[feature] Hashtag federation (in/out), hashtag client API endpoints (#2032)

* update go-fed

* do the things

* remove unused columns from tags

* update to latest lingo from main

* further tag shenanigans

* serve stub page at tag endpoint

* we did it lads

* tests, oh tests, ohhh tests, oh tests (doo doo doo doo)

* swagger docs

* document hashtag usage + federation

* instanceGet

* don't bother parsing tag href

* rename whereStartsWith -> whereStartsLike

* remove GetOrCreateTag

* dont cache status tag timelineability

2 files changed, 75 insertions, 2 deletions

diff --git a/internal/web/tag.go b/internal/web/tag.go
new file mode 100644
index 000000000..d52de81d8
--- /dev/null
+++ b/internal/web/tag.go
@@ -0,0 +1,71 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package web
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
+	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+)
+
+func (m *Module) tagGETHandler(c *gin.Context) {
+	ctx := c.Request.Context()
+
+	// We'll need the instance later, and we can also use it
+	// before then to make it easier to return a web error.
+	instance, errWithCode := m.processor.InstanceGetV1(ctx)
+	if errWithCode != nil {
+		apiutil.WebErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	// Return instance we already got from the db,
+	// don't try to fetch it again when erroring.
+	instanceGet := func(ctx context.Context) (*apimodel.InstanceV1, gtserror.WithCode) {
+		return instance, nil
+	}
+
+	// We only serve text/html at this endpoint.
+	if _, err := apiutil.NegotiateAccept(c, []apiutil.MIME{apiutil.TextHTML}...); err != nil {
+		apiutil.WebErrorHandler(c, gtserror.NewErrorNotAcceptable(err, err.Error()), instanceGet)
+		return
+	}
+
+	tagName, errWithCode := apiutil.ParseTagName(c.Param(apiutil.TagNameKey))
+	if errWithCode != nil {
+		apiutil.WebErrorHandler(c, errWithCode, instanceGet)
+		return
+	}
+
+	stylesheets := []string{
+		assetsPathPrefix + "/Fork-Awesome/css/fork-awesome.min.css",
+		distPathPrefix + "/status.css",
+		distPathPrefix + "/tag.css",
+	}
+
+	c.HTML(http.StatusOK, "tag.tmpl", gin.H{
+		"instance":    instance,
+		"ogMeta":      ogBase(instance),
+		"tagName":     tagName,
+		"stylesheets": stylesheets,
+	})
+}
diff --git a/internal/web/web.go b/internal/web/web.go
index 5c1c4750d..6d785667b 100644
--- a/internal/web/web.go
+++ b/internal/web/web.go
@@ -25,6 +25,7 @@ import (
 
 	"codeberg.org/gruf/go-cache/v3"
 	"github.com/gin-gonic/gin"
+	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
 	"github.com/superseriousbusiness/gotosocial/internal/config"
 	"github.com/superseriousbusiness/gotosocial/internal/db"
 	"github.com/superseriousbusiness/gotosocial/internal/log"
@@ -37,7 +38,8 @@ import (
 const (
 	confirmEmailPath   = "/" + uris.ConfirmEmailPath
 	profileGroupPath   = "/@:" + usernameKey
-	statusPath         = "/statuses/:" + statusIDKey // leave out the '/@:username' prefix as this will be served within the profile group
+	statusPath         = "/statuses/:" + apiutil.WebStatusIDKey // leave out the '/@:username' prefix as this will be served within the profile group
+	tagsPath           = "/tags/:" + apiutil.TagNameKey
 	customCSSPath      = profileGroupPath + "/custom.css"
 	rssFeedPath        = profileGroupPath + "/feed.rss"
 	assetsPathPrefix   = "/assets"
@@ -49,7 +51,6 @@ const (
 
 	tokenParam  = "token"
 	usernameKey = "username"
-	statusIDKey = "status"
 
 	cacheControlHeader    = "Cache-Control"     // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control
 	cacheControlNoCache   = "no-cache"          // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control#response_directives
@@ -107,6 +108,7 @@ func (m *Module) Route(r router.Router, mi ...gin.HandlerFunc) {
 	r.AttachHandler(http.MethodGet, robotsPath, m.robotsGETHandler)
 	r.AttachHandler(http.MethodGet, aboutPath, m.aboutGETHandler)
 	r.AttachHandler(http.MethodGet, domainBlockListPath, m.domainBlockListGETHandler)
+	r.AttachHandler(http.MethodGet, tagsPath, m.tagGETHandler)
 
 	// Attach redirects from old endpoints to current ones for backwards compatibility
 	r.AttachHandler(http.MethodGet, "/auth/edit", func(c *gin.Context) { c.Redirect(http.StatusMovedPermanently, userPanelPath) })