Add redirect base setup and tests.

source/redirect/base.ts

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+import {HostnameParameters} from './hostname.js';
+
+export type RedirectParameters = HostnameParameters;
+
+export abstract class Redirect<P extends RedirectParameters> {
+  constructor(public parameters: P) {}
+
+  public abstract redirect(url: URL | string): URL;
+}

source/redirect/exports.ts

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+import {RedirectParameters} from './base.js';
+import {HostnameRedirect} from './hostname.js';
+
+export * from './base.js';
+export * from './hostname.js';
+
+export type Redirects = HostnameRedirect;
+
+export function parseRedirect<P extends RedirectParameters>(
+  parameters: P,
+): Redirects | undefined {
+  if (parameters.type === 'hostname') {
+    return new HostnameRedirect(parameters);
+  }
+}

source/redirect/hostname.ts

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+import {Redirect} from './base.js';
+
+export type HostnameParameters = {
+  hostname: string;
+  type: 'hostname';
+};
+
+export class HostnameRedirect extends Redirect<HostnameParameters> {
+  public redirect(url: URL | string): URL {
+    const redirected = new URL(url);
+    redirected.hostname = this.parameters.hostname;
+    return redirected;
+  }
+}

tests/redirect.test.ts

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+/// <reference path="../source/types.d.ts" />
+
+import test from 'ava';
+
+import {
+  parseRedirect,
+  HostnameRedirect,
+  Redirect,
+  RedirectParameters,
+} from '../source/redirect/exports.js';
+
+test('parseRedirect', (t) => {
+  const samples: RedirectParameters[] = [
+    {
+      test: 'Invalid parameters',
+    } as unknown as RedirectParameters,
+    {
+      hostname: 'example.org',
+      type: 'hostname',
+    },
+  ];
+
+  for (const sample of samples) {
+    const redirect = parseRedirect(sample);
+
+    if (redirect === undefined) {
+      t.pass('parseRedirect returned undefined');
+    } else {
+      t.snapshot(redirect, `Class ${redirect.constructor.name}`);
+    }
+  }
+});
+
+test('Redirect.redirect', (t) => {
+  const hostnameRedirect = new HostnameRedirect({
+    hostname: 'example.org',
+    type: 'hostname',
+  });
+
+  const samples: Array<[string, Redirect<RedirectParameters>]> = [
+    ['https://example.com', hostnameRedirect],
+    ['https://example.com/path#hash?query=test', hostnameRedirect],
+  ];
+
+  for (const [index, [url, redirect]] of samples.entries()) {
+    t.snapshot(
+      {
+        original: url,
+        redirected: redirect.redirect(url).href,
+      },
+      `${index} ${redirect.constructor.name}`,
+    );
+  }
+});

tests/snapshots/tests/redirect.test.ts.md

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+# Snapshot report for `tests/redirect.test.ts`
+
+The actual snapshot is saved in `redirect.test.ts.snap`.
+
+Generated by [AVA](https://avajs.dev).
+
+## parseRedirect
+
+> Class HostnameRedirect
+
+    HostnameRedirect {
+      parameters: {
+        hostname: 'example.org',
+        type: 'hostname',
+      },
+    }
+
+## Redirect.redirect
+
+> 0 HostnameRedirect
+
+    {
+      original: 'https://example.com',
+      redirected: 'https://example.org/',
+    }
+
+> 1 HostnameRedirect
+
+    {
+      original: 'https://example.com/path#hash?query=test',
+      redirected: 'https://example.org/path#hash?query=test',
+    }