Add App Store in-app-purchase price monitor (#581)

DO NOT MERGE before #580

docs/en/README.md

@@ -160,7 +160,19 @@ Parameters：
 
 -   type, App type，either `iOS` or `mac`
 
--   id, App Store app id, obtain from the app URL https://itunes.apple.com/cn/app/id1152443474, in this case, `id1152443474`.
+-   id, App Store app id, obtain from the app URL https://itunes.apple.com/us/app/id1152443474, in this case, `id1152443474`.
+
+### App Store/Mac App Store In-App-Purchase Price Drop Alert <Author uid="HenryQW"/>
+
+Eg: [https://rsshub.app/appstore/iap/cn/id1152443474](https://rsshub.app/appstore/price/cn/id1152443474)
+
+Route: `/appstore/iap/:country/:id`
+
+Parameters:
+
+-   country, App Store Country, obtain from the app URL https://itunes.apple.com/us/app/id953286746, in this case, `us`.
+
+-   id, App Store app id, obtain from the app URL https://itunes.apple.com/us/app/id953286746, in this case, `id953286746`.
 
 ## pixiv
 

router.js

@@ -434,6 +434,7 @@ router.get('/imuseum/:city/:type', require('./routes/imuseum'));
 // AppStore
 router.get('/appstore/update/:country/:id', require('./routes/appstore/update'));
 router.get('/appstore/price/:country/:type/:id', require('./routes/appstore/price'));
+router.get('/appstore/iap/:country/:id', require('./routes/appstore/in-app-purchase'));
 
 // Hopper
 router.get('/hopper/:lowestOnly/:from/:to?', require('./routes/hopper/index'));

routes/appstore/in-app-purchase.js

@@ -0,0 +1,50 @@
+const axios = require('../../utils/axios');
+const url = require('url');
+const cheerio = require('cheerio');
+
+module.exports = async (ctx) => {
+    const country = ctx.params.country;
+    const id = ctx.params.id;
+    const link = `https://itunes.apple.com/${country}/app/${id}`;
+    const target = url.resolve(link, '?mt=8#see-all/in-app-purchases');
+
+    const res = await axios.get(target);
+    const $ = cheerio.load(res.data);
+    const titleTemp = $('h1')
+        .contents()
+        .first()
+        .text()
+        .trim();
+    const list = $('div.l-row div.we-lockup');
+    const item = list
+        .map((i, e) => ({
+            link,
+            guid:
+                `${titleTemp} ${$(e)
+                    .find('h3.we-lockup__title')
+                    .text()
+                    .trim()} is now ${$(e)
+                    .find('h5')
+                    .text()
+                    .trim()}` + Date.now(),
+            title: `${titleTemp} ${$(e)
+                .find('h3.we-lockup__title')
+                .text()
+                .trim()} is now ${$(e)
+                .find('h5')
+                .text()
+                .trim()}`,
+            pubDate: new Date(Date.now()).toUTCString(),
+        }))
+        .get();
+
+    const platform = $('.we-localnav__title__product').text();
+
+    const title = `${country === 'cn' ? '内购限免提醒' : 'IAP price watcher'}: ${titleTemp} for ${platform.startsWith('App') ? 'iOS' : 'macOS'}`;
+
+    ctx.state.data = {
+        title,
+        link,
+        item,
+    };
+};