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| 1 | +'use strict' |
| 2 | + |
| 3 | +/* eslint-disable no-constant-condition */ |
| 4 | + |
| 5 | +// See https://tools.ietf.org/html/rfc4647#section-3.1 |
| 6 | +// for more information on the algorithms. |
| 7 | + |
| 8 | +var dash = '-' |
| 9 | +var asterisk = '*' |
| 10 | + |
| 11 | +exports.basicFilter = factory(basic, true) |
| 12 | +exports.extendedFilter = factory(extended, true) |
| 13 | +exports.lookup = factory(lookup) |
| 14 | + |
| 15 | +// Basic Filtering (Section 3.3.1) matches a language priority list consisting |
| 16 | +// of basic language ranges (Section 2.1) to sets of language tags. |
| 17 | +function basic(tag, range) { |
| 18 | + tag = lower(tag) |
| 19 | + range = lower(range) |
| 20 | + return range === asterisk || tag === range || tag.indexOf(range + dash) !== -1 |
| 21 | +} |
| 22 | + |
| 23 | +// Extended Filtering (Section 3.3.2) matches a language priority list |
| 24 | +// consisting of extended language ranges (Section 2.2) to sets of language |
| 25 | +// tags. |
| 26 | +function extended(tag, range) { |
| 27 | + // 3.3.2.1 |
| 28 | + var tags = lower(tag).split(dash) |
| 29 | + var ranges = lower(range).split(dash) |
| 30 | + var length = ranges.length |
| 31 | + var rangeIndex = -1 |
| 32 | + var tagIndex = -1 |
| 33 | + |
| 34 | + tag = tags[++tagIndex] |
| 35 | + range = ranges[++rangeIndex] |
| 36 | + |
| 37 | + // 3.3.2.2 |
| 38 | + if (range !== asterisk && range !== tag) { |
| 39 | + return false |
| 40 | + } |
| 41 | + |
| 42 | + tag = tags[++tagIndex] |
| 43 | + range = ranges[++rangeIndex] |
| 44 | + |
| 45 | + // 3.3.2.3 |
| 46 | + while (rangeIndex < length) { |
| 47 | + // 3.3.2.3.A |
| 48 | + if (range === asterisk) { |
| 49 | + range = ranges[++rangeIndex] |
| 50 | + continue |
| 51 | + } |
| 52 | + |
| 53 | + // 3.3.2.3.B |
| 54 | + if (!tag) { |
| 55 | + return false |
| 56 | + } |
| 57 | + |
| 58 | + // 3.3.2.3.C |
| 59 | + if (tag === range) { |
| 60 | + tag = tags[++tagIndex] |
| 61 | + range = ranges[++rangeIndex] |
| 62 | + continue |
| 63 | + } |
| 64 | + |
| 65 | + // 3.3.2.3.D |
| 66 | + if (tag.length === 1) { |
| 67 | + return false |
| 68 | + } |
| 69 | + |
| 70 | + // 3.3.2.3.E |
| 71 | + tag = tags[++tagIndex] |
| 72 | + } |
| 73 | + |
| 74 | + // 3.3.2.4 |
| 75 | + return true |
| 76 | +} |
| 77 | + |
| 78 | +// Lookup (Section 3.4) matches a language priority list consisting of basic |
| 79 | +// language ranges to sets of language tags to find the one exact language tag |
| 80 | +// that best matches the range. |
| 81 | +function lookup(tag, range) { |
| 82 | + var pos |
| 83 | + |
| 84 | + tag = lower(tag) |
| 85 | + range = lower(range) |
| 86 | + |
| 87 | + while (true) { |
| 88 | + if (range === asterisk || tag === range) { |
| 89 | + return true |
| 90 | + } |
| 91 | + |
| 92 | + pos = range.lastIndexOf(dash) |
| 93 | + |
| 94 | + if (pos === -1) { |
| 95 | + return false |
| 96 | + } |
| 97 | + |
| 98 | + if (pos > 3 && range.charAt(pos - 2) === dash) { |
| 99 | + pos -= 2 |
| 100 | + } |
| 101 | + |
| 102 | + range = range.substring(0, pos) |
| 103 | + } |
| 104 | +} |
| 105 | + |
| 106 | +// Factory to perform a filter or a lookup. |
| 107 | +// This factory creates a function that accepts a list of tags and a list of |
| 108 | +// ranges, and contains logic to exit early for lookups. |
| 109 | +// `check` just has to deal with one tag and one range. |
| 110 | +// This match function iterates over ranges, and for each range, |
| 111 | +// iterates over tags. That way, earlier ranges matching any tag have |
| 112 | +// precedence over later ranges. |
| 113 | +function factory(check, filter) { |
| 114 | + return match |
| 115 | + |
| 116 | + function match(tags, ranges) { |
| 117 | + var values = normalize(tags, ranges) |
| 118 | + var result = [] |
| 119 | + var next |
| 120 | + var tagIndex |
| 121 | + var tagLength |
| 122 | + var tag |
| 123 | + var rangeIndex |
| 124 | + var rangeLength |
| 125 | + var range |
| 126 | + var matches |
| 127 | + |
| 128 | + tags = values.tags |
| 129 | + ranges = values.ranges |
| 130 | + rangeLength = ranges.length |
| 131 | + rangeIndex = -1 |
| 132 | + |
| 133 | + while (++rangeIndex < rangeLength) { |
| 134 | + range = ranges[rangeIndex] |
| 135 | + |
| 136 | + // Ignore wildcards in lookup mode. |
| 137 | + if (!filter && range === asterisk) { |
| 138 | + continue |
| 139 | + } |
| 140 | + |
| 141 | + tagLength = tags.length |
| 142 | + tagIndex = -1 |
| 143 | + next = [] |
| 144 | + |
| 145 | + while (++tagIndex < tagLength) { |
| 146 | + tag = tags[tagIndex] |
| 147 | + matches = check(tag, range) |
| 148 | + ;(matches ? result : next).push(tag) |
| 149 | + |
| 150 | + // Exit if this is a lookup and we have a match. |
| 151 | + if (!filter && matches) { |
| 152 | + return tag |
| 153 | + } |
| 154 | + } |
| 155 | + |
| 156 | + tags = next |
| 157 | + } |
| 158 | + |
| 159 | + // If this is a filter, return the list. If it’s a lookup, we didn’t find |
| 160 | + // a match, so return `undefined`. |
| 161 | + return filter ? result : undefined |
| 162 | + } |
| 163 | +} |
| 164 | + |
| 165 | +// Normalize options. |
| 166 | +function normalize(tags, ranges) { |
| 167 | + ranges = ranges === undefined || ranges === null ? asterisk : ranges |
| 168 | + |
| 169 | + return {tags: cast(tags, 'tag'), ranges: cast(ranges, 'range')} |
| 170 | +} |
| 171 | + |
| 172 | +// Validate tags or ranges, and cast them to arrays. |
| 173 | +function cast(values, name) { |
| 174 | + var value = values && typeof values === 'string' ? [values] : values |
| 175 | + |
| 176 | + if (!value || typeof value !== 'object' || !('length' in value)) { |
| 177 | + throw new Error( |
| 178 | + 'Invalid ' + name + ' `' + value + '`, expected non-empty string' |
| 179 | + ) |
| 180 | + } |
| 181 | + |
| 182 | + return value |
| 183 | +} |
| 184 | + |
| 185 | +function lower(value) { |
| 186 | + return value.toLowerCase() |
| 187 | +} |
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