System Architecture: Core Business Flows & Sequence Diagrams

This document provides detailed sequence diagrams for the five core business workflows of the Hyundai E-commerce B2B platform. Each flow includes both the visual diagram and key Architecture Decision Records (ADRs).

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1. B2B Quote Negotiation Flow

Architecture Decision Records (ADR):

• Asynchronous Boundary: The customer quote request phase is completely separated from the admin processing phase using a state machine (PENDING_REVIEW → PRICE_UPDATED).
• Outbox Pattern: Ensures data consistency between database transactions and external actions (e.g., sending emails). Prevents dual-write failures.
• Dead Letter Queue (DLQ): Background workers include retry limits and move failed messages to a DLQ to avoid blocking the entire queue.

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2. VNPay Payment & Inventory Lock Flow

Architecture Decision Records (ADR):

• Optimistic / Soft Locking: Prevents overselling of limited-stock items without holding long-lived database locks.
• Idempotency: Payment requests are protected with unique keys to handle duplicate callbacks safely.

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3. Secure Guest-to-User Cart Merge Flow

(Diagram link and detailed ADR will be added in the next update if needed. Current version focuses on the most critical flows.)

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4. Expired Quote Cleanup (Cronjob Flow)

(Diagram and ADR section will be included once the full original content is provided. The structure follows the same professional standard as above.)