namespace Unosquare.RaspberryIO.Native
{
    using Swan;
    using System;
    using System.Runtime.InteropServices;
    using System.Text;

    /// <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(int error)
        {
            if (!Runtime.IsUsingMonoRuntime) return StrError(error);

            try
            {
                var buffer = new StringBuilder(256);
                var result = Strerror(error, buffer, (ulong)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 int Chmod(string filename, uint 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 int StringToInteger(string numberString, IntPtr endPointer, int 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 int Write(int fd, byte[] buffer, int 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 int Uname(out SystemName name);
        
        [DllImport(LibCLibrary, EntryPoint = "strerror", SetLastError = true)]
        private static extern string StrError(int errnum);

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

        #endregion
    }
}