Translation and Interpolation

/**
 * Translate a key with optional interpolation and pluralization
 * @param {string} key - Translation key to look up
 * @param {Object|number} options - Interpolation options or smart_count shortcut
 * @param {string} options._ - Default value if key not found
 * @param {number} options.smart_count - Count for pluralization
 * @param {...any} options.[variable] - Variables for interpolation
 * @returns {string} Translated and interpolated string
 */
t(key, options);

const Polyglot = require('node-polyglot');

const polyglot = new Polyglot({
  phrases: {
    'hello': 'Hello',
    'hello_name': 'Hello, %{name}!',
    'welcome_user': 'Welcome %{name}, you have %{count} messages',
    'items_zero': 'No items',
    'items_one': 'One item', 
    'items_other': '%{smart_count} items'
  }
});

// Basic translation
polyglot.t('hello'); // "Hello"

// Translation with interpolation
polyglot.t('hello_name', { name: 'Alice' }); // "Hello, Alice!"

// Multiple variable interpolation  
polyglot.t('welcome_user', { 
  name: 'Bob', 
  count: 5 
}); // "Welcome Bob, you have 5 messages"

// Translation with default value
polyglot.t('missing_key', { 
  _: 'Default message' 
}); // "Default message"

// Pluralization using smart_count
polyglot.t('items', { smart_count: 0 }); // "No items"
polyglot.t('items', { smart_count: 1 }); // "One item"
polyglot.t('items', { smart_count: 5 }); // "5 items"

// Using number shortcut for smart_count
polyglot.t('items', 0); // "No items"
polyglot.t('items', 1); // "One item"
polyglot.t('items', 5); // "5 items"

// Missing key fallback (returns key itself by default)
polyglot.t('nonexistent_key'); // "nonexistent_key"

/**
 * Check if translation exists for given key
 * @param {string} key - Translation key to check
 * @returns {boolean} True if translation exists, false otherwise
 */
has(key);

const polyglot = new Polyglot({
  phrases: {
    'hello': 'Hello',
    'nested.key': 'Nested value'
  }
});

// Check existing keys
polyglot.has('hello'); // true
polyglot.has('nested.key'); // true

// Check non-existent keys
polyglot.has('goodbye'); // false
polyglot.has('nested.missing'); // false

// Use has() to conditionally translate
if (polyglot.has('optional_message')) {
  console.log(polyglot.t('optional_message'));
} else {
  console.log('No optional message available');
}

// Provide fallback translations
const message = polyglot.has('custom_greeting') 
  ? polyglot.t('custom_greeting', { name: 'User' })
  : polyglot.t('default_greeting', { name: 'User' });

const polyglot = new Polyglot({
  phrases: {
    'user_info': 'User: %{name}, Age: %{age}, Active: %{active}',
    'partial': 'Hello %{name}, your score is %{score}'
  }
});

// Complete interpolation
polyglot.t('user_info', {
  name: 'Alice',
  age: 25,
  active: true
}); // "User: Alice, Age: 25, Active: true"

// Partial interpolation (missing variables remain)
polyglot.t('partial', { 
  name: 'Bob' 
}); // "Hello Bob, your score is %{score}"

// Null/undefined values treated as missing
polyglot.t('partial', { 
  name: 'Charlie',
  score: null
}); // "Hello Charlie, your score is %{score}"

const polyglot = new Polyglot({
  phrases: {
    'existing': 'This exists'
  }
});

// Use default value for missing key
polyglot.t('missing_key', {
  _: 'This is the default value'
}); // "This is the default value"

// Default value with interpolation
polyglot.t('missing_greeting', {
  _: 'Hello, %{name}!',
  name: 'World'
}); // "Hello, World!"

// Existing key takes precedence over default
polyglot.t('existing', {
  _: 'This default will be ignored'
}); // "This exists"

// Default behavior - returns key
const polyglot = new Polyglot();
polyglot.t('missing'); // "missing"

// Custom missing key handler
const customPolyglot = new Polyglot({
  onMissingKey: (key) => `[MISSING: ${key}]`
});
customPolyglot.t('missing'); // "[MISSING: missing]"

// Allow missing keys (uses transformPhrase as handler)
const lenientPolyglot = new Polyglot({
  allowMissing: true
});
lenientPolyglot.t('missing', { smart_count: 1 }); // "missing"