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interface Selection {
pos: number
pref?: number
q: number
token: string
}
interface Options {
prefixMatch?: boolean
type: 'accept-language'
}
function parse(
raw: string,
preferences: readonly string[] | undefined,
options: Options
) {
const lowers = new Map<string, { orig: string; pos: number }>()
const header = raw.replace(/[ \t]/g, '')
if (preferences) {
let pos = 0
for (const preference of preferences) {
const lower = preference.toLowerCase()
lowers.set(lower, { orig: preference, pos: pos++ })
if (options.prefixMatch) {
const parts = lower.split('-')
while ((parts.pop(), parts.length > 0)) {
const joined = parts.join('-')
if (!lowers.has(joined)) {
lowers.set(joined, { orig: preference, pos: pos++ })
}
}
}
}
}
const parts = header.split(',')
const selections: Selection[] = []
const map = new Set<string>()
for (let i = 0; i < parts.length; ++i) {
const part = parts[i]
if (!part) {
continue
}
const params = part.split(';')
if (params.length > 2) {
throw new Error(`Invalid ${options.type} header`)
}
let token = params[0].toLowerCase()
if (!token) {
throw new Error(`Invalid ${options.type} header`)
}
const selection: Selection = { token, pos: i, q: 1 }
if (preferences && lowers.has(token)) {
selection.pref = lowers.get(token)!.pos
}
map.add(selection.token)
if (params.length === 2) {
const q = params[1]
const [key, value] = q.split('=')
if (!value || (key !== 'q' && key !== 'Q')) {
throw new Error(`Invalid ${options.type} header`)
}
const score = parseFloat(value)
if (score === 0) {
continue
}
if (Number.isFinite(score) && score <= 1 && score >= 0.001) {
selection.q = score
}
}
selections.push(selection)
}
selections.sort((a, b) => {
if (b.q !== a.q) {
return b.q - a.q
}
if (b.pref !== a.pref) {
if (a.pref === undefined) {
return 1
}
if (b.pref === undefined) {
return -1
}
return a.pref - b.pref
}
return a.pos - b.pos
})
const values = selections.map((selection) => selection.token)
if (!preferences || !preferences.length) {
return values
}
const preferred: string[] = []
for (const selection of values) {
if (selection === '*') {
for (const [preference, value] of lowers) {
if (!map.has(preference)) {
preferred.push(value.orig)
}
}
} else {
const lower = selection.toLowerCase()
if (lowers.has(lower)) {
preferred.push(lowers.get(lower)!.orig)
}
}
}
return preferred
}
export function acceptLanguage(header = '', preferences?: readonly string[]) {
return (
parse(header, preferences, {
type: 'accept-language',
prefixMatch: true,
})[0] || ''
)
}
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