Create a dedicated workflow type for creating logins.

Nasty design corner. Logins need to be created in three places:

1. In tests, using app.logins().create(…);
2. On initial setup, using app.setup().initial(…); and
3. When accepting invites, using app.invites().accept(…).

These three places do the same thing with respect to logins, but also do a varying mix of other things. Testing is the simplest and _only_ creates a login. Initial setup and invite acceptance both issue a token for the newly-created login. Accepting an invite also invalidates the invite. Previously, those three functions have been copy-pasted variations on a theme. Now that we have validation, the copy-paste approach is no longer tenable; it will become increasingly hard to ensure that the three functions (plus any future functions) remain in synch.

To accommodate the variations while consolidating login creation, I've added a typestate-based state machine, which is driven by method calls:

* A creation attempt begins with `let create = Create::begin()`. This always succeeds; it packages up arguments used in later steps, but does nothing else.
* A creation attempt can be validated using `let validated = create.validate()?`. This may fail. Input validation and password hashing are carried out at this stage, making it potentially expensive.
* A validated attempt can be stored in the DB, using `let stored = validated.store(&mut tx).await?`. This may fail. The login will be written to the DB; the caller is responsible for transaction demarcation, to allow other things to take place in the same transaction.
* A fully-stored attempt can be used to publish events, using `let login = stored.publish(self.events)`. This always succeeds, and unwraps the state machine to its final product (a `login::History`).

1 files changed, 21 insertions, 17 deletions

diff --git a/src/login/app.rs b/src/login/app.rs
index c1bfe6e..6da26e9 100644
--- a/src/login/app.rs
+++ b/src/login/app.rs
@@ -3,13 +3,12 @@ use sqlx::sqlite::SqlitePool;
 use super::repo::Provider as _;
 
 #[cfg(test)]
-use super::{validate, Login, Password};
-#[cfg(test)]
-use crate::{
-    clock::DateTime,
-    event::{repo::Provider as _, Broadcaster, Event},
-    name::Name,
+use super::{
+    create::{self, Create},
+    Login, Password,
 };
+#[cfg(test)]
+use crate::{clock::DateTime, event::Broadcaster, name::Name};
 
 pub struct Logins<'a> {
     db: &'a SqlitePool,
@@ -35,19 +34,14 @@ impl<'a> Logins<'a> {
         password: &Password,
         created_at: &DateTime,
     ) -> Result<Login, CreateError> {
-        if !validate::name(name) {
-            return Err(CreateError::InvalidName(name.clone()));
-        }
-
-        let password_hash = password.hash()?;
+        let create = Create::begin(name, password, created_at);
+        let validated = create.validate()?;
 
         let mut tx = self.db.begin().await?;
-        let created = tx.sequence().next(created_at).await?;
-        let login = tx.logins().create(name, &password_hash, &created).await?;
+        let stored = validated.store(&mut tx).await?;
         tx.commit().await?;
 
-        self.events
-            .broadcast(login.events().map(Event::from).collect::<Vec<_>>());
+        let login = stored.publish(self.events);
 
         Ok(login.as_created())
     }
@@ -67,7 +61,17 @@ pub enum CreateError {
     #[error("invalid login name: {0}")]
     InvalidName(Name),
     #[error(transparent)]
-    Database(#[from] sqlx::Error),
-    #[error(transparent)]
     PasswordHash(#[from] password_hash::Error),
+    #[error(transparent)]
+    Database(#[from] sqlx::Error),
+}
+
+#[cfg(test)]
+impl From<create::Error> for CreateError {
+    fn from(error: create::Error) -> Self {
+        match error {
+            create::Error::InvalidName(name) => Self::InvalidName(name),
+            create::Error::PasswordHash(error) => Self::PasswordHash(error),
+        }
+    }
 }