package com.nesterovskyBros; 

import java.util.AbstractList;
import java.util.Collections;
import java.util.List;

import javax.el.ValueExpression;

import javax.faces.context.FacesContext;

/**
 * JSF functions used in the application.
 */
public class Functions
{
  /**
   * Resolves resource url.
   * 
   * @param path resource path, possibly relative.
   * @return resolved path.
   */
  public static String url(String path)
    throws Exception
  {
    FacesContext facesContext = FacesContext.getCurrentInstance();

    return facesContext.getApplication().getViewHandler().
      getResourceURL(facesContext, path);
  }
   
  /**
   * A factory of {@link ScopeComponent} instances.
   */
  public static class ScopeProvider
  {
    /**
     * Gets an instance of {@link ScopeComponent}.
     * @return an instance of {@link ScopeComponent}.
     */
    public ScopeComponent getValue()
    {
      if (value == null)
      {
        value = new ScopeComponent();
      }
      
      return value;
    }
    
    /**
     * Sets a value of {@link ScopeComponent}.
     * @param value a value of {@link ScopeComponent}.
     */
    public void setValue(ScopeComponent value)
    {
      this.value = value;
    }

    /**
     * A scope component.
     */
    private ScopeComponent value;
  }
  
  /**
   * <p>Creates a scope component.</p>
   * <p>{@link ScopeComponent} introduces itself into the databinding scope 
   * using value of id attribute as name, allowing to acquire its clientId.</p>
   * <p>
   * &lt;f:subview id="name" binding="#{ex:scope()}"&gt;
   *   ...
   *   #{name.childId}:item
   * &lt;f:subview&gt;
   * </p>
   * <p>The other feature is uniqueId attribute, which is used to output 
   * something only once. uniqueId is used as a discriminator.
   * <p>
   * &lt;f:subview uniqueId="my-script-id" binding="ex:scope()"&gt;
   *   &lt;script ... 
   * &lt;f:subview&gt;
   * </p>
   * @return an instance of {@link ScopeComponent}.
   */
  public static Object scope()
    throws Exception
  {
    return new ScopeProvider();    
  }

  /**
   * Returns a list of integers with values from 0 and up to size not including.
   * @param size a size of list.
   * @return a list of integers.
   */
  public static List<Integer> sequence(final int size)
    throws Exception
  {
    return new AbstractList<Integer>()
    {
      @Override
      public Integer get(int index)
      {
        return index;
      }

      @Override
      public int size()
      {
        return size;
      }
    };
  }

  /**
   * Returns a list of indices of a specified list. 
   * @param list a list to get indices for.
   * @return a list of integers.
   */
  public static <T> List<Integer> indices(List<T> list)
    throws Exception
  {
    if (list == null)
    {
      return Collections.emptyList();
    }
      
    return sequence(list.size());
  }

  /**
   * Returns a value for the value expression.
   * @param value a value expression to get value for.
   * @return a a value for the value expression.
   */
  public static Object value(ValueExpression value)
    throws Exception
  {
    if (value == null)
    {
      return null;
    }
    
    return value.getValue(FacesContext.getCurrentInstance().getELContext());
  }
}