Prefer Effect's error types

Refs #1834

src/GhostPage.ts

@@ -1,7 +1,11 @@
-import { Context, type Effect } from 'effect'
+import { Context, Data, type Effect } from 'effect'
 import type { Html } from './html.js'
 
+export class PageIsNotFound extends Data.TaggedError('PageIsNotFound') {}
+
+export class PageIsUnavailable extends Data.TaggedError('PageIsUnavailable') {}
+
 export class GetPageFromGhost extends Context.Tag('GetPageFromGhost')<
   GetPageFromGhost,
-  (id: string) => Effect.Effect<Html, 'unavailable' | 'not-found'>
+  (id: string) => Effect.Effect<Html, PageIsUnavailable | PageIsNotFound>
 >() {}

src/Program.ts

@@ -12,7 +12,7 @@ import { collapseRequests, logFetch } from './fetch.js'
 import * as FptsToEffect from './FptsToEffect.js'
 import { getPreprint as getPreprintUtil } from './get-preprint.js'
 import { getPage, GhostApi } from './ghost.js'
-import { GetPageFromGhost } from './GhostPage.js'
+import * as GhostPage from './GhostPage.js'
 import { html } from './html.js'
 import * as Keyv from './keyv.js'
 import { getPseudonymFromLegacyPrereview } from './legacy-prereview.js'
@@ -360,15 +360,25 @@ export const Program = pipe(
       ),
       Layer.effect(Comments.GetComment, Comments.makeGetComment),
       Layer.effect(
-        GetPageFromGhost,
+        GhostPage.GetPageFromGhost,
         Effect.gen(function* () {
           const fetch = yield* FetchHttpClient.Fetch
           const ghostApi = yield* GhostApi
-          return id =>
-            FptsToEffect.readerTaskEither(getPage(id), {
-              fetch,
-              ghostApi,
-            })
+          return flow(
+            id =>
+              FptsToEffect.readerTaskEither(getPage(id), {
+                fetch,
+                ghostApi,
+              }),
+            Effect.mapError(
+              flow(
+                Match.value,
+                Match.when('not-found', () => new GhostPage.PageIsNotFound()),
+                Match.when('unavailable', () => new GhostPage.PageIsUnavailable()),
+                Match.exhaustive,
+              ),
+            ),
+          )
         }),
       ),
     ),

test/AboutUsPage/AboutUsPage.test.ts

@@ -4,7 +4,7 @@ import { Effect, TestContext } from 'effect'
 import { Status } from 'hyper-ts'
 import * as _ from '../../src/AboutUsPage/index.js'
 import { Locale } from '../../src/Context.js'
-import { GetPageFromGhost } from '../../src/GhostPage.js'
+import { GetPageFromGhost, PageIsNotFound, PageIsUnavailable } from '../../src/GhostPage.js'
 import * as Routes from '../../src/routes.js'
 import * as fc from '../fc.js'
 
@@ -31,7 +31,7 @@ describe('AboutUsPage', () => {
     ),
   )
 
-  test.prop([fc.supportedLocale(), fc.constantFrom('unavailable', 'not-found')])(
+  test.prop([fc.supportedLocale(), fc.oneof(fc.constant(new PageIsUnavailable()), fc.constant(new PageIsNotFound()))])(
     'when the page cannot be loaded',
     async (locale, error) =>
       Effect.gen(function* () {