[feature] Add List functionality (#1802)

* start working on lists

* further list work

* test list db functions nicely

* more work on lists

* peepoopeepoo

* poke

* start list timeline func

* we're getting there lads

* couldn't be me working on stuff... could it?

* hook up handlers

* fiddling

* weeee

* woah

* screaming, pissing

* fix streaming being a whiny baby

* lint, small test fix, swagger

* tidying up, testing

* fucked! by the linter

* move timelines to state like a boss

* add timeline start to tests using state

* invalidate lists

internal/processing/timeline/common.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 timeline
+
+import (
+	"context"
+
+	"github.com/superseriousbusiness/gotosocial/internal/timeline"
+)
+
+// SkipInsert returns a function that satisifes SkipInsertFunction.
+func SkipInsert() timeline.SkipInsertFunction {
+	// Gap to allow between a status or boost of status,
+	// and reinsertion of a new boost of that status.
+	// This is useful to avoid a heavily boosted status
+	// showing up way too often in a user's timeline.
+	const boostReinsertionDepth = 50
+
+	return func(
+		ctx context.Context,
+		newItemID string,
+		newItemAccountID string,
+		newItemBoostOfID string,
+		newItemBoostOfAccountID string,
+		nextItemID string,
+		nextItemAccountID string,
+		nextItemBoostOfID string,
+		nextItemBoostOfAccountID string,
+		depth int,
+	) (bool, error) {
+		if newItemID == nextItemID {
+			// Don't insert duplicates.
+			return true, nil
+		}
+
+		if newItemBoostOfID != "" {
+			if newItemBoostOfID == nextItemBoostOfID &&
+				depth < boostReinsertionDepth {
+				// Don't insert boosts of items
+				// we've seen boosted recently.
+				return true, nil
+			}
+
+			if newItemBoostOfID == nextItemID &&
+				depth < boostReinsertionDepth {
+				// Don't insert boosts of items when
+				// we've seen the original recently.
+				return true, nil
+			}
+		}
+
+		// Proceed with insertion
+		// (that's what she said!).
+		return false, nil
+	}
+}