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, 95 insertions, 0 deletions

diff --git a/src/login/create.rs b/src/login/create.rs
new file mode 100644
index 0000000..693daaf
--- /dev/null
+++ b/src/login/create.rs
@@ -0,0 +1,95 @@
+use sqlx::{sqlite::Sqlite, Transaction};
+
+use super::{password::StoredHash, repo::Provider as _, validate, History, Password};
+use crate::{
+    clock::DateTime,
+    event::{repo::Provider as _, Broadcaster, Event},
+    name::Name,
+};
+
+pub struct Create<'a> {
+    name: &'a Name,
+    password: &'a Password,
+    created_at: &'a DateTime,
+}
+
+impl<'a> Create<'a> {
+    #[must_use = "dropping a login creation attempt is likely a mistake"]
+    pub fn begin(name: &'a Name, password: &'a Password, created_at: &'a DateTime) -> Self {
+        Self {
+            name,
+            password,
+            created_at,
+        }
+    }
+
+    #[must_use = "dropping a login creation attempt is likely a mistake"]
+    pub fn validate(self) -> Result<Validated<'a>, Error> {
+        let Self {
+            name,
+            password,
+            created_at,
+        } = self;
+
+        if !validate::name(name) {
+            return Err(Error::InvalidName(name.clone()));
+        }
+
+        let password_hash = password.hash()?;
+
+        Ok(Validated {
+            name,
+            password_hash,
+            created_at,
+        })
+    }
+}
+
+pub struct Validated<'a> {
+    name: &'a Name,
+    password_hash: StoredHash,
+    created_at: &'a DateTime,
+}
+
+impl<'a> Validated<'a> {
+    #[must_use = "dropping a login creation attempt is likely a mistake"]
+    pub async fn store<'c>(self, tx: &mut Transaction<'c, Sqlite>) -> Result<Stored, sqlx::Error> {
+        let Self {
+            name,
+            password_hash,
+            created_at,
+        } = self;
+
+        let created = tx.sequence().next(created_at).await?;
+        let login = tx.logins().create(name, &password_hash, &created).await?;
+
+        Ok(Stored { login })
+    }
+}
+
+pub struct Stored {
+    login: History,
+}
+
+impl Stored {
+    #[must_use = "dropping a login creation attempt is likely a mistake"]
+    pub fn publish(self, events: &Broadcaster) -> History {
+        let Self { login } = self;
+
+        events.broadcast(login.events().map(Event::from).collect::<Vec<_>>());
+
+        login
+    }
+
+    pub fn login(&self) -> &History {
+        &self.login
+    }
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    #[error("invalid login name: {0}")]
+    InvalidName(Name),
+    #[error(transparent)]
+    PasswordHash(#[from] password_hash::Error),
+}