| 1 | /** |
| 2 | * Deterministic locale detection for the website middleware (#3091). |
| 3 | * |
| 4 | * Resolution order (first match wins, no ambient state): |
| 5 | * 1. The NEXT_LOCALE cookie (a previous explicit choice). |
| 6 | * 2. Accept-Language, in the header's stated preference order — descending |
| 7 | * `q` weight, original order breaking ties, and `q=0` ("not acceptable") |
| 8 | * dropped outright. Each tag matches: |
| 9 | * a. exact full tag against the routed set (pt-BR → pt-BR); |
| 10 | * b. its primary subtag against the routed set (ru-RU → ru, zh-Hant → zh); |
| 11 | * c. a declared base→variant mapping for bases we only serve as a |
| 12 | * regional variant (pt → pt-BR). |
| 13 | * 3. The default locale (en). |
| 14 | * |
| 15 | * The mapping table is deliberately tiny and explicit — no guessing that |
| 16 | * e.g. es-419 should route anywhere other than the shipped `es`. |
| 17 | */ |
| 18 | import { defaultLocale, locales } from "./config"; |
| 19 | |
| 20 | const ROUTED = locales as readonly string[]; |
| 21 | |
| 22 | /** Base subtags that route to a specific regional variant. */ |
| 23 | const BASE_TO_VARIANT: Record<string, string> = { |
| 24 | pt: "pt-BR", |
| 25 | }; |
| 26 | |
| 27 | /** Match one language tag (any case, optional region/script) to a routed locale. */ |
| 28 | export function matchLocaleTag(tag: string): string | null { |
| 29 | const t = tag.trim().toLowerCase(); |
| 30 | if (!t || t === "*") return null; |
| 31 | |
| 32 | // Exact full-tag match (case-insensitive; routed codes are lowercase). |
| 33 | const exact = ROUTED.find((l) => l.toLowerCase() === t); |
| 34 | if (exact) return exact; |
| 35 | |
| 36 | const base = t.split("-")[0]; |
| 37 | if (ROUTED.includes(base)) return base; |
| 38 | |
| 39 | const variant = BASE_TO_VARIANT[base]; |
| 40 | if (variant && ROUTED.includes(variant)) return variant; |
| 41 | |
| 42 | return null; |
| 43 | } |
| 44 | |
| 45 | /** |
| 46 | * Accept-Language tags in the client's stated preference order. |
| 47 | * |
| 48 | * The header carries weights, and its list order is not required to be the |
| 49 | * preference order: `en;q=0.2, ja;q=0.9` asks for Japanese, and `q=0` means |
| 50 | * "not acceptable" (RFC 9110 §12.4.2), not "least preferred". Reading the |
| 51 | * list positionally handed the first of those a reader English and the |
| 52 | * second one a language they had explicitly refused. |
| 53 | * |
| 54 | * Weights sort descending; original order breaks ties, so an unweighted |
| 55 | * `ru,uk` still resolves to Russian. A malformed weight is ignored rather |
| 56 | * than guessed at, leaving the tag at the default weight of 1. |
| 57 | */ |
| 58 | export function acceptLanguageTags(header: string): string[] { |
| 59 | const entries: { tag: string; q: number; order: number }[] = []; |
| 60 | |
| 61 | header.split(",").forEach((part, order) => { |
| 62 | const [rawTag, ...params] = part.split(";"); |
| 63 | const tag = rawTag.trim(); |
| 64 | if (!tag) return; |
| 65 | |
| 66 | let q = 1; |
| 67 | for (const param of params) { |
| 68 | const eq = param.indexOf("="); |
| 69 | if (eq === -1) continue; |
| 70 | if (param.slice(0, eq).trim().toLowerCase() !== "q") continue; |
| 71 | const parsed = Number.parseFloat(param.slice(eq + 1).trim()); |
| 72 | if (Number.isFinite(parsed)) q = Math.min(Math.max(parsed, 0), 1); |
| 73 | } |
| 74 | |
| 75 | if (q === 0) return; |
| 76 | entries.push({ tag, q, order }); |
| 77 | }); |
| 78 | |
| 79 | entries.sort((a, b) => b.q - a.q || a.order - b.order); |
| 80 | return entries.map((entry) => entry.tag); |
| 81 | } |
| 82 | |
| 83 | /** Resolve the locale for a request from its cookie and Accept-Language header. */ |
| 84 | export function detectLocaleFromHeaders( |
| 85 | cookie: string | undefined, |
| 86 | acceptLanguage: string | null, |
| 87 | ): string { |
| 88 | if (cookie) { |
| 89 | const match = matchLocaleTag(cookie); |
| 90 | if (match) return match; |
| 91 | } |
| 92 | |
| 93 | if (acceptLanguage) { |
| 94 | for (const tag of acceptLanguageTags(acceptLanguage)) { |
| 95 | const match = matchLocaleTag(tag); |
| 96 | if (match) return match; |
| 97 | } |
| 98 | } |
| 99 | |
| 100 | return defaultLocale; |
| 101 | } |
| 102 |