const exported = {};

class NodeVisitor {
  visit(node) {
    for (const child of node.preorder()) {
      const key = `visit${kindToString(child.kind)}`;
      if (this[key] !== undefined) {
        this[key](child);
      }
    }
  }
}

exported.NodeVisitor = NodeVisitor;

const nodeProto = {

  *getChildNodes() {
    for (const key of Object.keys(this)) {
      if (key === 'span' || key === 'parentNode') {
        continue
      }
      const value = this[key];
      if (Array.isArray(value)) {
        for (const element of value) {
          if (isSyntax(element)) {
            yield element;
          }
        }
      } else {
        if (isSyntax(value)) {
          yield value;
        }
      }
    }
  },

  visit(visitors) {
    const stack = [this];
    while (stack.length > 0) {
      const node = stack.pop();
      const key = `visit${kindToString(node.kind)}`
      for (const visitor of visitors) {
         if (visitor[key] !== undefined) {
           visitor[key](node);
         }
      }
      for (const childNode of node.getChildNodes()) {
        stack.push(childNode);
      }
    }
  },

  *preorder() {
    const stack = [this];
    while (stack.length > 0) {
      const node = stack.pop();
      yield node
      for (const childNode of node.getChildNodes()) {
        stack.push(childNode);
      }
    }
  },

  mayContainKind(kind) {
    // TODO
    return true;
  },

  getParentOfKind(kind) {
    let currNode = this.parentNode;
    while (currNode !== null) {
      if (currNode.kind === kind) {
        return currNode;
      }
      currNode = currNode.parentNode;
    }
    return null;
  },

  *findAllChildrenOfKind(kind) {
    for (const node of this.preorder()) {
      if (!node.mayContainKind(kind)) {
        break;
      }
      if (node.kind === kind) {
        yield node
      }
    }
  }

}

function isSyntax(value) {
  return typeof value === 'object'
      && value !== null
      && value.__NODE_TYPE !== undefined;
}

exported.isSyntax = isSyntax;

let nextNodeId = 1;

function createNode(nodeType) {
  const obj = Object.create(nodeProto);
  Object.defineProperty(obj, '__NODE_TYPE', {
    enumerable: false,
    writable: false,
    configurable: true,
    value: nodeType,
  });
  Object.defineProperty(obj, 'kind', {
    enumerable: false,
    configurable: true,
    get() {
      return this.__NODE_TYPE.index;
    }
  });
  Object.defineProperty(obj, 'errors', {
    enumerable: false,
    configurable: true,
    value: [],
  })
  Object.defineProperty(obj, 'id', {
    enumerable: true,
    configurable: true,
    value: nextNodeId++,
  })
  obj.span = null;
  return obj;
}

for (const nodeName of Object.keys(NODE_TYPES)) {

  exported[`create${nodeName}`] = function (...args) {
    const nodeType = NODE_TYPES[nodeName];
    const node = createNode(nodeType);
    let i = 0;
    const iter = nodeType.fields[Symbol.iterator]();
    for (; i < args.length; i++) {
      const { done, value } = iter.next();
      if (done) {
        break;
      }
      const [fieldName, fieldType] = value;
      node[fieldName] = args[i];
    }
    while (true) {
      const { done, value } = iter.next();
      if (done) {
        break;
      }
      const [fieldName, fieldType] = value;
      throw new Error(`No argument provided for field '${fieldName}'`);
    }
    if (i < args.length) {
      node.span = args[i++];
    }
    if (i < args.length) {
      throw new Error(`Too many arguments provided to function create${nodeName}`);
    }
    return node;
  }

}

exported.setParents = function setParents(node, parentNode = null) {
  node.parentNode = parentNode;
  for (const child of node.getChildNodes()) {
    setParents(child, node)
  }
}

if (typeof module !== 'undefined') {
  module.exports = exports;
}