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// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
import { MAP_FORMAT_TO_EXTRACTOR_RX, MAP_FORMAT_TO_RECOGNIZER_RX,} from "./_formats.ts";
type Format = "yaml" | "toml" | "json" | "unknown";
export type Extract<T> = { frontMatter: string; body: string; attrs: T;};
export type Extractor = <T = Record<string, unknown>>( str: string,) => Extract<T>;
export type Parser = <T = Record<string, unknown>>(str: string) => T;
function _extract<T>( str: string, rx: RegExp, parse: Parser,): Extract<T> { const match = rx.exec(str); if (!match || match.index !== 0) { throw new TypeError("Unexpected end of input"); } const frontMatter = match.at(-1)?.replace(/^\s+|\s+$/g, "") || ""; const attrs = parse(frontMatter) as T; const body = str.replace(match[0], ""); return { frontMatter, body, attrs };}
/** * Recognizes the format of the front matter in a string. Supports YAML, TOML and JSON. * * @param str String to recognize. * @param formats A list of formats to recognize. Defaults to all supported formats. * * ```ts * import { recognize } from "https://deno.land/std@$STD_VERSION/front_matter/mod.ts"; * import { assertEquals } from "https://deno.land/std@$STD_VERSION/assert/assert_equals.ts"; * * assertEquals(recognize("---\ntitle: Three dashes marks the spot\n---\n"), "yaml"); * assertEquals(recognize("---toml\ntitle = 'Three dashes followed by format marks the spot'\n---\n"), "toml"); * assertEquals(recognize("---json\n{\"title\": \"Three dashes followed by format marks the spot\"}\n---\n"), "json"); * assertEquals(recognize("---xml\n<title>Three dashes marks the spot</title>\n---\n"), "unknown"); * * assertEquals(recognize("---json\n<title>Three dashes marks the spot</title>\n---\n", ["yaml"]), "unknown"); */function recognize(str: string, formats?: Format[]): Format { if (!formats) { formats = Object.keys(MAP_FORMAT_TO_RECOGNIZER_RX) as Format[]; }
const [firstLine] = str.split(/(\r?\n)/);
for (const format of formats) { if (format === "unknown") { continue; }
if (MAP_FORMAT_TO_RECOGNIZER_RX[format].test(firstLine)) { return format; } }
return "unknown";}
/** * Factory that creates a function that extracts front matter from a string with the given parsers. * Supports YAML, TOML and JSON. * * @param formats A descriptor containing Format-parser pairs to use for each format. * @returns A function that extracts front matter from a string with the given parsers. * * ```ts * import { createExtractor, Parser } from "https://deno.land/std@$STD_VERSION/front_matter/mod.ts"; * import { assertEquals } from "https://deno.land/std@$STD_VERSION/assert/assert_equals.ts"; * import { parse as parseYAML } from "https://deno.land/std@$STD_VERSION/yaml/parse.ts"; * import { parse as parseTOML } from "https://deno.land/std@$STD_VERSION/toml/parse.ts"; * const extractYAML = createExtractor({ yaml: parseYAML as Parser }); * const extractTOML = createExtractor({ toml: parseTOML as Parser }); * const extractJSON = createExtractor({ json: JSON.parse as Parser }); * const extractYAMLOrJSON = createExtractor({ * yaml: parseYAML as Parser, * json: JSON.parse as Parser, * }); * * let { attrs, body, frontMatter } = extractYAML<{ title: string }>("---\ntitle: Three dashes marks the spot\n---\nferret"); * assertEquals(attrs.title, "Three dashes marks the spot"); * assertEquals(body, "ferret"); * assertEquals(frontMatter, "title: Three dashes marks the spot"); * * ({ attrs, body, frontMatter } = extractTOML<{ title: string }>("---toml\ntitle = 'Three dashes followed by format marks the spot'\n---\n")); * assertEquals(attrs.title, "Three dashes followed by format marks the spot"); * assertEquals(body, ""); * assertEquals(frontMatter, "title = 'Three dashes followed by format marks the spot'"); * * ({ attrs, body, frontMatter } = extractJSON<{ title: string }>("---json\n{\"title\": \"Three dashes followed by format marks the spot\"}\n---\ngoat")); * assertEquals(attrs.title, "Three dashes followed by format marks the spot"); * assertEquals(body, "goat"); * assertEquals(frontMatter, "{\"title\": \"Three dashes followed by format marks the spot\"}"); * * ({ attrs, body, frontMatter } = extractYAMLOrJSON<{ title: string }>("---\ntitle: Three dashes marks the spot\n---\nferret")); * assertEquals(attrs.title, "Three dashes marks the spot"); * assertEquals(body, "ferret"); * assertEquals(frontMatter, "title: Three dashes marks the spot"); * * ({ attrs, body, frontMatter } = extractYAMLOrJSON<{ title: string }>("---json\n{\"title\": \"Three dashes followed by format marks the spot\"}\n---\ngoat")); * assertEquals(attrs.title, "Three dashes followed by format marks the spot"); * assertEquals(body, "goat"); * assertEquals(frontMatter, "{\"title\": \"Three dashes followed by format marks the spot\"}"); * ``` */export function createExtractor( formats: Partial<Record<"yaml" | "toml" | "json" | "unknown", Parser>>,): Extractor { const formatKeys = Object.keys(formats) as Format[];
return function extract<T>(str: string): Extract<T> { const format = recognize(str, formatKeys); const parser = formats[format];
if (format === "unknown" || !parser) { throw new TypeError(`Unsupported front matter format`); }
return _extract(str, MAP_FORMAT_TO_EXTRACTOR_RX[format], parser); };}