Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

internal/database/database.go

@@ -0,0 +1,77 @@
+// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package database // import "miniflux.app/v2/internal/database"
+
+import (
+	"database/sql"
+	"fmt"
+	"time"
+
+	// Postgresql driver import
+	_ "github.com/lib/pq"
+)
+
+// NewConnectionPool configures the database connection pool.
+func NewConnectionPool(dsn string, minConnections, maxConnections int, connectionLifetime time.Duration) (*sql.DB, error) {
+	db, err := sql.Open("postgres", dsn)
+	if err != nil {
+		return nil, err
+	}
+
+	db.SetMaxOpenConns(maxConnections)
+	db.SetMaxIdleConns(minConnections)
+	db.SetConnMaxLifetime(connectionLifetime)
+
+	return db, nil
+}
+
+// Migrate executes database migrations.
+func Migrate(db *sql.DB) error {
+	var currentVersion int
+	db.QueryRow(`SELECT version FROM schema_version`).Scan(&currentVersion)
+
+	fmt.Println("-> Current schema version:", currentVersion)
+	fmt.Println("-> Latest schema version:", schemaVersion)
+
+	for version := currentVersion; version < schemaVersion; version++ {
+		newVersion := version + 1
+		fmt.Println("* Migrating to version:", newVersion)
+
+		tx, err := db.Begin()
+		if err != nil {
+			return fmt.Errorf("[Migration v%d] %v", newVersion, err)
+		}
+
+		if err := migrations[version](tx); err != nil {
+			tx.Rollback()
+			return fmt.Errorf("[Migration v%d] %v", newVersion, err)
+		}
+
+		if _, err := tx.Exec(`DELETE FROM schema_version`); err != nil {
+			tx.Rollback()
+			return fmt.Errorf("[Migration v%d] %v", newVersion, err)
+		}
+
+		if _, err := tx.Exec(`INSERT INTO schema_version (version) VALUES ($1)`, newVersion); err != nil {
+			tx.Rollback()
+			return fmt.Errorf("[Migration v%d] %v", newVersion, err)
+		}
+
+		if err := tx.Commit(); err != nil {
+			return fmt.Errorf("[Migration v%d] %v", newVersion, err)
+		}
+	}
+
+	return nil
+}
+
+// IsSchemaUpToDate checks if the database schema is up to date.
+func IsSchemaUpToDate(db *sql.DB) error {
+	var currentVersion int
+	db.QueryRow(`SELECT version FROM schema_version`).Scan(&currentVersion)
+	if currentVersion < schemaVersion {
+		return fmt.Errorf(`the database schema is not up to date: current=v%d expected=v%d`, currentVersion, schemaVersion)
+	}
+	return nil
+}