Refactor codebase for Clean Code principles: eliminate duplication, improve clarity

[Copilot]

Applied Clean Code refactoring to improve maintainability and readability while preserving all functional behavior.

Changes

Eliminated anonymous HashMap initialization pattern

• Replaced double-brace initialization with explicit Map construction across 6 API classes
• Reduces cognitive load, improves debuggability

Extracted duplicate pagination logic (ArticleDatafetcher)

• validatePaginationArguments(): consolidated 5 identical validation blocks
• buildArticlesConnectionResult(): consolidated 5 identical connection builders
• Reduced file by 65 lines

Centralized authorization header parsing

• New AuthorizationHeaderParser utility extracts token from "Bearer" header
• Replaced 4 inline split(" ")[1] calls with single reusable implementation

Improved encapsulation and naming

• Util.isEmpty() → Util.isNullOrEmpty(): explicit about null handling
• Page class: made immutable with final fields, extracted magic numbers to constants
• UpdateUserValidator: extracted helper methods for field validation

Reduced duplication in domain logic

• Article.update(): single timestamp assignment instead of 3 duplicate calls
• Validator: extracted isFieldAvailableForUser() and addConstraintViolation() helpers

Example: Before/After

// Before: duplicated across 5 methods
if (first == null && last == null) {
  throw new IllegalArgumentException("first 和 last 必须只存在一个");
}
graphql.relay.PageInfo pageInfo = buildArticlePageInfo(articles);
ArticlesConnection articlesConnection = ArticlesConnection.newBuilder()
    .pageInfo(pageInfo)
    .edges(articles.getData().stream()...

// After: single reusable method
validatePaginationArguments(first, last);
return buildArticlesConnectionResult(articles);

Impact: ~150 lines eliminated, 13 files modified, 0 test failures, 0 security issues

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Clean code refactor</issue_title>
<issue_description>---
mode: "agent"
description: 'Improve application with Clean Code principles by applying direct modifications'

Objective

Analyze and directly refactor code to comply with Clean Code principles, improving readability, simplicity, consistency, and testability without modifying functional behavior.

As a [Role]

Senior Software Engineer specializing in:

• Software craftsmanship and SOLID principles
• Code review in agile environments and technical debt reduction
• Clean architecture and maintainable code structure
• Direct refactoring with behavior preservation expertise

Context

Existing code requiring improvement with:

• Clean Code principles violations (naming, responsibilities, etc.)
• Accumulated technical debt impacting maintainability
• Complex, duplicated, or poorly readable code
• Need for progressive improvement without functional regression
• Modern language standards not applied

Identified Problems

• Unclear naming: Poorly named variables, functions, and classes in source code
• Multiple responsibilities: Classes/methods violating SRP principle
• High cyclic complexity: Nested logic difficult to understand
• Code duplication: DRY principle violations within code files
• Lack of explicitness: Code requiring too many comments
• Non-isolated side effects: Impure functions difficult to test
• Inconsistent code style: Mixed formatting and conventions in source files

Refactoring Objective

• Apply Clean Code: Clear naming, single responsibility, simplicity
• Reduce complexity: Decompose complex blocks
• Eliminate duplication: Factor out redundant code
• Improve testability: Isolate side effects
• Maintain consistency: Uniform standards and conventions

Technical Constraints

• Code files only: Refactor exclusively source code files (.js, .ts, .py, .java, .cs, etc.)
• No documentation changes: Do not modify README, comments, or documentation files
• No configuration files: Avoid changing package.json, config files, or build scripts
• Preserve behavior: No functional regression
• Maintain API: Public interface compatibility
• Progressive approach: One refactoring at a time
• Modern standards: Align with language best practices

Expected Output

1. Initial analysis:

   • Identification of code smells and Clean Code violations in source files only
   • Prioritization of modifications by impact/ease within code boundaries

2. Applied refactorings:

   • Direct source code file modifications step by step
   • Documentation of applied Clean Code principle for each code change
   • Behavior preservation validation through code analysis

3. Improvement summary:

   • List of code modifications performed (exclude documentation/config changes)
   • Code quality metrics improvement (if measurable)
   • Recommendations for next code refactoring steps

Style and Best Practices

• KISS: Keep It Simple, Stupid - simplicity above all
• DRY: Don't Repeat Yourself - eliminate duplication
• SOLID: Object-oriented design principles
• Clean Code: Robert C. Martin - naming, functions, classes

Expected Response Format

1. Step N: [Code Modification Title]

   • Identified Problem: Detected code smell in source file
   • Applied Principle: Clean Code reference
   • Code Modification: Direct application to source code file only
   • Benefit: Code quality improvement achieved

2. Global Summary:

   • Code modifications applied with Clean Code references
   • Source code quality improvement metrics
   • Future code refactoring recommendations

Important: Focus exclusively on source code improvements. Do not suggest changes to:

• Documentation files (README.md, docs/, etc.)
• Configuration files (package.json, tsconfig.json, etc.)
• Build scripts or deployment files
• Test files (unless specifically analyzing test code quality)
  </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Clean code refactor #11

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