Refactoring

Refactoring

Safe, systematic refactoring procedures for the @dotcontext/cli codebase.

When to Use

• Extracting logic into a new service or utility
• Consolidating duplicate code across services or generators
• Restructuring MCP gateway handlers
• Improving type safety or removing any usage
• Simplifying complex functions (high cyclomatic complexity)
• Migrating between patterns (e.g., callback to async/await)

Pre-Refactoring Checklist

Before starting any refactoring:

• All tests pass: npm test
• Build succeeds: npm run build
• Create a branch or ensure changes can be reverted
• Identify all callers of the code being refactored (use grep or IDE references)

Common Refactoring Scenarios

Extracting a New Service

The project follows a directory-per-service pattern. To extract logic into a new service:

1. Create src/services/<name>/ directory
2. Create the service class:

// src/services/cache/cacheService.ts
export interface CacheServiceOptions {
  repoPath: string;
  cacheDir?: string;
}

export class CacheService {
  private readonly repoPath: string;
  private readonly cacheDir: string;

  constructor(options: CacheServiceOptions) {
    this.repoPath = options.repoPath;
    this.cacheDir = options.cacheDir || '.context/.cache';
  }

  async get(key: string): Promise<string | null> { /* ... */ }
  async set(key: string, value: string): Promise<void> { /* ... */ }
}

3. Create src/services/<name>/index.ts barrel:

export { CacheService, CacheServiceOptions } from './cacheService';

4. Update callers to import from the new service
5. Write tests in src/services/<name>/cacheService.test.ts

Splitting a Large Gateway Handler

Gateway handlers in src/services/mcp/gateway/ can grow large. To split:

1. Identify action groups that share logic
2. Extract helper functions within the same file first
3. If helpers grow, extract into a separate utility or service
4. Keep the main handler function as a thin dispatcher:

export async function handleContext(params: ContextParams, options: ContextOptions): Promise<MCPToolResponse> {
  switch (params.action) {
    case 'check': return handleCheck(options);
    case 'init': return handleInit(params, options);
    // Each case delegates to a focused function
  }
}

Improving Type Safety

Common type improvements:

1. Replace any with unknown: Then add type guards:

// Before
function process(data: any) { return data.value; }

// After
function process(data: unknown): string {
  if (typeof data === 'object' && data !== null && 'value' in data) {
    return String((data as { value: unknown }).value);
  }
  throw new Error('Invalid data shape');
}

2. Add discriminated unions for action-based params:

type ContextParams =
  | { action: 'check'; repoPath?: string }
  | { action: 'init'; repoPath?: string; type?: string }
  | { action: 'fill'; repoPath?: string; target?: string };

3. Extract interface from implementation: When a class has grown, extract its public interface for dependency injection (pattern used by AIContextMCPServer with contextBuilder).

Consolidating Duplicate Logic

Common duplication spots in this project:

• Path resolution: Multiple services resolve repoPath + outputDir. Extract to src/services/shared/.
• Frontmatter parsing: Used in generators, scaffold tools, and MCP flows. Centralized in src/utils/frontMatter.ts.
• File listing with glob: Used in semantic analysis, generators, and export. Check src/services/shared/ for existing utilities.
• Error response creation: MCP handlers should all use createErrorResponse() from response.ts.

Updating Barrel Exports

When moving or renaming files, update the export chain:

src/services/mcp/gateway/<file>.ts  -- implementation
  -> src/services/mcp/gateway/index.ts  -- gateway barrel
    -> src/services/mcp/gatewayTools.ts  -- compatibility barrel
      -> src/services/mcp/mcpServer.ts  -- consumer

Step-by-Step Refactoring Process

1. Identify: Find the code smell (large function, duplication, poor typing)
2. Plan: Determine the target structure and list affected files
3. Test: Ensure existing tests pass and cover the code being changed
4. Extract: Move code to the new location, keeping the old code as a thin wrapper
5. Redirect: Update all callers to use the new location
6. Remove: Delete the old wrapper once all callers are redirected
7. Verify: Run npm test and npm run build
8. Commit: Use refactor(<scope>): prefix

Refactoring Safety Rails

Tests as Safety Net

• Never refactor code that lacks tests. Write tests first.
• Run npx jest --testPathPattern="<area>" after each step.

Preserve Public APIs

• MCP tool names and schemas are public API. Do not rename tools or remove actions without a deprecation strategy.
• CLI command names and flags are public API.
• Barrel export paths are consumed by other modules. Keep backward-compatible re-exports.

TypeScript Compiler as Guard

• npm run build will catch broken imports, type mismatches, and missing exports.
• Enable noUnusedLocals temporarily to find dead code after extraction.

Small Commits

• Commit after each logical step (extract, redirect, remove).
• This makes it easy to bisect if something breaks.

Anti-Patterns to Watch For

• Big bang refactors: Changing everything at once. Prefer incremental changes.
• Refactoring while adding features: Do one or the other per commit.
• Changing test behavior during refactoring: Refactoring should not change test expectations.
• Forgetting barrel exports: New file locations need updated export chains.
• Breaking MCP backward compatibility: Clients depend on stable tool names and schemas.