Sequence Diagram

sequenceDiagram
	autonumber
	actor user as User
	participant S8 as Game8 Store
	participant pub as Game (publisher API）
	participant pay as Payment system

	%% Enter in-game ID and confirm player
	user->>S8: Enter in-game user ID
	S8->>+pub: Get player info (GET /user_info）
	pub->>-S8: Return player info
	note left of pub: user_name, user_level
	S8->>user: Show player name and level

	%% Purchase product
	user->>S8: Purchase in-game item
	note right of user: Item, payment info, points and coupon
	opt When points or a coupon are used
	note over S8: Calculate payment amount (billing_amount)
	end

	%% Purchase eligibility check
	note over S8: transaction_id issued
	S8->>+pub: Check purchase eligibility (GET /check）
	note right of S8: transaction_id, item, billing_amount
	note over pub: Check age group, purchase limit, and stock, then reserve the item
	pub->>-S8: Return check result
	note left of pub: result_code, purchasable

	alt result_code is not PUB0000
	S8->>user: Show purchase unavailable (message based on result_code )
	else result_code is PUB0000
	note over S8: Create order (status: pending）
	opt billing_amount is 1 yen or more
	S8->>+pay: Execute payment
	note right of S8: Payment info, payment amount
	pay->>-S8: Return payment result
	note left of pay: Payment status
	end
	note over S8: status: payment_confirmed

	%% Immediate notification after successful payment
	S8->>+pub: Register purchase (POST /register）
	note right of S8: transaction_id, item, contents
	opt When the publisher checks the order status
	pub->>+S8: Verify order (GET /orders/verify）
	note left of pub: paid_transaction_id
	S8->>-pub: Return order status
	note right of S8: status (at this point payment_confirmed）
	end
	note over pub: Grant item
	pub->>-S8: Return registration result
	note left of pub: result_code, item_granted

	alt result_code is PUB0000
	note over S8: Record purchase result (status: completed）
	S8->>user: Display purchase completion screen
	S8->>user: Send purchase notification email
	else result_code is not PUB0000
	S8->>pay: Cancel payment (refund) if a payment was made
	note over S8: Return points and coupons and cancel order (status: cancelled）
	S8->>user: Show purchase failed
	end
	end