Function resolveParent

packages/effect/src/JsonPatch.ts:362–395

(
  doc: Schema.Json,
  pointer: string
)

// Walk to the parent of `pointer`, recording the path.
// Returns null if the parent path cannot be resolved.
function resolveParent(
  doc: Schema.Json,
  pointer: string
): { readonly stack: ReadonlyArray<StackEntry>; readonly parent: unknown; readonly lastToken: string } | null {
  const tokens = tokenize(pointer)
  if (tokens.length === 0) return null // caller handles root

  const lastToken = tokens[tokens.length - 1]
  const stack: Array<StackEntry> = []
  let cur: unknown = doc

  for (let i = 0; i < tokens.length - 1; i++) {
    const token = tokens[i]

    if (Array.isArray(cur)) {
      const idx = toIndex(token)
      if (idx >= cur.length) return null
      stack.push({ container: cur, token: idx })
      cur = cur[idx]
      continue
    }

    if (isJsonObject(cur)) {
      if (!Object.hasOwn(cur, token)) return null
      stack.push({ container: cur, token })
      cur = cur[token]
      continue
    }

    return null
  }

  return { stack, parent: cur, lastToken }
}

// Rebuild the document by writing `newParent` back through `stack`.
function rebuildFromStack(stack: ReadonlyArray<StackEntry>, newParent: Schema.Json): Schema.Json {