Improve the crontab snippet in the "Check Details" page

Fixes: #465

CHANGELOG.md

@@ -7,6 +7,7 @@ All notable changes to this project will be documented in this file.
 - Add tighter parameter checks in hc.front.views.serve_doc
 - Update OpsGenie instructions (#450)
 - Update the email notification template to include more check and last ping details
+- Improve the crontab snippet in the "Check Details" page (#465)
 
 ## v1.18.0 - 2020-12-09
 

hc/front/templatetags/hc_extras.py

@@ -157,3 +157,33 @@ def format_headers(headers):
 @register.simple_tag
 def now_isoformat():
     return now().replace(microsecond=0).isoformat()
+
+
+@register.filter
+def guess_schedule(check):
+    if check.kind == "cron":
+        return check.schedule
+
+    v = int(check.timeout.total_seconds())
+
+    # every minute
+    if v == 60:
+        return "* * * * *"
+
+    # every hour
+    if v == 3600:
+        return "0 * * * *"
+
+    # every day
+    if v == 3600 * 24:
+        return "0 0 * * *"
+
+    # every X minutes, if 60 is divisible by X
+    minutes, seconds = divmod(v, 60)
+    if minutes in (2, 3, 4, 5, 6, 10, 12, 15, 20, 30) and seconds == 0:
+        return f"*/{minutes} * * * *"
+
+    # every X hours, if 24 is divisible by X
+    hours, seconds = divmod(v, 3600)
+    if hours in (2, 3, 4, 6, 8, 12) and seconds == 0:
+        return f"0 */{hours} * * *"

hc/front/tests/test_details.py

@@ -1,3 +1,5 @@
+from datetime import timedelta as td
+
 from hc.api.models import Check, Ping
 from hc.test import BaseTestCase
 
@@ -74,3 +76,32 @@ class DetailsTestCase(BaseTestCase):
         r = self.client.get(self.url)
 
         self.assertNotContains(r, "resume-btn", status_code=200)
+
+    def test_crontab_example_guesses_schedules(self):
+        self.client.login(username="alice@example.org", password="password")
+
+        pairs = [
+            (td(minutes=1), "* * * * *"),
+            (td(minutes=12), "*/12 * * * *"),
+            (td(hours=1), "0 * * * *"),
+            (td(hours=6), "0 */6 * * *"),
+            (td(days=1), "0 0 * * *"),
+        ]
+
+        for timeout, expression in pairs:
+            self.check.timeout = timeout
+            self.check.save()
+
+            r = self.client.get(self.url)
+            self.assertContains(r, f"{expression} /your/command.sh")
+            self.assertNotContains(r, 'FIXME: replace "* * * * *"')
+
+    def test_crontab_example_handles_unsupported_timeout_values(self):
+        self.client.login(username="alice@example.org", password="password")
+
+        self.check.timeout = td(minutes=13)
+        self.check.save()
+
+        r = self.client.get(self.url)
+        self.assertContains(r, f"* * * * * /your/command.sh")
+        self.assertContains(r, 'FIXME: replace "* * * * *"')

templates/front/show_usage_modal.html

@@ -1,9 +1,13 @@
+{% load hc_extras %}
 <div id="show-usage-modal" class="modal">
     <div class="modal-dialog">
         <div class="modal-content">
             <div class="modal-header">
                 <button type="button" class="close" data-dismiss="modal">&times;</button>
-                <h4 id="usage-examples-title">Usage Examples</h4>
+                <h4 id="usage-examples-title">
+                    {% if check.name %}"{{ check.name }}"{% endif %}
+                    Usage Examples
+                </h4>
                 <ul class="nav nav-pills" role="tablist">
                     <li class="active">
                         <a href="#crontab" data-toggle="tab">Crontab</a>
@@ -42,9 +46,20 @@
             </div>
             <div class="modal-body">
                 <div class="tab-content">
-                    {% with ping_url=check.url|default:'<span class="ex"></span>' %}
+                    {% with ping_url=check.url %}
                     <div role="tabpanel" class="tab-pane active" id="crontab">
-                        {% include "front/snippets/crontab.html" %}
+                        {% with check|guess_schedule as schedule %}
+                        <div class="highlight">
+                            <pre><span class="c1"># A sample crontab entry. Note the curl call appended after the command.</span>{% if not schedule %}
+<span class="c1"># FIXME: replace "* * * * *" below with the correct cron expression!</span>{% endif %}
+<span class="c1"># FIXME: replace "/your/command.sh" below with the correct command!</span>
+{{ schedule|default:"* * * * *" }} /your/command.sh && curl -fsS -m 10 --retry 5 -o /dev/null {{ ping_url }}</pre>
+                        </div>
+                        <div class="highlight">
+                            <pre><span class="c1"># Here's the part you need to append, provided here separately for easy copy/pasting:</span>
+&& curl -fsS -m 10 --retry 5 -o /dev/null {{ ping_url }}</pre>
+                        </div>
+                        {% endwith %}
                     </div>
                     <div role="tabpanel" class="tab-pane" id="bash">
                         {% include "front/snippets/bash_curl.html" %}