Parse string with "parameter:value" style search syntax to object.

parseQueryStatement.js

/**
 * Parse string with `parameter:value` style search syntax to object.
 *
 * Examples:
 *     state:ut        --> {state: ['ut']}
 *     state:ut,az,id  --> {state: ['ut', 'az', 'id]}
 *     complete        --> {complete: 1}                   // defaults to value of 1
 *     {air_temp > 10} --> {filter_on: '(air_temp > 10)'}  // explicit statement
 *
 * @param {string} blob, query
 * @returns {object}, Mesonet API formatted query parameters
 *
 * (C) 2018 Adam C. Abernathy, [email protected]. Licence MIT
 * https://gist.github.com/adamabernathy/fb6f10bd046839cad933248385551eec
 */
const parseQueryStatement = blob => {
  if (typeof blob === 'undefined' || blob === null || blob === '') return null;
  const ast = {};

  blob = blob.toLowerCase();

  // Need to seperate any filter expressions from parameter tokens
  if (blob.indexOf('{') !== -1 && blob.indexOf('}' !== -1)) {
    const filterStartPos = blob.indexOf('{');
    const filterStopPos = blob.indexOf('}');
    ast.filter_on = `(${blob.slice(filterStartPos + 1, filterStopPos)})`;
    blob = `${blob.slice(0, filterStartPos)}${blob.slice(filterStopPos + 1)}`.trim();
  }

  // Parse out the tokens assuming there will be escaped strings
  // The idea here is to keep track of if we are inside an escaped string or not
  const statements = blob.match(/\\?.|^$/g).reduce(
    (tokens, lex) => {
      if (lex === '"') {
        tokens.quote ^= 1; // XOR inside quote is true
      } else if (!tokens.quote && lex === ' ') {
        tokens.expression.push('');
      } else {
        // put the string together to comprise the expression
        tokens.expression[tokens.expression.length - 1] += lex.replace(/\\(.)/, '$1');
      }
      return tokens;
    },
    { expression: [''] },
  ).expression;

  for (let i = 0, l = statements.length; i < l; i++) {
    if (statements[i] !== '') {
      const token = statements[i].split(':');
      token[1] = token[1] || 1;
      ast[token[0]] = typeof token[1] === 'string' ? token[1].split(',') : token[1];
    }
  }

  return ast;
};