import { clone } from './clone.ts';
import { cloneDeep } from './cloneDeep.ts';
import { mergeWith } from './mergeWith.ts';
import { isPlainObject } from '../predicate/isPlainObject.ts';

/**
 * Merges the properties of the source object into a deep clone of the target object.
 * Unlike `merge`, This function does not modify the original target object.
 *
 * This function performs a deep merge, meaning nested objects and arrays are merged recursively.
 *
 * - If a property in the source object is an array or object and the corresponding property in the target object is also an array or object, they will be merged.
 * - If a property in the source object is undefined, it will not overwrite a defined property in the target object.
 *
 * Note that this function does not mutate the target object.
 *
 * @param target - The target object to be cloned and merged into. This object is not modified directly.
 * @param source - The source object whose properties will be merged into the cloned target object.
 * @returns A new object with properties from the source object merged into a deep clone of the target object.
 *
 * @template T - Type of the target object.
 * @template S - Type of the source object.
 *
 * @example
 * const target = { a: 1, b: { x: 1, y: 2 } };
 * const source = { b: { y: 3, z: 4 }, c: 5 };
 *
 * const result = toMerged(target, source);
 * console.log(result);
 * // Output: { a: 1, b: { x: 1, y: 3, z: 4 }, c: 5 }
 *
 * @example
 * const target = { a: [1, 2], b: { x: 1 } };
 * const source = { a: [3], b: { y: 2 } };
 *
 * const result = toMerged(target, source);
 * console.log(result);
 * // Output: { a: [3, 2], b: { x: 1, y: 2 } }
 *
 * @example
 * const target = { a: null };
 * const source = { a: [1, 2, 3] };
 *
 * const result = toMerged(target, source);
 * console.log(result);
 * // Output: { a: [1, 2, 3] }
 */
export function toMerged<T extends Record<PropertyKey, any>, S extends Record<PropertyKey, any>>(
  target: T,
  source: S
): T & S {
  return mergeWith(cloneDeep(target), source, function mergeRecursively(targetValue, sourceValue) {
    if (Array.isArray(sourceValue)) {
      if (Array.isArray(targetValue)) {
        return mergeWith(clone(targetValue), sourceValue, mergeRecursively);
      } else {
        return mergeWith([], sourceValue, mergeRecursively);
      }
    } else if (isPlainObject(sourceValue)) {
      if (isPlainObject(targetValue)) {
        return mergeWith(clone(targetValue), sourceValue, mergeRecursively);
      } else {
        return mergeWith({}, sourceValue, mergeRecursively);
      }
    }
  });
}
