/*
 * Loader Implementation
 *
 * 2018, Operating Systems
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <signal.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>


#include "exec_parser.h"

int fd;
static so_exec_t *exec;
struct sigaction signals;
static struct sigaction old_action;

static void segv_handler(int signum, siginfo_t *info, void *context) {
	so_seg_t *seg;
	so_seg_t *segment;
	uintptr_t addr;
	if (info->si_code == SEGV_ACCERR) {
			old_action.sa_sigaction(signum, info, context);
			return;
		}
	switch (signum) {
	case SIGSEGV:
		addr = (uintptr_t)info->si_addr;
		int found = 0;
		for(int i = 0; i < exec->segments_no; i++) {
			seg = exec->segments + i;
			if(seg->vaddr <= addr && addr <= (seg->vaddr + seg->mem_size)) {
				segment = seg;
				found = 1;
			}
		}
		if(found == 0) {
			goto default_h;
		}
		uintptr_t page = ALIGN_DOWN((uintptr_t)info->si_addr, getpagesize());
		uintptr_t offset_p = page - ALIGN_DOWN(segment->vaddr, getpagesize());
		if(page + getpagesize() <= (segment->vaddr + segment->file_size) || segment->file_size == segment->mem_size) {
			void* rc = mmap((void *)page, getpagesize(), segment->perm,
			 MAP_PRIVATE | MAP_FIXED, fd, segment->offset + offset_p);

		} else if(page <= (segment->vaddr + segment->file_size)) {
			void* rc =  mmap((void *)page, getpagesize(), segment->perm,
			 MAP_PRIVATE | MAP_ANONYMOUS, -1, segment->offset + offset_p);
			if(rc == MAP_FAILED) {
				goto default_h;
			}
			lseek(fd, segment->offset + offset_p, SEEK_SET);
			read(fd, rc, segment->vaddr + segment->file_size - page);
		} else if(page >= (segment->vaddr + segment->file_size)) {
			mmap((void *)page, getpagesize(), segment->perm,
			 MAP_PRIVATE | MAP_ANONYMOUS, -1, segment->offset + offset_p);
		}
		break;
	default:
	default_h:
		old_action.sa_sigaction(signum, info, context);
	}
}

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

	action.sa_flags = SA_SIGINFO;
	action.sa_sigaction = segv_handler;

	rc = sigaction(SIGSEGV, &action, &old_action);

	return rc;
}

int so_execute(char *path, char *argv[])
{
	exec = so_parse_exec(path);
	if (!exec)
		return -1;

	fd = open(path, O_RDONLY);

	so_start_exec(exec, argv);

	return -1;
}