1 files changed, 36 insertions, 0 deletions
diff --git a/u/process/env.ts b/u/process/env.ts
new file mode 100644
index 0000000..0e41b4f
--- /dev/null
+++ b/u/process/env.ts
@@ -0,0 +1,36 @@
+import { Either, type IEither } from "@emprespresso/pengueno";
+
+export const getRequiredEnv = <V extends string>(name: V): IEither<Error, V> =>
+  Either
+    .fromFailable<Error, V>(() => Deno.env.get(name) as V) // could throw when no permission.
+    .flatMap((v) =>
+      (v && Either.right(v)) ||
+      Either.left(
+        new Error(`environment variable "${name}" is required D:`),
+      )
+    );
+
+type ObjectFromList<T extends ReadonlyArray<string>, V = string> = {
+  [K in (T extends ReadonlyArray<infer U> ? U : never)]: V;
+};
+
+export const getRequiredEnvVars = <V extends string>(vars: ReadonlyArray<V>) =>
+  vars
+    .map((envVar) => [envVar, getRequiredEnv(envVar)] as [V, IEither<Error, V>])
+    .reduce(
+      (
+        acc: IEither<Error, ObjectFromList<typeof vars>>,
+        x: [V, IEither<Error, V>],
+      ) => {
+        const [envVar, eitherVal] = x;
+        return acc.flatMap((args) => {
+          return eitherVal.mapRight((envValue) =>
+            ({
+              ...args,
+              [envVar]: envValue,
+            }) as ObjectFromList<typeof vars>
+          );
+        });
+      },
+      Either.right({} as ObjectFromList<typeof vars>),
+    );