Extracted post/page cache invalidation logic to service

refs https://github.com/TryGhost/Team/issues/949

- The code is exactly the same in six (!) places. It's beyond unmaintainable to add another line to any of these place, which will be needed for `email_only` handling.
- The newly created posts service is a temporary, slightly better solution that complies with codebase's best practice of extracting new services using class with DI pattern

core/server/api/canary/pages.js

@@ -2,9 +2,18 @@ const models = require('../../models');
 const i18n = require('../../../shared/i18n');
 const errors = require('@tryghost/errors');
 const urlUtils = require('../../../shared/url-utils');
+const PostsService = require('../../services/posts/posts-service');
 const ALLOWED_INCLUDES = ['tags', 'authors', 'authors.roles'];
 const UNSAFE_ATTRS = ['status', 'authors', 'visibility'];
 
+const postsService = new PostsService({
+    apiVersion: 'canary',
+    mega: null,
+    urlUtils: urlUtils,
+    i18n: i18n,
+    models: models
+});
+
 module.exports = {
     docName: 'pages',
     browse: {
@@ -150,23 +159,7 @@ module.exports = {
         async query(frame) {
             const model = await models.Post.edit(frame.data.pages[0], frame.options);
 
-            if (
-                model.get('status') === 'published' && model.wasChanged() ||
-                model.get('status') === 'draft' && model.previous('status') === 'published'
-            ) {
-                this.headers.cacheInvalidate = true;
-            } else if (
-                model.get('status') === 'draft' && model.previous('status') !== 'published' ||
-                model.get('status') === 'scheduled' && model.wasChanged()
-            ) {
-                this.headers.cacheInvalidate = {
-                    value: urlUtils.urlFor({
-                        relativeUrl: urlUtils.urlJoin('/p', model.get('uuid'), '/')
-                    })
-                };
-            } else {
-                this.headers.cacheInvalidate = false;
-            }
+            this.headers.cacheInvalidate = postsService.handleCacheInvalidation(model);
 
             return model;
         }

core/server/api/canary/posts.js

@@ -3,10 +3,18 @@ const i18n = require('../../../shared/i18n');
 const errors = require('@tryghost/errors');
 const urlUtils = require('../../../shared/url-utils');
 const {mega} = require('../../services/mega');
-const {BadRequestError} = require('@tryghost/errors');
+const PostsService = require('../../services/posts/posts-service');
 const allowedIncludes = ['tags', 'authors', 'authors.roles', 'email'];
 const unsafeAttrs = ['status', 'authors', 'visibility'];
 
+const postsService = new PostsService({
+    apiVersion: 'canary',
+    mega: mega,
+    urlUtils: urlUtils,
+    i18n: i18n,
+    models: models
+});
+
 module.exports = {
     docName: 'posts',
     browse: {
@@ -209,24 +217,8 @@ module.exports = {
                 }
             }
 
-            /**Handle cache invalidation */
-            if (
-                model.get('status') === 'published' && model.wasChanged() ||
-                model.get('status') === 'draft' && model.previous('status') === 'published'
-            ) {
-                this.headers.cacheInvalidate = true;
-            } else if (
-                model.get('status') === 'draft' && model.previous('status') !== 'published' ||
-                model.get('status') === 'scheduled' && model.wasChanged()
-            ) {
-                this.headers.cacheInvalidate = {
-                    value: urlUtils.urlFor({
-                        relativeUrl: urlUtils.urlJoin('/p', model.get('uuid'), '/')
-                    })
-                };
-            } else {
-                this.headers.cacheInvalidate = false;
-            }
+            this.headers.cacheInvalidate = postsService.handleCacheInvalidation(model);
+
             return model;
         }
     },

core/server/api/v2/pages.js

@@ -2,9 +2,18 @@ const models = require('../../models');
 const i18n = require('../../../shared/i18n');
 const errors = require('@tryghost/errors');
 const urlUtils = require('../../../shared/url-utils');
+const PostsService = require('../../services/posts/posts-service');
 const ALLOWED_INCLUDES = ['tags', 'authors', 'authors.roles'];
 const UNSAFE_ATTRS = ['status', 'authors', 'visibility'];
 
+const postsService = new PostsService({
+    apiVersion: 'v2',
+    mega: null,
+    urlUtils: urlUtils,
+    i18n: i18n,
+    models: models
+});
+
 module.exports = {
     docName: 'pages',
     browse: {
@@ -147,23 +156,7 @@ module.exports = {
         async query(frame) {
             const model = await models.Post.edit(frame.data.pages[0], frame.options);
 
-            if (
-                model.get('status') === 'published' && model.wasChanged() ||
-                model.get('status') === 'draft' && model.previous('status') === 'published'
-            ) {
-                this.headers.cacheInvalidate = true;
-            } else if (
-                model.get('status') === 'draft' && model.previous('status') !== 'published' ||
-                model.get('status') === 'scheduled' && model.wasChanged()
-            ) {
-                this.headers.cacheInvalidate = {
-                    value: urlUtils.urlFor({
-                        relativeUrl: urlUtils.urlJoin('/p', model.get('uuid'), '/')
-                    })
-                };
-            } else {
-                this.headers.cacheInvalidate = false;
-            }
+            this.headers.cacheInvalidate = postsService.handleCacheInvalidation(model);
 
             return model;
         }

core/server/api/v2/posts.js

@@ -2,9 +2,18 @@ const models = require('../../models');
 const i18n = require('../../../shared/i18n');
 const errors = require('@tryghost/errors');
 const urlUtils = require('../../../shared/url-utils');
+const PostsService = require('../../services/posts/posts-service');
 const allowedIncludes = ['tags', 'authors', 'authors.roles'];
 const unsafeAttrs = ['status', 'authors', 'visibility'];
 
+const postsService = new PostsService({
+    apiVersion: 'v2',
+    mega: null,
+    urlUtils: urlUtils,
+    i18n: i18n,
+    models: models
+});
+
 module.exports = {
     docName: 'posts',
     browse: {
@@ -143,23 +152,7 @@ module.exports = {
         async query(frame) {
             const model = await models.Post.edit(frame.data.posts[0], frame.options);
 
-            if (
-                model.get('status') === 'published' && model.wasChanged() ||
-                model.get('status') === 'draft' && model.previous('status') === 'published'
-            ) {
-                this.headers.cacheInvalidate = true;
-            } else if (
-                model.get('status') === 'draft' && model.previous('status') !== 'published' ||
-                model.get('status') === 'scheduled' && model.wasChanged()
-            ) {
-                this.headers.cacheInvalidate = {
-                    value: urlUtils.urlFor({
-                        relativeUrl: urlUtils.urlJoin('/p', model.get('uuid'), '/')
-                    })
-                };
-            } else {
-                this.headers.cacheInvalidate = false;
-            }
+            this.headers.cacheInvalidate = postsService.handleCacheInvalidation(model);
 
             return model;
         }

core/server/api/v3/pages.js

@@ -2,9 +2,18 @@ const models = require('../../models');
 const i18n = require('../../../shared/i18n');
 const errors = require('@tryghost/errors');
 const urlUtils = require('../../../shared/url-utils');
+const PostsService = require('../../services/posts/posts-service');
 const ALLOWED_INCLUDES = ['tags', 'authors', 'authors.roles'];
 const UNSAFE_ATTRS = ['status', 'authors', 'visibility'];
 
+const postsService = new PostsService({
+    apiVersion: 'v3',
+    mega: null,
+    urlUtils: urlUtils,
+    i18n: i18n,
+    models: models
+});
+
 module.exports = {
     docName: 'pages',
     browse: {
@@ -150,23 +159,7 @@ module.exports = {
         async query(frame) {
             const model = await models.Post.edit(frame.data.pages[0], frame.options);
 
-            if (
-                model.get('status') === 'published' && model.wasChanged() ||
-                model.get('status') === 'draft' && model.previous('status') === 'published'
-            ) {
-                this.headers.cacheInvalidate = true;
-            } else if (
-                model.get('status') === 'draft' && model.previous('status') !== 'published' ||
-                model.get('status') === 'scheduled' && model.wasChanged()
-            ) {
-                this.headers.cacheInvalidate = {
-                    value: urlUtils.urlFor({
-                        relativeUrl: urlUtils.urlJoin('/p', model.get('uuid'), '/')
-                    })
-                };
-            } else {
-                this.headers.cacheInvalidate = false;
-            }
+            this.headers.cacheInvalidate = postsService.handleCacheInvalidation(model);
 
             return model;
         }

core/server/api/v3/posts.js

@@ -3,10 +3,18 @@ const i18n = require('../../../shared/i18n');
 const errors = require('@tryghost/errors');
 const urlUtils = require('../../../shared/url-utils');
 const {mega} = require('../../services/mega');
-const {BadRequestError} = require('@tryghost/errors');
+const PostsService = require('../../services/posts/posts-service');
 const allowedIncludes = ['tags', 'authors', 'authors.roles', 'email'];
 const unsafeAttrs = ['status', 'authors', 'visibility'];
 
+const postsService = new PostsService({
+    apiVersion: 'v3',
+    mega: mega,
+    urlUtils: urlUtils,
+    i18n: i18n,
+    models: models
+});
+
 module.exports = {
     docName: 'posts',
     browse: {
@@ -209,24 +217,8 @@ module.exports = {
                 }
             }
 
-            /**Handle cache invalidation */
-            if (
-                model.get('status') === 'published' && model.wasChanged() ||
-                model.get('status') === 'draft' && model.previous('status') === 'published'
-            ) {
-                this.headers.cacheInvalidate = true;
-            } else if (
-                model.get('status') === 'draft' && model.previous('status') !== 'published' ||
-                model.get('status') === 'scheduled' && model.wasChanged()
-            ) {
-                this.headers.cacheInvalidate = {
-                    value: urlUtils.urlFor({
-                        relativeUrl: urlUtils.urlJoin('/p', model.get('uuid'), '/')
-                    })
-                };
-            } else {
-                this.headers.cacheInvalidate = false;
-            }
+            this.headers.cacheInvalidate = postsService.handleCacheInvalidation(model);
+
             return model;
         }
     },

core/server/services/posts/posts-service.js

@@ -0,0 +1,37 @@
+const {BadRequestError} = require('@tryghost/errors');
+
+class PostsService {
+    constructor({mega, apiVersion, urlUtils, i18n, models}) {
+        this.apiVersion = apiVersion;
+        this.mega = mega;
+        this.urlUtils = urlUtils;
+        this.i18n = i18n;
+        this.models = models;
+    }
+
+    handleCacheInvalidation(model) {
+        let cacheInvalidate;
+
+        if (
+            model.get('status') === 'published' && model.wasChanged() ||
+            model.get('status') === 'draft' && model.previous('status') === 'published'
+        ) {
+            cacheInvalidate = true;
+        } else if (
+            model.get('status') === 'draft' && model.previous('status') !== 'published' ||
+            model.get('status') === 'scheduled' && model.wasChanged()
+        ) {
+            cacheInvalidate = {
+                value: this.urlUtils.urlFor({
+                    relativeUrl: this.urlUtils.urlJoin('/p', model.get('uuid'), '/')
+                })
+            };
+        } else {
+            cacheInvalidate = false;
+        }
+
+        return cacheInvalidate;
+    }
+}
+
+module.exports = PostsService;