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CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Commands
+
+- `mix compile` - Compile source files
+- `mix test` - Run all tests
+- `mix test test/path/to/test.exs` - Run a specific test file
+- `mix test test/path/to/test.exs:LINE` - Run a specific test at a line number
+- `mix deps.get` - Install dependencies
+- `mix clean` - Clean build artifacts
+
+## Architecture
+
+This is an Elixir library that provides email allowlist functionality for restricting account creation. The library consists of two main modules:
+
+1. **BasicSignupAllowlist** (lib/basic_signup_allowlist.ex) - Public API module that reads the `SIGNUP_ALLOWLIST_EMAILS` environment variable and delegates to the functional core
+2. **FunCore.BasicSignupAllowlist** (lib/fun_core/basic_signup_allowlist.ex) - Pure functional core that handles the allowlist logic without side effects
+
+The architecture follows a functional core/imperative shell pattern where:
+- The functional core contains pure functions for email normalization and allowlist checking
+- The outer module handles environment variable reading and provides the public interface
+
+## Environment Variables
+
+- `SIGNUP_ALLOWLIST_EMAILS` - Comma-separated list of allowed email addresses, or "*" to allow all emails
+
+## Project Configuration
+
+- Elixir version: ~> 1.18 (managed via mise)
+- No external dependencies currently
+- Test framework: ExUnit with async: false for integration tests that modify environment variables

lib/fun_core/basic_signup_allowlist.ex

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+defmodule FunCore.BasicSignupAllowlist do
+  def normalize(email) do
+    email |> String.trim() |> String.downcase()
+  end
+
+  def addresses_as_list(addresses_str) do
+    addresses_str
+    |> String.split(",")
+    |> Enum.map(&normalize/1)
+  end
+
+  def mail_allowlisted_fun(signups_allowed, email_received) do
+    case signups_allowed do
+      nil -> false
+      "*" -> true
+      list_str -> normalize(email_received) in addresses_as_list(list_str)
+    end
+  end
+end

test/fun_core/basic_signup_allowlist_test.exs

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+defmodule FunCore.BasicSignupAllowlistTest do
+  use ExUnit.Case
+  import FunCore.BasicSignupAllowlist
+
+  test "addresses_as_list" do
+    assert addresses_as_list("joe@example.com, jane@example.com") == [
+             "joe@example.com",
+             "jane@example.com"
+           ]
+  end
+
+  test "jane in list" do
+    lst = addresses_as_list("joe@example.com, jane@example.com")
+    assert "jane@example.com" in lst
+  end
+
+  describe "Not allowlisted when allowed list is" do
+    test "not set" do
+      refute(mail_allowlisted_fun(nil, "joe@example.com"))
+    end
+
+    test "empty" do
+      refute(mail_allowlisted_fun("j", "joe@example.com"))
+    end
+  end
+
+  describe "Allowlisted when" do
+    test "*" do
+      assert(mail_allowlisted_fun("*", "jane@example.com"))
+    end
+
+    test "Multiple set and one match" do
+      assert(mail_allowlisted_fun("joe@example.com, jane@example.com", "jane@example.com"))
+    end
+
+    test "Matches with different casings" do
+      assert(mail_allowlisted_fun("joe@Example.com, jane@example.com", "Joe@example.com"))
+    end
+  end
+end