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// Copyright 2023-latest the httpland authors. All rights reserved. MIT license.// This module is browser compatible.
import {  concat,  type ETag,  filterKeys,  RepresentationHeader,  toHashString,} from "./deps.ts";import type { ComputeETag, ETagStrategy } from "./types.ts";
/** Catch error utility. */export function reason(  message: string,  error: ErrorConstructor = Error,): (cause: unknown) => never {  return (cause) => {    throw error(message, { cause });  };}
const enum FailBy {  Fetch = "fail to fetch resource",  CalcHash = "fail to calculate hash",  CalcHashString = "fail to calculate hash string",}
/** Digest algorithm. */const enum Algorithm {  Sha1 = "SHA-1",}
function digestSha1(data: ArrayBuffer): Promise<ArrayBuffer> {  return crypto.subtle.digest(Algorithm.Sha1, data);}
export const DefaultStrategy: ETagStrategy = {  strong: false,  digest: digestSha1,  headers: [RepresentationHeader.ContentType],};
export async function computeETagByStrategy(  response: Response,  strategy: ETagStrategy = DefaultStrategy,): Promise<ETag> {  const filteredHeaders = filterKeys(    response.headers,    strategy.headers.includes.bind(strategy.headers),  );  const headersStr = stringifyHeaders(filteredHeaders);  const hasHeader = !!headersStr;  const encoder = new TextEncoder();
  const buffer = await response    .clone()    .arrayBuffer()    .catch(reason(FailBy.Fetch));  const data = concat(    encoder.encode(headersStr),    ...hasHeader ? [encoder.encode("\n\n")] : [],    new Uint8Array(buffer),  );
  const tag = await Promise.resolve(strategy.digest(data.buffer))    .catch(reason(FailBy.CalcHash))    .then(toHashString)    .catch(reason(FailBy.CalcHashString));
  return { weak: !strategy.strong, tag };}
export function strategy2ComputeETag(strategy: ETagStrategy): ComputeETag {  return (response) => computeETagByStrategy(response, strategy);}
/** Deserialize {@link Headers} into string. */export function stringifyHeaders(headers: Headers): string {  return [...headers.entries()]    .map(formatEntry)    .join("\n");}
function formatEntry(entry: readonly [unknown, unknown]): string {  return `${entry[0]}: ${entry[1]}`;}