newsletter

newsletter/src/newsletter.gleam

@@ -0,0 +1,55 @@
+import gleam/string
+import simplifile
+
+pub fn read_emails(path: String) -> Result(List(String), Nil) {
+  case simplifile.read(path) {
+    Error(_) -> Error(Nil)
+    Ok(content) ->
+      string.trim(content)
+      |> string.split("\n")
+      |> Ok
+  }
+}
+
+pub fn create_log_file(path: String) -> Result(Nil, Nil) {
+  case simplifile.create_file(path) {
+    Error(_) -> Error(Nil)
+    Ok(_) -> Ok(Nil)
+  }
+}
+
+pub fn log_sent_email(path: String, email: String) -> Result(Nil, Nil) {
+  case simplifile.append(path, email <> "\n") {
+    Error(_) -> Error(Nil)
+    Ok(_) -> Ok(Nil)
+  }
+}
+
+pub fn send_newsletter(
+  emails_path: String,
+  log_path: String,
+  send_email: fn(String) -> Result(Nil, Nil),
+) -> Result(Nil, Nil) {
+  case create_log_file(log_path), read_emails(emails_path) {
+    Ok(_), Ok(emails) -> send_emails_and_log(emails, send_email, log_path)
+    _, _ -> Error(Nil)
+  }
+}
+
+fn send_emails_and_log(
+  emails: List(String),
+  send_fn: fn(String) -> Result(Nil, Nil),
+  log_path: String,
+) -> Result(Nil, Nil) {
+  let _ = case emails {
+    [] -> Ok(Nil)
+    [email, ..rest] -> {
+      let _ = case send_fn(email) {
+        Error(_) -> Error(Nil)
+        Ok(_) -> log_sent_email(log_path, email)
+      }
+      send_emails_and_log(rest, send_fn, log_path)
+    }
+  }
+}
+// It should read all the email addresses from the given file and attempt to send an email to every one of them. If the anonymous function that sends the email returns an `Ok` value, write the email address to the log file. Make sure to do it as soon as the email is sent.