import {
  semanticArrayIndex,
  type JavaScriptSemanticPropertyPath as PropertyPath,
} from "./javascriptSemanticPropertyPaths.js";
import { compareUnicodeCodePoints } from "../unicodeCodePointOrder.js";

interface CopiedReferenceSource {
  readonly projection: PropertyPath;
  readonly copyKind?: "object-rest" | "array-rest";
  readonly copyProjectionOffset?: number;
  readonly copyExcludedKeys?: readonly string[];
  readonly copyStartIndex?: number;
}

/** Map copied child selections once; the fresh copy itself keeps its own identity. */
export const semanticCopiedReferencePath = (
  initializer: CopiedReferenceSource,
  path: PropertyPath,
  effect: "write" | "escape" | "identity",
): PropertyPath | null => {
  const offset = initializer.copyProjectionOffset;
  if (offset === undefined) return [...initializer.projection, ...path];
  const copiedPath = [...initializer.projection.slice(offset + 1), ...path];
  if (effect === "identity" && copiedPath.length === 0) return null;
  if (effect === "write" && copiedPath.length < 2) return null;
  let [key, ...remaining] = copiedPath;
  if (initializer.copyKind === "array-rest") {
    const startIndex = initializer.copyStartIndex ?? 0;
    if (key === undefined || key === null)
      key = { excludedKeys: [], startIndex };
    else if (typeof key === "object")
      key = {
        excludedKeys: key.excludedKeys.flatMap((name) => {
          const index = semanticArrayIndex(name);
          return index === null ? [] : [String(index + startIndex)];
        }),
        startIndex: (key.startIndex ?? 0) + startIndex,
      };
    else {
      const index = semanticArrayIndex(key);
      if (index === null) return null;
      key = index + startIndex;
    }
  } else {
    const excludedKeys = initializer.copyExcludedKeys ?? [];
    if (key === undefined || key === null) key = { excludedKeys };
    else if (typeof key === "object")
      key = {
        ...key,
        excludedKeys: [...new Set([...key.excludedKeys, ...excludedKeys])].sort(
          compareUnicodeCodePoints,
        ),
      };
    else if (excludedKeys.includes(String(key))) return null;
  }
  return [...initializer.projection.slice(0, offset), key, ...remaining];
};