#define _POSIX_C_SOURCE 200112L
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <limits.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "elf.h"

int main(int ac, char **av) {
	void *elfbase;
	int elffd, i;
	struct stat sbuf;
	Elf64_Ehdr *hdr;
	Elf64_Shdr *shdr;
	Elf64_Shdr *dynsect = 0;
	Elf64_Shdr *strtab = 0, *dyntab = 0;
	char *name, *dynname;
	Elf64_Dyn *dent;

	if (ac < 2) {
		fprintf(stderr, "usage: soname <file>\n");
		exit(EXIT_FAILURE);
	}

	if (lstat(av[1], &sbuf) == -1) {
		exit(1);
	}
	if (!S_ISREG(sbuf.st_mode)) {
		exit(1);
	}

	elffd = open(av[1], O_RDONLY);
	if (elffd == -1) {
		exit(1);
	}
	if (fstat(elffd, &sbuf) == -1) {
		exit(1);
	}
	/* not a regular file? */
	if (!S_ISREG(sbuf.st_mode)) {
		exit(1);
	}
	/* not at least the size of the elf header? */
	if ((size_t)sbuf.st_size < sizeof(Elf64_Ehdr)) {
		exit(1);
	}

	elfbase = mmap(0, sbuf.st_size, PROT_READ,MAP_PRIVATE, elffd, 0);
	if (!elfbase) {
		exit(2);
	}

	hdr = elfbase;
	if (hdr->e_ident[EI_MAG0] != ELFMAG0
			|| hdr->e_ident[EI_MAG1] != ELFMAG1
			|| hdr->e_ident[EI_MAG2] != ELFMAG2
			|| hdr->e_ident[EI_MAG3] != ELFMAG3
	   ) {
		exit(3);
	}

	/* only dynamic files will have an soname */
	if (hdr->e_type != ET_DYN) {
		exit(4);
	}
	
	switch (hdr->e_ident[EI_CLASS]) {
		case ELFCLASS64:
		case ELFCLASS32:
		case ELFCLASSNONE:
			break;
		default:
			exit(5);
	}

	/* check endian ness */
	switch (hdr->e_ident[EI_DATA]) {
		case ELFDATA2LSB: break;
		case ELFDATA2MSB: break;
		default:
			exit(6);
	}

	/* find the section header table */
	for (i = 0; i < hdr->e_shnum; i++) {
		shdr = (Elf64_Shdr *)((char *)elfbase + hdr->e_shoff + i * hdr->e_shentsize);
		if (shdr->sh_type == SHT_DYNAMIC) {
			dynsect = shdr;
		} else if (shdr->sh_type == SHT_STRTAB && i == hdr->e_shstrndx) {
			strtab = shdr;
		}
	}
	if (!strtab) {
		exit(8);
	}
	if (!dynsect) {
		exit(9);
	}

	name = (char *) elfbase + strtab->sh_offset;
	for (i = 0; i < hdr->e_shnum; i++) {
		shdr = (Elf64_Shdr *)((char *)elfbase + hdr->e_shoff + i * hdr->e_shentsize);
		if (shdr->sh_type == SHT_STRTAB && !strcmp(".dynstr", name+shdr->sh_name)) {
			dyntab = shdr;
		}
	}
	if (!dyntab) {
		exit(10);
	}

	dynname = (char *) elfbase + dyntab->sh_offset;
	for (dent = (Elf64_Dyn *)((char *)elfbase + dynsect->sh_offset); dent->d_tag != DT_NULL; dent++) {
		if (dent->d_tag == DT_SONAME) {
			printf("%s\n", dynname + dent->d_un.d_val);
			/* TODO can there be more than one? */
			exit(0);
		}
	}

	return 11;
}