using System;
using System.Collections.Generic;
using System.IO;

namespace StellaOps.Scanner.Analyzers.Lang.Go.Internal;

internal static class GoBinaryScanner
{
    private static readonly ReadOnlyMemory<byte> BuildInfoMagic = new byte[]
    {
        0xFF, (byte)' ', (byte)'G', (byte)'o', (byte)' ', (byte)'b', (byte)'u', (byte)'i', (byte)'l', (byte)'d', (byte)'i', (byte)'n', (byte)'f', (byte)':'
    };

    public static IEnumerable<string> EnumerateCandidateFiles(string rootPath)
    {
        var enumeration = new EnumerationOptions
        {
            RecurseSubdirectories = true,
            IgnoreInaccessible = true,
            AttributesToSkip = FileAttributes.Device | FileAttributes.ReparsePoint,
            MatchCasing = MatchCasing.CaseSensitive,
        };

        foreach (var path in Directory.EnumerateFiles(rootPath, "*", enumeration))
        {
            yield return path;
        }
    }

    public static bool TryReadBuildInfo(string filePath, out string? goVersion, out string? moduleData)
    {
        goVersion = null;
        moduleData = null;

        try
        {
            var info = new FileInfo(filePath);
            if (!info.Exists || info.Length < 64 || info.Length > 128 * 1024 * 1024)
            {
                return false;
            }

            var data = File.ReadAllBytes(filePath);
            var span = new ReadOnlySpan<byte>(data);
            var offset = span.IndexOf(BuildInfoMagic.Span);
            if (offset < 0)
            {
                return false;
            }

            var view = span[offset..];
            return GoBuildInfoDecoder.TryDecode(view, out goVersion, out moduleData);
        }
        catch (IOException)
        {
            return false;
        }
        catch (UnauthorizedAccessException)
        {
            return false;
        }
    }
}