using System.Text.Json;

namespace Sdt.Config;

public static class ConfigLoader
{
    private static readonly JsonSerializerOptions JsonOptions = new()
    {
        PropertyNameCaseInsensitive = true,
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
        AllowTrailingCommas = true,
        ReadCommentHandling = JsonCommentHandling.Skip,
    };

    /// <summary>
    /// Walks up from <paramref name="startDir"/> (or CWD) until it finds devtool.json.
    /// Returns null if not found.
    /// </summary>
    public static (DevToolConfig Config, string ProjectRoot)? FindAndLoad(string? startDir = null)
    {
        var dir = new DirectoryInfo(startDir ?? Directory.GetCurrentDirectory());
        while (dir is not null)
        {
            var candidate = Path.Combine(dir.FullName, "devtool.json");
            if (File.Exists(candidate))
            {
                try
                {
                    var json = File.ReadAllText(candidate);
                    var config = JsonSerializer.Deserialize<DevToolConfig>(json, JsonOptions)
                        ?? throw new InvalidOperationException("devtool.json deserialized to null.");
                    return (config, dir.FullName);
                }
                catch (Exception ex)
                {
                    throw new InvalidOperationException(
                        $"Failed to parse devtool.json at {candidate}: {ex.Message}", ex);
                }
            }
            dir = dir.Parent!;
        }
        return null;
    }
}