wip parse range

.gitignore

@@ -1,4 +1,4 @@
-*.c
+vieter.c
 /data/
 
 # Build artifacts

src/cron/expression/c/parse.c

@@ -0,0 +1,60 @@
+#include "expression.h"
+
+typedef enum parse_error {
+    ParseOk,
+    ParseInvalidExpression,
+    ParseInvalidNumber,
+    ParseOutOfRange
+} ParseError;
+
+/**
+ * Given a range expression, produce a bit field defining what numbers in the
+ * min-max range the expression represents. The first bit corresponds to min,
+ * the max - min + 1'th bit to max. All trailing bits after this should be
+ * ignored.
+ *
+ * A range expression has one of the following forms:
+ *
+ * - *
+ * - a
+ * - a-b
+ * - a/c
+ * - a-b/c
+ */
+ParseError ce_parse_range(uint64_t *out, char *s, uint8_t min, uint8_t max) {
+    // The * expression means "every possible value"
+    if (s[0] == '*') {
+        // A '*' is only valid on its own
+        if (s[1] != '\0') {
+            return ParseInvalidExpression;
+        }
+
+        *out = ~0;
+
+        return ParseOk;
+    }
+
+    uint64_t bf = 0;
+
+    size_t slash_index = 0;
+    size_t dash_index = 0;
+    size_t i = 0;
+
+    // We first iterate over the string to determine whether it contains a slash
+    // and/or a dash. We know the dash can only be valid if it appears before
+    // the slash.
+    while (s[i] != '\0' && slash_index == 0) {
+        if (s[i] == '/') {
+            slash_index = i;
+
+            s[i] = '\0';
+        } else if (s[i] == '-') {
+            dash_index = i;
+
+            s[i] = '\0';
+        }
+    }
+
+    *out = bf;
+    return ParseOk;
+}