refactor(snapshot): store unified patches in file diffs (#21244)

Co-authored-by: Adam <2363879+adamdotdevin@users.noreply.github.com>

packages/ui/src/components/session-diff.ts

@@ -0,0 +1,83 @@
+import { parsePatchFiles, type FileDiffMetadata } from "@pierre/diffs"
+import { sampledChecksum } from "@opencode-ai/util/encode"
+import { formatPatch, structuredPatch } from "diff"
+import type { SnapshotFileDiff, VcsFileDiff } from "@opencode-ai/sdk/v2"
+
+type LegacyDiff = {
+  file: string
+  patch?: string
+  before?: string
+  after?: string
+  additions: number
+  deletions: number
+  status?: "added" | "deleted" | "modified"
+}
+
+type ReviewDiff = SnapshotFileDiff | VcsFileDiff | LegacyDiff
+
+export type ViewDiff = {
+  file: string
+  patch: string
+  additions: number
+  deletions: number
+  status?: "added" | "deleted" | "modified"
+  fileDiff: FileDiffMetadata
+}
+
+const cache = new Map<string, FileDiffMetadata>()
+
+function empty(file: string, key: string) {
+  return {
+    name: file,
+    type: "change",
+    hunks: [],
+    splitLineCount: 0,
+    unifiedLineCount: 0,
+    isPartial: true,
+    deletionLines: [],
+    additionLines: [],
+    cacheKey: key,
+  } satisfies FileDiffMetadata
+}
+
+function patch(diff: ReviewDiff) {
+  if (typeof diff.patch === "string") return diff.patch
+  return formatPatch(
+    structuredPatch(
+      diff.file,
+      diff.file,
+      "before" in diff && typeof diff.before === "string" ? diff.before : "",
+      "after" in diff && typeof diff.after === "string" ? diff.after : "",
+      "",
+      "",
+      { context: Number.MAX_SAFE_INTEGER },
+    ),
+  )
+}
+
+function file(file: string, patch: string) {
+  const hit = cache.get(patch)
+  if (hit) return hit
+
+  const key = sampledChecksum(patch) ?? file
+  const value = parsePatchFiles(patch, key).flatMap((item) => item.files)[0] ?? empty(file, key)
+  cache.set(patch, value)
+  return value
+}
+
+export function normalize(diff: ReviewDiff): ViewDiff {
+  const next = patch(diff)
+  return {
+    file: diff.file,
+    patch: next,
+    additions: diff.additions,
+    deletions: diff.deletions,
+    status: diff.status,
+    fileDiff: file(diff.file, next),
+  }
+}
+
+export function text(diff: ViewDiff, side: "deletions" | "additions") {
+  if (side === "deletions") return diff.fileDiff.deletionLines.join("")
+  return diff.fileDiff.additionLines.join("")
+}