using System.Net.Http.Headers;
using System.Text.Json;

namespace AnchorCli.Providers;

/// <summary>
/// Generic token extractor for any OpenAI-compatible endpoint.
/// Tries common header names and JSON body parsing.
/// </summary>
internal sealed class GenericTokenExtractor : ITokenExtractor
{
    public string ProviderName => "Generic";

    public (int inputTokens, int outputTokens)? ExtractTokens(HttpResponseHeaders headers, string? responseBody)
    {
        // Try various common header names
        var headerNames = new[] {
            "x-total-tokens",
            "x-ai-response-tokens",
            "x-tokens",
            "x-prompt-tokens",
            "x-completion-tokens"
        };

        foreach (var headerName in headerNames)
        {
            if (headers.TryGetValues(headerName, out var values))
            {
                if (int.TryParse(values.FirstOrDefault(), out var tokens))
                {
                    // Assume all tokens are output if we can't determine split
                    return (0, tokens);
                }
            }
        }

        // Fallback: try parsing from response body JSON
        if (!string.IsNullOrEmpty(responseBody))
        {
            try
            {
                using var doc = JsonDocument.Parse(responseBody);
                var root = doc.RootElement;

                // Try standard OpenAI format: usage.prompt_tokens, usage.completion_tokens
                if (root.TryGetProperty("usage", out var usage))
                {
                    var prompt = usage.TryGetProperty("prompt_tokens", out var p) ? p.GetInt32() : 0;
                    var completion = usage.TryGetProperty("completion_tokens", out var c) ? c.GetInt32() : 0;

                    if (prompt > 0 || completion > 0)
                    {
                        return (prompt, completion);
                    }
                }
            }
            catch
            {
                // Ignore parsing errors
            }
        }

        return null;
    }

    public int? ExtractLatency(HttpResponseHeaders headers)
    {
        // Try various common latency headers
        var headerNames = new[] {
            "x-response-time",
            "x-response-timing",
            "x-latency-ms",
            "x-duration-ms"
        };

        foreach (var headerName in headerNames)
        {
            if (headers.TryGetValues(headerName, out var values))
            {
                if (int.TryParse(values.FirstOrDefault(), out var latency))
                {
                    return latency;
                }
            }
        }

        return null;
    }
}