import { BREAK, Kind } from '@0no-co/graphql.web';
import { getEnterLeaveForKind } from 'graphql/language/visitor';

export { getEnterLeaveForKind, getVisitFn } from 'graphql/language/visitor';
export { BREAK, visit, Kind } from '@0no-co/graphql.web';

export function visitInParallel(visitors) {
  const skipping = new Array(visitors.length).fill(null);
  const mergedVisitor = Object.create(null);

  for (const kind of Object.values(Kind)) {
    let hasVisitor = false;
    const enterList = new Array(visitors.length).fill(undefined);
    const leaveList = new Array(visitors.length).fill(undefined);

    for (let i = 0; i < visitors.length; ++i) {
      const { enter, leave } = getEnterLeaveForKind(visitors[i], kind);
      hasVisitor = hasVisitor || enter != null || leave != null;
      enterList[i] = enter;
      leaveList[i] = leave;
    }

    if (!hasVisitor) {
      continue;
    }

    const mergedEnterLeave = {
      enter(...args) {
        const node = args[0];
        for (let i = 0; i < visitors.length; i++) {
          if (skipping[i] === null) {
            const result = enterList[i] && enterList[i].apply(visitors[i], args);
            if (result === false) {
              skipping[i] = node;
            } else if (result === BREAK) {
              skipping[i] = BREAK;
            } else if (result !== undefined) {
              return result;
            }
          }
        }
      },
      leave(...args) {
        const node = args[0];
        for (let i = 0; i < visitors.length; i++) {
          if (skipping[i] === null) {
            const result = leaveList[i] && leaveList[i].apply(visitors[i], args);
            if (result === BREAK) {
              skipping[i] = BREAK;
            } else if (result !== undefined && result !== false) {
              return result;
            }
          } else if (skipping[i] === node) {
            skipping[i] = null;
          }
        }
      },
    };

    mergedVisitor[kind] = mergedEnterLeave;
  }

  return mergedVisitor;
}