Some repository refactors (#17950)

* some repository refactors

* remove unnecessary code

* Fix test

* Remove unnecessary banner

models/repo/fork.go

@@ -0,0 +1,69 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package repo
+
+import (
+	"context"
+
+	"code.gitea.io/gitea/models/db"
+)
+
+func getRepositoriesByForkID(e db.Engine, forkID int64) ([]*Repository, error) {
+	repos := make([]*Repository, 0, 10)
+	return repos, e.
+		Where("fork_id=?", forkID).
+		Find(&repos)
+}
+
+// GetRepositoriesByForkID returns all repositories with given fork ID.
+func GetRepositoriesByForkID(ctx context.Context, forkID int64) ([]*Repository, error) {
+	return getRepositoriesByForkID(db.GetEngine(ctx), forkID)
+}
+
+// GetForkedRepo checks if given user has already forked a repository with given ID.
+func GetForkedRepo(ownerID, repoID int64) *Repository {
+	repo := new(Repository)
+	has, _ := db.GetEngine(db.DefaultContext).
+		Where("owner_id=? AND fork_id=?", ownerID, repoID).
+		Get(repo)
+	if has {
+		return repo
+	}
+	return nil
+}
+
+// HasForkedRepo checks if given user has already forked a repository with given ID.
+func HasForkedRepo(ownerID, repoID int64) bool {
+	has, _ := db.GetEngine(db.DefaultContext).
+		Table("repository").
+		Where("owner_id=? AND fork_id=?", ownerID, repoID).
+		Exist()
+	return has
+}
+
+// GetUserFork return user forked repository from this repository, if not forked return nil
+func GetUserFork(repoID, userID int64) (*Repository, error) {
+	var forkedRepo Repository
+	has, err := db.GetEngine(db.DefaultContext).Where("fork_id = ?", repoID).And("owner_id = ?", userID).Get(&forkedRepo)
+	if err != nil {
+		return nil, err
+	}
+	if !has {
+		return nil, nil
+	}
+	return &forkedRepo, nil
+}
+
+// GetForks returns all the forks of the repository
+func GetForks(repo *Repository, listOptions db.ListOptions) ([]*Repository, error) {
+	if listOptions.Page == 0 {
+		forks := make([]*Repository, 0, repo.NumForks)
+		return forks, db.GetEngine(db.DefaultContext).Find(&forks, &Repository{ForkID: repo.ID})
+	}
+
+	sess := db.GetPaginatedSession(&listOptions)
+	forks := make([]*Repository, 0, listOptions.PageSize)
+	return forks, sess.Find(&forks, &Repository{ForkID: repo.ID})
+}