Added PostgreSQL initialization function and module

Author: PythonHacker24

internal/session/postgresql/postgresql.go

@@ -1 +1,39 @@
-package postgresql 
+package postgresql
+
+import (
+	"database/sql"
+	"fmt"
+)
+
+/*
+	PostgreSQL database stores logs of all expired sessions and processed transactions results
+	this is an archival database and is used to serve archived information to users and admin panel
+*/
+
+/* 
+	TODO: when application shutsdown, all sessions in Redis are marked expired
+	make sure to push those expired sessions to PostreSQL database for archival
+*/
+
+/* PostgreSQL client */
+type PGClient struct {
+	db *sql.DB
+}
+
+/* create new PostgreSQL client */
+func NewPGClient(connStr string) (*PGClient, error) {
+
+	/* initiate PostgreSQL connection */
+	db, err := sql.Open("postgres", connStr)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open PostgreSQL connection: %w", err)
+	}
+
+	/* ping PostgreSQL connection */
+	if err := db.Ping(); err != nil {
+		return nil, fmt.Errorf("failed to ping PostgreSQL: %w", err)
+	}
+
+	/* return the PostgreSQL client */
+	return &PGClient{db: db}, nil
+}