feat!: Abusive content reporting (#6977)

This implements milestones 1. and 4. from **Task F. Moderation features: Reporting** (part of [amendment of the workplan](https://codeberg.org/forgejo/sustainability/src/branch/main/2022-12-01-nlnet/2025-02-07-extended-workplan.md#task-f-moderation-features-reporting) for NLnet 2022-12-035):

> 1. A reporting feature is implemented in the database. It ensures that content remains available for review, even if a user deletes it after a report was sent.

> 4. Users can report the most relevant content types (at least: issue comments, repositories, users)

### See also:
- forgejo/discussions#291
- forgejo/discussions#304
- forgejo/design#30

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/6977
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Reviewed-by: Otto <otto@codeberg.org>
Co-authored-by: floss4good <floss4good@disroot.org>
Co-committed-by: floss4good <floss4good@disroot.org>

models/repo/moderation.go

@@ -0,0 +1,70 @@
+// Copyright 2025 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package repo
+
+import (
+	"context"
+
+	"forgejo.org/models/moderation"
+	"forgejo.org/modules/json"
+	"forgejo.org/modules/timeutil"
+)
+
+// RepositoryData represents a trimmed down repository that is used for preserving
+// only the fields needed for abusive content reports (mainly string fields).
+type RepositoryData struct {
+	OwnerID     int64
+	OwnerName   string
+	Name        string
+	Description string
+	Website     string
+	Topics      []string
+	Avatar      string
+	CreatedUnix timeutil.TimeStamp
+	UpdatedUnix timeutil.TimeStamp
+}
+
+// newRepositoryData creates a trimmed down repository to be used just to create a JSON structure
+// (keeping only the fields relevant for moderation purposes)
+func newRepositoryData(repo *Repository) RepositoryData {
+	return RepositoryData{
+		OwnerID:     repo.OwnerID,
+		OwnerName:   repo.OwnerName,
+		Name:        repo.Name,
+		Description: repo.Description,
+		Website:     repo.Website,
+		Topics:      repo.Topics,
+		Avatar:      repo.Avatar,
+		CreatedUnix: repo.CreatedUnix,
+		UpdatedUnix: repo.UpdatedUnix,
+	}
+}
+
+// IfNeededCreateShadowCopyForRepository checks if for the given repository there are any reports of abusive content submitted
+// and if found a shadow copy of relevant repository fields will be stored into DB and linked to the above report(s).
+// This function should be called when a repository is deleted or updated.
+func IfNeededCreateShadowCopyForRepository(ctx context.Context, repo *Repository, forUpdates bool) error {
+	shadowCopyNeeded, err := moderation.IsShadowCopyNeeded(ctx, moderation.ReportedContentTypeRepository, repo.ID)
+	if err != nil {
+		return err
+	}
+
+	if shadowCopyNeeded {
+		if forUpdates {
+			// get the unmodified repository fields
+			repo, err = GetRepositoryByID(ctx, repo.ID)
+			if err != nil {
+				return err
+			}
+		}
+		repoData := newRepositoryData(repo)
+		content, err := json.Marshal(repoData)
+		if err != nil {
+			return err
+		}
+		return moderation.CreateShadowCopyForRepository(ctx, repo.ID, string(content))
+	}
+
+	return nil
+}