From 8ba4035afcc05080c7fec31b44e9da846b19b673 Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cdo@wip.sh>
Date: Thu, 24 Oct 2024 14:39:44 +0100
Subject: [PATCH] Add basic sum parsing

---
 lib/reader.c         | 79 ++++++++++++++++++++++++++++++++++++++------
 tests/reader_tests.c | 20 +++++++++++
 2 files changed, 88 insertions(+), 11 deletions(-)

diff --git a/lib/reader.c b/lib/reader.c
index 9a2e20d..0900f66 100644
--- a/lib/reader.c
+++ b/lib/reader.c
@@ -3,19 +3,76 @@
 #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 *result = allocate_expression(pool);
-	if (NULL == result)
+	expression_t *expression = allocate_expression(pool);
+	if (NULL == expression)
 		return NULL;
-	result->is_number = true;
-	result->number = 0;
-	while (isdigit(*input)) {
-		result->number *= 10;
-		result->number += *input - '0';
-		++input;
-		++len;
-	}
-	return result;
+	parse_expression(pool, input, len, expression);
+	return expression;
 }
diff --git a/tests/reader_tests.c b/tests/reader_tests.c
index f50c091..f20538e 100644
--- a/tests/reader_tests.c
+++ b/tests/reader_tests.c
@@ -21,10 +21,30 @@ static void input_4321_is_read_as_number_with_expected_value(void)
 	ASSERT_EQUAL(4321, result->number);
 }
 
+static void input_1234_with_len_3_is_read_as_123(void)
+{
+	init_memory_pool(&pool);
+	const expression_t *result = read_expression(&pool, "1234", 3);
+	ASSERT_NOT_NULL(result);
+	ASSERT_TRUE(result->is_number);
+	ASSERT_EQUAL(123, result->number);
+}
+
+static void input_1_plus_2_with_no_spaces_is_read_as_an_add_application(void)
+{
+	init_memory_pool(&pool);
+	const expression_t *result = read_expression(&pool, "1+2", 3);
+	ASSERT_NOT_NULL(result);
+	ASSERT_FALSE(result->is_number);
+	ASSERT_EQUAL(OPERATOR_ADD, result->application.operator);
+}
+
 int main(void)
 {
 	TESTING_BEGIN();
 	RUN_TEST(input_1234_is_read_as_number_with_expected_value);
 	RUN_TEST(input_4321_is_read_as_number_with_expected_value);
+	RUN_TEST(input_1234_with_len_3_is_read_as_123);
+	RUN_TEST(input_1_plus_2_with_no_spaces_is_read_as_an_add_application);
 	TESTING_END();
 }