using Unosquare.Swan;
using System;
using System.Runtime.InteropServices;
using System.Text;

namespace Unosquare.RaspberryIO.Native {
  /// <summary>
  /// Provides standard libc calls using platform-invoke
  /// </summary>
  internal static class Standard {
    internal const String LibCLibrary = "libc";

    #region LibC Calls

    /// <summary>
    /// Strerrors the specified error.
    /// </summary>
    /// <param name="error">The error.</param>
    /// <returns></returns>
    public static String Strerror(Int32 error) {
      if(!Runtime.IsUsingMonoRuntime) {
        return StrError(error);
      }

      try {
        StringBuilder buffer = new StringBuilder(256);
        Int32 result = Strerror(error, buffer, (UInt64)buffer.Capacity);
        return (result != -1) ? buffer.ToString() : null;
      } catch(EntryPointNotFoundException) {
        return null;
      }
    }

    /// <summary>
    /// Changes file permissions on a Unix file system
    /// </summary>
    /// <param name="filename">The filename.</param>
    /// <param name="mode">The mode.</param>
    /// <returns>The result</returns>
    [DllImport(LibCLibrary, EntryPoint = "chmod", SetLastError = true)]
    public static extern Int32 Chmod(String filename, UInt32 mode);

    /// <summary>
    /// Converts a string to a 32 bit integer. Use endpointer as IntPtr.Zero
    /// </summary>
    /// <param name="numberString">The number string.</param>
    /// <param name="endPointer">The end pointer.</param>
    /// <param name="numberBase">The number base.</param>
    /// <returns>The result</returns>
    [DllImport(LibCLibrary, EntryPoint = "strtol", SetLastError = true)]
    public static extern Int32 StringToInteger(String numberString, IntPtr endPointer, Int32 numberBase);

    /// <summary>
    /// The write() function attempts to write nbytes from buffer to the file associated with handle. On text files, it expands each LF to a CR/LF.
    /// The function returns the number of bytes written to the file. A return value of -1 indicates an error, with errno set appropriately.
    /// </summary>
    /// <param name="fd">The fd.</param>
    /// <param name="buffer">The buffer.</param>
    /// <param name="count">The count.</param>
    /// <returns>The result</returns>
    [DllImport(LibCLibrary, EntryPoint = "write", SetLastError = true)]
    public static extern Int32 Write(Int32 fd, Byte[] buffer, Int32 count);

    /// <summary>
    /// Fills in the structure with information about the system.
    /// </summary>
    /// <param name="name">The name.</param>
    /// <returns>The result</returns>
    [DllImport(LibCLibrary, EntryPoint = "uname", SetLastError = true)]
    public static extern Int32 Uname(out SystemName name);

    [DllImport(LibCLibrary, EntryPoint = "strerror", SetLastError = true)]
    private static extern String StrError(Int32 errnum);

    [DllImport("MonoPosixHelper", EntryPoint = "Mono_Posix_Syscall_strerror_r", SetLastError = true)]
    private static extern Int32 Strerror(Int32 error, [Out] StringBuilder buffer, UInt64 length);

    #endregion
  }
}