using System.Net.Http.Headers;
using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;
using Api.Services.Contracts.Rag;
using Api.Settings;
using Microsoft.Extensions.Options;

namespace Api.Services.Rag;

public sealed class OpenAiRagClient : IAiRagClient
{
    private readonly HttpClient _httpClient;
    private readonly OpenAiSettings _settings;
    private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web)
    {
        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull
    };

    public OpenAiRagClient(HttpClient httpClient, IOptions<OpenAiSettings> options)
    {
        _httpClient = httpClient;
        _settings = options.Value;

        if (!string.IsNullOrWhiteSpace(_settings.ApiKey))
        {
            _httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", _settings.ApiKey);
        }

        _httpClient.Timeout = TimeSpan.FromSeconds(Math.Max(15, _settings.TimeoutSeconds));
        _httpClient.BaseAddress = new Uri("https://api.openai.com/v1/");
    }

    public async Task<float[]> CreateEmbeddingAsync(string input, CancellationToken ct)
    {
        EnsureConfigured();
        var payload = new { model = _settings.EmbeddingModel, input };
        using var response = await _httpClient.PostAsync("embeddings", ToJson(payload), ct);
        var json = await response.Content.ReadAsStringAsync(ct);
        if (!response.IsSuccessStatusCode)
        {
            throw new InvalidOperationException($"OpenAI embeddings request failed: {(int)response.StatusCode} {json}");
        }

        using var document = JsonDocument.Parse(json);
        var embedding = document.RootElement.GetProperty("data")[0].GetProperty("embedding");
        var result = new float[embedding.GetArrayLength()];
        var i = 0;
        foreach (var value in embedding.EnumerateArray())
        {
            result[i++] = value.GetSingle();
        }
        return result;
    }

    public async Task<string> CreateChatCompletionAsync(string systemPrompt, string userPrompt, CancellationToken ct)
    {
        EnsureConfigured();
        var payload = new
        {
            model = _settings.ChatModel,
            temperature = 0.2,
            response_format = new { type = "json_object" },
            messages = new[]
            {
                new { role = "system", content = systemPrompt },
                new { role = "user", content = userPrompt }
            }
        };

        using var response = await _httpClient.PostAsync("chat/completions", ToJson(payload), ct);
        var json = await response.Content.ReadAsStringAsync(ct);
        if (!response.IsSuccessStatusCode)
        {
            throw new InvalidOperationException($"OpenAI chat request failed: {(int)response.StatusCode} {json}");
        }

        using var document = JsonDocument.Parse(json);
        return document.RootElement
            .GetProperty("choices")[0]
            .GetProperty("message")
            .GetProperty("content")
            .GetString() ?? "{}";
    }

    private void EnsureConfigured()
    {
        if (string.IsNullOrWhiteSpace(_settings.ApiKey))
        {
            throw new InvalidOperationException("OpenAI API key is not configured. Set OpenAI__ApiKey.");
        }
    }

    private static StringContent ToJson<T>(T payload) => new(
        JsonSerializer.Serialize(payload, JsonOptions),
        Encoding.UTF8,
        "application/json"
    );
}