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.

7 files changed, 764 insertions, 0 deletions

diff --git a/src/conversation/handlers/create/mod.rs b/src/conversation/handlers/create/mod.rs
new file mode 100644
index 0000000..18eca1f
--- /dev/null
+++ b/src/conversation/handlers/create/mod.rs
@@ -0,0 +1,67 @@
+use axum::{
+    extract::{Json, State},
+    http::StatusCode,
+    response::{self, IntoResponse},
+};
+
+use crate::{
+    app::App,
+    clock::RequestedAt,
+    conversation::{Conversation, app},
+    error::Internal,
+    name::Name,
+    token::extract::Identity,
+};
+
+#[cfg(test)]
+mod test;
+
+pub async fn handler(
+    State(app): State<App>,
+    _: Identity, // requires auth, but doesn't actually care who you are
+    RequestedAt(created_at): RequestedAt,
+    Json(request): Json<Request>,
+) -> Result<Response, Error> {
+    let conversation = app
+        .conversations()
+        .create(&request.name, &created_at)
+        .await
+        .map_err(Error)?;
+
+    Ok(Response(conversation))
+}
+
+#[derive(serde::Deserialize)]
+pub struct Request {
+    pub name: Name,
+}
+
+#[derive(Debug)]
+pub struct Response(pub Conversation);
+
+impl IntoResponse for Response {
+    fn into_response(self) -> response::Response {
+        let Self(conversation) = self;
+        (StatusCode::ACCEPTED, Json(conversation)).into_response()
+    }
+}
+
+#[derive(Debug)]
+pub struct Error(pub app::CreateError);
+
+impl IntoResponse for Error {
+    fn into_response(self) -> response::Response {
+        let Self(error) = self;
+        match error {
+            app::CreateError::DuplicateName(_) => {
+                (StatusCode::CONFLICT, error.to_string()).into_response()
+            }
+            app::CreateError::InvalidName(_) => {
+                (StatusCode::BAD_REQUEST, error.to_string()).into_response()
+            }
+            app::CreateError::Name(_) | app::CreateError::Database(_) => {
+                Internal::from(error).into_response()
+            }
+        }
+    }
+}
diff --git a/src/conversation/handlers/create/test.rs b/src/conversation/handlers/create/test.rs
new file mode 100644
index 0000000..bc05b00
--- /dev/null
+++ b/src/conversation/handlers/create/test.rs
@@ -0,0 +1,250 @@
+use std::future;
+
+use axum::extract::{Json, State};
+use futures::stream::StreamExt as _;
+use itertools::Itertools;
+
+use crate::{
+    conversation::app,
+    name::Name,
+    test::fixtures::{self, future::Expect as _},
+};
+
+#[tokio::test]
+async fn new_conversation() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+    let creator = fixtures::identity::create(&app, &fixtures::now()).await;
+    let resume_point = fixtures::boot::resume_point(&app).await;
+
+    // Call the endpoint
+
+    let name = fixtures::conversation::propose();
+    let request = super::Request { name: name.clone() };
+    let super::Response(response) =
+        super::handler(State(app.clone()), creator, fixtures::now(), Json(request))
+            .await
+            .expect("creating a conversation in an empty app succeeds");
+
+    // Verify the structure of the response
+
+    assert_eq!(name, response.name);
+
+    // Verify the semantics
+
+    let snapshot = app.boot().snapshot().await.expect("boot always succeeds");
+    let created = snapshot
+        .events
+        .into_iter()
+        .filter_map(fixtures::event::conversation)
+        .filter_map(fixtures::event::conversation::created)
+        .exactly_one()
+        .expect("only one conversation has been created");
+    assert_eq!(response, created.conversation);
+
+    let conversation = app
+        .conversations()
+        .get(&response.id)
+        .await
+        .expect("the newly-created conversation exists");
+    assert_eq!(response, conversation);
+
+    let mut events = app
+        .events()
+        .subscribe(resume_point)
+        .await
+        .expect("subscribing never fails")
+        .filter_map(fixtures::event::stream::conversation)
+        .filter_map(fixtures::event::stream::conversation::created)
+        .filter(|event| future::ready(event.conversation == response));
+
+    let event = events.next().expect_some("creation event published").await;
+
+    assert_eq!(event.conversation, response);
+}
+
+#[tokio::test]
+async fn duplicate_name() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+    let creator = fixtures::identity::create(&app, &fixtures::now()).await;
+    let conversation = fixtures::conversation::create(&app, &fixtures::now()).await;
+
+    // Call the endpoint
+
+    let request = super::Request {
+        name: conversation.name.clone(),
+    };
+    let super::Error(error) =
+        super::handler(State(app.clone()), creator, fixtures::now(), Json(request))
+            .await
+            .expect_err("duplicate conversation name should fail the request");
+
+    // Verify the structure of the response
+
+    assert!(matches!(
+        error,
+        app::CreateError::DuplicateName(name) if conversation.name == name
+    ));
+}
+
+#[tokio::test]
+async fn conflicting_canonical_name() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+    let creator = fixtures::identity::create(&app, &fixtures::now()).await;
+
+    let existing_name = Name::from("rijksmuseum");
+    app.conversations()
+        .create(&existing_name, &fixtures::now())
+        .await
+        .expect("creating a conversation in an empty environment succeeds");
+
+    let conflicting_name = Name::from("r\u{0133}ksmuseum");
+
+    // Call the endpoint
+
+    let request = super::Request {
+        name: conflicting_name.clone(),
+    };
+    let super::Error(error) =
+        super::handler(State(app.clone()), creator, fixtures::now(), Json(request))
+            .await
+            .expect_err("duplicate conversation name should fail the request");
+
+    // Verify the structure of the response
+
+    assert!(matches!(
+        error,
+        app::CreateError::DuplicateName(name) if conflicting_name == name
+    ));
+}
+
+#[tokio::test]
+async fn invalid_name() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+    let creator = fixtures::identity::create(&app, &fixtures::now()).await;
+
+    // Call the endpoint
+
+    let name = fixtures::conversation::propose_invalid_name();
+    let request = super::Request { name: name.clone() };
+    let super::Error(error) = crate::conversation::handlers::create::handler(
+        State(app.clone()),
+        creator,
+        fixtures::now(),
+        Json(request),
+    )
+    .await
+    .expect_err("invalid conversation name should fail the request");
+
+    // Verify the structure of the response
+
+    assert!(matches!(
+        error,
+        app::CreateError::InvalidName(error_name) if name == error_name
+    ));
+}
+
+#[tokio::test]
+async fn name_reusable_after_delete() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+    let creator = fixtures::identity::create(&app, &fixtures::now()).await;
+    let name = fixtures::conversation::propose();
+
+    // Call the endpoint (first time)
+
+    let request = super::Request { name: name.clone() };
+    let super::Response(response) = super::handler(
+        State(app.clone()),
+        creator.clone(),
+        fixtures::now(),
+        Json(request),
+    )
+    .await
+    .expect("new conversation in an empty app");
+
+    // Delete the conversation
+
+    app.conversations()
+        .delete(&response.id, &fixtures::now())
+        .await
+        .expect("deleting a newly-created conversation succeeds");
+
+    // Call the endpoint (second time)
+
+    let request = super::Request { name: name.clone() };
+    let super::Response(response) =
+        super::handler(State(app.clone()), creator, fixtures::now(), Json(request))
+            .await
+            .expect("creation succeeds after original conversation deleted");
+
+    // Verify the structure of the response
+
+    assert_eq!(name, response.name);
+
+    // Verify the semantics
+
+    let conversation = app
+        .conversations()
+        .get(&response.id)
+        .await
+        .expect("the newly-created conversation exists");
+    assert_eq!(response, conversation);
+}
+
+#[tokio::test]
+async fn name_reusable_after_expiry() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+    let creator = fixtures::identity::create(&app, &fixtures::ancient()).await;
+    let name = fixtures::conversation::propose();
+
+    // Call the endpoint (first time)
+
+    let request = super::Request { name: name.clone() };
+    let super::Response(_) = super::handler(
+        State(app.clone()),
+        creator.clone(),
+        fixtures::ancient(),
+        Json(request),
+    )
+    .await
+    .expect("new conversation in an empty app");
+
+    // Expire the conversation
+
+    app.conversations()
+        .expire(&fixtures::now())
+        .await
+        .expect("expiry always succeeds");
+
+    // Call the endpoint (second time)
+
+    let request = super::Request { name: name.clone() };
+    let super::Response(response) =
+        super::handler(State(app.clone()), creator, fixtures::now(), Json(request))
+            .await
+            .expect("creation succeeds after original conversation expired");
+
+    // Verify the structure of the response
+
+    assert_eq!(name, response.name);
+
+    // Verify the semantics
+
+    let conversation = app
+        .conversations()
+        .get(&response.id)
+        .await
+        .expect("the newly-created conversation exists");
+    assert_eq!(response, conversation);
+}
diff --git a/src/conversation/handlers/delete/mod.rs b/src/conversation/handlers/delete/mod.rs
new file mode 100644
index 0000000..272165a
--- /dev/null
+++ b/src/conversation/handlers/delete/mod.rs
@@ -0,0 +1,61 @@
+use axum::{
+    extract::{Json, Path, State},
+    http::StatusCode,
+    response::{self, IntoResponse},
+};
+
+use crate::{
+    app::App,
+    clock::RequestedAt,
+    conversation::{self, app, handlers::PathInfo},
+    error::{Internal, NotFound},
+    token::extract::Identity,
+};
+
+#[cfg(test)]
+mod test;
+
+pub async fn handler(
+    State(app): State<App>,
+    Path(conversation): Path<PathInfo>,
+    RequestedAt(deleted_at): RequestedAt,
+    _: Identity,
+) -> Result<Response, Error> {
+    app.conversations()
+        .delete(&conversation, &deleted_at)
+        .await?;
+
+    Ok(Response { id: conversation })
+}
+
+#[derive(Debug, serde::Serialize)]
+pub struct Response {
+    pub id: conversation::Id,
+}
+
+impl IntoResponse for Response {
+    fn into_response(self) -> response::Response {
+        (StatusCode::ACCEPTED, Json(self)).into_response()
+    }
+}
+
+#[derive(Debug, thiserror::Error)]
+#[error(transparent)]
+pub struct Error(#[from] pub app::DeleteError);
+
+impl IntoResponse for Error {
+    fn into_response(self) -> response::Response {
+        let Self(error) = self;
+        match error {
+            app::DeleteError::NotFound(_) | app::DeleteError::Deleted(_) => {
+                NotFound(error).into_response()
+            }
+            app::DeleteError::NotEmpty(_) => {
+                (StatusCode::CONFLICT, error.to_string()).into_response()
+            }
+            app::DeleteError::Name(_) | app::DeleteError::Database(_) => {
+                Internal::from(error).into_response()
+            }
+        }
+    }
+}
diff --git a/src/conversation/handlers/delete/test.rs b/src/conversation/handlers/delete/test.rs
new file mode 100644
index 0000000..2718d3b
--- /dev/null
+++ b/src/conversation/handlers/delete/test.rs
@@ -0,0 +1,184 @@
+use axum::extract::{Path, State};
+use itertools::Itertools;
+
+use crate::{conversation::app, test::fixtures};
+
+#[tokio::test]
+pub async fn valid_conversation() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+    let conversation = fixtures::conversation::create(&app, &fixtures::now()).await;
+
+    // Send the request
+
+    let deleter = fixtures::identity::create(&app, &fixtures::now()).await;
+    let response = super::handler(
+        State(app.clone()),
+        Path(conversation.id.clone()),
+        fixtures::now(),
+        deleter,
+    )
+    .await
+    .expect("deleting a valid conversation succeeds");
+
+    // Verify the response
+
+    assert_eq!(conversation.id, response.id);
+
+    // Verify the semantics
+
+    let snapshot = app.boot().snapshot().await.expect("boot always succeeds");
+    let created = snapshot
+        .events
+        .into_iter()
+        .filter_map(fixtures::event::conversation)
+        .filter_map(fixtures::event::conversation::created)
+        .exactly_one()
+        .expect("only one conversation has been created");
+    // We don't expect `conversation` to match the event exactly, as the name will have
+    // been tombstoned and the conversation given a `deleted_at` date.
+    assert_eq!(conversation.id, created.conversation.id);
+}
+
+#[tokio::test]
+pub async fn invalid_conversation_id() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+
+    // Send the request
+
+    let deleter = fixtures::identity::create(&app, &fixtures::now()).await;
+    let conversation = fixtures::conversation::fictitious();
+    let super::Error(error) = super::handler(
+        State(app.clone()),
+        Path(conversation.clone()),
+        fixtures::now(),
+        deleter,
+    )
+    .await
+    .expect_err("deleting a nonexistent conversation fails");
+
+    // Verify the response
+
+    assert!(matches!(error, app::DeleteError::NotFound(id) if id == conversation));
+}
+
+#[tokio::test]
+pub async fn conversation_deleted() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+    let conversation = fixtures::conversation::create(&app, &fixtures::now()).await;
+
+    app.conversations()
+        .delete(&conversation.id, &fixtures::now())
+        .await
+        .expect("deleting a recently-created conversation succeeds");
+
+    // Send the request
+
+    let deleter = fixtures::identity::create(&app, &fixtures::now()).await;
+    let super::Error(error) = super::handler(
+        State(app.clone()),
+        Path(conversation.id.clone()),
+        fixtures::now(),
+        deleter,
+    )
+    .await
+    .expect_err("deleting a deleted conversation fails");
+
+    // Verify the response
+
+    assert!(matches!(error, app::DeleteError::Deleted(id) if id == conversation.id));
+}
+
+#[tokio::test]
+pub async fn conversation_expired() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+    let conversation = fixtures::conversation::create(&app, &fixtures::ancient()).await;
+
+    app.conversations()
+        .expire(&fixtures::now())
+        .await
+        .expect("expiring conversations always succeeds");
+
+    // Send the request
+
+    let deleter = fixtures::identity::create(&app, &fixtures::now()).await;
+    let super::Error(error) = super::handler(
+        State(app.clone()),
+        Path(conversation.id.clone()),
+        fixtures::now(),
+        deleter,
+    )
+    .await
+    .expect_err("deleting an expired conversation fails");
+
+    // Verify the response
+
+    assert!(matches!(error, app::DeleteError::Deleted(id) if id == conversation.id));
+}
+
+#[tokio::test]
+pub async fn conversation_purged() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+    let conversation = fixtures::conversation::create(&app, &fixtures::ancient()).await;
+
+    app.conversations()
+        .expire(&fixtures::old())
+        .await
+        .expect("expiring conversations always succeeds");
+
+    app.conversations()
+        .purge(&fixtures::now())
+        .await
+        .expect("purging conversations always succeeds");
+
+    // Send the request
+
+    let deleter = fixtures::identity::create(&app, &fixtures::now()).await;
+    let super::Error(error) = super::handler(
+        State(app.clone()),
+        Path(conversation.id.clone()),
+        fixtures::now(),
+        deleter,
+    )
+    .await
+    .expect_err("deleting a purged conversation fails");
+
+    // Verify the response
+
+    assert!(matches!(error, app::DeleteError::NotFound(id) if id == conversation.id));
+}
+
+#[tokio::test]
+pub async fn conversation_not_empty() {
+    // Set up the environment
+
+    let app = fixtures::scratch_app().await;
+    let conversation = fixtures::conversation::create(&app, &fixtures::now()).await;
+    let sender = fixtures::user::create(&app, &fixtures::now()).await;
+    fixtures::message::send(&app, &conversation, &sender, &fixtures::now()).await;
+
+    // Send the request
+
+    let deleter = fixtures::identity::create(&app, &fixtures::now()).await;
+    let super::Error(error) = super::handler(
+        State(app.clone()),
+        Path(conversation.id.clone()),
+        fixtures::now(),
+        deleter,
+    )
+    .await
+    .expect_err("deleting a conversation with messages fails");
+
+    // Verify the response
+
+    assert!(matches!(error, app::DeleteError::NotEmpty(id) if id == conversation.id));
+}
diff --git a/src/conversation/handlers/mod.rs b/src/conversation/handlers/mod.rs
new file mode 100644
index 0000000..2fe727c
--- /dev/null
+++ b/src/conversation/handlers/mod.rs
@@ -0,0 +1,9 @@
+mod create;
+mod delete;
+mod send;
+
+pub use create::handler as create;
+pub use delete::handler as delete;
+pub use send::handler as send;
+
+type PathInfo = crate::conversation::Id;
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
+    ));
+}