Second checkpoint

internal/messaging/rabbitmq/connection.go

@@ -0,0 +1,80 @@
+// Package rabbitmq provides the RabbitMQ connection, a publisher, and consumers
+// used by the worker. A single durable topic exchange is declared on connect;
+// each consumer declares and binds its own queue.
+package rabbitmq
+
+import (
+	"fmt"
+
+	"gis/internal/config"
+
+	amqp "github.com/rabbitmq/amqp091-go"
+)
+
+// Connection wraps an AMQP connection and a dedicated publishing channel, and
+// owns the topic exchange.
+type Connection struct {
+	conn     *amqp.Connection
+	pubCh    *amqp.Channel
+	exchange string
+}
+
+// Connect dials RabbitMQ, opens a publishing channel, and declares the exchange.
+func Connect(cfg config.RabbitMQConfig) (*Connection, error) {
+	conn, err := amqp.Dial(cfg.URL)
+	if err != nil {
+		return nil, fmt.Errorf("dial rabbitmq: %w", err)
+	}
+
+	ch, err := conn.Channel()
+	if err != nil {
+		conn.Close()
+		return nil, fmt.Errorf("open channel: %w", err)
+	}
+
+	if err := ch.ExchangeDeclare(
+		cfg.Exchange, amqp.ExchangeTopic,
+		true,  // durable
+		false, // auto-deleted
+		false, // internal
+		false, // no-wait
+		nil,
+	); err != nil {
+		ch.Close()
+		conn.Close()
+		return nil, fmt.Errorf("declare exchange: %w", err)
+	}
+
+	return &Connection{conn: conn, pubCh: ch, exchange: cfg.Exchange}, nil
+}
+
+// Exchange returns the topic exchange name.
+func (c *Connection) Exchange() string { return c.exchange }
+
+// publishChannel returns the shared publishing channel.
+func (c *Connection) publishChannel() *amqp.Channel { return c.pubCh }
+
+// openChannel opens a fresh channel (each consumer uses its own).
+func (c *Connection) openChannel() (*amqp.Channel, error) { return c.conn.Channel() }
+
+// Ping reports whether the connection is still open (used by readiness checks).
+func (c *Connection) Ping() error {
+	if c.conn.IsClosed() {
+		return fmt.Errorf("rabbitmq connection closed")
+	}
+	return nil
+}
+
+// Close tears down the publishing channel and the connection.
+func (c *Connection) Close() error {
+	var chErr error
+	if c.pubCh != nil {
+		chErr = c.pubCh.Close()
+	}
+	if c.conn != nil {
+		if err := c.conn.Close(); err != nil {
+			return err
+		}
+	}
+	return chErr
+}