#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

bool writeall(int fd, const void* buffer, size_t len)
{
	const char* buf = (const char*) buffer;
	while ( len )
	{
		ssize_t byteswritten = write(fd, buf, len);
		if ( byteswritten < 0 ) { return false; }
		buf += byteswritten;
		len -= byteswritten;
	}

	return true;
}

const char* basename(const char* path)
{
	size_t len = strlen(path);
	while ( len-- ) { if ( path[len] == '/' ) { return path + len + 1; } }
	return path;
}

int main(int argc, char* argv[])
{
	if ( argc != 3 ) { printf("usage: %s <from> <to>\n", argv[0]); return 0; }

	const char* frompath = argv[1];
	const char* topath = argv[2];
	char tobuffer[256];

	int fromfd = open(frompath, O_RDONLY);
	if ( fromfd < 0 ) { printf("%s: %s: %s\n", argv[0], frompath, strerror(errno)); return 1; }

	int tofd = open(topath, O_WRONLY | O_TRUNC | O_CREAT, 0777);
	if ( tofd < 0 )
	{
		if ( errno == EISDIR )
		{
			strcpy(tobuffer, topath);
			if ( tobuffer[strlen(tobuffer)-1] != '/' ) { strcat(tobuffer, "/"); }
			strcat(tobuffer, basename(frompath));
			topath = tobuffer;
			tofd = open(topath, O_WRONLY | O_TRUNC | O_CREAT, 0777);
		}

		if ( tofd < 0 )
		{
			printf("%s: %s: %s\n", argv[0], topath, strerror(errno));
			return 1;
		}
	}

	while ( true )
	{
		const size_t BUFFER_SIZE = 4096;
		char buffer[BUFFER_SIZE];
		ssize_t bytesread = read(fromfd, buffer, BUFFER_SIZE);
		if ( bytesread < 0 ) { printf("%s: %s: %s\n", argv[0], frompath, strerror(errno)); return 1; }
		if ( bytesread == 0 ) { return 0; }
		if ( !writeall(tofd, buffer, bytesread) ) { printf("%s: %s: %s\n", argv[0], topath, strerror(errno)); return 1; }
	}
}