#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 <errno.h>

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

#include "elf.h"

void *libelf_map(char *path, size_t *fsize);
int libelf_iself(void *elf);
char *libelf_soname(void *elf);
int libelf_type(void *elf);

Elf64_Ehdr *libelf_header(void *elf) {
	return elf;
}

#if 0
Elf64_Shdr *libelf_shdr(void *elf, int n) {
	return 0;
}
#endif

Elf64_Shdr *libelf_sht_strtab(void *elf) {
	int i;
	Elf64_Ehdr *hdr;
	Elf64_Shdr *shdr;

	hdr = libelf_header(elf);

	for (i = 0; i < hdr->e_shnum; i++) {
		shdr = (Elf64_Shdr *)((char *)elf + hdr->e_shoff + i * hdr->e_shentsize);
		if (shdr->sh_type == SHT_STRTAB && i == hdr->e_shstrndx) {
			return shdr;
		}
	}
	return 0;
}

char *libelf_sectionname(Elf64_Shdr *section, Elf64_Shdr *strtab) {
	return (char *)strtab + section->sh_name;
}

Elf64_Shdr *libelf_section_n(void *elf, int n) {
	Elf64_Ehdr *hdr;

	hdr = libelf_header(elf);

	if (n > hdr->e_shnum) {
		return 0;
	}

	return (Elf64_Shdr *)((char *)elf + hdr->e_shoff + n * hdr->e_shentsize);
}

Elf64_Shdr *libelf_section(void *elf, unsigned int type) {
	int i;
	Elf64_Ehdr *hdr;
	Elf64_Shdr *shdr;

	hdr = libelf_header(elf);

	for (i = 0; i < hdr->e_shnum; i++) {
		shdr = (Elf64_Shdr *)((char *)elf + hdr->e_shoff + i * hdr->e_shentsize);
		if (shdr->sh_type == type) {
			return shdr;
		}
	}
	return 0;
}

int libelf_type(void *elf) {
	return libelf_iself(elf) ? libelf_header(elf)->e_type : 0;
}

int libelf_iself(void *elf) {
	Elf64_Ehdr *hdr;
	hdr = elf;
	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
	   ) {
		return 0;
	}
	return 1;
}

void *libelf_map(char *path, size_t *fsize) {
	int elffd;
	struct stat sbuf;
	void *elfbase;

	errno = 0;

	elffd = open(path, O_RDONLY);
	if (elffd == -1) {
		perror("open");
		return NULL;
	}
	if (fstat(elffd, &sbuf) == -1) {
		close(elffd);
		return NULL;
	}
	/* not a regular file? */
	if (!S_ISREG(sbuf.st_mode)) {
		close(elffd);
		return NULL;
	}
	/* not at least the size of the elf header? */
	if ((size_t)sbuf.st_size < sizeof(Elf64_Ehdr)) {
		close(elffd);
		return NULL;
	}

	elfbase = mmap(0, sbuf.st_size, PROT_READ,MAP_PRIVATE, elffd, 0);
	close(elffd);
	if (!elfbase) {
		return NULL;
	}

	if (!libelf_iself(elfbase)) {
		munmap(elfbase, sbuf.st_size);
		return NULL;
	}

	*fsize = sbuf.st_size;

	return elfbase;
}

char *libelf_soname(void *elfbase) {
	Elf64_Ehdr *hdr;
	int i;
	Elf64_Shdr *shdr;
	Elf64_Shdr *dynsect = 0;
	Elf64_Shdr *strtab = 0, *dyntab = 0;
	char *name, *dynname;
	Elf64_Dyn *dent;

	if (!libelf_iself(elfbase)) {
		return 0;
	}
	hdr = libelf_header(elfbase);

	/* only dynamic files will have an soname */
	if (hdr->e_type != ET_DYN) {
		return 0;
	}

	switch (hdr->e_ident[EI_CLASS]) {
		case ELFCLASS64:
		case ELFCLASS32:
		case ELFCLASSNONE:
			break;
		default: return 0; break;
	}

	/* check endian ness */
	switch (hdr->e_ident[EI_DATA]) {
		case ELFDATA2LSB: break;
		case ELFDATA2MSB: break;
		default: return 0; break;
	}
	
	/* 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) {
		return 0;
	}
	if (!dynsect) {
		return 0;
	}

	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) {
		return 0;
	}

	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) {
			return dynname + dent->d_un.d_val;
		}
	}

	return 0;
}