using System;
using System.IO;
using System.Text;

namespace DrillTools
{
    /// <summary>
    /// 钻带/参数文件统一读取入口。
    /// 默认按 ANSI/GB2312(code page 936) 解码，等价于历史 `cmd type` 实现的字节透传语义，
    /// 但不经过命令行，因此路径中的特殊字符（如 `(` `)` `&` `%` `!` `^` `@` 空格）不会影响读取。
    /// </summary>
    internal static class AnsiFileReader
    {
        private const int Gb2312CodePage = 936;

        public static string ReadAllText(string filePath)
        {
            return ReadAllText(filePath, CreateAnsiEncoding());
        }

        public static string ReadAllText(string filePath, Encoding encoding)
        {
            string normalizedPath = ValidateAndNormalizePath(filePath);

            try
            {
                using var stream = new FileStream(normalizedPath, FileMode.Open, FileAccess.Read, FileShare.Read);

                // detectEncodingFromByteOrderMarks: true 与历史实现保持一致：
                // 原先经 Process.StandardOutput(StreamReader) 解码，默认会探测 BOM，
                // 因此带 UTF-8/UTF-16 BOM 的文件解码结果保持不变。
                using var reader = new StreamReader(stream, encoding, detectEncodingFromByteOrderMarks: true);
                return reader.ReadToEnd();
            }
            catch (Exception ex) when (ex is IOException || ex is UnauthorizedAccessException)
            {
                throw new InvalidOperationException($"读取文件失败：{normalizedPath}（{ex.Message}）", ex);
            }
        }

        private static string ValidateAndNormalizePath(string filePath)
        {
            if (string.IsNullOrWhiteSpace(filePath))
                throw new ArgumentException("文件路径不能为空", nameof(filePath));

            string normalizedPath = Path.GetFullPath(filePath);

            if (!File.Exists(normalizedPath))
                throw new FileNotFoundException($"文件不存在：{normalizedPath}", normalizedPath);

            return normalizedPath;
        }

        private static Encoding CreateAnsiEncoding()
        {
            return Encoding.GetEncoding(Gb2312CodePage);
        }
    }
}