import { ParserFunction, Plugin } from 'unified';
// import {Node as UnistNode} from 'unist';
import { VFile } from 'vfile';
import nearley from 'nearley';

import grammar from './gram-grammar';
import * as errors from './gram-errors';

import { Point } from 'unist';
import { LexerState } from 'nearley';
import { Token } from 'moo';

const lexerLocation = (state: LexerState): Point => {
  return {
    line: state.line,
    column: state.col,
  };
};

const tokenLocation = (token: Token) => {
  return {
    line: token.line,
    column: token.col,
  };
};

export const parse: ParserFunction = (text: string, file: VFile) => {
  const nearleyParser = new nearley.Parser(
    nearley.Grammar.fromCompiled(grammar)
  );
  try {
    const parsed = nearleyParser.feed(text);
    if (parsed.results[0] === undefined && parsed.lexerState) {
      const location = lexerLocation(parsed.lexerState);
      file.fail(errors.INCOMPLETE_PARSE, location);
    }
    if (parsed.results.length > 1) {
      file.info('[WARN] parsing is ambiguous');
    }
    return parsed.results[0] || { type: 'error' };
  } catch (e) {
    const location = e.token ? tokenLocation(e.token) : { line: 0, column: 0 };
    file.fail(e.message, location);
  }
};
export interface GramParserSettings {
  strict: boolean;
}

const gramParserPlugin: Plugin<GramParserSettings[]> = function() {
  this.Parser = parse;
};

export default gramParserPlugin;