Rename "channels" to "conversations."

The term "channel" for a conversational container has a long and storied history, but is mostly evocative of IRC and of other, ah, "nerd-centric" services. It does show up in more widespread contexts: Discord and Slack both refer to their primary conversational containers as "channels," for example. However, I think it's unnecessary jargon, and I'd like to do away with it.

To that end, this change pervasively changes one term to the other wherever it appears, with the following exceptions:

* A `channel` concept (unrelated to conversations) is also provided by an external library; we can't and shouldn't try to rename that.
* The code to deal with the `pilcrow:channelData` and `pilcrow:lastActiveChannel` local storage properties is still present, to migrate existing data to new keys. It will be removed in a later change.

This is a **breaking API change**. As we are not yet managing any API compatibility promises, this is formally not an issue, but it is something to be aware of practically. The major API changes are:

* Paths beginning with `/api/channels` are now under `/api/conversations`, without other modifications.
* Fields labelled with `channel…` terms are now labelled with `conversation…` terms. For example, a `message` `sent` event is now sent to a `conversation`, not a `channel`.

This is also a **breaking UI change**. Specifically, any saved paths for `/ch/CHANNELID` will now lead to a 404. The corresponding paths are `/c/CONVERSATIONID`. While I've made an effort to migrate the location of stored data, I have not tried to provide adapters to fix this specific issue, because the disruption is short-lived and very easily addressed by opening a channel in the client UI.

This change is obnoxiously large and difficult to review, for which I apologize. If this shows up in `git annotate`, please forgive me. These kinds of renamings are hard to carry out without a major disruption, especially when the concept ("channel" in this case) is used so pervasively throughout the system.

I think it's worth making this change that pervasively so that we don't have an indefinitely-long tail of "well, it's a conversation in the docs, but the table is called `channel` for historical reasons" type issues.

Merges conversations-not-channels into main.

2 files changed, 193 insertions, 0 deletions

diff --git a/src/conversation/handlers/send/mod.rs b/src/conversation/handlers/send/mod.rs
new file mode 100644
index 0000000..9ec020a
--- /dev/null
+++ b/src/conversation/handlers/send/mod.rs
@@ -0,0 +1,63 @@
+use axum::{
+    extract::{Json, Path, State},
+    http::StatusCode,
+    response::{self, IntoResponse},
+};
+
+use crate::conversation::handlers::PathInfo;
+use crate::{
+    app::App,
+    clock::RequestedAt,
+    error::{Internal, NotFound},
+    message::{Body, Message, app::SendError},
+    token::extract::Identity,
+};
+
+#[cfg(test)]
+mod test;
+
+pub async fn handler(
+    State(app): State<App>,
+    Path(conversation): Path<PathInfo>,
+    RequestedAt(sent_at): RequestedAt,
+    identity: Identity,
+    Json(request): Json<Request>,
+) -> Result<Response, Error> {
+    let message = app
+        .messages()
+        .send(&conversation, &identity.user, &sent_at, &request.body)
+        .await?;
+
+    Ok(Response(message))
+}
+
+#[derive(serde::Deserialize)]
+pub struct Request {
+    pub body: Body,
+}
+
+#[derive(Debug)]
+pub struct Response(pub Message);
+
+impl IntoResponse for Response {
+    fn into_response(self) -> response::Response {
+        let Self(message) = self;
+        (StatusCode::ACCEPTED, Json(message)).into_response()
+    }
+}
+
+#[derive(Debug, thiserror::Error)]
+#[error(transparent)]
+pub struct Error(#[from] pub SendError);
+
+impl IntoResponse for Error {
+    fn into_response(self) -> response::Response {
+        let Self(error) = self;
+        match error {
+            SendError::ConversationNotFound(_) | SendError::ConversationDeleted(_) => {
+                NotFound(error).into_response()
+            }
+            SendError::Name(_) | SendError::Database(_) => Internal::from(error).into_response(),
+        }
+    }
+}
diff --git a/src/conversation/handlers/send/test.rs b/src/conversation/handlers/send/test.rs
new file mode 100644
index 0000000..bd32510
--- /dev/null
+++ b/src/conversation/handlers/send/test.rs
@@ -0,0 +1,130 @@
+use axum::extract::{Json, Path, State};
+use futures::stream::{self, StreamExt as _};
+
+use crate::{
+    conversation,
+    event::Sequenced,
+    message::app::SendError,
+    test::fixtures::{self, future::Expect as _},
+};
+
+#[tokio::test]
+async fn messages_in_order() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+    let sender = fixtures::identity::create(&app, &fixtures::now()).await;
+    let conversation = fixtures::conversation::create(&app, &fixtures::now()).await;
+    let resume_point = fixtures::boot::resume_point(&app).await;
+
+    // Call the endpoint (twice)
+
+    let requests = vec![
+        (fixtures::now(), fixtures::message::propose()),
+        (fixtures::now(), fixtures::message::propose()),
+    ];
+
+    for (sent_at, body) in &requests {
+        let request = super::Request { body: body.clone() };
+
+        let _ = super::handler(
+            State(app.clone()),
+            Path(conversation.id.clone()),
+            sent_at.clone(),
+            sender.clone(),
+            Json(request),
+        )
+        .await
+        .expect("sending to a valid conversation succeeds");
+    }
+
+    // Verify the semantics
+
+    let mut events = app
+        .events()
+        .subscribe(resume_point)
+        .await
+        .expect("subscribing always succeeds")
+        .filter_map(fixtures::event::stream::message)
+        .filter_map(fixtures::event::stream::message::sent)
+        .zip(stream::iter(requests));
+
+    while let Some((event, (sent_at, body))) = events
+        .next()
+        .expect_ready("an event should be ready for each message")
+        .await
+    {
+        assert_eq!(*sent_at, event.at());
+        assert_eq!(sender.user.id, event.message.sender);
+        assert_eq!(body, event.message.body);
+    }
+}
+
+#[tokio::test]
+async fn nonexistent_conversation() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+    let sender = fixtures::identity::create(&app, &fixtures::now()).await;
+
+    // Call the endpoint
+
+    let sent_at = fixtures::now();
+    let conversation = conversation::Id::generate();
+    let request = super::Request {
+        body: fixtures::message::propose(),
+    };
+    let super::Error(error) = super::handler(
+        State(app),
+        Path(conversation.clone()),
+        sent_at,
+        sender,
+        Json(request),
+    )
+    .await
+    .expect_err("sending to a nonexistent conversation fails");
+
+    // Verify the structure of the response
+
+    assert!(matches!(
+        error,
+        SendError::ConversationNotFound(error_conversation) if conversation == error_conversation
+    ));
+}
+
+#[tokio::test]
+async fn deleted_conversation() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+    let sender = fixtures::identity::create(&app, &fixtures::now()).await;
+    let conversation = fixtures::conversation::create(&app, &fixtures::now()).await;
+
+    app.conversations()
+        .delete(&conversation.id, &fixtures::now())
+        .await
+        .expect("deleting a new conversation succeeds");
+
+    // Call the endpoint
+
+    let sent_at = fixtures::now();
+    let request = super::Request {
+        body: fixtures::message::propose(),
+    };
+    let super::Error(error) = super::handler(
+        State(app),
+        Path(conversation.id.clone()),
+        sent_at,
+        sender,
+        Json(request),
+    )
+    .await
+    .expect_err("sending to a deleted conversation fails");
+
+    // Verify the structure of the response
+
+    assert!(matches!(
+        error,
+        SendError::ConversationDeleted(error_conversation) if conversation.id == error_conversation
+    ));
+}