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