appview: repo/compare: conditionally show a create pull button

appview/pages/pages.go

···
 	Tags         []*types.TagReference
 	Base         string
 	Head         string
+	AllowPull    bool
 
 	Active string
 }
···
 func (p *Pages) RepoCompare(w io.Writer, params RepoCompareParams) error {
 	params.Active = "overview"
 	return p.executeRepo("repo/compare", w, params)
+}
+
+type RepoCompareAllowPullParams struct {
+	LoggedInUser *oauth.User
+	RepoInfo     repoinfo.RepoInfo
+	Base         string
+	Head         string
+}
+
+func (p *Pages) RepoCompareAllowPullFragment(w io.Writer, params RepoCompareAllowPullParams) error {
+	return p.executePlain("repo/fragments/compareAllowPull", w, params)
 }
 
 type RepoCompareDiffParams struct {

appview/pages/templates/repo/compare.html

···
-{{ define "title" }}new comparison{{ end }}
+{{ define "title" }}
+    {{ if and .Head .Base }}
+        comparing {{ .Base }} and
+        {{ .Head }}
+    {{ else }}
+        new comparison
+    {{ end }}
+{{ end }}
 
 {{ define "repoContent" }}
     <section>
···
             </div>
         </form>
     </section>
-    <section class="hidden"></section>
 
   <script>
     var templatedBase = `{{ .Base }}`;
···
         if (baseToUse && headToUse) {
             const url = `/{{ .RepoInfo.FullName }}/compare/diff/${baseToUse}/${headToUse}`;
             htmx.ajax('GET', url, { target: '#compare-diff' });
+            document.title = `comparing ${baseToUse} and ${headToUse}`;
+
+            const allowPull = `{{ .AllowPull }}`
+            if (allowPull) {
+              htmx.ajax('GET',
+                `/{{ .RepoInfo.FullName }}/compare/allow-pull/${baseToUse}/${headToUse}`,
+                { target: '#allow-pull'},
+              )
+            }
         }
     }
     </script>
+    <section id="allow-pull" class="pt-4"></section>
 {{ end }}
 
 {{ define "repoAfter" }}

appview/pages/templates/repo/fragments/compareAllowPull.html

···
+{{ define "repo/fragments/compareAllowPull" }}
+    <div class="flex items-baseline justify-normal gap-4">
+        <p>
+            This comparison can be turned into a pull request to be reviewed and
+            discussed.
+        </p>
+
+        {{ $newPullUrl := printf "/%s/pulls/new?strategy=branch&targetBranch=%s&sourceBranch=%s" .RepoInfo.FullName .Base .Head }}
+
+
+        <div class="flex justify-start items-center gap-2 mt-2">
+            <a
+                href="{{ $newPullUrl }}"
+                class="btn flex items-center gap-2 no-underline hover:no-underline"
+            >
+                {{ i "git-pull-request-create" "w-4 h-4" }}
+                create pull
+                <span id="create-pull-spinner" class="group">
+                    {{ i "loader-circle" "w-4 h-4 animate-spin hidden group-[.htmx-request]:inline" }}
+                </span>
+            </a>
+        </div>
+    </div>
+{{ end }}

appview/state/repo.go

···
 		}
 	}
 
+	var allowPull bool = false
+	if user != nil {
+		if slices.ContainsFunc(branches.Branches, func(branch types.Branch) bool {
+			return branch.Name == head || branch.Name == base
+		}) {
+			allowPull = true
+		}
+	}
+
 	s.pages.RepoCompare(w, pages.RepoCompareParams{
 		LoggedInUser: user,
 		RepoInfo:     f.RepoInfo(s, user),
···
 		Tags:         tags.Tags,
 		Base:         base,
 		Head:         head,
+		AllowPull:    allowPull,
+	})
+
+}
+
+func (s *State) RepoCompareAllowPullFragment(w http.ResponseWriter, r *http.Request) {
+	user := s.oauth.GetUser(r)
+	f, err := s.fullyResolvedRepo(r)
+	if err != nil {
+		log.Println("failed to get repo and knot", err)
+		return
+	}
+
+	s.pages.RepoCompareAllowPullFragment(w, pages.RepoCompareAllowPullParams{
+		Head:         chi.URLParam(r, "head"),
+		Base:         chi.URLParam(r, "base"),
+		RepoInfo:     f.RepoInfo(s, user),
+		LoggedInUser: user,
 	})
 }
 

appview/state/router.go

···
 				//   /compare/master...some/feature
 				//   /compare/master...example.com:another/feature <- this is a fork
 				r.Get("/{base}/{head}", s.RepoCompare)
+				r.Get("/diff/{base}/{head}", s.RepoCompareDiffFragment)
+				r.Get("/allow-pull/{base}/{head}", s.RepoCompareAllowPullFragment)
 				r.Get("/*", s.RepoCompare)
-				r.Get("/diff/{base}/{head}", s.RepoCompareDiffFragment)
 			})
 
 			r.Route("/pulls", func(r chi.Router) {