refactoring-suggester

• Extract Method: 長いメソッドを分割
• Rename: 分かりやすい命名に変更
• Remove Duplication: 重複排除
• Simplify Conditionals: 条件式の簡略化
• Design Patterns: パターン適用提案

Extract Method

```javascript

// Before

function processOrder(order) {

// 検証

if (!order.items || order.items.length === 0) {

throw new Error('No items');

}

if (!order.customer) {

throw new Error('No customer');

}

// 価格計算

let total = 0;

for (const item of order.items) {

total += item.price * item.quantity;

}

const tax = total * 0.1;

total += tax;

// 保存

const saved = db.orders.save(order);

return saved;

}

// After: Extract Method

function processOrder(order) {

validateOrder(order);

const total = calculateTotal(order);

return saveOrder(order, total);

}

function validateOrder(order) {

if (!order.items || order.items.length === 0) {

throw new Error('No items');

}

if (!order.customer) {

throw new Error('No customer');

}

}

function calculateTotal(order) {

const subtotal = order.items.reduce(

(sum, item) => sum + item.price * item.quantity,

0

);

return subtotal * 1.1; // +10% tax

}

function saveOrder(order, total) {

order.total = total;

return db.orders.save(order);

}

```

Replace Magic Numbers

```python

# Before

def calculate_price(item):

if item.category == 'premium':

return item.price * 0.9

elif item.category == 'vip':

return item.price * 0.8

return item.price * 1.0

# After

DISCOUNT_RATES = {

'premium': 0.9,

'vip': 0.8,

'regular': 1.0

}

def calculate_price(item):

rate = DISCOUNT_RATES.get(item.category, 1.0)

return item.price * rate

```

Simplify Conditionals

```typescript

// Before

function getShippingCost(weight: number, distance: number): number {

if (weight < 5) {

if (distance < 100) {

return 10;

} else {

return 15;

}

} else {

if (distance < 100) {

return 20;

} else {

return 25;

}

}

}

// After: Guard Clauses

function getShippingCost(weight: number, distance: number): number {

const isLight = weight < 5;

const isNear = distance < 100;

if (isLight && isNear) return 10;

if (isLight && !isNear) return 15;

if (!isLight && isNear) return 20;

return 25;

}

// Better: Lookup table

const SHIPPING_RATES = {

'light_near': 10,

'light_far': 15,

'heavy_near': 20,

'heavy_far': 25

};

function getShippingCost(weight: number, distance: number): number {

const weightKey = weight < 5 ? 'light' : 'heavy';

const distanceKey = distance < 100 ? 'near' : 'far';

const key = ${weightKey}_${distanceKey};

return SHIPPING_RATES[key];

}

```

• Version: 1.0.0