GenServer managing a single collaborative document via Operational Transform.

Each document gets its own CollabServer process that maintains the authoritative document state, version counter, and operation history. Clients submit operations along with their last-known version; the server transforms against any intervening operations before applying.

Architecture

Client A ──apply_op──> CollabServer ──broadcast──> PubSub ──> Client B
Client B ──apply_op──> CollabServer ──broadcast──> PubSub ──> Client A

State

• :doc_id — unique document identifier
• :content — current document text (string)
• :version — monotonically increasing integer (starts at 0)
• :history — list of {version, delta, client_id} tuples (newest first)
• :clients — MapSet of connected client identifiers

Usage

# Start a server for a document
{:ok, pid} = PhiaUi.Editor.CollabServer.start_link(doc_id: "doc-123")

# Client submits an operation
{:ok, transformed_op, new_version} =
  PhiaUi.Editor.CollabServer.apply_op(pid, [%{retain: 5}, %{insert: "!"}], 0)

# Read current state
{"Hello!", 1} = PhiaUi.Editor.CollabServer.get_document(pid)

PubSub Broadcasting

After each successful operation, the server broadcasts on "collab:doc:<doc_id>" via Phoenix.PubSub (configured in :phia_ui, :collab_pubsub). The broadcast payload is:

%{
  event: :op_applied,
  doc_id: doc_id,
  op: transformed_delta,
  version: new_version,
  client_id: client_id
}

History Pruning

History is capped at 1000 entries. Older entries are discarded to bound memory usage. Clients that fall behind by more than 1000 versions must re-fetch the full document.