On initial install, link existing Customers to Mailboxes

The link is set only for Customers that are linked to exactly one Mailbox,
through the Conversations they are linked to.

database/migrations/2024_07_03_135202_add_mailbox_id_column_to_customers_table.php

@@ -30,6 +30,11 @@ class AddMailboxIdColumnToCustomersTable extends Migration {
 				// On mailbox deletion, delete all customer entries that are linked to it.
 				->onDelete('cascade');
 		});
+		// Link Customers to Mailboxes, through their Conversation information.
+		$customers = Customer::all();
+		$customers->each(function ($customer) {
+			$customer->linkToMailboxThroughConversations();
+		});
 	}
 
 	/**

src/Customer.php

@@ -82,4 +82,26 @@ class Customer extends BaseCustomer {
 			->whereIn('mailbox_id', $mailboxes)
 			->first($columns);
 	}
+
+	/**
+	 * Get the Mailboxes this Customer is linked to through Conversations.
+	 *
+	 * @return array
+	 */
+	public function mailboxesThroughConversations() {
+		return $this
+			->conversations
+			->pluck('mailbox');
+	}
+
+	/**
+	 * If this Customer is linked to a single Mailbox through Conversations, link it to it.
+	 */
+	public function linkToMailboxThroughConversations() {
+		$mailboxes = $this->mailboxesThroughConversations();
+		if ( $mailboxes->count() == 1 ) {
+			$this->mailbox_id = $mailboxes->first()->id;
+			$this->save();
+		}
+	}
 }