using System.Text.Json;
using MoShiro.Backend.Application;

namespace MoShiro.Backend;

/// <summary>
/// 用 IP 归属查询服务（<c>GET {地址}/lookup?ip=…</c>）查国家和运营商。
/// 失败（超时、网络不通、服务返回错误）一律返回 null，不往外抛：展示信息没有也不影响别的功能。
/// </summary>
public sealed class HttpGeoLookup : IGeoLookup, IDisposable
{
    private readonly HttpClient _http;

    public HttpGeoLookup(string baseUrl)
    {
        _http = new HttpClient { BaseAddress = new Uri(baseUrl.TrimEnd('/') + "/"), Timeout = TimeSpan.FromSeconds(6) };
        _http.DefaultRequestHeaders.UserAgent.ParseAdd("MoShiro");
    }

    public async ValueTask<GeoInfo?> LookupAsync(string host, CancellationToken ct)
    {
        try
        {
            using HttpResponseMessage response = await _http.GetAsync("lookup?ip=" + Uri.EscapeDataString(host), ct);
            if (!response.IsSuccessStatusCode)
            {
                return null;
            }

            using JsonDocument doc = await JsonDocument.ParseAsync(await response.Content.ReadAsStreamAsync(ct), cancellationToken: ct);
            return Parse(doc.RootElement);
        }
        catch (Exception ex) when (ex is HttpRequestException or TaskCanceledException or JsonException or InvalidOperationException)
        {
            return null;
        }
    }

    /// <summary>只取国家代码、ASN、组织名；其余字段（城市、经纬度、网段……）一概不读。</summary>
    public static GeoInfo? Parse(JsonElement root)
    {
        if (root.TryGetProperty("found", out JsonElement found) && found.ValueKind == JsonValueKind.False)
        {
            return null;
        }

        bool isPrivate = root.TryGetProperty("is_private", out JsonElement priv) && priv.ValueKind == JsonValueKind.True;
        string? country = root.TryGetProperty("country_region", out JsonElement region) && region.TryGetProperty("iso_code", out JsonElement code) && code.ValueKind == JsonValueKind.String ? code.GetString() : null;
        int? asn = null;
        string? organization = null;
        if (root.TryGetProperty("network", out JsonElement network))
        {
            if (network.TryGetProperty("asn", out JsonElement asnValue) && asnValue.TryGetInt32(out int number))
            {
                asn = number;
            }

            string? isp = network.TryGetProperty("isp", out JsonElement ispValue) && ispValue.ValueKind == JsonValueKind.String ? ispValue.GetString() : null;
            string? org = network.TryGetProperty("organization", out JsonElement orgValue) && orgValue.ValueKind == JsonValueKind.String ? orgValue.GetString() : null;
            organization = string.IsNullOrWhiteSpace(isp) ? org : isp;
        }

        return new GeoInfo(country, asn, organization, isPrivate);
    }

    public void Dispose() => _http.Dispose();
}

/// <summary>不查（<c>MoShiro__GeoLookupUrl</c> 留空）。</summary>
public sealed class NoGeoLookup : IGeoLookup
{
    public ValueTask<GeoInfo?> LookupAsync(string host, CancellationToken ct) => ValueTask.FromResult<GeoInfo?>(null);
}