Add live preview in admin

articles/models.py

@@ -30,6 +30,18 @@ class AdminUrlMixin:
         )
 
 
+def format_article_content(content):
+    md = markdown.Markdown(
+        extensions=[
+            "extra",
+            CodeHiliteExtension(linenums=False, guess_lang=False),
+            LazyLoadingImageExtension(),
+        ]
+    )
+    content = re.sub(r"(\s)#(\w+)", r"\1\#\2", content)
+    return md.convert(content)
+
+
 class Article(AdminUrlMixin, models.Model):
     DRAFT = "draft"
     PUBLISHED = "published"
@@ -85,16 +97,7 @@ class Article(AdminUrlMixin, models.Model):
 
     @cached_property
     def get_formatted_content(self):
-        md = markdown.Markdown(
-            extensions=[
-                "extra",
-                CodeHiliteExtension(linenums=False, guess_lang=False),
-                LazyLoadingImageExtension(),
-            ]
-        )
-        content = self.content
-        content = re.sub(r"(\s)#(\w+)", r"\1\#\2", content)
-        return md.convert(content)
+        return format_article_content(self.content)
 
     def publish(self):
         if not self.published_at:

articles/static/live-preview.js

@@ -0,0 +1,56 @@
+// Returns a function, that, as long as it continues to be invoked, will not
+// be triggered. The function will be called after it stops being called for
+// N milliseconds. If `immediate` is passed, trigger the function on the
+// leading edge, instead of the trailing.
+function debounce(func, wait, immediate) {
+    var timeout;
+    return function () {
+        var context = this, args = arguments;
+        var later = function () {
+            timeout = null;
+            if (!immediate) func.apply(context, args);
+        };
+        var callNow = immediate && !timeout;
+        clearTimeout(timeout);
+        timeout = setTimeout(later, wait);
+        if (callNow) func.apply(context, args);
+    };
+}
+
+let preview = null;
+window.onload = function () {
+    const previewButton = document.querySelector("input#_live_preview");
+    previewButton.addEventListener("click", event => {
+        event.preventDefault();
+        const params = "width=800,height=1000,menubar=no,toolbar=no,location=no,status=no,resizable=yes,scrollbars=yes";
+        if (preview !== null) {
+            preview.close();
+        }
+        preview = window.open("about:blank", "Preview", params);
+        const id = Number(window.location.pathname.match(/\d+/)[0]);
+        const loadPreview = debounce(function () {
+            const body = new FormData();
+            const articleContent = document.getElementById("id_content").value;
+            body.set("content", articleContent);
+            const csrfToken = document.querySelector("input[name=csrfmiddlewaretoken]").value;
+            body.set("csrfmiddlewaretoken", csrfToken);
+            fetch(`/api/render/${id}/`, {method: "POST", body: body})
+                .then(function (response) {
+                    response.text().then(value => {
+                        preview.document.querySelector("html").innerHTML = value
+                    });
+                })
+        }, 500);
+        preview.onload = loadPreview;
+        const content = document.getElementById("id_content");
+        content.addEventListener("input", event => {
+            event.preventDefault();
+            loadPreview();
+        });
+    })
+};
+window.onbeforeunload = function () {
+    if (preview !== null) {
+        preview.close();
+    }
+};

articles/templates/admin/articles/article/submit_line.html

@@ -1,11 +1,15 @@
 {% extends "admin/submit_line.html" %}
-{% load i18n admin_urls %}
+{% load static %}
 {% block submit-row %}
     {{ block.super }}
     {% if original.status != original.PUBLISHED %}
-        <input type="submit" value="Save & publish" name="_publish">
+        <input type="submit" value="Save and publish" name="_publish">
     {% elif original.status != original.DRAFT %}
-        <input type="submit" value="Save & unpublish" name="_unpublish">
+        <input type="submit" value="Save and unpublish" name="_unpublish">
     {% endif %}
-    <input type="submit" value="Save & preview" name="_preview">
+    <input type="submit" value="Save and view" name="_preview">
+    {% if original %}
+        <input type="button" value="Live preview" id="_live_preview">
+    {% endif %}
+    <script type="text/javascript" src="{% static "live-preview.js" %}"></script>
 {% endblock %}

articles/tests/test_api_views.py

@@ -0,0 +1,65 @@
+import pytest
+from django.test import Client
+from django.urls import reverse
+
+from articles.models import Article, format_article_content
+
+
+@pytest.mark.django_db
+def test_unauthenticated_render_redirects(published_article: Article, client: Client):
+    api_res = client.post(
+        reverse("api-render-article", kwargs={"article_pk": published_article.pk}),
+        data={"content": published_article.content},
+    )
+    assert api_res.status_code == 302
+
+
+@pytest.mark.django_db
+def test_render_article_same_content(published_article: Article, client: Client):
+    client.force_login(published_article.author)
+    api_res = client.post(
+        reverse("api-render-article", kwargs={"article_pk": published_article.pk}),
+        data={"content": published_article.content},
+    )
+    standard_res = client.get(
+        reverse("article-detail", kwargs={"slug": published_article.slug})
+    )
+    assert api_res.status_code == 200
+    assert standard_res.status_code == 200
+    # ignore an expected difference
+    api_content = api_res.content.decode("utf-8")  # type: str
+    standard_content = standard_res.content.decode("utf-8")
+    api_content = api_content.replace(
+        "?next=/api/render/1/",
+        "?next=/some-article-slug/",
+    )
+
+    assert api_content == standard_content
+
+
+@pytest.mark.django_db
+def test_render_article_change_content(published_article: Article, client: Client):
+    client.force_login(published_article.author)
+    preview_content = "This is a different content **with strong emphasis**"
+    api_res = client.post(
+        reverse("api-render-article", kwargs={"article_pk": published_article.pk}),
+        data={"content": preview_content},
+    )
+    assert api_res.status_code == 200
+    api_content = api_res.content.decode("utf-8")  # type: str
+    html_preview_content = format_article_content(preview_content)
+    assert html_preview_content in api_content
+
+
+@pytest.mark.django_db
+def test_render_article_doesnt_save(published_article, client: Client):
+    client.force_login(published_article.author)
+    original_content = published_article.content
+    preview_content = "This is a different content **with strong emphasis**"
+    api_res = client.post(
+        reverse("api-render-article", kwargs={"article_pk": published_article.pk}),
+        data={"content": preview_content},
+    )
+    assert api_res.status_code == 200
+    published_article.refresh_from_db()
+    assert published_article.content == original_content

articles/views/api.py

@@ -0,0 +1,16 @@
+from django.contrib.auth.decorators import login_required
+from django.http import HttpResponse
+from django.shortcuts import render
+from django.views.decorators.http import require_POST
+
+from articles.models import Article
+
+
+@login_required
+@require_POST
+def render_article(request, article_pk):
+    template = "articles/article_detail.html"
+    article = Article.objects.get(pk=article_pk)
+    article.content = request.POST.get("content")
+    html = render(request, template, context={"article": article})
+    return HttpResponse(html)

blog/urls.py

@@ -18,7 +18,7 @@ from django.contrib import admin
 from django.urls import path
 from django.views.generic import TemplateView
 
-from articles.views import feeds, html
+from articles.views import api, feeds, html
 from blog import settings
 
 urlpatterns = [
@@ -32,6 +32,7 @@ urlpatterns = [
     path("", html.ArticlesListView.as_view(), name="articles-list"),
     path("drafts/", html.DraftsListView.as_view(), name="drafts-list"),
     path("feed/", feeds.CompleteFeed(), name="complete-feed"),
+    path("api/render/<int:article_pk>/", api.render_article, name="api-render-article"),
     path("<slug:slug>", html.ArticleDetailView.as_view(), name="article-detail-old"),
     path("<slug:slug>/", html.ArticleDetailView.as_view(), name="article-detail"),
 ]