// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

import { parseMediaType } from "./parse_media_type.ts";
import { getCharset } from "./get_charset.ts";
import { formatMediaType } from "./format_media_type.ts";
import type { db } from "./_db.ts";
import { typeByExtension } from "./type_by_extension.ts";

/** MIME-types database. */
export type DB = typeof db;
/** Maps content types to their corresponding file extensions. */
export type ContentTypeToExtension = {
  /**
   * Maps each content type key to its corresponding file extension.
   */
  [K in keyof DB]: DB[K] extends { "extensions": readonly string[] }
    ? DB[K]["extensions"][number]
    : never;
};

/** Known extension or type. Used in {@linkcode contentType}. */
export 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 "@std/media-types/content_type";
 *
 * 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;
}