Code Generator Skill

Structured workflow for implementing code from design documents with clear phase separation, cost estimation, and modification tracking.

When to Use

Use this skill when you need to:

• Implement a new module or system from a design document
• Add features to existing codebase
• Refactor or replace existing components
• Generate implementation code with clear execution plan

Core Principles

1. Phase-Based Execution

• Break implementation into logical phases
• Each phase has clear dependencies
• Execute sequentially, phase by phase

2. Operation Type Declaration

• Create: New file that doesn't exist
• Modify: Existing file requiring changes
• Delete: Remove existing file (rare, requires explicit confirmation)

3. Cost Transparency

• Estimate token cost for each operation
• Calculate total cost before execution
• Allow user to adjust scope based on budget

4. Modification Preview

• For modify operations, show before/after diff
• Highlight key changes
• No surprises for user

5. Capability Boundaries

• Can Do: Code generation, file read/write
• Cannot Do: Git operations, database changes, compilation, external API calls

Workflow

Step 1: Analyze Design Document

Read and understand:

• Architecture overview
• File list and dependencies
• Key design decisions
• Interface contracts

Step 2: Create Execution Plan

Use this format:

## 📋 [ProjectName] Implementation Plan

### Execution Capability Statement

| Operation | Capability |
|-----------|------------|
| Code generation | ✅ Can execute |
| Database operations | ❌ Cannot execute (user handles) |
| Git/SVN operations | ❌ Do not execute |
| Compilation | ❌ Do not execute (user triggers) |

### Phase [N]: [Phase Name]

| Order | File | Path | Operation | Content | Time | Token Cost |
|-------|------|------|-----------|---------|------|------------|
| 1 | `FileName.h` | `Path/` | Create/Modify | Brief description | X min | ~X,XXX |

**Phase Subtotal**: ~X,XXX tokens

### Modification Preview

For modify operations only:

`FileName.h`:
```cpp
// Before: [current state or "None"]
// After: [new code to be added]

Phase Dependencies

Phase 1 ──► Phase 2 ──► Phase 3

Total Cost Summary

Phase	Time	Token Cost
1	X min	~X,XXX
2	X min	~X,XXX
Total	X hours	~XX,XXX

User Confirmation Items

1. [Specific question 1]
2. [Specific question 2]
3. Start confirmation: Reply "批准计划" to begin

### Step 3: Execute Phase by Phase

After user approval with "批准计划":

1. **Announce current phase**
2. **Execute operations** in order
3. **Report progress** after each file
4. **Confirm phase completion** before next phase

### Step 4: Completion Report

```markdown
## ✅ Implementation Complete

### Generated Files

| File | Path | Lines |
|------|------|-------|
| `File.h` | `Path/` | XXX |

### Modified Files

| File | Path | Changes |
|------|------|---------|
| `File.cpp` | `Path/` | Added X methods |

### Next Steps (User Action Required)

1. [Database setup, compilation, etc.]

### Token Usage

- **Estimated**: ~XX,XXX
- **Actual**: ~XX,XXX

Token Cost Guidelines

File Type	Lines	Estimated Tokens
Header (declaration)	50-100	500-1,000
Implementation	200-300	2,000-4,000
Simple modification	-	300-800
Complex modification	-	1,000-2,000
CSV/Data file	20-50	200-500
Test file	100-200	1,000-2,000

Template: Complete Example

## 📋 PlayerSystem Implementation Plan

### Execution Capability Statement

| Operation | Capability |
|-----------|------------|
| Code generation | ✅ Can execute |
| Database operations | ❌ Cannot execute |
| Git/SVN operations | ❌ Do not execute |
| Compilation | ❌ Do not execute |

### Phase 1: Data Structures

| Order | File | Path | Operation | Content | Time | Token Cost |
|-------|------|------|-----------|---------|------|------------|
| 1 | `SystemDefines.h` | `Project/` | Create | Enums and utilities | 5m | ~500 |
| 2 | `SystemInstance.h` | `Project/` | Create | Struct with Save/Load | 10m | ~800 |

**Phase 1 Subtotal**: ~1,300 tokens

### Phase 2: Core Implementation

| Order | File | Path | Operation | Content | Time | Token Cost |
|-------|------|------|-----------|---------|------|------------|
| 3 | `PlayerSystem.h` | `Project/` | Create | Class declaration | 10m | ~1,000 |
| 4 | `PlayerSystem.cpp` | `Project/` | Create | Core methods | 30m | ~3,500 |

**Phase 2 Subtotal**: ~4,500 tokens

### Phase 3: Integration

| Order | File | Path | Operation | Content | Time | Token Cost |
|-------|------|------|-----------|---------|------|------------|
| 5 | `Player.h` | `Project/` | Modify | Add accessor method | 5m | ~300 |

**Modification Preview**:

`Player.h`:
```cpp
// Before: No System member
class Player {
    // existing members
};

// After: Added System
class Player {
    // existing members
public:
    PlayerSystem& GetSystem() { return mSystem; }
private:
    PlayerSystem mSystem;
};

Phase 3 Subtotal: ~300 tokens

Total Cost Summary

Phase	Time	Token Cost
1	15m	~1,300
2	40m	~4,500
3	5m	~300
Total	1 hour	~6,100

User Confirmation

1. Database table: I provide SQL / You create manually
2. Start: Reply "批准计划"

## Anti-Patterns

### ❌ Don't
- Start coding without user approval
- Skip modification previews for modify operations
- Omit token cost estimation
- Perform Git/database/compilation operations
- Combine multiple phases without checkpoint

### ✅ Do
- Wait for "批准计划" before execution
- Show before/after for all modifications
- Estimate costs conservatively
- Stay within code generation scope only
- Execute phase by phase with progress reports

## Integration with Other Skills

- **mvp-design**: Use as input (design doc → implementation)
- **code-analysis**: Verify existing files before modification
- **skill-creator**: Extract patterns into reusable skills

## Quick Reference

### Cost Estimation Formula

Header file: 10 tokens per line Implementation: 15 tokens per line Modification: 20 tokens per line (includes context) Test file: 12 tokens per line

### Modification Preview Format

```cpp
// File: Path/Filename.ext

// Before: [describe current state]
[code snippet or "None - new addition"]

// After: [describe new state]
[code snippet to be added/modified]

// Key changes:
// - Change 1
// - Change 2

Version History

• v1.0 (2026-02-10) - Initial release
  • Phase-based execution model
  • Token cost estimation
  • Modification preview requirement
  • Clear capability boundaries