using System.Net.Http.Headers;

namespace Service;

public interface IOpenAiService
{
    Task<string?> ChatAsync(string systemPrompt, string userPrompt);
}

public class OpenAiService(
    IOptions<AISettings> aiSettings,
    ILogger<OpenAiService> logger
) : IOpenAiService
{
    public async Task<string?> ChatAsync(string systemPrompt, string userPrompt)
    {
        var cfg = aiSettings.Value;
        if (string.IsNullOrWhiteSpace(cfg.Endpoint) || 
            string.IsNullOrWhiteSpace(cfg.Key) || 
            string.IsNullOrWhiteSpace(cfg.Model))
        {
            logger.LogWarning("未配置 OpenAI/DeepSeek 接口，无法调用 AI");
            return null;
        }

        using var http = new HttpClient();
        http.Timeout = TimeSpan.FromSeconds(15);
        http.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", cfg.Key);

        var payload = new
        {
            model = cfg.Model,
            temperature = 0,
            messages = new object[]
            {
                new { role = "system", content = systemPrompt },
                new { role = "user", content = userPrompt }
            }
        };

        var url = cfg.Endpoint.TrimEnd('/') + "/chat/completions";
        var json = JsonSerializer.Serialize(payload);
        using var content = new StringContent(json, Encoding.UTF8, "application/json");
        
        try
        {
            using var resp = await http.PostAsync(url, content);
            if (!resp.IsSuccessStatusCode)
            {
                var err = await resp.Content.ReadAsStringAsync();
                throw new InvalidOperationException($"AI接口调用失败: {(int)resp.StatusCode} {resp.ReasonPhrase}, {err}");
            }

            var respText = await resp.Content.ReadAsStringAsync();

            using var doc = JsonDocument.Parse(respText);
            var root = doc.RootElement;
            var contentText = root.GetProperty("choices")[0]
                .GetProperty("message")
                .GetProperty("content")
                .GetString();

            return contentText;
        }
        catch (Exception ex)
        {
            logger.LogError(ex, "AI 调用失败");
            throw;
        }
    }
}