#include "reader.h"

#include <ctype.h>
#include <stddef.h>

static int parse_number(
    memory_pool_t *pool, const char *input, int len, expression_t **out)
{
	(void)pool;

	int value = 0, used = 0;
	while (used < len && isdigit(input[used])) {
		value *= 10;
		value += input[used] - '0';
		++used;
	}
	if (0 == used)
		return 0;

	expression_t *number = allocate_expression(pool);
	number->is_number = true;
	number->number = value;
	*out = number;
	return used;
}

static int parse_expression(
    memory_pool_t *pool, const char *input, int len, expression_t **out)
{
	int result, used = 0;

	expression_t *number;
	result = parse_number(pool, input, len, &number);
	if (0 >= result)
		return 0;
	used += result;
	if (used >= len) {
		*out = number;
		return used;
	}

	operator_t operator;
	switch (input[used]) {
	case '+':
		operator= OPERATOR_ADD;
		break;
	case '-':
		operator= OPERATOR_SUBTRACT;
		break;
	default:
		return 0;
	}
	++used;

	expression_t *subexpr;
	result = parse_expression(pool, input + used, len - used, &subexpr);
	if (0 >= result)
		return 0;
	used += result;

	expression_t *expr = allocate_expression(pool);
	expr->is_number = false;
	expr->application.operator= operator;
	expr->application.operands[0] = number;
	expr->application.operands[1] = subexpr;

	*out = expr;
	return used;
}

const expression_t *
read_expression(memory_pool_t *pool, const char *input, int len)
{
	expression_t *expression;
	parse_expression(pool, input, len, &expression);
	return expression;
}