#include <merror.h>
#include <melf.h>
#include <elf.h>
#include <sys/mman.h>

#include "link.h"

/**
 * Read the phdr for this segment
 */
static int load_phdr(struct object *obj, struct segment *seg, size_t index)
{
	if (index >= obj->phdr_len) {
		ERROR("phdr index [%d] out of bounds", index);
		return M_ERROR;
	}

	seg->phdr = &obj->phdr[index];
	seg->phdr_idx = index;
	return M_SUCCESS;
}

/**
 * Read the shdr for this segment
 */
static int load_shdr(struct object *obj, struct segment *seg, size_t index)
{
	bool found = false;

	for (size_t i = 0; i < obj->shdr_len; i++) {
		Elf32_Shdr *hdr = &obj->shdr[i];

		// find shdr that matches  the offset in phdr
		if (seg->phdr->p_offset != hdr->sh_offset)
			continue;


		// get name
		uint32_t name = B32(hdr->sh_name);
		if (name >= obj->shstrtab->len) {
			ERROR("section name index [%d] out of bounds", name);
			return M_ERROR;
		}
		seg->name = &obj->shstrtab->data[name];

		// map bytes
		uint32_t len = B32(hdr->sh_size);
		uint32_t off = B32(hdr->sh_offset);
		seg->bytes = (unsigned char *) (obj->mapped + off);

		if (BOUND_CHK(obj, len, off)) {
			ERROR("cannot map seg %s:%d", seg->name, index);
			return M_ERROR;
		}

		found = true;
		seg->shdr = hdr;
		seg->shdr_idx = i;
		break;
	}

	if (!found) {
		ERROR("cannot find shdr for segment [%d]", index);
		return M_ERROR;
	}

	return M_SUCCESS;
}

/**
 * Read the relocation table for this segment (if one exists)
 */
static int load_reltab(struct object *obj, struct segment *seg)
{
	// default to none
	seg->reltab.len = 0;

	for (size_t i = 0; i < obj->shdr_len; i++) {
		Elf32_Shdr *hdr = &obj->shdr[i];
		uint32_t type = B32(hdr->sh_type);

		if (type != SHT_REL && type != SHT_RELA)
			continue;

		if (B32(hdr->sh_info) != seg->shdr_idx)
			continue;

		uint32_t symtab_idx = B32(hdr->sh_link);
		if (symtab_idx >= obj->shdr_len) {
			ERROR("reltab [%d] symtab index [%d] out of bounds",
				i, symtab_idx);
			return M_ERROR;
		}

		struct symbol_table *symtab = &obj->symtabs[symtab_idx];
		if (symtab->len < 1) {
			ERROR("reltab [%d] symtab is empty or invalid", i);
			return M_ERROR;
		}

		uint32_t len = B32(hdr->sh_size);
		uint32_t off = B32(hdr->sh_offset);


		seg->reltab.symtab = symtab;
		seg->reltab.len = len;
		seg->reltab.raw = obj->mapped + off;
		seg->reltab.type = type;

		if (BOUND_CHK(obj, len, off)) {
			ERROR("cannot map reltab [%d] for %s",
				i, seg->name);
			return M_ERROR;
		}

		break;
	}

	return M_SUCCESS;
}

int segment_load(struct object *obj, struct segment *seg, size_t index)
{

	if (load_phdr(obj, seg, index))
		return M_ERROR;

	if (load_shdr(obj, seg, index))
		return M_ERROR;

	if (load_reltab(obj, seg))
		return M_ERROR;

	return M_SUCCESS;
}