Timeline manager (#40)

* start messing about with timeline manager

* i have no idea what i'm doing

* i continue to not know what i'm doing

* it's coming along

* bit more progress

* update timeline with new posts as they come in

* lint and fmt

* Select accounts where empty string

* restructure a bunch, get unfaves working

* moving stuff around

* federate status deletes properly

* mention regex better but not 100% there

* fix regex

* some more hacking away at the timeline code phew

* fix up some little things

* i can't even

* more timeline stuff

* move to ulid

* fiddley

* some lil fixes for kibou compatibility

* timelines working pretty alright!

* tidy + lint

1 files changed, 139 insertions, 0 deletions

diff --git a/internal/timeline/timeline.go b/internal/timeline/timeline.go
new file mode 100644
index 000000000..7408436dc
--- /dev/null
+++ b/internal/timeline/timeline.go
@@ -0,0 +1,139 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 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 (
+	"sync"
+	"time"
+
+	"github.com/sirupsen/logrus"
+	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
+	"github.com/superseriousbusiness/gotosocial/internal/db"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/typeutils"
+)
+
+// Timeline represents a timeline for one account, and contains indexed and prepared posts.
+type Timeline interface {
+	/*
+		RETRIEVAL FUNCTIONS
+	*/
+
+	Get(amount int, maxID string, sinceID string, minID string) ([]*apimodel.Status, error)
+	// GetXFromTop returns x amount of posts from the top of the timeline, from newest to oldest.
+	GetXFromTop(amount int) ([]*apimodel.Status, error)
+	// GetXBehindID returns x amount of posts from the given id onwards, from newest to oldest.
+	// This will NOT include the status with the given ID.
+	//
+	// This corresponds to an api call to /timelines/home?max_id=WHATEVER
+	GetXBehindID(amount int, fromID string) ([]*apimodel.Status, error)
+	// GetXBeforeID returns x amount of posts up to the given id, from newest to oldest.
+	// This will NOT include the status with the given ID.
+	//
+	// This corresponds to an api call to /timelines/home?since_id=WHATEVER
+	GetXBeforeID(amount int, sinceID string, startFromTop bool) ([]*apimodel.Status, error)
+	// GetXBetweenID returns x amount of posts from the given maxID, up to the given id, from newest to oldest.
+	// This will NOT include the status with the given IDs.
+	//
+	// This corresponds to an api call to /timelines/home?since_id=WHATEVER&max_id=WHATEVER_ELSE
+	GetXBetweenID(amount int, maxID string, sinceID string) ([]*apimodel.Status, error)
+
+	/*
+		INDEXING FUNCTIONS
+	*/
+
+	// IndexOne puts a status into the timeline at the appropriate place according to its 'createdAt' property.
+	IndexOne(statusCreatedAt time.Time, statusID string) error
+
+	// OldestIndexedPostID returns the id of the rearmost (ie., the oldest) indexed post, or an error if something goes wrong.
+	// If nothing goes wrong but there's no oldest post, an empty string will be returned so make sure to check for this.
+	OldestIndexedPostID() (string, error)
+
+	/*
+		PREPARATION FUNCTIONS
+	*/
+
+	// PrepareXFromTop instructs the timeline to prepare x amount of posts from the top of the timeline.
+	PrepareFromTop(amount int) error
+	// PrepareBehind instructs the timeline to prepare the next amount of entries for serialization, from position onwards.
+	// If include is true, then the given status ID will also be prepared, otherwise only entries behind it will be prepared.
+	PrepareBehind(statusID string, amount int) error
+	// IndexOne puts a status into the timeline at the appropriate place according to its 'createdAt' property,
+	// and then immediately prepares it.
+	IndexAndPrepareOne(statusCreatedAt time.Time, statusID string) error
+	// OldestPreparedPostID returns the id of the rearmost (ie., the oldest) prepared post, or an error if something goes wrong.
+	// If nothing goes wrong but there's no oldest post, an empty string will be returned so make sure to check for this.
+	OldestPreparedPostID() (string, error)
+
+	/*
+		INFO FUNCTIONS
+	*/
+
+	// ActualPostIndexLength returns the actual length of the post index at this point in time.
+	PostIndexLength() int
+
+	/*
+		UTILITY FUNCTIONS
+	*/
+
+	// Reset instructs the timeline to reset to its base state -- cache only the minimum amount of posts.
+	Reset() error
+	// Remove removes a status from both the index and prepared posts.
+	//
+	// If a status has multiple entries in a timeline, they will all be removed.
+	//
+	// The returned int indicates the amount of entries that were removed.
+	Remove(statusID string) (int, error)
+}
+
+// timeline fulfils the Timeline interface
+type timeline struct {
+	postIndex     *postIndex
+	preparedPosts *preparedPosts
+	accountID     string
+	account       *gtsmodel.Account
+	db            db.DB
+	tc            typeutils.TypeConverter
+	log           *logrus.Logger
+	sync.Mutex
+}
+
+// NewTimeline returns a new Timeline for the given account ID
+func NewTimeline(accountID string, db db.DB, typeConverter typeutils.TypeConverter, log *logrus.Logger) Timeline {
+	return &timeline{
+		postIndex:     &postIndex{},
+		preparedPosts: &preparedPosts{},
+		accountID:     accountID,
+		db:            db,
+		tc:            typeConverter,
+		log:           log,
+	}
+}
+
+func (t *timeline) Reset() error {
+	return nil
+}
+
+func (t *timeline) PostIndexLength() int {
+	if t.postIndex == nil || t.postIndex.data == nil {
+		return 0
+	}
+
+	return t.postIndex.data.Len()
+}