Validation Strategy

The application enforces data quality through a layered validation pipeline. Each layer owns a clearly defined set of responsibilities so that validation code stays maintainable, testable, and consistent across domains.

Layer Overview

Layer	Entry Points	Responsibilities	Tooling
UI / Renderer	React components, form hooks	Basic UX guards (required fields, formatting hints). Never trusts its own input—server-side validation still runs.	React Hook Form, client-side helpers
Preload Bridge & IPC Schema	electron/preload APIs, registerStandardizedIpcHandler	Type- and shape-level validation for incoming IPC payloads before they reach the main process. Rejects malformed or unexpected input early.	Zod schemas in @shared/validation, custom validators in IpcService
Managers (Domain Logic)	SiteManager, MonitorManager, DatabaseManager	Business rule validation: cross-entity invariants, referential checks, domain-specific constraints. Must assume shape-level validation already happened.	Dedicated domain validators, helper utilities (e.g., validateSite)
Repositories & Database Layer	electron/services/database	Enforce persistence invariants: unique constraints, transactional safety, data normalization. Never trust upstream layers to have done the right thing.	sqlite constraints, repository helpers, transactions
Background Services	Monitoring scheduler, notification pipelines	Runtime guardrails (e.g., dropping invalid schedules, retry logic). Should surface issues to managers via structured errors.	Domain services, telemetry hooks

Principles

1. Single Responsibility Per Layer: Do not duplicate validation logic across layers. Shape validation lives in preload/IPC, business rules in managers, persistence guarantees in repositories.
2. Fail Fast: Reject invalid data as early as possible with actionable error messages. IPC handlers should never pass an invalid payload to managers.
3. Structured Errors: Use ApplicationError (or a more specific subclass) when propagating validation failures up the stack. Include metadata that helps renderer code present meaningful feedback.
4. Immutable Inputs: Treat incoming data as immutable. Create sanitized copies rather than mutating caller arguments.
5. Tests at the Source: Each validation rule must have unit tests in the layer that owns it. Avoid “integration-only” validation coverage unless the rule spans multiple layers.

Implementing New Validation Rules

1. Define the Contract

   • Add or update the relevant Zod schema in shared/validation for IPC payloads.
   • Extend typed validators in IpcService (e.g., SiteHandlerValidators, MonitoringHandlerValidators).

2. Enforce Business Rules

   • Implement domain checks inside the appropriate manager (often before calling repositories).
   • Throw an ApplicationError with code, operation, and details describing the violated rule.

3. Persist Safely

   • Ensure repository methods use transactions and SQL constraints to guarantee data integrity.
   • Normalize data (e.g., trimming strings, coercing booleans) right before persistence.

4. Test Thoroughly

   • Add schema tests (fast-check or unit) for IPC validators.
   • Add manager-level tests covering business rule branches.
   • Add repository tests for constraint enforcement when practical.

Cross-Layer Example

When adding a new monitor type:

1. IPC Schema: Update the monitor configuration Zod schema so preload rejects malformed input.
2. Manager Rule: Extend MonitorManager to verify business requirements (e.g., mutually exclusive options, interval bounds) and throw an ApplicationError if invalid.
3. Repository Guard: Ensure monitor persistence paths normalize identifiers and wrap writes in DatabaseService.executeTransaction.
4. Testing: Cover each validation stage with targeted tests to prevent regressions.

Checklist for Reviews

• [ ] IPC handler rejects invalid payloads before reaching managers.
• [ ] Managers throw structured errors with remediation-friendly messages.
• [ ] Repositories never assume the data is valid—transactions or constraints enforce integrity.
• [ ] Tests exist for new validation logic at each layer.
• [ ] Documentation (schemas, guides) reflects the new rule.

Following this strategy keeps validation consistent, discoverable, and verifiable as the codebase grows.