import R = require('./regexes')

/**
 * Regex for replacing of jscc varnames ($1 = prefix, $2 = varname).
 */
const VARS_TO_EVL = RegExp(`${R.S_STRINGS}|${R.S_VARNAMES}`, 'g')

/**
 * Replacing function
 */
const _repVars = function (this: any, match: string, prech: string, vname: string) {
  return vname ? prech + (vname in this ? `this.${vname}` : `global.${vname}`) : match
}

/**
 * Method to perform the evaluation of the given string using a function
 * instantiated dynamically.
 *
 * @param ctx Context with the current variables and the error handler
 * @param exprStr String to evaluate, can include other defined vars
 */
const evalExpr = function _evalExpr (ctx: JsccProps, exprStr: string) {
  const values = ctx.values

  // var replacement
  const expr = exprStr
    .replace(/\n/g, '\\n')
    .replace(/\r/g, '\\r')
    .replace(VARS_TO_EVL, _repVars.bind(values))

  let result
  try {
    // The '\n' in the Function ctor will support single-line comments,
    // if required by a future version.
    // tslint:disable-next-line:function-constructor
    const fn = new Function('', `return (${expr}\n);`)
    result = fn.call(values)
  } catch (e) {
    result = exprStr
    ctx.errorHandler(`${e.message} in expression "${expr}"`)
  }

  return result
}

export = evalExpr