#include "env.h"

#include <assert.h>
#include <string.h>

static bool symbol_eq(symbol_t *s, symbol_t *t)
{
	return s->len == t->len && memcmp(s->buf, t->buf, s->len) == 0;
}

static expr_t **lookup(am_t *am, bool *found)
{
	assert(am->expr != NULL);
	assert(am->expr->is_atom);
	assert(am->expr->atom.type == ATOM_TYPE_SYMBOL);

	if (am->env->is_atom) {
		assert(am->env->atom.type == ATOM_TYPE_EMPTY_LIST);
		*found = false;
		return &am->env;
	}

	expr_t *prev;
	for (expr_t *list = am->env; !list->is_atom; list = list->pair.cdr) {
		assert(list != NULL);

		expr_t *entry = list->pair.car;
		assert(!entry->is_atom);

		expr_t *key = entry->pair.car;
		assert(key != NULL);
		assert(key->is_atom);
		assert(key->atom.type == ATOM_TYPE_SYMBOL);

		if (symbol_eq(&am->expr->atom.symbol, &key->atom.symbol)) {
			*found = true;
			return &entry->pair.cdr;
		}

		prev = list;
	}

	assert(!prev->is_atom);
	assert(prev->pair.cdr->is_atom);
	assert(prev->pair.cdr->atom.type == ATOM_TYPE_EMPTY_LIST);
	*found = false;
	return &prev->pair.cdr;
}

void env_init(am_t *am, store_t *store)
{
	am->env = store_alloc(store);
	am->env->is_atom = true;
	am->env->atom.type = ATOM_TYPE_EMPTY_LIST;
}

void env_fetch(am_t *am)
{
	bool found;
	expr_t *val = *lookup(am, &found);
	am->val = found ? val : NULL;
}

void env_set(am_t *am, store_t *store)
{
	bool found;
	expr_t **loc = lookup(am, &found);
	if (found) {
		*loc = am->val;
	} else {
		(*loc)->is_atom = false;
		(*loc)->pair.cdr = store_alloc(store);
		(*loc)->pair.cdr->is_atom = true;
		(*loc)->pair.cdr->atom.type = ATOM_TYPE_EMPTY_LIST;

		expr_t *entry = (*loc)->pair.car = store_alloc(store);
		entry->pair.car = am->expr;
		entry->pair.cdr = am->val;
	}
}