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// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.import { parseMediaType } from "./parse_media_type.ts";import { typeByExtension } from "./type_by_extension.ts";import { getCharset } from "./get_charset.ts";import { formatMediaType } from "./format_media_type.ts";import type { db } from "./_db.ts";
type DB = typeof db;type ContentTypeToExtension = {  [K in keyof DB]: DB[K] extends { "extensions": readonly string[] }    ? DB[K]["extensions"][number]    : never;};
type KnownExtensionOrType =  | keyof ContentTypeToExtension  | ContentTypeToExtension[keyof ContentTypeToExtension]  | `.${ContentTypeToExtension[keyof ContentTypeToExtension]}`;
/** * Given an extension or media type, return a full `Content-Type` or * `Content-Disposition` header value. * * The function will treat the `extensionOrType` as a media type when it * contains a `/`, otherwise it will process it as an extension, with or without * the leading `.`. * * Returns `undefined` if unable to resolve the media type. * * > Note: a side effect of `deno/x/media_types` was that you could pass a file * > name (e.g. `file.json`) and it would return the content type. This behavior * > is intentionally not supported here. If you want to get an extension for a * > file name, use `extname()` from `std/path/mod.ts` to determine the * > extension and pass it here. * * @example * ```ts * import { contentType } from "https://deno.land/std@$STD_VERSION/media_types/content_type.ts"; * * contentType(".json"); // `application/json; charset=UTF-8` * contentType("text/html"); // `text/html; charset=UTF-8` * contentType("text/html; charset=UTF-8"); // `text/html; charset=UTF-8` * contentType("txt"); // `text/plain; charset=UTF-8` * contentType("foo"); // undefined * contentType("file.json"); // undefined * ``` */export function contentType<  // Workaround to autocomplete for parameters: https://github.com/microsoft/TypeScript/issues/29729#issuecomment-567871939  // deno-lint-ignore ban-types  T extends (string & {}) | KnownExtensionOrType,>(  extensionOrType: T,): Lowercase<T> extends KnownExtensionOrType ? string : string | undefined {  try {    const [mediaType, params = {}] = extensionOrType.includes("/")      ? parseMediaType(extensionOrType)      : [typeByExtension(extensionOrType), undefined];    if (!mediaType) {      return undefined as Lowercase<T> extends KnownExtensionOrType ? string        : string | undefined;    }    if (!("charset" in params)) {      const charset = getCharset(mediaType);      if (charset) {        params.charset = charset;      }    }    return formatMediaType(mediaType, params);  } catch {    // just swallow returning undefined  }  return undefined as Lowercase<T> extends KnownExtensionOrType ? string    : string | undefined;}