Added [GithubGoModGoVersion GitHub] badge (#4232)

* Added Go version badge

* Using destructuring assignment

* Allowing a client to specify a filename

* Turned a test to live one

* Added golang to keywords

* Renamed parseContent to transform

* Added an example with branch and filename

services/github/github-go-mod.service.js

@@ -0,0 +1,109 @@
+'use strict'
+
+const Joi = require('@hapi/joi')
+const { renderVersionBadge } = require('../version')
+const { ConditionalGithubAuthV3Service } = require('./github-auth-service')
+const { fetchRepoContent } = require('./github-common-fetch')
+const { documentation } = require('./github-helpers')
+const { InvalidResponse } = require('..')
+
+const queryParamSchema = Joi.object({
+  filename: Joi.string(),
+}).required()
+
+const goVersionRegExp = new RegExp('^go (.+)$', 'm')
+
+const keywords = ['golang']
+
+module.exports = class GithubGoModGoVersion extends ConditionalGithubAuthV3Service {
+  static get category() {
+    return 'version'
+  }
+
+  static get route() {
+    return {
+      base: 'github/go-mod/go-version',
+      pattern: ':user/:repo/:branch*',
+      queryParamSchema,
+    }
+  }
+
+  static get examples() {
+    return [
+      {
+        title: 'GitHub go.mod Go version',
+        pattern: ':user/:repo',
+        namedParams: { user: 'gohugoio', repo: 'hugo' },
+        staticPreview: this.render({ version: '1.12' }),
+        documentation,
+        keywords,
+      },
+      {
+        title: 'GitHub go.mod Go version (branch)',
+        pattern: ':user/:repo/:branch',
+        namedParams: {
+          user: 'gohugoio',
+          repo: 'hugo',
+          branch: 'master',
+        },
+        staticPreview: this.render({ version: '1.12', branch: 'master' }),
+        documentation,
+        keywords,
+      },
+      {
+        title: 'GitHub go.mod Go version (subfolder of monorepo)',
+        pattern: ':user/:repo',
+        namedParams: { user: 'golang', repo: 'go' },
+        queryParams: { filename: 'src/go.mod' },
+        staticPreview: this.render({ version: '1.14' }),
+        documentation,
+        keywords,
+      },
+      {
+        title: 'GitHub go.mod Go version (branch & subfolder of monorepo)',
+        pattern: ':user/:repo/:branch',
+        namedParams: { user: 'golang', repo: 'go', branch: 'master' },
+        queryParams: { filename: 'src/go.mod' },
+        staticPreview: this.render({ version: '1.14' }),
+        documentation,
+        keywords,
+      },
+    ]
+  }
+
+  static get defaultBadgeData() {
+    return { label: 'Go' }
+  }
+
+  static render({ version, branch }) {
+    return renderVersionBadge({
+      version,
+      tag: branch,
+      defaultLabel: 'Go',
+    })
+  }
+
+  static transform(content) {
+    const match = goVersionRegExp.exec(content)
+    if (!match) {
+      throw new InvalidResponse({
+        prettyMessage: 'Go version missing in go.mod',
+      })
+    }
+
+    return {
+      go: match[1],
+    }
+  }
+
+  async handle({ user, repo, branch }, { filename = 'go.mod' }) {
+    const content = await fetchRepoContent(this, {
+      user,
+      repo,
+      branch,
+      filename,
+    })
+    const { go } = this.constructor.transform(content)
+    return this.constructor.render({ version: go, branch })
+  }
+}