// <copyright file="GitHubCodeScanningClient.cs" company="StellaOps">
// Copyright (c) StellaOps. Licensed under the AGPL-3.0-or-later.
// </copyright>

using System.IO.Compression;
using System.Net;
using System.Net.Http.Headers;
using System.Text;
using System.Text.Json;
using Microsoft.Extensions.Logging;

namespace StellaOps.Integrations.Plugin.GitHubApp.CodeScanning;

/// <summary>
/// Client for GitHub Code Scanning API.
/// Sprint: SPRINT_20260109_010_002 Task: Implement GitHubCodeScanningClient
/// </summary>
public sealed class GitHubCodeScanningClient : IGitHubCodeScanningClient
{
    private readonly IHttpClientFactory _httpClientFactory;
    private readonly ILogger<GitHubCodeScanningClient> _logger;
    private readonly TimeProvider _timeProvider;

    private static readonly JsonSerializerOptions JsonOptions = new()
    {
        PropertyNameCaseInsensitive = true,
        PropertyNamingPolicy = JsonNamingPolicy.SnakeCaseLower
    };

    /// <summary>
    /// HTTP client name for IHttpClientFactory.
    /// </summary>
    public const string HttpClientName = "GitHubCodeScanning";

    public GitHubCodeScanningClient(
        IHttpClientFactory httpClientFactory,
        ILogger<GitHubCodeScanningClient> logger,
        TimeProvider timeProvider)
    {
        _httpClientFactory = httpClientFactory;
        _logger = logger;
        _timeProvider = timeProvider;
    }

    /// <inheritdoc />
    public async Task<SarifUploadResult> UploadSarifAsync(
        string owner,
        string repo,
        SarifUploadRequest request,
        CancellationToken ct)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(owner);
        ArgumentException.ThrowIfNullOrWhiteSpace(repo);
        ArgumentNullException.ThrowIfNull(request);
        request.Validate();

        _logger.LogInformation(
            "Uploading SARIF to {Owner}/{Repo} for commit {CommitSha}",
            owner, repo, request.CommitSha[..7]);

        // Compress and encode SARIF content
        var compressedSarif = await CompressGzipAsync(request.SarifContent, ct);
        var encodedSarif = Convert.ToBase64String(compressedSarif);

        _logger.LogDebug(
            "SARIF compressed from {OriginalSize} to {CompressedSize} bytes",
            request.SarifContent.Length, compressedSarif.Length);

        // Build request body
        var body = new Dictionary<string, object?>
        {
            ["commit_sha"] = request.CommitSha,
            ["ref"] = request.Ref,
            ["sarif"] = encodedSarif
        };

        if (!string.IsNullOrEmpty(request.CheckoutUri))
            body["checkout_uri"] = request.CheckoutUri;

        if (request.StartedAt.HasValue)
            body["started_at"] = request.StartedAt.Value.ToString("O");

        if (!string.IsNullOrEmpty(request.ToolName))
            body["tool_name"] = request.ToolName;

        var client = _httpClientFactory.CreateClient(HttpClientName);
        var url = $"/repos/{owner}/{repo}/code-scanning/sarifs";

        var content = new StringContent(
            JsonSerializer.Serialize(body, JsonOptions),
            Encoding.UTF8,
            "application/json");

        var response = await client.PostAsync(url, content, ct);
        await EnsureSuccessStatusCodeAsync(response, "upload SARIF", ct);

        var responseBody = await response.Content.ReadAsStringAsync(ct);
        var uploadResponse = JsonSerializer.Deserialize<GitHubSarifUploadResponse>(responseBody, JsonOptions)
            ?? throw new InvalidOperationException("Failed to parse upload response");

        _logger.LogInformation("SARIF uploaded successfully. ID: {SarifId}", uploadResponse.Id);

        return SarifUploadResult.FromApiResponse(uploadResponse);
    }

    /// <inheritdoc />
    public async Task<SarifUploadStatus> GetUploadStatusAsync(
        string owner,
        string repo,
        string sarifId,
        CancellationToken ct)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(owner);
        ArgumentException.ThrowIfNullOrWhiteSpace(repo);
        ArgumentException.ThrowIfNullOrWhiteSpace(sarifId);

        var client = _httpClientFactory.CreateClient(HttpClientName);
        var url = $"/repos/{owner}/{repo}/code-scanning/sarifs/{sarifId}";

        var response = await client.GetAsync(url, ct);
        await EnsureSuccessStatusCodeAsync(response, "get upload status", ct);

        var responseBody = await response.Content.ReadAsStringAsync(ct);
        var statusResponse = JsonSerializer.Deserialize<GitHubSarifStatusResponse>(responseBody, JsonOptions)
            ?? throw new InvalidOperationException("Failed to parse status response");

        return SarifUploadStatus.FromApiResponse(statusResponse);
    }

    /// <inheritdoc />
    public async Task<SarifUploadStatus> WaitForProcessingAsync(
        string owner,
        string repo,
        string sarifId,
        TimeSpan timeout,
        CancellationToken ct)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(owner);
        ArgumentException.ThrowIfNullOrWhiteSpace(repo);
        ArgumentException.ThrowIfNullOrWhiteSpace(sarifId);

        var deadline = _timeProvider.GetUtcNow() + timeout;
        var delay = TimeSpan.FromSeconds(2);
        const int maxDelaySeconds = 30;

        _logger.LogInformation(
            "Waiting for SARIF {SarifId} processing (timeout: {Timeout})",
            sarifId, timeout);

        while (_timeProvider.GetUtcNow() < deadline)
        {
            ct.ThrowIfCancellationRequested();

            var status = await GetUploadStatusAsync(owner, repo, sarifId, ct);

            if (status.IsComplete)
            {
                _logger.LogInformation(
                    "SARIF {SarifId} processing complete. Status: {Status}",
                    sarifId, status.Status);
                return status;
            }

            _logger.LogDebug("SARIF {SarifId} still processing, waiting {Delay}...", sarifId, delay);
            await Task.Delay(delay, ct);

            // Exponential backoff with max
            delay = TimeSpan.FromSeconds(Math.Min(delay.TotalSeconds * 1.5, maxDelaySeconds));
        }

        throw new TimeoutException($"SARIF processing did not complete within {timeout}");
    }

    /// <inheritdoc />
    public async Task<IReadOnlyList<CodeScanningAlert>> ListAlertsAsync(
        string owner,
        string repo,
        AlertFilter? filter,
        CancellationToken ct)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(owner);
        ArgumentException.ThrowIfNullOrWhiteSpace(repo);

        var client = _httpClientFactory.CreateClient(HttpClientName);
        var queryString = filter?.ToQueryString() ?? "";
        var url = $"/repos/{owner}/{repo}/code-scanning/alerts{queryString}";

        var response = await client.GetAsync(url, ct);
        await EnsureSuccessStatusCodeAsync(response, "list alerts", ct);

        var responseBody = await response.Content.ReadAsStringAsync(ct);
        var alertResponses = JsonSerializer.Deserialize<GitHubAlertResponse[]>(responseBody, JsonOptions)
            ?? [];

        return alertResponses.Select(CodeScanningAlert.FromApiResponse).ToList();
    }

    /// <inheritdoc />
    public async Task<CodeScanningAlert> GetAlertAsync(
        string owner,
        string repo,
        int alertNumber,
        CancellationToken ct)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(owner);
        ArgumentException.ThrowIfNullOrWhiteSpace(repo);

        var client = _httpClientFactory.CreateClient(HttpClientName);
        var url = $"/repos/{owner}/{repo}/code-scanning/alerts/{alertNumber}";

        var response = await client.GetAsync(url, ct);
        await EnsureSuccessStatusCodeAsync(response, "get alert", ct);

        var responseBody = await response.Content.ReadAsStringAsync(ct);
        var alertResponse = JsonSerializer.Deserialize<GitHubAlertResponse>(responseBody, JsonOptions)
            ?? throw new InvalidOperationException("Failed to parse alert response");

        return CodeScanningAlert.FromApiResponse(alertResponse);
    }

    /// <inheritdoc />
    public async Task<CodeScanningAlert> UpdateAlertAsync(
        string owner,
        string repo,
        int alertNumber,
        AlertUpdate update,
        CancellationToken ct)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(owner);
        ArgumentException.ThrowIfNullOrWhiteSpace(repo);
        ArgumentNullException.ThrowIfNull(update);
        update.Validate();

        _logger.LogInformation(
            "Updating alert {AlertNumber} in {Owner}/{Repo} to state {State}",
            alertNumber, owner, repo, update.State);

        var client = _httpClientFactory.CreateClient(HttpClientName);
        var url = $"/repos/{owner}/{repo}/code-scanning/alerts/{alertNumber}";

        var body = new Dictionary<string, object?>
        {
            ["state"] = update.State
        };

        if (!string.IsNullOrEmpty(update.DismissedReason))
            body["dismissed_reason"] = update.DismissedReason;

        if (!string.IsNullOrEmpty(update.DismissedComment))
            body["dismissed_comment"] = update.DismissedComment;

        var content = new StringContent(
            JsonSerializer.Serialize(body, JsonOptions),
            Encoding.UTF8,
            "application/json");

        var request = new HttpRequestMessage(HttpMethod.Patch, url) { Content = content };
        var response = await client.SendAsync(request, ct);
        await EnsureSuccessStatusCodeAsync(response, "update alert", ct);

        var responseBody = await response.Content.ReadAsStringAsync(ct);
        var alertResponse = JsonSerializer.Deserialize<GitHubAlertResponse>(responseBody, JsonOptions)
            ?? throw new InvalidOperationException("Failed to parse alert response");

        return CodeScanningAlert.FromApiResponse(alertResponse);
    }

    private static async Task<byte[]> CompressGzipAsync(string content, CancellationToken ct)
    {
        var bytes = Encoding.UTF8.GetBytes(content);
        using var output = new MemoryStream();
        await using (var gzip = new GZipStream(output, CompressionLevel.Optimal, leaveOpen: true))
        {
            await gzip.WriteAsync(bytes, ct);
        }
        return output.ToArray();
    }

    private async Task EnsureSuccessStatusCodeAsync(HttpResponseMessage response, string operation, CancellationToken ct)
    {
        if (response.IsSuccessStatusCode)
            return;

        var body = await response.Content.ReadAsStringAsync(ct);

        var errorMessage = response.StatusCode switch
        {
            HttpStatusCode.Unauthorized => "GitHub authentication failed. Check your token.",
            HttpStatusCode.Forbidden => "Access forbidden. Check repository permissions.",
            HttpStatusCode.NotFound => "Repository or resource not found.",
            HttpStatusCode.UnprocessableEntity => $"Validation failed: {body}",
            _ => $"GitHub API error ({response.StatusCode}): {body}"
        };

        _logger.LogError("Failed to {Operation}: {Error}", operation, errorMessage);
        throw new GitHubApiException(errorMessage, response.StatusCode);
    }
}

/// <summary>
/// Exception for GitHub API errors.
/// </summary>
public sealed class GitHubApiException : Exception
{
    public HttpStatusCode StatusCode { get; }

    public GitHubApiException(string message, HttpStatusCode statusCode)
        : base(message)
    {
        StatusCode = statusCode;
    }
}