import { compareSpecs, isQuality, Specificity } from "./common.ts";
interface CharsetSpecificity extends Specificity { charset: string;}
const SIMPLE_CHARSET_REGEXP = /^\s*([^\s;]+)\s*(?:;(.*))?$/;
function parseCharset(str: string, i: number): CharsetSpecificity | undefined { const match = SIMPLE_CHARSET_REGEXP.exec(str); if (!match) { return; }
const [, charset] = match; let q = 1; if (match[2]) { const params = match[2].split(";"); for (const param of params) { const [key, value] = param.trim().split("="); if (key === "q") { q = parseFloat(value); break; } } }
return { charset, q, i };}
function parseAcceptCharset(accept: string): CharsetSpecificity[] { const accepts = accept.split(","); const result: CharsetSpecificity[] = [];
for (let i = 0; i < accepts.length; i++) { const charset = parseCharset(accepts[i].trim(), i); if (charset) { result.push(charset); } } return result;}
function specify( charset: string, spec: CharsetSpecificity, i: number,): Specificity | undefined { let s = 0; if (spec.charset.toLowerCase() === charset.toLocaleLowerCase()) { s |= 1; } else if (spec.charset !== "*") { return; }
return { i, o: spec.i, q: spec.q, s };}
function getCharsetPriority( charset: string, accepted: CharsetSpecificity[], index: number,): Specificity { let priority: Specificity = { i: -1, o: -1, q: 0, s: 0 }; for (const accepts of accepted) { const spec = specify(charset, accepts, index); if ( spec && ((priority.s ?? 0) - (spec.s ?? 0) || priority.q - spec.q || (priority.o ?? 0) - (spec.o ?? 0)) < 0 ) { priority = spec; } } return priority;}
export function preferredCharsets(accept = "*", provided?: string[]): string[] { const accepts = parseAcceptCharset(accept);
if (!provided) { return accepts .filter(isQuality) .sort(compareSpecs) .map((spec) => spec.charset); }
const priorities = provided .map((type, index) => getCharsetPriority(type, accepts, index));
return priorities .filter(isQuality) .sort(compareSpecs) .map((priority) => provided[priorities.indexOf(priority)]);}