From 373d9ec700c0097a22cf665a8e33cf48998d1dc2 Mon Sep 17 00:00:00 2001
From: Elizabeth <me@liz.coffee>
Date: Mon, 2 Jun 2025 11:14:52 -0700
Subject: Minor things

---
 u/process/argv.ts | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 u/process/mod.ts  |  1 +
 2 files changed, 66 insertions(+)
 create mode 100644 u/process/argv.ts

(limited to 'u/process')

diff --git a/u/process/argv.ts b/u/process/argv.ts
new file mode 100644
index 0000000..657c9a7
--- /dev/null
+++ b/u/process/argv.ts
@@ -0,0 +1,65 @@
+import { Either, type IEither } from "@emprespresso/pengueno";
+
+export const isArgKey = <K extends string>(k: string): k is K =>
+  k.startsWith("--");
+
+export const getArg = <K extends string, V extends string>(
+  arg: K,
+  args: Array<K>,
+): IEither<Error, V> => {
+  const result = args.findIndex((_arg) => _arg.startsWith(arg));
+  if (result < 0) return Either.left(new Error("no argument found for " + arg));
+  const [resultArg, next]: Array<string | undefined> = [
+    args[result],
+    args.at(result + 1),
+  ];
+  if (resultArg && resultArg.includes("=")) {
+    return Either.right(resultArg.split("=")[1] as V);
+  }
+  if (typeof next === "undefined")
+    return Either.left(new Error("no value specified for " + arg));
+  if (isArgKey(next))
+    return Either.left(
+      new Error("next value for arg " + arg + " is another arg " + next),
+    );
+  return Either.right(next as V);
+};
+
+type ObjectFromList<T extends ReadonlyArray<string>, V = string> = {
+  [K in T extends ReadonlyArray<infer U> ? U : never]: V;
+};
+export const argv = <K extends string, V extends string>(
+  args: ReadonlyArray<K>,
+  defaultArgs?: Partial<Record<K, V>>,
+  argv = Deno.args,
+) => {
+  return args
+    .map((arg) => [arg, getArg(arg, argv)] as [K, IEither<Error, V>])
+    .map(([arg, specified]): [K, IEither<Error, V>] => [
+      arg,
+      specified.fold((e, val) => {
+        const hasDefaultVal = e && defaultArgs && arg in defaultArgs;
+        if (hasDefaultVal) {
+          return Either.right<Error, V>(defaultArgs[arg]!);
+        } else if (!val || e) {
+          return Either.left<Error, V>(e ?? new Error("unknown"));
+        }
+        return Either.right<Error, V>(val);
+      }),
+    ])
+    .reduce(
+      (
+        acc: IEither<Error, ObjectFromList<typeof args, V>>,
+        x: [K, IEither<Error, V>],
+      ): IEither<Error, ObjectFromList<typeof args, V>> => {
+        const [arg, eitherVal] = x;
+        return acc.flatMap((args) => {
+          return eitherVal.mapRight((envValue) => ({
+            ...args,
+            [arg]: envValue,
+          }));
+        });
+      },
+      Either.right({} as ObjectFromList<typeof args, V>),
+    );
+};
diff --git a/u/process/mod.ts b/u/process/mod.ts
index 3f02d46..211e9a7 100644
--- a/u/process/mod.ts
+++ b/u/process/mod.ts
@@ -1,3 +1,4 @@
 export * from "./env.ts";
 export * from "./run.ts";
 export * from "./validate_identifier.ts";
+export * from "./argv.ts";
-- 
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