basant307/AI_Governance_Project

1'use strict'2 3// The ABNF grammar in the spec is totally ambiguous.4//5// This parser follows the operator precedence defined in the6// `Order of Precedence and Parentheses` section.7 8module.exports = function (tokens) {9  var index = 010 11  function hasMore () {12    return index < tokens.length13  }14 15  function token () {16    return hasMore() ? tokens[index] : null17  }18 19  function next () {20    if (!hasMore()) {21      throw new Error()22    }23    index++24  }25 26  function parseOperator (operator) {27    var t = token()28    if (t && t.type === 'OPERATOR' && operator === t.string) {29      next()30      return t.string31    }32  }33 34  function parseWith () {35    if (parseOperator('WITH')) {36      var t = token()37      if (t && t.type === 'EXCEPTION') {38        next()39        return t.string40      }41      throw new Error('Expected exception after `WITH`')42    }43  }44 45  function parseLicenseRef () {46    // TODO: Actually, everything is concatenated into one string47    // for backward-compatibility but it could be better to return48    // a nice structure.49    var begin = index50    var string = ''51    var t = token()52    if (t.type === 'DOCUMENTREF') {53      next()54      string += 'DocumentRef-' + t.string + ':'55      if (!parseOperator(':')) {56        throw new Error('Expected `:` after `DocumentRef-...`')57      }58    }59    t = token()60    if (t.type === 'LICENSEREF') {61      next()62      string += 'LicenseRef-' + t.string63      return { license: string }64    }65    index = begin66  }67 68  function parseLicense () {69    var t = token()70    if (t && t.type === 'LICENSE') {71      next()72      var node = { license: t.string }73      if (parseOperator('+')) {74        node.plus = true75      }76      var exception = parseWith()77      if (exception) {78        node.exception = exception79      }80      return node81    }82  }83 84  function parseParenthesizedExpression () {85    var left = parseOperator('(')86    if (!left) {87      return88    }89 90    var expr = parseExpression()91 92    if (!parseOperator(')')) {93      throw new Error('Expected `)`')94    }95 96    return expr97  }98 99  function parseAtom () {100    return (101      parseParenthesizedExpression() ||102      parseLicenseRef() ||103      parseLicense()104    )105  }106 107  function makeBinaryOpParser (operator, nextParser) {108    return function parseBinaryOp () {109      var left = nextParser()110      if (!left) {111        return112      }113 114      if (!parseOperator(operator)) {115        return left116      }117 118      var right = parseBinaryOp()119      if (!right) {120        throw new Error('Expected expression')121      }122      return {123        left: left,124        conjunction: operator.toLowerCase(),125        right: right126      }127    }128  }129 130  var parseAnd = makeBinaryOpParser('AND', parseAtom)131  var parseExpression = makeBinaryOpParser('OR', parseAnd)132 133  var node = parseExpression()134  if (!node || hasMore()) {135    throw new Error('Syntax error')136  }137  return node138}139