feat: update frontend to integrate translation

frontend/src/translate.ts

@@ -0,0 +1,44 @@
+// Applying a French → English translation computed in Go: which elements
+// the selection covers, and the transaction that puts the translated
+// elements in place.
+import type { EditorState, Transaction } from 'prosemirror-state'
+import type { Revision, TranslatedElement } from './backend'
+import { flatElements, fromElement, schema } from './schema'
+import { ownLocks, type CurrentRevision } from './revisions'
+
+/** Flat indexes of the elements the selection touches; null for the whole script. */
+export function selectedElements(state: EditorState): number[] | null {
+  const { from, to, empty } = state.selection
+  if (empty) return null
+  const out: number[] = []
+  flatElements(state.doc).forEach(({ node, pos }, i) => {
+    if (pos + node.nodeSize > from && pos < to) out.push(i)
+  })
+  return out
+}
+
+/**
+ * Replaces each translated element, in one undoable step. Go has already
+ * placed the element's locked pages in the translated text, so the lock
+ * plugin is told to leave them; translated text is marked with the current
+ * revision set when revisions are being marked.
+ */
+export function applyTranslation(
+  state: EditorState,
+  changes: TranslatedElement[],
+  revisions: Revision[],
+  current: CurrentRevision | null,
+): Transaction {
+  const flat = flatElements(state.doc)
+  const tr = state.tr
+  const mark = current && schema.marks.revision.create(current)
+  // From the end, so the positions of the elements before stay valid.
+  for (const change of [...changes].sort((a, b) => b.index - a.index)) {
+    const at = flat[change.index]
+    if (!at) continue
+    const node = fromElement(change.element, revisions)
+    tr.replaceWith(at.pos, at.pos + at.node.nodeSize, node)
+    if (mark && node.content.size) tr.addMark(at.pos + 1, at.pos + 1 + node.content.size, mark)
+  }
+  return ownLocks(tr)
+}