Technical Blog: Architecting a Multi-Tiered Promotional Engine & Reactive Session Extensions

By Harshit Agarwal

In the latest evolution of the FamCare platform, we moved beyond standard CRUD operations to implement two complex, high-impact features: a Hierarchical Introductory Pricing Engine and a Parent-Child Reactive Extension Flow.

Here is the "deep tech" breakdown of how these systems were engineered to handle scale, edge cases, and real-time state synchronization.

1. The Hierarchical Promotional Engine (The "Try at" System)

The Challenge

Standard discount systems are usually flat. For a service marketplace, this is insufficient. Different services have different margins, and a 1-hour session has a different value proposition than a 4-hour session. We needed a way to offer "Entry-Level" pricing that could be overridden at any level of the service hierarchy.

The Solution: A Resolution-Priority Fallback Engine

We engineered a Resolution-Priority Strategy across the entire stack. Instead of a hardcoded "First Order Price," the system now performs a recursive lookup to find the most specific price defined by the admin.

  • The Hierarchy: Pricing Tier (Most Specific) → Sub-Service → Service Category → Original Price (Fallback).
Pricing tier
→
Sub-service
→
Service category
→
Original price
Fig. 1 — the resolution-priority fallback chain. Lookup walks left to right and stops at the first level with an override defined.
* **Implementation Details:** * **Database Schema:** Extended the `services` and `pricing_tiers` tables via **Alembic** migrations to support nullable promotional fields. * **Frontend Resolution Logic:** In Flutter, we implemented a memoized resolution helper `_getTrialPrice(sub, tier)` that calculates the "Best Available Promotion" in *O(1)* time during the build cycle, ensuring zero UI lag. * **Eligibility Guard:** A reactive `_isTrialEligible` state that synchronizes guest-mode heuristics with authenticated `booking_count` checks.

2. Parent-Child Reactive Service Extensions

The Challenge

In-home services are unpredictable. A 2-hour babysitting session often needs a 1-hour extension. Re-booking from scratch creates friction and breaks the "Live Tracking" experience.

The Solution: Atomic Linked Request Mapping

Instead of modifying the original request, we implemented a Linked-Node Architecture.

  • Relational Logic: When an extension is requested, the system spawns a new Request object with a parent_request_id pointer. This creates an "Extension Chain."
  • State Merging: Once the extension (the child) is paid, a background trigger adds those hours back to the Parent task. The user's live tracker "absorbs" the new time seamlessly.
Parent
request
→
Child request
(extension)
→
Merged
tracker
Fig. 2 — extension chain. The child is paid independently, then a background trigger merges its hours back into the parent without a page reload.
* **UI Synchronization:** The `LiveTrackingScreen` was refactored into a state-aware consumer. It listens for child-requests and dynamically shifts the UI from a "Tracking State" to a "Payment-Gated Extension State" without a page reload.

3. The "Genius" in the Full-Stack Connection

  1. Admin Panel (Next.js): Built a dynamic form system that allows admins to set these prices at any level.
  2. Sutram (FastAPI/PostgreSQL): The backend serves as the "Source of Truth," preventing any frontend price manipulation.
  3. Praja (Flutter): Implemented a "Premium Aesthetics" UI overhaul with Vertical Intrinsic Dividers, Slashed-Price Visuals, and Micro-animations for the "Try at" badge.
Admin Panel
(Next.js)
→
Sutram
(FastAPI/PostgreSQL)
→
Praja
(Flutter)
Fig. 3 — the full-stack connection. Admins set prices, Sutram acts as the source of truth preventing frontend manipulation, and Praja renders the resolved price to the user.

Summary of Impact

  • Conversion: Lowered the entry barrier for the most popular services.
  • Revenue Continuity: Ensuring caregivers are paid for every extra minute while providing a seamless one-tap payment experience.
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entry barrier lowered for the most popular services
1-tap
payment experience for session extensions