using System;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Text.Json;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;
using StellaOps.Auth.Abstractions;
using StellaOps.Auth.Client;
using StellaOps.Cli.Extensions;
using StellaOps.Cli.Services.Models;

namespace StellaOps.Cli.Services;

/// <summary>
/// HTTP client for VEX observation queries.
/// Per CLI-LNM-22-002.
/// </summary>
internal sealed class VexObservationsClient : IVexObservationsClient
{
    private readonly HttpClient _httpClient;
    private readonly IStellaOpsTokenClient? _tokenClient;
    private readonly ILogger<VexObservationsClient> _logger;
    private string? _cachedToken;
    private DateTimeOffset _tokenExpiry;

    private static readonly JsonSerializerOptions SerializerOptions = new(JsonSerializerDefaults.Web)
    {
        PropertyNameCaseInsensitive = true
    };

    public VexObservationsClient(
        HttpClient httpClient,
        ILogger<VexObservationsClient> logger,
        IStellaOpsTokenClient? tokenClient = null)
    {
        _httpClient = httpClient ?? throw new ArgumentNullException(nameof(httpClient));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        _tokenClient = tokenClient;
    }

    public async Task<VexObservationResponse> GetObservationsAsync(
        VexObservationQuery query,
        CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(query);

        await EnsureAuthorizationAsync(cancellationToken).ConfigureAwait(false);

        var requestUri = BuildObservationRequestUri(query);
        _logger.LogDebug("Fetching VEX observations from {Uri}", requestUri);

        using var response = await _httpClient.GetAsync(requestUri, cancellationToken).ConfigureAwait(false);

        if (!response.IsSuccessStatusCode)
        {
            var errorBody = await response.Content.ReadAsStringAsync(cancellationToken).ConfigureAwait(false);
            _logger.LogError("VEX observations request failed: {StatusCode} - {Body}",
                response.StatusCode, errorBody);
            throw new HttpRequestException($"Failed to fetch VEX observations: {response.StatusCode}");
        }

        var content = await response.Content.ReadAsStringAsync(cancellationToken).ConfigureAwait(false);
        return JsonSerializer.Deserialize<VexObservationResponse>(content, SerializerOptions)
            ?? new VexObservationResponse();
    }

    public async Task<VexLinksetResponse> GetLinksetAsync(
        VexLinksetQuery query,
        CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(query);

        await EnsureAuthorizationAsync(cancellationToken).ConfigureAwait(false);

        var requestUri = BuildLinksetRequestUri(query);
        _logger.LogDebug("Fetching VEX linkset from {Uri}", requestUri);

        using var response = await _httpClient.GetAsync(requestUri, cancellationToken).ConfigureAwait(false);

        if (!response.IsSuccessStatusCode)
        {
            var errorBody = await response.Content.ReadAsStringAsync(cancellationToken).ConfigureAwait(false);
            _logger.LogError("VEX linkset request failed: {StatusCode} - {Body}",
                response.StatusCode, errorBody);
            throw new HttpRequestException($"Failed to fetch VEX linkset: {response.StatusCode}");
        }

        var content = await response.Content.ReadAsStringAsync(cancellationToken).ConfigureAwait(false);
        return JsonSerializer.Deserialize<VexLinksetResponse>(content, SerializerOptions)
            ?? new VexLinksetResponse();
    }

    public async Task<VexObservation?> GetObservationByIdAsync(
        string tenant,
        string observationId,
        CancellationToken cancellationToken)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(tenant);
        ArgumentException.ThrowIfNullOrWhiteSpace(observationId);

        await EnsureAuthorizationAsync(cancellationToken).ConfigureAwait(false);

        var requestUri = $"api/v1/tenants/{Uri.EscapeDataString(tenant)}/vex/observations/{Uri.EscapeDataString(observationId)}";
        _logger.LogDebug("Fetching VEX observation {ObservationId} from {Uri}", observationId, requestUri);

        using var response = await _httpClient.GetAsync(requestUri, cancellationToken).ConfigureAwait(false);

        if (response.StatusCode == HttpStatusCode.NotFound)
        {
            return null;
        }

        if (!response.IsSuccessStatusCode)
        {
            var errorBody = await response.Content.ReadAsStringAsync(cancellationToken).ConfigureAwait(false);
            _logger.LogError("VEX observation request failed: {StatusCode} - {Body}",
                response.StatusCode, errorBody);
            throw new HttpRequestException($"Failed to fetch VEX observation: {response.StatusCode}");
        }

        var content = await response.Content.ReadAsStringAsync(cancellationToken).ConfigureAwait(false);
        return JsonSerializer.Deserialize<VexObservation>(content, SerializerOptions);
    }

    private async Task EnsureAuthorizationAsync(CancellationToken cancellationToken)
    {
        if (_tokenClient is null)
        {
            return;
        }

        if (!string.IsNullOrWhiteSpace(_cachedToken) && DateTimeOffset.UtcNow < _tokenExpiry)
        {
            _httpClient.DefaultRequestHeaders.Authorization =
                new AuthenticationHeaderValue("Bearer", _cachedToken);
            return;
        }

        try
        {
            var tokenResult = await _tokenClient.GetAccessTokenAsync(
                StellaOpsScopes.VexRead,
                cancellationToken).ConfigureAwait(false);

            if (!string.IsNullOrWhiteSpace(tokenResult.AccessToken))
            {
                _cachedToken = tokenResult.AccessToken;
                _tokenExpiry = DateTimeOffset.UtcNow.AddMinutes(55);
                _httpClient.DefaultRequestHeaders.Authorization =
                    new AuthenticationHeaderValue("Bearer", _cachedToken);
            }
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "Failed to acquire token for VEX API access.");
        }
    }

    private static string BuildObservationRequestUri(VexObservationQuery query)
    {
        var sb = new StringBuilder();
        sb.Append($"api/v1/tenants/{Uri.EscapeDataString(query.Tenant)}/vex/observations?");

        foreach (var vulnId in query.VulnerabilityIds)
        {
            sb.Append($"vulnerabilityId={Uri.EscapeDataString(vulnId)}&");
        }

        foreach (var productKey in query.ProductKeys)
        {
            sb.Append($"productKey={Uri.EscapeDataString(productKey)}&");
        }

        foreach (var purl in query.Purls)
        {
            sb.Append($"purl={Uri.EscapeDataString(purl)}&");
        }

        foreach (var cpe in query.Cpes)
        {
            sb.Append($"cpe={Uri.EscapeDataString(cpe)}&");
        }

        foreach (var status in query.Statuses)
        {
            sb.Append($"status={Uri.EscapeDataString(status)}&");
        }

        foreach (var providerId in query.ProviderIds)
        {
            sb.Append($"providerId={Uri.EscapeDataString(providerId)}&");
        }

        if (query.Limit.HasValue)
        {
            sb.Append($"limit={query.Limit.Value}&");
        }

        if (!string.IsNullOrWhiteSpace(query.Cursor))
        {
            sb.Append($"cursor={Uri.EscapeDataString(query.Cursor)}&");
        }

        return sb.ToString().TrimEnd('&', '?');
    }

    private static string BuildLinksetRequestUri(VexLinksetQuery query)
    {
        var sb = new StringBuilder();
        sb.Append($"api/v1/tenants/{Uri.EscapeDataString(query.Tenant)}/vex/linkset/{Uri.EscapeDataString(query.VulnerabilityId)}?");

        foreach (var productKey in query.ProductKeys)
        {
            sb.Append($"productKey={Uri.EscapeDataString(productKey)}&");
        }

        foreach (var purl in query.Purls)
        {
            sb.Append($"purl={Uri.EscapeDataString(purl)}&");
        }

        foreach (var status in query.Statuses)
        {
            sb.Append($"status={Uri.EscapeDataString(status)}&");
        }

        return sb.ToString().TrimEnd('&', '?');
    }
}