package org.codefilarete.stalactite.query.api;

/**
 * Contract for elements to be put in a Select clause to be transformed to SQL
 * 
 * @see SimpleSelectable
 * @author Guillaume Mary
 */
public interface Selectable<C> {
	
	/**
	 * Gives the SQL string that must be put in the select clause.
	 * Expected to be a valid and security-proof expression: don't consider any validation will be done.
	 * 
	 * @return any non-null SQL statement for a select clause
	 */
	String getExpression();
	
	Class<C> getJavaType();
	
	static Selectable<String> selectableString(String expression) {
		return new SimpleSelectable<>(expression, String.class);
	}
	
	/**
	 * Implementation for String to be put in Select clause or as a criteria.
	 * Be aware that expression given at constructor will be rendered as it is to SQL without transformation.
	 */
	class SimpleSelectable<C> implements Selectable<C> {
		
		private final String expression;
		
		private final Class<C> javaType;
		
		/**
		 * Straight constructor.
		 * Be aware that expression will be rendered as it is to SQL without transformation.
		 * 
		 * @param expression the text to be put into SQL
		 * @param javaType type returned by expression
		 */
		public SimpleSelectable(String expression, Class<C> javaType) {
			this.expression = expression;
			this.javaType = javaType;
		}
		
		@Override
		public String getExpression() {
			return expression;
		}
		
		@Override
		public Class<C> getJavaType() {
			return javaType;
		}
	}
}
