feat(generic): introduce a generic merge view

This view shows the values before and after merge instead of simply
merging.

apis_core/generic/abc.py

@@ -28,6 +28,10 @@ def get_delete_url(self):
         ct = ContentType.objects.get_for_model(self)
         return reverse("apis_core:generic:delete", args=[ct, self.id])
 
+    def get_merge_url(self, other_id):
+        ct = ContentType.objects.get_for_model(self)
+        return reverse("apis_core:generic:merge", args=[ct, self.id, other_id])
+
     def get_create_success_url(self):
         return self.get_absolute_url()
 

apis_core/generic/forms/__init__.py

@@ -86,3 +86,10 @@ def __init__(self, *args, **kwargs):
                         url, attrs={"data-html": True}
                     )
                     self.fields[field].widget.choices = self.fields[field].choices
+
+
+class GenericMergeForm(forms.Form):
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.helper = FormHelper()
+        self.helper.add_input(Submit("submit", "Merge"))

apis_core/generic/templates/generic/generic_merge.html

@@ -0,0 +1,42 @@
+{% extends basetemplate|default:"base.html" %}
+{% load apisgeneric %}
+{% load apis_history_templatetags %}
+{% load crispy_forms_tags %}
+{% load static %}
+
+{% block styles %}
+  {{ block.super }}
+  <link rel="stylesheet" href="{% static 'css/history.css' %}" />
+{% endblock styles %}
+
+{% block content %}
+  <div class="container">
+    <h4 class="mb-4">
+      Merging values of <a href="{{ other.get_absolute_url }}">{{ other }}</a> into <a href="{{ object.get_absolute_url }}">{{ object }}</a>
+    </h4>
+    <div class="alert alert-warning" role="alert">
+      After the merge <a href="{{ other.get_absolute_url }}">{{ other }}</a> will be deleted!
+    </div>
+    <table class="table table-sm table-hover table-bordered difftable">
+      <thead>
+        <tr>
+          <th></th>
+          <th>Old value</th>
+          <th>New value</th>
+        </tr>
+      </thead>
+      <tbody>
+        {% for change in changes %}
+          <tr>
+            <th>{{ change.field }}</th>
+            <td>{{ change|get_diff_old }}</td>
+            <td>{{ change|get_diff_new }}</td>
+          </tr>
+        {% endfor %}
+      </tbody>
+    </table>
+    {% if form %}
+      {% crispy form form.helper %}
+    {% endif %}
+  </div>
+{% endblock %}

apis_core/generic/urls.py

@@ -49,6 +49,11 @@ def to_url(self, value):
                 path("create", views.Create.as_view(), name="create"),
                 path("delete/<int:pk>", views.Delete.as_view(), name="delete"),
                 path("update/<int:pk>", views.Update.as_view(), name="update"),
+                path(
+                    "merge/<int:pk>/<int:otherpk>",
+                    views.MergeWith.as_view(),
+                    name="merge",
+                ),
                 path("autocomplete", views.Autocomplete.as_view(), name="autocomplete"),
                 path("import", views.Import.as_view(), name="import"),
                 path(

apis_core/generic/views.py

@@ -1,8 +1,12 @@
+from collections import namedtuple
+
 from dal import autocomplete
 from django import forms, http
 from django.conf import settings
+from django.contrib import messages
 from django.contrib.auth.mixins import PermissionRequiredMixin
 from django.forms import modelform_factory
+from django.shortcuts import get_object_or_404
 from django.template.exceptions import TemplateDoesNotExist
 from django.template.loader import select_template
 from django.urls import reverse, reverse_lazy
@@ -19,7 +23,7 @@
 from apis_core.utils.helpers import create_object_from_uri
 
 from .filtersets import GenericFilterSet
-from .forms import GenericImportForm, GenericModelForm
+from .forms import GenericImportForm, GenericMergeForm, GenericModelForm
 from .helpers import (
     first_member_match,
     generate_search_filter,
@@ -331,3 +335,44 @@ def form_valid(self, form):
 
     def get_success_url(self):
         return self.object.get_absolute_url()
+
+
+class MergeWith(GenericModelMixin, PermissionRequiredMixin, FormView):
+    """
+    Generic merge view.
+    """
+
+    permission_action_required = "change"
+    form_class = GenericMergeForm
+    template_name = "generic/generic_merge.html"
+
+    def setup(self, *args, **kwargs):
+        super().setup(*args, **kwargs)
+        self.object = get_object_or_404(self.model, pk=self.kwargs["pk"])
+        self.other = get_object_or_404(self.model, pk=self.kwargs["otherpk"])
+
+    def get_context_data(self, **kwargs):
+        """
+        The context consists of the two objects that are merged as well
+        as a list of changes. Those changes are presented in the view as
+        a table with diffs
+        """
+        Change = namedtuple("Change", "field old new")
+        ctx = super().get_context_data(**kwargs)
+        ctx["changes"] = []
+        for field in self.object._meta.fields:
+            newval = self.object.get_field_value_after_merge(self.other, field)
+            ctx["changes"].append(
+                Change(field.verbose_name, getattr(self.object, field.name), newval)
+            )
+        ctx["object"] = self.object
+        ctx["other"] = self.other
+        return ctx
+
+    def form_valid(self, form):
+        self.object.merge_with([self.other])
+        messages.info(self.request, f"Merged values of {self.other} into {self.object}")
+        return super().form_valid(form)
+
+    def get_success_url(self):
+        return self.object.get_absolute_url()