#include "reader.h"

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

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

	int value = 0, used = 0;
	while (remaining > 0 && isdigit(*input)) {
		value *= 10;
		value += *input - '0';
		++used;
		--remaining;
		++input;
	}

	out->is_number = true;
	out->number = value;
	return used;
}

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

	expression_t *operand0 = allocate_expression(pool);
	result = parse_number(pool, input, remaining, operand0);
	if (0 == result)
		return 0;
	used += result;
	remaining -= result;
	input += result;

	if (remaining <= 0 || *input != '+')
		return 0;
	++used;
	--remaining;
	++input;

	expression_t *operand1 = allocate_expression(pool);
	result = parse_number(pool, input, remaining, operand1);
	if (0 == result)
		return 0;
	used += result;
	remaining -= result;
	input += result;

	out->is_number = false;
	out->application.operator = OPERATOR_ADD;
	out->application.operands[0] = operand0;
	out->application.operands[1] = operand1;

	return used;
}

static int parse_expression(
    memory_pool_t *pool, const char *input, int remaining, expression_t *out)
{
	int result = parse_application(pool, input, remaining, out);
	if (0 != result)
		return result;
	else
		return parse_number(pool, input, remaining, out);
}

const expression_t *
read_expression(memory_pool_t *pool, const char *input, int len)
{
	expression_t *expression = allocate_expression(pool);
	if (NULL == expression)
		return NULL;
	parse_expression(pool, input, len, expression);
	return expression;
}