How should I practice HTTP Accept-Language with Quality Scores (q-factors)?

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HTTP Accept-Language with Quality Scores (q-factors)

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Problem statement

Practice sequence: Exact, prefix, and wildcard matching → Quality scores (q-factors).

This is Part 4 of the HTTP Accept-Language matcher. Each requested language may carry a numeric quality factor in the form tag;q=value, where 0 <= value <= 1. An entry without ;q= has quality 1.

Matching against supportedLanguages still uses the earlier exact, generic-language, and wildcard rules. Each supported tag receives the quality of the header entry that selected it. A supported tag is selected only once.

Return the matched supported tags in descending quality order. When qualities tie, keep their match order. Return only the tag names as a String[].

Function

parseAcceptLanguageWithQuality(acceptHeader: String, supportedLanguages: String[]) → String[]

Examples

Example 1

acceptHeader = "fr-FR;q=1, fr-CA;q=0, fr;q=0.5"supportedLanguages = ["fr-FR", "fr-CA", "fr-BG"]return = ["fr-FR", "fr-BG", "fr-CA"]

fr-FR matches exactly with q=1.0. The generic fr (q=0.5) matches the remaining supported French variant fr-BG. fr-CA matches exactly with q=0. Sorting by score descending: fr-FR (1.0), fr-BG (0.5), fr-CA (0).

Example 2

acceptHeader = "fr-FR;q=1, fr-CA;q=0, *;q=0.5"supportedLanguages = ["fr-FR", "fr-CA", "fr-BG", "en-US"]return = ["fr-FR", "fr-BG", "en-US", "fr-CA"]

fr-FR matches with q=1.0. fr-CA matches with q=0. The wildcard *;q=0.5 matches the remaining supported tags fr-BG and en-US, both with q=0.5. Sorting by score descending and keeping match order for ties: fr-FR (1.0), then fr-BG and en-US (0.5, in match order), then fr-CA (0).

Example 3

acceptHeader = "en;q=0.8, fr;q=0.9, de;q=0.7"supportedLanguages = ["en-US", "fr-FR", "de-DE"]return = ["fr-FR", "en-US", "de-DE"]

Generic en matches en-US (q=0.8), fr matches fr-FR (q=0.9), de matches de-DE (q=0.7). Sorted by score descending: fr-FR (0.9), en-US (0.8), de-DE (0.7).

Constraints

Each header entry is tag or tag;q=value; missing q defaults to 1.0.
Matching uses exact, prefix (generic), and wildcard rules; a matched supported tag takes the matching entry's quality score.
Sort matched tags by quality descending; ties keep match order (stable); q=0 sorts last.
Never output a supported tag twice.
Return the tag names as a String[].