Rewrite individual entry pagination SQL queries

storage/entry_pagination_builder.go

@@ -0,0 +1,158 @@
+// Copyright 2018 Frédéric Guillot. All rights reserved.
+// Use of this source code is governed by the Apache 2.0
+// license that can be found in the LICENSE file.
+
+package storage
+
+import (
+	"database/sql"
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/miniflux/miniflux/model"
+	"github.com/miniflux/miniflux/timer"
+)
+
+// EntryPaginationBuilder is a builder for entry prev/next queries.
+type EntryPaginationBuilder struct {
+	store      *Storage
+	conditions []string
+	args       []interface{}
+	entryID    int64
+	direction  string
+}
+
+// WithStarred adds starred to the condition.
+func (e *EntryPaginationBuilder) WithStarred() {
+	e.conditions = append(e.conditions, "e.starred is true")
+}
+
+// WithFeedID adds feed_id to the condition.
+func (e *EntryPaginationBuilder) WithFeedID(feedID int64) {
+	if feedID != 0 {
+		e.conditions = append(e.conditions, fmt.Sprintf("e.feed_id = $%d", len(e.args)+1))
+		e.args = append(e.args, feedID)
+	}
+}
+
+// WithCategoryID adds category_id to the condition.
+func (e *EntryPaginationBuilder) WithCategoryID(categoryID int64) {
+	if categoryID != 0 {
+		e.conditions = append(e.conditions, fmt.Sprintf("f.category_id = $%d", len(e.args)+1))
+		e.args = append(e.args, categoryID)
+	}
+}
+
+// WithStatus adds status to the condition.
+func (e *EntryPaginationBuilder) WithStatus(status string) {
+	if status != "" {
+		e.conditions = append(e.conditions, fmt.Sprintf("e.status = $%d", len(e.args)+1))
+		e.args = append(e.args, status)
+	}
+}
+
+// Entries returns previous and next entries.
+func (e *EntryPaginationBuilder) Entries() (*model.Entry, *model.Entry, error) {
+	tx, err := e.store.db.Begin()
+	if err != nil {
+		return nil, nil, fmt.Errorf("begin transaction for entry pagination: %v", err)
+	}
+
+	prevID, nextID, err := e.getPrevNextID(tx)
+	if err != nil {
+		tx.Rollback()
+		return nil, nil, err
+	}
+
+	prevEntry, err := e.getEntry(tx, prevID)
+	if err != nil {
+		tx.Rollback()
+		return nil, nil, err
+	}
+
+	nextEntry, err := e.getEntry(tx, nextID)
+	if err != nil {
+		tx.Rollback()
+		return nil, nil, err
+	}
+
+	tx.Commit()
+
+	if e.direction == "desc" {
+		return nextEntry, prevEntry, nil
+	}
+
+	return prevEntry, nextEntry, nil
+}
+
+func (e *EntryPaginationBuilder) getPrevNextID(tx *sql.Tx) (prevID int64, nextID int64, err error) {
+	defer timer.ExecutionTime(time.Now(), fmt.Sprintf("[EntryPaginationBuilder] %v, %v", e.conditions, e.args))
+
+	cte := `
+		WITH entry_pagination AS (
+			SELECT
+				e.id,
+				lag(e.id) over (order by e.published_at asc, e.id desc) as prev_id,
+				lead(e.id) over (order by e.published_at asc, e.id desc) as next_id
+			FROM entries AS e
+			LEFT JOIN feeds AS f ON f.id=e.feed_id
+			WHERE %s
+			ORDER BY e.published_at asc, e.id desc
+		)
+		SELECT prev_id, next_id FROM entry_pagination AS ep WHERE %s;
+	`
+
+	subCondition := strings.Join(e.conditions, " AND ")
+	finalCondition := fmt.Sprintf("ep.id = $%d", len(e.args)+1)
+	query := fmt.Sprintf(cte, subCondition, finalCondition)
+	e.args = append(e.args, e.entryID)
+
+	var pID, nID sql.NullInt64
+	err = tx.QueryRow(query, e.args...).Scan(&pID, &nID)
+	switch {
+	case err == sql.ErrNoRows:
+		return 0, 0, nil
+	case err != nil:
+		return 0, 0, fmt.Errorf("entry pagination: %v", err)
+	}
+
+	if pID.Valid {
+		prevID = pID.Int64
+	}
+
+	if nID.Valid {
+		nextID = nID.Int64
+	}
+
+	return prevID, nextID, nil
+}
+
+func (e *EntryPaginationBuilder) getEntry(tx *sql.Tx, entryID int64) (*model.Entry, error) {
+	var entry model.Entry
+
+	err := tx.QueryRow(`SELECT id, title FROM entries WHERE id = $1`, entryID).Scan(
+		&entry.ID,
+		&entry.Title,
+	)
+
+	switch {
+	case err == sql.ErrNoRows:
+		return nil, nil
+	case err != nil:
+		return nil, fmt.Errorf("fetching sibling entry: %v", err)
+	}
+
+	return &entry, nil
+}
+
+// NewEntryPaginationBuilder returns a new EntryPaginationBuilder.
+func NewEntryPaginationBuilder(store *Storage, userID, entryID int64, direction string) *EntryPaginationBuilder {
+	return &EntryPaginationBuilder{
+		store:      store,
+		args:       []interface{}{userID, "removed"},
+		conditions: []string{"e.user_id = $1", "e.status <> $2"},
+		entryID:    entryID,
+		direction:  direction,
+	}
+}