import { isScalar, isAlias, isSeq, isMap } from '../../nodes/identity.mjs';
import { Scalar } from '../../nodes/Scalar.mjs';

// If the value associated with a merge key is a single mapping node, each of
// its key/value pairs is inserted into the current mapping, unless the key
// already exists in it. If the value associated with the merge key is a
// sequence, then this sequence is expected to contain mapping nodes and each
// of these nodes is merged in turn according to its order in the sequence.
// Keys in mapping nodes earlier in the sequence override keys specified in
// later mapping nodes. -- http://yaml.org/type/merge.html
const MERGE_KEY = '<<';
const merge = {
  identify: value => value === MERGE_KEY || typeof value === 'symbol' && value.description === MERGE_KEY,
  default: 'key',
  tag: 'tag:yaml.org,2002:merge',
  test: /^<<$/,
  resolve: () => Object.assign(new Scalar(Symbol(MERGE_KEY)), {
    addToJSMap: addMergeToJSMap
  }),
  stringify: () => MERGE_KEY
};
const isMergeKey = (ctx, key) => (merge.identify(key) || isScalar(key) && (!key.type || key.type === Scalar.PLAIN) && merge.identify(key.value)) && ctx?.doc.schema.tags.some(tag => tag.tag === merge.tag && tag.default);
function addMergeToJSMap(ctx, map, value) {
  value = ctx && isAlias(value) ? value.resolve(ctx.doc) : value;
  if (isSeq(value)) for (const it of value.items) mergeValue(ctx, map, it);else if (Array.isArray(value)) for (const it of value) mergeValue(ctx, map, it);else mergeValue(ctx, map, value);
}
function mergeValue(ctx, map, value) {
  const source = ctx && isAlias(value) ? value.resolve(ctx.doc) : value;
  if (!isMap(source)) throw new Error('Merge sources must be maps or map aliases');
  const srcMap = source.toJSON(null, ctx, Map);
  for (const [key, value] of srcMap) {
    if (map instanceof Map) {
      if (!map.has(key)) map.set(key, value);
    } else if (map instanceof Set) {
      map.add(key);
    } else if (!Object.prototype.hasOwnProperty.call(map, key)) {
      Object.defineProperty(map, key, {
        value,
        writable: true,
        enumerable: true,
        configurable: true
      });
    }
  }
  return map;
}

export { addMergeToJSMap, isMergeKey, merge };
