolute, out var uri))
            return false;

        if (uri.Scheme == Uri.UriSchemeHttps)
            return true;

        return uri.Scheme == Uri.UriSchemeHttp && uri.IsLoopback;
    }

    public async Task<JsonElement> PostAsync(string path, object payload, CancellationToken ct)
    {
        using var request = new HttpRequestMessage(HttpMethod.Post, BaseUrl + path)
        {
            Content = new StringContent(
                JsonSerializer.Serialize(payload, JsonOpts), Encoding.UTF8, "application/json")
        };

        return await SendAsync(request, ct).ConfigureAwait(false);
    }

    public async Task<JsonElement> GetAsync(string path, CancellationToken ct)
    {
        using var request = new HttpRequestMessage(HttpMethod.Get, BaseUrl + path);
        return await SendAsync(request, ct).ConfigureAwait(false);
    }

    private async Task<JsonElement> SendAsync(HttpRequestMessage request, CancellationToken ct)
    {
        if (_token.Length > 0)
            request.Headers.TryAddWithoutValidation("Authorization", "Bearer " + _token);

        using var response = await _http.SendAsync(request, ct).ConfigureAwait(false);
        var body = await response.Content.ReadAsStringAsync(ct).ConfigureAwait(false);

        JsonElement root;
        try
        {
            // Cloned because the JsonDocument is released at the end of this block —
            // a JsonElement from it would no longer be readable afterwards.
            using var document = JsonDocument.Parse(string.IsNullOrWhiteSpace(body) ? "{}" : body);
            root = document.RootElement.Clone();
        }
        catch (JsonException)
        {
            throw new DeploymentcenterException(
                "invalid_response",
                $"Antwort war kein JSON (HTTP {(int)response.StatusCode}).",
                response.StatusCode);
        }

        if (IsErrorEnvelope(root, out var code, out var message))
            throw new DeploymentcenterException(code, message, response.StatusCode);

        if (!response.IsSuccessStatusCode)
        {
            throw new DeploymentcenterException(
                "http_error",
                $"Deploymentcenter antwortete HTTP {(int)response.StatusCode}.",
                response.StatusCode);
        }

        return root;
    }

    private static bool IsErrorEnvelope(JsonElement root, out string code, out string message)
    {
        code = "error";
        message = "Unbekannter Fehler.";

        if (root.ValueKind != JsonValueKind.Object)
            return false;

        if (!root.TryGetProperty("status", out var status)
            || status.ValueKind != JsonValueKind.String
            || !string.Equals(status.GetString(), "error", StringComparison.OrdinalIgnoreCase))
        {
            return false;
        }

        if (root.TryGetProperty("error", out var error) && error.ValueKind == JsonValueKind.Object)
        {
            if (error.TryGetProperty("code", out var c) && c.ValueKind == JsonValueKind.String)
                code = c.GetString() ?? code;

            if (error.TryGetProperty("message", out var m) && m.ValueKind == JsonValueKind.String)
                message = m.GetString() ?? message;
        }

        return true;
    }

    public void Dispose()
    {
        if (_ownsHttp)
            _http.Dispose();
    }
}

/// <summary>
/// A call rejected by the Deploymentcenter. <see cref="Code"/> is the stable
/// error code from the envelope (<c>unauthorized</c>, <c>rate_limited</c>, …) — it is
/// meant for evaluation, the text is not.
/// </summary>
public sealed class DeploymentcenterException(string code, string message, HttpStatusCode statusCode)
    : Exception($"{message} [{code}]")
{
    public string Code { get; } = code;

    public HttpStatusCode StatusCode { get; } = statusCode;

    /// <summary>Token is missing, expired or does not cover the necessary right.</summary>
    public bool IsAuthorizationProblem =>
        StatusCode is HttpStatusCode.Unauthorized or HttpStatusCode.Forbidden;
}