[example | RFC] refactor(BE): fix linter errors in server 2, introduce zod & http errors

[Muatasim-Aswad]

Note

This PR is an RFC to get an earlier feedback. The reason for this is the size and the scope of the refactoring. It can be closed later.

Intro

• Major part of the linter errors in the server controllers are caused by inputs, e.g. req.x | res.x, and by try catch blocks. As a solution the main changes are made.
• Since the main changes will result in a major refactoring, I see that including another refactorings within the same scope is possible with less effort. These additional changes are supposed to increase readability and code consistency.

Main Changes

• Zod is introduced as a replacement for the existing native validations.
• All encountered unnecessary try catch blocks were removed, as express current version handles rejected promises automatically.

Additional Changes

• HttpErrors are introduced for common failure responses, and the global error handler is expanded to handle them.
• Request handlers are made more consistent in terms of naming and the code order where possible.
• Library types are used where possible instead of the mirroring types. e.g. RequestHandler.
• Constructors param shortcuts are used where possible.
• Helper methods/classes are created where the same functionality is used multiple times.

Notes about Zod Schemas and Their Types

• The created schemas only mirrors the existing models' types and validation functions, except for obvious characteristics, e.g. age > 0.
• Currently the schemas coexist with the models' types. This creates multiple sources for the truth about models. While, generally speaking, schemas are a bit less readable than TS declarations, zod is flexible in manipulating the schemas and its inferred types can totally replace the model type declarations. An example is shown in the code.

[Copilot]

Pull Request Overview

This PR refactors backend error handling and input validation by introducing Zod for schema validation and HttpErrors for standardized error responses. The changes remove try-catch blocks and replace native validation functions with Zod schemas.

• Introduces HttpError classes for standardized HTTP error responses
• Replaces native validation functions with Zod schemas for type safety
• Removes unnecessary try-catch blocks and centralizes error handling
• Creates reusable helper classes to reduce code duplication

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
server/src/utils/httpErrors.ts	Defines HttpError base class and specific error types with Zod integration
server/src/types.ts	Adds global type definitions for Express locals and utility types
server/src/models/ResponseError.ts	Removes legacy ResponseError class
server/src/models/Interaction.ts	Replaces validation function with Zod schema
server/src/models/EmploymentHistory.ts	Replaces validation function with Zod schema
server/src/middlewares/errorHandlerMiddleware.ts	Implements centralized error handling middleware
server/src/index.ts	Updates application setup to use new error handling
server/src/controllers/Trainee/TraineeHelper.ts	Creates helper class for common trainee operations
server/src/controllers/Trainee/InteractionController.ts	Refactors to use Zod validation and HttpErrors
server/src/controllers/Trainee/EmploymentHistoryController.ts	Refactors to use Zod validation and HttpErrors
server/eslint.config.js	Updates ESLint configuration

[Copilot]

This comment indicates confusion about the data structure. The comment should be resolved or removed, and if there's genuinely duplicate reporterID fields, the type definition should be clarified.

Suggested change

// ! reporterID is already part of the interface Interaction?