api/models/posts/move.go

package posts

import (
	"errors"

	"git.aiterp.net/rpdata/api/models"
	"github.com/globalsign/mgo/bson"
)

// Move the post
func Move(post models.Post, toPosition int) ([]models.Post, error) {
	if toPosition < 1 {
		return nil, errors.New("Invalid position")
	}

	mutex.Lock()
	defer mutex.Unlock()

	// To avoid problems, only allow target indices that are allowed. If it's 1, then there is bound to
	// be a post at the position.
	if toPosition > 1 {
		existing := models.Post{}
		err := collection.Find(bson.M{"logId": post.LogID, "position": toPosition}).One(&existing)

		if err != nil || existing.Position != toPosition {
			return nil, errors.New("No post found at the position")
		}
	}

	query := bson.M{"logId": post.LogID}
	operation := bson.M{"$inc": bson.M{"position": 1}}

	if toPosition < post.Position {
		query["$and"] = []bson.M{
			bson.M{"position": bson.M{"$gte": toPosition}},
			bson.M{"position": bson.M{"$lt": post.Position}},
		}
	} else {
		query["$and"] = []bson.M{
			bson.M{"position": bson.M{"$gt": post.Position}},
			bson.M{"position": bson.M{"$lte": toPosition}},
		}

		operation["$inc"] = bson.M{"position": -1}
	}

	_, err := collection.UpdateAll(query, operation)
	if err != nil {
		return nil, errors.New("Moving others failed: " + err.Error())
	}

	err = collection.UpdateId(post.ID, bson.M{"$set": bson.M{"position": toPosition}})
	if err != nil {
		return nil, errors.New("Moving failed: " + err.Error() + " (If you see this on the page, please let me know ASAP)")
	}

	from, to := post.Position, toPosition
	if to < from {
		from, to = to, from
	}

	posts := make([]models.Post, 0, (to-from)+1)
	err = collection.Find(bson.M{"logId": post.LogID, "position": bson.M{"$gte": from, "$lte": to}}).Sort("position").All(&posts)
	if err != nil {
		return nil, errors.New("The move completed successfully, but finding the moved posts failed: " + err.Error())
	}

	return posts, nil
}