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, 20 insertions, 12 deletions

diff --git a/src/setup/app.rs b/src/setup/app.rs
index cab7c4b..c1f7b69 100644
--- a/src/setup/app.rs
+++ b/src/setup/app.rs
@@ -3,8 +3,11 @@ use sqlx::sqlite::SqlitePool;
 use super::repo::Provider as _;
 use crate::{
     clock::DateTime,
-    event::{repo::Provider as _, Broadcaster, Event},
-    login::{repo::Provider as _, validate, Login, Password},
+    event::Broadcaster,
+    login::{
+        create::{self, Create},
+        Login, Password,
+    },
     name::Name,
     token::{repo::Provider as _, Secret},
 };
@@ -25,24 +28,20 @@ impl<'a> Setup<'a> {
         password: &Password,
         created_at: &DateTime,
     ) -> Result<(Login, Secret), Error> {
-        if !validate::name(name) {
-            return Err(Error::InvalidName(name.clone()));
-        }
+        let create = Create::begin(name, password, created_at);
 
-        let password_hash = password.hash()?;
+        let validated = create.validate()?;
 
         let mut tx = self.db.begin().await?;
-        let login = if tx.setup().completed().await? {
+        let stored = if tx.setup().completed().await? {
             Err(Error::SetupCompleted)?
         } else {
-            let created = tx.sequence().next(created_at).await?;
-            tx.logins().create(name, &password_hash, &created).await?
+            validated.store(&mut tx).await?
         };
-        let secret = tx.tokens().issue(&login, created_at).await?;
+        let secret = tx.tokens().issue(stored.login(), created_at).await?;
         tx.commit().await?;
 
-        self.events
-            .broadcast(login.events().map(Event::from).collect::<Vec<_>>());
+        let login = stored.publish(self.events);
 
         Ok((login.as_created(), secret))
     }
@@ -67,3 +66,12 @@ pub enum Error {
     #[error(transparent)]
     PasswordHash(#[from] password_hash::Error),
 }
+
+impl From<create::Error> for Error {
+    fn from(error: create::Error) -> Self {
+        match error {
+            create::Error::InvalidName(name) => Self::InvalidName(name),
+            create::Error::PasswordHash(error) => Self::PasswordHash(error),
+        }
+    }
+}