Simplify PackagistVersion

* Extract latest version string logics from
  BasePackagistService.findLatestRelease into findLatestVersion.

* Reuse BasePackagistService.findLatestVersion in PackagistVersion
  to find the latest release. Remove duplicated logics.

services/packagist/packagist-base.js

@@ -1,5 +1,5 @@
 import Joi from 'joi'
-import { BaseJsonService } from '../index.js'
+import { BaseJsonService, NotFound } from '../index.js'
 import { isStable, latest } from '../php-version.js'
 
 const packageSchema = Joi.array().items(
@@ -125,9 +125,42 @@ class BasePackagistService extends BaseJsonService {
     return expanded
   }
 
+  /**
+   * From an array of package, derive the latest release
+   * version string.
+   *
+   * @param {Array} versions An array of package versions.
+   * @param {boolean} includePrereleases Should pre-release version id be included.
+   *
+   * @throws {NotFound} If the packages array is empty or not an array.
+   * @returns {string} The version string of the latest version.
+   */
+  findLatestVersion(versions, includePrereleases = false) {
+    if (!Array.isArray(versions) || versions.length === 0) {
+      throw new NotFound({ prettyMessage: 'no released version found' })
+    }
+
+    const versionStrings = versions
+      .map(version => version.version)
+      .filter(
+        versionString =>
+          typeof versionString === 'string' || versionString instanceof String
+      )
+
+    let version = latest(versionStrings)
+    if (!includePrereleases) {
+      version =
+        latest(versionStrings.filter(isStable)) || latest(versionStrings)
+    }
+
+    if (version === undefined) {
+      throw new NotFound({ prettyMessage: 'no released version found' })
+    }
+    return version
+  }
+
   findLatestRelease(json) {
-    const versions = json.map(version => version.version)
-    const release = latest(versions.filter(isStable)) || latest(versions)
+    const release = this.findLatestVersion(json)
     return json.filter(version => version.version === release)[0]
   }
 }

services/packagist/packagist-version.service.js

@@ -1,6 +1,5 @@
 import Joi from 'joi'
 import { renderVersionBadge } from '../version.js'
-import { isStable, latest } from '../php-version.js'
 import { optionalUrl } from '../validators.js'
 import { NotFound, redirector } from '../index.js'
 import {
@@ -77,18 +76,6 @@ class PackagistVersion extends BasePackagistService {
     return renderVersionBadge({ version })
   }
 
-  transform({ includePrereleases, json, user, repo }) {
-    const versionsData = json.packages[this.getPackageName(user, repo)]
-    const versions = versionsData.map(version => version.version)
-
-    if (includePrereleases) {
-      return { version: latest(versions) }
-    } else {
-      const stableVersion = latest(versions.filter(isStable))
-      return { version: stableVersion || latest(versions) }
-    }
-  }
-
   async handle(
     { user, repo },
     { include_prereleases: includePrereleases, server }
@@ -100,7 +87,8 @@ class PackagistVersion extends BasePackagistService {
       schema: includePrereleases ? schema : allVersionsSchema,
       server,
     })
-    const { version } = this.transform({ includePrereleases, json, user, repo })
+    const packageJson = json.packages[this.getPackageName(user, repo)]
+    const version = this.findLatestVersion(packageJson, includePrereleases)
     if (version === undefined) {
       throw new NotFound({ prettyMessage: 'no released version found' })
     }