class Translations {
		var $entries = array();
		var $headers = array();

		/**
		 * Add entry to the PO structure
		 *
		 * @param array|Translation_Entry $entry
		 * @return bool true on success, false if the entry doesn't have a key
		 */
		function add_entry( $entry ) {
			if ( is_array( $entry ) ) {
				$entry = new Translation_Entry( $entry );
			}
			$key = $entry->key();
			if ( false === $key ) {
				return false;
			}
			$this->entries[ $key ] = &$entry;
			return true;
		}

		/**
		 * @param array|Translation_Entry $entry
		 * @return bool
		 */
		function add_entry_or_merge( $entry ) {
			if ( is_array( $entry ) ) {
				$entry = new Translation_Entry( $entry );
			}
			$key = $entry->key();
			if ( false === $key ) {
				return false;
			}
			if ( isset( $this->entries[ $key ] ) ) {
				$this->entries[ $key ]->merge_with( $entry );
			} else {
				$this->entries[ $key ] = &$entry;
			}
			return true;
		}

		/**
		 * Sets $header PO header to $value
		 *
		 * If the header already exists, it will be overwritten
		 *
		 * TODO: this should be out of this class, it is gettext specific
		 *
		 * @param string $header header name, without trailing :
		 * @param string $value header value, without trailing \n
		 */
		function set_header( $header, $value ) {
			$this->headers[ $header ] = $value;
		}

		/**
		 * @param array $headers
		 */
		function set_headers( $headers ) {
			foreach ( $headers as $header => $value ) {
				$this->set_header( $header, $value );
			}
		}

		/**
		 * @param string $header
		 */
		function get_header( $header ) {
			return isset( $this->headers[ $header ] ) ? $this->headers[ $header ] : false;
		}

		/**
		 * @param Translation_Entry $entry
		 */
		function translate_entry( &$entry ) {
			$key = $entry->key();
			return isset( $this->entries[ $key ] ) ? $this->entries[ $key ] : false;
		}

		/**
		 * @param string $singular
		 * @param string $context
		 * @return string
		 */
		function translate( $singular, $context = null ) {
			$entry      = new Translation_Entry(
				array(
					'singular' => $singular,
					'context'  => $context,
				)
			);
			$translated = $this->translate_entry( $entry );
			return ( $translated && ! empty( $translated->translations ) ) ? $translated->translations[0] : $singular;
		}

		/**
		 * Given the number of items, returns the 0-based index of the plural form to use
		 *
		 * Here, in the base Translations class, the common logic for English is implemented:
		 *  0 if there is one element, 1 otherwise
		 *
		 * This function should be overridden by the sub-classes. For example MO/PO can derive the logic
		 * from their headers.
		 *
		 * @param integer $count number of items
		 */
		function select_plural_form( $count ) {
			return 1 == $count ? 0 : 1;
		}

		/**
		 * @return int
		 */
		function get_plural_forms_count() {
			return 2;
		}

		/**
		 * @param string $singular
		 * @param string $plural
		 * @param int    $count
		 * @param string $context
		 */
		function translate_plural( $singular, $plural, $count, $context = null ) {
			$entry              = new Translation_Entry(
				array(
					'singular' => $singular,
					'plural'   => $plural,
					'context'  => $context,
				)
			);
			$translated         = $this->translate_entry( $entry );
			$index              = $this->select_plural_form( $count );
			$total_plural_forms = $this->get_plural_forms_count();
			if ( $translated && 0 <= $index && $index < $total_plural_forms &&
				is_array( $translated->translations ) &&
				isset( $translated->translations[ $index ] ) ) {
				return $translated->translations[ $index ];
			} else {
				return 1 == $count ? $singular : $plural;
			}
		}

		/**
		 * Merge $other in the current object.
		 *
		 * @param Object $other Another Translation object, whose translations will be merged in this one (passed by reference).
		 * @return void
		 */
		function merge_with( &$other ) {
			foreach ( $other->entries as $entry ) {
				$this->entries[ $entry->key() ] = $entry;
			}
		}

		/**
		 * @param object $other
		 */
		function merge_originals_with( &$other ) {
			foreach ( $other->entries as $entry ) {
				if ( ! isset( $this->entries[ $entry->key() ] ) ) {
					$this->entries[ $entry->key() ] = $entry;
				} else {
					$this->entries[ $entry->key() ]->merge_with( $entry );
				}
			}
		}
	}