refactor-for-clarity

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# Refactor for Clarity

## Overview

Refactor code so it communicates clearly — to the next developer, and to future-you. The goal is not fewer lines — it's code that's easier to read, follow, and modify without a mental detour. Every change must pass: "Would a new team member understand this faster than the original?"

## When to Use

- After a feature is working and tests pass, but the implementation feels heavier than it needs to be
- During code review when readability or complexity issues are flagged
- When you encounter deeply nested logic, long functions, or unclear names
- When refactoring code written under time pressure

**When NOT to use:**

- Code is already clean and readable — don't refactor for the sake of it
- You don't understand what the code does yet — comprehend before you refactor
- The code is performance-critical and the "simpler" version would be measurably slower
- You're about to rewrite the module entirely — refactoring throwaway code wastes effort
- The issue is duplication, dead code, or missing extraction — use `refactor-for-reuse` instead

## The Five Principles

### 1. Preserve Behavior Exactly

Don't change what the code does — only how it expresses it. All inputs, outputs, side effects, error behavior, and edge cases must remain identical. If you're not sure a refactoring preserves behavior, don't make it.

```
ASK BEFORE EVERY CHANGE:
→ Does this produce the same output for every input?
→ Does this maintain the same error behavior?
→ Does this preserve the same side effects and ordering?
→ Do all existing tests still pass without modification?
```

### 2. Follow Project Conventions

Refactoring means making code more consistent with the codebase, not imposing external preferences. Before refactoring:

```
1. Read AGENTS.md or CLAUDE.md / project conventions
2. Study how neighboring code handles similar patterns
3. Match the project's style for:
   - Import ordering and module system
   - Function declaration style
   - Naming conventions
   - Error handling patterns
   - Type annotation depth
```

Refactoring that breaks project consistency is not improvement — it's churn.

### 3. Prefer Clarity Over Cleverness

Explicit code is better than compact code when the compact version requires a mental pause to parse.

```python
# UNCLEAR: Chained ternary
label = 'New' if item.is_new else 'Updated' if item.is_updated else 'Archived' if item.is_archived else 'Active'

# CLEAR: Readable early-return function
def get_status_label(item):
    if item.is_new:
        return 'New'
    if item.is_updated:
        return 'Updated'
    if item.is_archived:
        return 'Archived'
    return 'Active'
```

```python
# UNCLEAR: Dense one-liner accumulation
from functools import reduce
count_by_id = reduce(lambda acc, x: {**acc, x.id: acc.get(x.id, 0) + 1}, items, {})

# CLEAR: Named loop
count_by_id = {}
for item in items:
    count_by_id[item.id] = count_by_id.get(item.id, 0) + 1
```

### 4. Maintain Balance

Clarity refactoring has a failure mode: over-simplification. Watch for these traps:

- **Inlining too aggressively** — removing a helper that gave a concept a name makes the call site harder to read
- **Combining unrelated logic** — two simple functions merged into one complex function is not simpler
- **Removing "unnecessary" abstraction** — some abstractions exist for extensibility or testability, not complexity
- **Optimizing for line count** — fewer lines is not the goal; easier comprehension is

### 5. Scope to What Changed

Default to refactoring recently modified code. Avoid drive-by changes to unrelated code unless explicitly asked to broaden scope. Unscoped refactoring creates noise in diffs and risks unintended regressions.

## The Refactoring Process

### Step 1: Verify Test Coverage

Before touching anything, confirm the code you're about to refactor is covered by tests. Tests are the only proof that behavior is preserved after structural changes.

If coverage is missing: invoke **`test-driven-development`** to write characterization tests first — tests that pin the current behavior before any refactoring begins. Commit them before proceeding.

If the code's behavior is unclear before writing tests: invoke **`verify-before-claim`** — open the actual files and confirm what the code does before asserting it.

### Step 2: Understand Before Touching (Chesterton's Fence)

Before changing or removing anything, understand why it exists. This is Chesterton's Fence: if you see a fence across a road and don't understand why it's there, don't tear it down. First understand the reason, then decide if the reason still applies.

```
BEFORE REFACTORING, ANSWER:
- What is this code's responsibility?
- What calls it? What does it call?
- What are the edge cases and error paths?
- Are there tests that define the expected behavior?
- Why might it have been written this way? (Performance? Platform constraint? Historical reason?)
- Check git blame: what was the original context for this code?
```

From eyalgo/kensaiapp, MIT.

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