Improve codebase quality: documentation, type safety, and error handling

[Copilot]

Repository lacked documentation, had type safety issues, and used generic error handling. Code contained commented-out debug statements and an empty file.

Documentation

• README.md: Usage examples, installation, project structure, API overview
• CONTRIBUTING.md: Development workflow, code style, PR guidelines
• CHANGELOG.md: Version tracking
• JSDoc comments: All classes and public methods documented
• .editorconfig: Consistent formatting rules

Type Safety

• Fixed Normalization.normalizeType(): proper type guards for schema.items, handles arrays without item definitions
• OpenAPIVersion: Template literal type 3.0.${number} instead of loose string
• Custom error types: ValidationError, FetchError, FileSystemError for better error handling

Validation

• OpenAPI document validation in Fetcher: structure checks, version format (3.0.x regex), non-empty paths
• Enhanced error messages with context

Code Cleanup

• Removed empty Structure.ts
• Removed commented-out code (5 instances)
• Removed debug console.log statements
• Fixed CLI name: "easy" → "openapi-ofetch-gen"

Example

Before:

// Generic error, poor type safety
throw new Error(`Failed to fetch Swagger document: ${error}`);

// Type access without guards
if (something.schema.items.$ref) { ... }

After:

// Specific error types with cause
throw new FetchError(`Failed to fetch Swagger document from ${this.url}`, error);

// Proper type guards
if (something.schema.type === 'array') {
  if (!something.schema.items) {
    finale = 'unknown[]';
  } else if (something.schema.items.$ref) { ... }
}

Security: CodeQL scan passed (0 vulnerabilities)

Original prompt

review this repo, make suggestions for improving the overall quality

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.