initial

.gitignore

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+bin
+!bin/.githold

Makefile

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+build:
+	amber build src/index.amber bin/some-cli
+
+clean:
+	rm -rf bin
+	mkdir bin
+	touch bin/.githold

src/command-hooks/help.amber

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+import { bold, echo_info, underlined } from "std/env"
+
+pub fun help(): Null {
+  const usage = underlined(bold("Usage"))
+  const commands = underlined(bold("Commands"))
+  echo_info("{usage}: some-cli <command> [--flag[=value]] [-f[=value]]")
+  echo_info("")
+  echo_info("{commands}")
+  echo_info("  help         Print this message or the help of the given command")
+}

src/helpers/arg-parser.amber

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+import { array_find, array_find_all, array_remove_at } from "std/array"
+import { slice, split_chars, starts_with, text_contains } from "std/text"
+
+fun remove_prefix(arg: Text): Text? {
+
+  if starts_with(arg, "--") {
+    return slice(arg, 2)
+  }
+
+  if starts_with(arg, "-") {
+    return slice(arg, 1)
+  }
+
+  fail 2 // "Flags must start with `--` or `-` given {arg}"
+}
+
+fun safe_split_flag(arg: Text): [Text] {
+
+  const string_of_chars = split_chars(arg)
+  const first_equals = array_find(string_of_chars, "=")
+
+  if first_equals == -1 {
+    return [arg, ""]
+  }
+
+  const flag = slice(arg, 0, first_equals)
+  const value = slice(arg, first_equals+1)
+  echo "{flag} {value}"
+  return [flag, value]
+}
+
+// Returns associative map of flagName -> value or flagName -> "" if just present
+pub fun arg_parser(arguments: [Text]): [Text]? {
+
+  if len(arguments) < 3 {
+    return [Text]
+  }
+
+  let results = [Text]
+
+  for i in 2..len(arguments) {
+    const arg = remove_prefix(arguments[i]) failed {
+      fail status
+    }
+
+    if text_contains(arg, "=") {
+      results = results + safe_split_flag(arg)
+      continue
+    }
+
+    results = results + [arg, ""]
+  }
+
+  return results
+}

src/helpers/resolve-status-code.amber

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+pub fun resolve_status_code(code: Num): Text {
+  if {
+    code == 0: return ""
+    code == 1: return "Unknown error..."
+    code == 2: return "Flags must start with `--` or `-`"
+    else: return "Unknown error... {code}"
+  }
+}

src/index.amber

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+import { arg_parser } from "./helpers/arg-parser.amber"
+import { resolve_status_code } from "./helpers/resolve-status-code.amber"
+import { help } from "./command-hooks/help.amber"
+import { echo_error } from "std/env"
+
+main(cli_params) {
+
+  const command = cli_params[1]
+  const flags = arg_parser(cli_params) failed {
+    echo_error(resolve_status_code(status))
+    fail 1
+  }
+
+  echo "We parsed: command={command} flags={flags}"
+
+  if {
+    command == "help": help()
+    else: help()
+  }
+}