[feature] Client API endpoints + v. basic web view for pinned posts (#1547)

* implement status pin client api + web handler

* make test names + comments more descriptive

* don't use separate table for status pins

* remove unused add + remove checking

* tidy up + add some more tests

1 files changed, 140 insertions, 0 deletions

diff --git a/internal/processing/status/pin.go b/internal/processing/status/pin.go
new file mode 100644
index 000000000..addd2515b
--- /dev/null
+++ b/internal/processing/status/pin.go
@@ -0,0 +1,140 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2023 GoToSocial Authors admin@gotosocial.org
+
+   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 status
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+
+	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+)
+
+const allowedPinnedCount = 10
+
+// getPinnableStatus fetches targetStatusID status and ensures that requestingAccountID
+// can pin or unpin it.
+//
+// It checks:
+//   - Status belongs to requesting account.
+//   - Status is public, unlisted, or followers-only.
+//   - Status is not a boost.
+func (p *Processor) getPinnableStatus(ctx context.Context, targetStatusID string, requestingAccountID string) (*gtsmodel.Status, gtserror.WithCode) {
+	targetStatus, err := p.db.GetStatusByID(ctx, targetStatusID)
+	if err != nil {
+		err = fmt.Errorf("error fetching status %s: %w", targetStatusID, err)
+		return nil, gtserror.NewErrorNotFound(err)
+	}
+
+	if targetStatus.AccountID != requestingAccountID {
+		err = fmt.Errorf("status %s does not belong to account %s", targetStatusID, requestingAccountID)
+		return nil, gtserror.NewErrorUnprocessableEntity(err, err.Error())
+	}
+
+	if targetStatus.Visibility == gtsmodel.VisibilityDirect {
+		err = errors.New("cannot pin direct messages")
+		return nil, gtserror.NewErrorUnprocessableEntity(err, err.Error())
+	}
+
+	if targetStatus.BoostOfID != "" {
+		err = errors.New("cannot pin boosts")
+		return nil, gtserror.NewErrorUnprocessableEntity(err, err.Error())
+	}
+
+	return targetStatus, nil
+}
+
+// PinCreate pins the target status to the top of requestingAccount's profile, if possible.
+//
+// Conditions for a pin to work:
+//   - Status belongs to requesting account.
+//   - Status is public, unlisted, or followers-only.
+//   - Status is not a boost.
+//   - Status is not already pinnd.
+//   - Limit of pinned statuses not yet met or exceeded.
+//
+// If the conditions can't be met, then code 422 Unprocessable Entity will be returned.
+func (p *Processor) PinCreate(ctx context.Context, requestingAccount *gtsmodel.Account, targetStatusID string) (*apimodel.Status, gtserror.WithCode) {
+	targetStatus, errWithCode := p.getPinnableStatus(ctx, targetStatusID, requestingAccount.ID)
+	if errWithCode != nil {
+		return nil, errWithCode
+	}
+
+	if !targetStatus.PinnedAt.IsZero() {
+		err := errors.New("status already pinned")
+		return nil, gtserror.NewErrorUnprocessableEntity(err, err.Error())
+	}
+
+	pinnedCount, err := p.db.CountAccountPinned(ctx, requestingAccount.ID)
+	if err != nil {
+		return nil, gtserror.NewErrorInternalError(fmt.Errorf("error checking number of pinned statuses: %w", err))
+	}
+
+	if pinnedCount >= allowedPinnedCount {
+		err = fmt.Errorf("status pin limit exceeded, you've already pinned %d status(es) out of %d", pinnedCount, allowedPinnedCount)
+		return nil, gtserror.NewErrorUnprocessableEntity(err, err.Error())
+	}
+
+	targetStatus.PinnedAt = time.Now()
+	if err := p.db.UpdateStatus(ctx, targetStatus); err != nil {
+		return nil, gtserror.NewErrorInternalError(fmt.Errorf("db error pinning status: %w", err))
+	}
+
+	apiStatus, err := p.tc.StatusToAPIStatus(ctx, targetStatus, requestingAccount)
+	if err != nil {
+		return nil, gtserror.NewErrorInternalError(fmt.Errorf("error converting status %s to frontend representation: %w", targetStatus.ID, err))
+	}
+
+	return apiStatus, nil
+}
+
+// PinRemove unpins the target status from the top of requestingAccount's profile, if possible.
+//
+// Conditions for an unpin to work:
+//   - Status belongs to requesting account.
+//   - Status is public, unlisted, or followers-only.
+//   - Status is not a boost.
+//
+// If the conditions can't be met, then code 422 Unprocessable Entity will be returned.
+//
+// Unlike with PinCreate, statuses that are already unpinned will not return 422, but just do
+// nothing and return the api model representation of the status, to conform to the masto API.
+func (p *Processor) PinRemove(ctx context.Context, requestingAccount *gtsmodel.Account, targetStatusID string) (*apimodel.Status, gtserror.WithCode) {
+	targetStatus, errWithCode := p.getPinnableStatus(ctx, targetStatusID, requestingAccount.ID)
+	if errWithCode != nil {
+		return nil, errWithCode
+	}
+
+	if targetStatus.PinnedAt.IsZero() {
+		targetStatus.PinnedAt = time.Time{}
+		if err := p.db.UpdateStatus(ctx, targetStatus); err != nil {
+			return nil, gtserror.NewErrorInternalError(fmt.Errorf("db error unpinning status: %w", err))
+		}
+	}
+
+	apiStatus, err := p.tc.StatusToAPIStatus(ctx, targetStatus, requestingAccount)
+	if err != nil {
+		return nil, gtserror.NewErrorInternalError(fmt.Errorf("error converting status %s to frontend representation: %w", targetStatus.ID, err))
+	}
+
+	return apiStatus, nil
+}