Don't do a full page load when clicking the follow button (#28872)

- Use htmx to perform the button request
- `hx-headers='{"x-csrf-token": "{{.CsrfToken}}"}'` to authenticate (we
should probably learn to reuse this)
- `hx-post="{{.ContextUser.HomeLink}}?action=follow"` to send a POST
request to follow the user
- `hx-target="#profile-avatar-card"` to target the card div for
replacement
- `hx-swap="outerHTML"` to replace the card (as opposed to its inner
content) with the new card that shows the new follower count and button
color
- Change the backend response to return a `<div>` tag (the card) instead
of a redirect to the user page

# Before

![before](https://github.com/go-gitea/gitea/assets/20454870/86899d15-41c9-42ed-bd85-253b9caac7f8)

# After

![after](https://github.com/go-gitea/gitea/assets/20454870/59455d96-548c-4a81-a5b0-fab1dc1e87ef)

Signed-off-by: Yarden Shoham <git@yardenshoham.com>

routers/web/user/profile.go

@@ -14,6 +14,7 @@ import (
 	"code.gitea.io/gitea/models/db"
 	repo_model "code.gitea.io/gitea/models/repo"
 	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/log"
@@ -26,6 +27,10 @@ import (
 	shared_user "code.gitea.io/gitea/routers/web/shared/user"
 )
 
+const (
+	tplProfileBigAvatar base.TplName = "shared/user/profile_big_avatar"
+)
+
 // OwnerProfile render profile page for a user or a organization (aka, repo owner)
 func OwnerProfile(ctx *context.Context) {
 	if strings.Contains(ctx.Req.Header.Get("Accept"), "application/rss+xml") {
@@ -309,8 +314,10 @@ func Action(ctx *context.Context) {
 
 	if err != nil {
 		log.Error("Failed to apply action %q: %v", ctx.FormString("action"), err)
-		ctx.JSONError(fmt.Sprintf("Action %q failed", ctx.FormString("action")))
+		ctx.Error(http.StatusBadRequest, fmt.Sprintf("Action %q failed", ctx.FormString("action")))
 		return
 	}
-	ctx.JSONOK()
+
+	shared_user.PrepareContextForProfileBigAvatar(ctx)
+	ctx.HTML(http.StatusOK, tplProfileBigAvatar)
 }

templates/shared/user/profile_big_avatar.tmpl

@@ -1,4 +1,4 @@
-<div class="ui card">
+<div id="profile-avatar-card" class="ui card">
 	<div id="profile-avatar" class="content gt-df">
 	{{if eq .SignedUserID .ContextUser.ID}}
 		<a class="image" href="{{AppSubUrl}}/user/settings" data-tooltip-content="{{ctx.Locale.Tr "user.change_avatar"}}">
@@ -110,13 +110,13 @@
 			</li>
 			{{end}}
 			{{if and .IsSigned (ne .SignedUserID .ContextUser.ID)}}
-			<li class="follow">
+			<li class="follow" hx-headers='{"x-csrf-token": "{{.CsrfToken}}"}' hx-target="#profile-avatar-card" hx-swap="outerHTML">
 				{{if $.IsFollowing}}
-					<button class="ui basic red button link-action" data-url="{{.ContextUser.HomeLink}}?action=unfollow">
+					<button hx-post="{{.ContextUser.HomeLink}}?action=unfollow" class="ui basic red button">
 						{{svg "octicon-person"}} {{ctx.Locale.Tr "user.unfollow"}}
 					</button>
 				{{else}}
-					<button class="ui basic primary button link-action" data-url="{{.ContextUser.HomeLink}}?action=follow">
+					<button hx-post="{{.ContextUser.HomeLink}}?action=follow" class="ui basic primary button">
 						{{svg "octicon-person"}} {{ctx.Locale.Tr "user.follow"}}
 					</button>
 				{{end}}