gotosocial/internal/timeline/timeline.go

/*
   GoToSocial
   Copyright (C) 2021-2022 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 timeline

import (
	"context"
	"sync"
	"time"
)

// GrabFunction is used by a Timeline to grab more items to index.
//
// It should be provided to NewTimeline when the caller is creating a timeline
// (of statuses, notifications, etc).
//
//	timelineAccountID: the owner of the timeline
//	maxID: the maximum item ID desired.
//	sinceID: the minimum item ID desired.
//	minID: see sinceID
//	limit: the maximum amount of items to be returned
//
// If an error is returned, the timeline will stop processing whatever request called GrabFunction,
// and return the error. If no error is returned, but stop = true, this indicates to the caller of GrabFunction
// that there are no more items to return, and processing should continue with the items already grabbed.
type GrabFunction func(ctx context.Context, timelineAccountID string, maxID string, sinceID string, minID string, limit int) (items []Timelineable, stop bool, err error)

// FilterFunction is used by a Timeline to filter whether or not a grabbed item should be indexed.
type FilterFunction func(ctx context.Context, timelineAccountID string, item Timelineable) (shouldIndex bool, err error)

// PrepareFunction converts a Timelineable into a Preparable.
//
// For example, this might result in the converstion of a *gtsmodel.Status with the given itemID into a serializable *apimodel.Status.
type PrepareFunction func(ctx context.Context, timelineAccountID string, itemID string) (Preparable, error)

// SkipInsertFunction indicates whether a new item about to be inserted in the prepared list should be skipped,
// based on the item itself, the next item in the timeline, and the depth at which nextItem has been found in the list.
//
// This will be called for every item found while iterating through a timeline, so callers should be very careful
// not to do anything expensive here.
type SkipInsertFunction func(ctx context.Context,
	newItemID string,
	newItemAccountID string,
	newItemBoostOfID string,
	newItemBoostOfAccountID string,
	nextItemID string,
	nextItemAccountID string,
	nextItemBoostOfID string,
	nextItemBoostOfAccountID string,
	depth int) (bool, error)

// Timeline represents a timeline for one account, and contains indexed and prepared items.
type Timeline interface {
	/*
		RETRIEVAL FUNCTIONS
	*/

	// Get returns an amount of prepared items with the given parameters.
	// If prepareNext is true, then the next predicted query will be prepared already in a goroutine,
	// to make the next call to Get faster.
	Get(ctx context.Context, amount int, maxID string, sinceID string, minID string, prepareNext bool) ([]Preparable, error)

	/*
		INDEXING + PREPARATION FUNCTIONS
	*/

	// IndexOne puts a item into the timeline at the appropriate place according to its 'createdAt' property.
	//
	// The returned bool indicates whether or not the item was actually inserted into the timeline. This will be false
	// if the item is a boost and the original item or another boost of it already exists < boostReinsertionDepth back in the timeline.
	IndexOne(ctx context.Context, itemID string, boostOfID string, accountID string, boostOfAccountID string) (bool, error)
	// IndexAndPrepareOne puts a item into the timeline at the appropriate place according to its 'createdAt' property,
	// and then immediately prepares it.
	//
	// The returned bool indicates whether or not the item was actually inserted into the timeline. This will be false
	// if the item is a boost and the original item or another boost of it already exists < boostReinsertionDepth back in the timeline.
	IndexAndPrepareOne(ctx context.Context, itemID string, boostOfID string, accountID string, boostOfAccountID string) (bool, error)
	// PrepareXFromTop instructs the timeline to prepare x amount of items from the top of the timeline, useful during init.
	PrepareFromTop(ctx context.Context, amount int) error

	/*
		INFO FUNCTIONS
	*/

	// ActualPostIndexLength returns the actual length of the item index at this point in time.
	ItemIndexLength(ctx context.Context) int
	// OldestIndexedItemID returns the id of the rearmost (ie., the oldest) indexed item, or an error if something goes wrong.
	// If nothing goes wrong but there's no oldest item, an empty string will be returned so make sure to check for this.
	OldestIndexedItemID(ctx context.Context) (string, error)
	// NewestIndexedItemID returns the id of the frontmost (ie., the newest) indexed item, or an error if something goes wrong.
	// If nothing goes wrong but there's no newest item, an empty string will be returned so make sure to check for this.
	NewestIndexedItemID(ctx context.Context) (string, error)

	/*
		UTILITY FUNCTIONS
	*/

	// LastGot returns the time that Get was last called.
	LastGot() time.Time
	// Prune prunes preparedItems and indexedItems in this timeline to the desired lengths.
	// This will be a no-op if the lengths are already < the desired values.
	// Prune acquires a lock on the timeline before pruning.
	// The return value is the combined total of items pruned from preparedItems and indexedItems.
	Prune(desiredPreparedItemsLength int, desiredIndexedItemsLength int) int
	// Remove removes a item from both the index and prepared items.
	//
	// If a item has multiple entries in a timeline, they will all be removed.
	//
	// The returned int indicates the amount of entries that were removed.
	Remove(ctx context.Context, itemID string) (int, error)
	// RemoveAllBy removes all items by the given accountID, from both the index and prepared items.
	//
	// The returned int indicates the amount of entries that were removed.
	RemoveAllBy(ctx context.Context, accountID string) (int, error)
}

// timeline fulfils the Timeline interface
type timeline struct {
	indexedItems    *indexedItems
	preparedItems   *preparedItems
	grabFunction    GrabFunction
	filterFunction  FilterFunction
	prepareFunction PrepareFunction
	accountID       string
	lastGot         time.Time
	sync.Mutex
}

// NewTimeline returns a new Timeline for the given account ID
func NewTimeline(
	ctx context.Context,
	timelineAccountID string,
	grabFunction GrabFunction,
	filterFunction FilterFunction,
	prepareFunction PrepareFunction,
	skipInsertFunction SkipInsertFunction,
) (Timeline, error) {
	return &timeline{
		indexedItems: &indexedItems{
			skipInsert: skipInsertFunction,
		},
		preparedItems: &preparedItems{
			skipInsert: skipInsertFunction,
		},
		grabFunction:    grabFunction,
		filterFunction:  filterFunction,
		prepareFunction: prepareFunction,
		accountID:       timelineAccountID,
		lastGot:         time.Time{},
	}, nil
}