using System.Net.Http.Json;
using System.Text.Json;
using Tiku.Application.Auth;

namespace Tiku.Infrastructure.Auth;

public sealed class WechatOAuthClient(HttpClient httpClient) : IWechatOAuthClient
{
    private static readonly Uri WebAccessTokenEndpoint = new("https://api.weixin.qq.com/sns/oauth2/access_token");
    private static readonly Uri WebUserInfoEndpoint = new("https://api.weixin.qq.com/sns/userinfo");
    private static readonly Uri MiniAppCode2SessionEndpoint = new("https://api.weixin.qq.com/sns/jscode2session");

    public async Task<WechatIdentity> ExchangeWebCodeAsync(
        WechatProviderOptions options,
        string code,
        CancellationToken cancellationToken = default)
    {
        var tokenUri = BuildUri(WebAccessTokenEndpoint, new Dictionary<string, string>
        {
            ["appid"] = options.AppId,
            ["secret"] = options.AppSecret,
            ["code"] = code,
            ["grant_type"] = "authorization_code"
        });
        using var tokenDocument = await GetWechatJsonAsync(tokenUri, cancellationToken);
        var token = tokenDocument.RootElement;
        var accessToken = RequiredString(token, "access_token", "wechat_access_token_missing");
        var openId = RequiredString(token, "openid", "wechat_openid_missing");
        var unionId = OptionalString(token, "unionid");

        var userInfoUri = BuildUri(WebUserInfoEndpoint, new Dictionary<string, string>
        {
            ["access_token"] = accessToken,
            ["openid"] = openId,
            ["lang"] = "zh_CN"
        });
        using var userDocument = await GetWechatJsonAsync(userInfoUri, cancellationToken);
        var user = userDocument.RootElement;

        return new WechatIdentity(
            openId,
            OptionalString(user, "unionid") ?? unionId,
            OptionalString(user, "nickname"),
            OptionalString(user, "headimgurl"),
            null,
            user.GetRawText());
    }

    public async Task<WechatIdentity> ExchangeMiniAppCodeAsync(
        WechatProviderOptions options,
        string code,
        CancellationToken cancellationToken = default)
    {
        var uri = BuildUri(MiniAppCode2SessionEndpoint, new Dictionary<string, string>
        {
            ["appid"] = options.AppId,
            ["secret"] = options.AppSecret,
            ["js_code"] = code,
            ["grant_type"] = "authorization_code"
        });
        using var document = await GetWechatJsonAsync(uri, cancellationToken);
        var root = document.RootElement;

        return new WechatIdentity(
            RequiredString(root, "openid", "wechat_openid_missing"),
            OptionalString(root, "unionid"),
            null,
            null,
            RequiredString(root, "session_key", "wechat_session_key_missing"),
            root.GetRawText());
    }

    private async Task<JsonDocument> GetWechatJsonAsync(
        Uri uri,
        CancellationToken cancellationToken)
    {
        using var response = await httpClient.GetAsync(uri, cancellationToken);
        response.EnsureSuccessStatusCode();
        var document = await response.Content.ReadFromJsonAsync<JsonDocument>(cancellationToken)
            ?? throw new InvalidCredentialsException("wechat_empty_response");

        if (document.RootElement.TryGetProperty("errcode", out var errcode) &&
            errcode.ValueKind == JsonValueKind.Number &&
            errcode.GetInt32() != 0)
        {
            throw new InvalidCredentialsException("wechat_code_exchange_failed");
        }

        return document;
    }

    private static Uri BuildUri(Uri endpoint, IReadOnlyDictionary<string, string> query)
    {
        var builder = new UriBuilder(endpoint);
        builder.Query = string.Join(
            '&',
            query.Select(pair =>
                $"{Uri.EscapeDataString(pair.Key)}={Uri.EscapeDataString(pair.Value)}"));
        return builder.Uri;
    }

    private static string RequiredString(JsonElement element, string property, string errorCode)
    {
        return OptionalString(element, property) ?? throw new InvalidCredentialsException(errorCode);
    }

    private static string? OptionalString(JsonElement element, string property)
    {
        return element.TryGetProperty(property, out var value) &&
               value.ValueKind == JsonValueKind.String &&
               !string.IsNullOrWhiteSpace(value.GetString())
            ? value.GetString()!.Trim()
            : null;
    }
}