refactor version resolving (#353)

src/version/specifier.ts

@@ -0,0 +1,57 @@
+import * as tc from "@actions/tool-cache";
+
+export type ParsedVersionSpecifier =
+  | {
+      kind: "exact";
+      normalized: string;
+      raw: string;
+    }
+  | {
+      kind: "latest";
+      normalized: "latest";
+      raw: string;
+    }
+  | {
+      kind: "range";
+      normalized: string;
+      raw: string;
+    };
+
+export function normalizeVersionSpecifier(specifier: string): string {
+  const trimmedSpecifier = specifier.trim();
+
+  if (trimmedSpecifier.startsWith("==")) {
+    return trimmedSpecifier.slice(2);
+  }
+
+  return trimmedSpecifier;
+}
+
+export function parseVersionSpecifier(
+  specifier: string,
+): ParsedVersionSpecifier {
+  const raw = specifier.trim();
+  const normalized = normalizeVersionSpecifier(raw);
+
+  if (normalized === "latest") {
+    return {
+      kind: "latest",
+      normalized: "latest",
+      raw,
+    };
+  }
+
+  if (tc.isExplicitVersion(normalized)) {
+    return {
+      kind: "exact",
+      normalized,
+      raw,
+    };
+  }
+
+  return {
+    kind: "range",
+    normalized,
+    raw,
+  };
+}