/*
 * Loader Implementation
 *
 * 2018, Operating Systems
 */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>
#include "exec_parser.h"
#define page_size sysconf(_SC_PAGE_SIZE)

static so_exec_t *exec;
static int fd;

static void* sigsegv_handler(int signum, siginfo_t *info, void *ucontext)
{
	int i;

	for (i = 0; i < exec->segments_no; ++i) {

		int addr_to_map = (int)info->si_addr;

		if (addr_to_map < exec->segments[i].vaddr +
			exec->segments[i].mem_size
			&& addr_to_map >= exec->segments[i].vaddr) {

			if (exec->segments[i].data == NULL) {
				int nr = exec->segments[i].mem_size / page_size;

				exec->segments[i].data =
					(int *)calloc(nr + 1, sizeof(int));
			}

			int addr = exec->segments[i].vaddr;
			int page_count = 0;

			while (addr + page_size <= addr_to_map) {
				addr += page_size;
				page_count++;
			}

			int *p = exec->segments[i].data;

			if (p[page_count] != 0) {
				signal(SIGSEGV, SIG_DFL);
				raise(SIGSEGV);
				signal(SIGSEGV, (void *)(int)sigsegv_handler);
			}
			p[page_count] = 1;

			void *x = mmap((void *)addr, page_size,
				PROT_WRITE,
				MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
			if (x < 0)
				return (void *)-1;

			void *read_buf = malloc(page_size);

			lseek(fd, exec->segments[i].offset +
				page_count * page_size, SEEK_SET);

			int to_read = page_size;

			if (addr + page_size >
				exec->segments[i].vaddr +
				exec->segments[i].file_size)
				to_read = exec->segments[i].file_size %
					page_size;


			if (addr > exec->segments[i].vaddr +
				exec->segments[i].file_size)
				to_read = 0;


			int rc = read(fd, read_buf, to_read);

			if (rc < 0)
				return (void *)-1;


			if (rc < page_size)
				memset(read_buf + rc, 0, page_size - rc);

			memcpy((void *)addr, read_buf, page_size);

			rc = mprotect((void *)addr, page_size,
				exec->segments[i].perm);
			free(read_buf);
			return 0;
		}
	}
	signal(SIGSEGV, SIG_DFL);
	raise(SIGSEGV);
	signal(SIGSEGV, (void *)(int)sigsegv_handler);

	return (void *)-1;
}

int so_init_loader(void)
{
	/* TODO: initialize on-demand loader */
	struct sigaction sa;

	memset(&sa, 0, sizeof(sa));
	sa.sa_sigaction = (void *)&sigsegv_handler;
	sa.sa_flags = SA_SIGINFO | SA_NODEFER;

	sigaction(SIGSEGV, &sa, NULL);


	return -1;
}

int so_execute(char *path, char *argv[])
{

	exec = so_parse_exec(path);
	if (!exec)
		return -1;

	fd = open(path, O_RDONLY);
	if (fd < 0)
		exit(-1);


	so_start_exec(exec, argv);

	close(fd);

	return -1;
}