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'use strict'
// The ABNF grammar in the spec is totally ambiguous.
//
// This parser follows the operator precedence defined in the
// `Order of Precedence and Parentheses` section.
module.exports = function (tokens) {
var index = 0
function hasMore () {
return index < tokens.length
}
function token () {
return hasMore() ? tokens[index] : null
}
function next () {
if (!hasMore()) {
throw new Error()
}
index++
}
function parseOperator (operator) {
var t = token()
if (t && t.type === 'OPERATOR' && operator === t.string) {
next()
return t.string
}
}
function parseWith () {
if (parseOperator('WITH')) {
var t = token()
if (t && t.type === 'EXCEPTION') {
next()
return t.string
}
throw new Error('Expected exception after `WITH`')
}
}
function parseLicenseRef () {
// TODO: Actually, everything is concatenated into one string
// for backward-compatibility but it could be better to return
// a nice structure.
var begin = index
var string = ''
var t = token()
if (t.type === 'DOCUMENTREF') {
next()
string += 'DocumentRef-' + t.string + ':'
if (!parseOperator(':')) {
throw new Error('Expected `:` after `DocumentRef-...`')
}
}
t = token()
if (t.type === 'LICENSEREF') {
next()
string += 'LicenseRef-' + t.string
return {license: string}
}
index = begin
}
function parseLicense () {
var t = token()
if (t && t.type === 'LICENSE') {
next()
var node = {license: t.string}
if (parseOperator('+')) {
node.plus = true
}
var exception = parseWith()
if (exception) {
node.exception = exception
}
return node
}
}
function parseParenthesizedExpression () {
var left = parseOperator('(')
if (!left) {
return
}
var expr = parseExpression()
if (!parseOperator(')')) {
throw new Error('Expected `)`')
}
return expr
}
function parseAtom () {
return (
parseParenthesizedExpression() ||
parseLicenseRef() ||
parseLicense()
)
}
function makeBinaryOpParser (operator, nextParser) {
return function parseBinaryOp () {
var left = nextParser()
if (!left) {
return
}
if (!parseOperator(operator)) {
return left
}
var right = parseBinaryOp()
if (!right) {
throw new Error('Expected expression')
}
return {
left: left,
conjunction: operator.toLowerCase(),
right: right
}
}
}
var parseAnd = makeBinaryOpParser('AND', parseAtom)
var parseExpression = makeBinaryOpParser('OR', parseAnd)
var node = parseExpression()
if (!node || hasMore()) {
throw new Error('Syntax error')
}
return node
}
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