/*
 * Copyright 2002-2008 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.tags.form;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.BodyContent;
import javax.servlet.jsp.tagext.BodyTag;

import org.springframework.util.Assert;
import org.springframework.web.servlet.support.BindStatus;
import org.springframework.web.util.TagUtils;

/**
 * JSP tag for rendering an HTML '<code>option</code>' tag.
 * 
 * <p><b>Must be used nested inside a {@link SelectTag}.</b>
 * 
 * <p>Provides full support for databinding by marking an
 * '<code>option</code>' as 'selected' if the {@link #setValue value}
 * matches the value bound to the out {@link SelectTag}.
 *
 * <p>The {@link #setValue value} property is required and corresponds to
 * the '<code>value</code>' attribute of the rendered '<code>option</code>'.
 *
 * <p>An optional {@link #setLabel label} property can be specified, the
 * value of which corresponds to inner text of the rendered
 * '<code>option</code>' tag. If no {@link #setLabel label} is specified
 * then the {@link #setValue value} property will be used when rendering
 * the inner text.
 *
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @since 2.0
 */
public class OptionTag extends AbstractHtmlElementBodyTag implements BodyTag {

	/**
	 * The name of the JSP variable used to expose the value for this tag.
	 */
	public static final String VALUE_VARIABLE_NAME = "value";

	/**
	 * The name of the JSP variable used to expose the display value for this tag.
	 */
	public static final String DISPLAY_VALUE_VARIABLE_NAME = "displayValue";

	/**
	 * The name of the '<code>selected</code>' attribute.
	 */
	private static final String SELECTED_ATTRIBUTE = "selected";

	/**
	 * The name of the '<code>value</code>' attribute.
	 */
	private static final String VALUE_ATTRIBUTE = VALUE_VARIABLE_NAME;
	
	/**
	 * The name of the '<code>disabled</code>' attribute.
	 */
	private static final String DISABLED_ATTRIBUTE = "disabled";


	/**
	 * The 'value' attribute of the rendered HTML <code>&lt;option&gt;</code> tag.
	 */
	private Object value;

	/**
	 * The text body of the rendered HTML <code>&lt;option&gt;</code> tag.
	 */
	private String label;

	private Object oldValue;

	private Object oldDisplayValue;
	
	private String disabled;


	/**
	 * Set the 'value' attribute of the rendered HTML <code>&lt;option&gt;</code> tag.
	 * <p>May be a runtime expression.
	 */
	public void setValue(Object value) {
		this.value = value;
	}

	/**
	 * Get the 'value' attribute of the rendered HTML <code>&lt;option&gt;</code> tag.
	 */
	protected Object getValue() {
		return this.value;
	}
	
	/**
	 * Set the value of the '<code>disabled</code>' attribute.
	 * <p>May be a runtime expression.
	 * @param disabled the value of the '<code>disabled</code>' attribute
	 */
	public void setDisabled(String disabled) {
		this.disabled = disabled;
	}

	/**
	 * Get the value of the '<code>disabled</code>' attribute.
	 */
	protected String getDisabled() {
		return this.disabled;
	}
	
	/**
	 * Is the current HTML tag disabled?
	 * @return <code>true</code> if this tag is disabled 
	 */
	protected boolean isDisabled() {
		return "true".equals(getDisabled());
	}

	/**
	 * Set the text body of the rendered HTML <code>&lt;option&gt;</code> tag.
	 * <p>May be a runtime expression.
	 */
	public void setLabel(String label) {
		Assert.notNull(label, "'label' must not be null");
		this.label = label;
	}

	/**
	 * Get the text body of the rendered HTML <code>&lt;option&gt;</code> tag.
	 */
	protected String getLabel() {
		return this.label;
	}


	protected void renderDefaultContent(TagWriter tagWriter) throws JspException {
		Object value = this.pageContext.getAttribute(VALUE_VARIABLE_NAME);
		String label = getLabelValue(value);
		renderOption(value,  label, tagWriter);
	}

	protected void renderFromBodyContent(BodyContent bodyContent, TagWriter tagWriter) throws JspException {
		Object value = this.pageContext.getAttribute(VALUE_VARIABLE_NAME);
		String label = bodyContent.getString();
		renderOption(value, label, tagWriter);
	}

	/**
	 * Make sure we are under a '<code>select</code>' tag before proceeding.
	 */
	protected void onWriteTagContent() {
		assertUnderSelectTag();
	}

	protected void exposeAttributes() throws JspException {
		Object value = resolveValue();
		this.oldValue = this.pageContext.getAttribute(VALUE_VARIABLE_NAME);
		this.pageContext.setAttribute(VALUE_VARIABLE_NAME, value);
		this.oldDisplayValue = this.pageContext.getAttribute(DISPLAY_VALUE_VARIABLE_NAME);
		this.pageContext.setAttribute(DISPLAY_VALUE_VARIABLE_NAME, getDisplayString(value, getBindStatus().getEditor()));
	}

	protected BindStatus getBindStatus() {
		return (BindStatus) this.pageContext.getAttribute(SelectTag.LIST_VALUE_PAGE_ATTRIBUTE);
	}

	protected void removeAttributes() {
		if (this.oldValue != null) {
			this.pageContext.setAttribute(VALUE_ATTRIBUTE, this.oldValue);
			this.oldValue = null;
		}
		else {
			this.pageContext.removeAttribute(VALUE_VARIABLE_NAME);
		}

		if (this.oldDisplayValue != null) {
			this.pageContext.setAttribute(DISPLAY_VALUE_VARIABLE_NAME, this.oldDisplayValue);
			this.oldDisplayValue = null;
		}
		else {
			this.pageContext.removeAttribute(DISPLAY_VALUE_VARIABLE_NAME);
		}
	}

	private void renderOption(Object value, String label, TagWriter tagWriter) throws JspException {
		tagWriter.startTag("option");
		writeOptionalAttribute(tagWriter, "id", resolveId());
		writeOptionalAttributes(tagWriter);
		String renderedValue = getDisplayString(value, getBindStatus().getEditor());
		tagWriter.writeAttribute(VALUE_ATTRIBUTE, renderedValue);
		if (isSelected(value)) {
			tagWriter.writeAttribute(SELECTED_ATTRIBUTE, SELECTED_ATTRIBUTE);
		}
		if (isDisabled()) {
			tagWriter.writeAttribute(DISABLED_ATTRIBUTE, "disabled");
		}
		tagWriter.appendValue(label);
		tagWriter.endTag();
	}

	protected String autogenerateId() throws JspException {
		return null;
	}

	/**
	 * Returns the value of the label for this '<code>option</code>' element.
	 * If the {@link #setLabel label} property is set then the resolved value
	 * of that property is used, otherwise the value of the <code>resolvedValue</code>
	 * argument is used.
	 */
	private String getLabelValue(Object resolvedValue) throws JspException {
		String label = getLabel();
		Object labelObj = (label == null ? resolvedValue : evaluate("label", label));
		return  getDisplayString(labelObj, getBindStatus().getEditor());
	}

	private void assertUnderSelectTag() {
		TagUtils.assertHasAncestorOfType(this, SelectTag.class, "option", "select");
	}

	private boolean isSelected(Object resolvedValue) {
		return SelectedValueComparator.isSelected(getBindStatus(), resolvedValue);
	}

	private Object resolveValue() throws JspException {
		return evaluate(VALUE_VARIABLE_NAME, getValue());
	}

}
