SQLCheckConstraintVariableResolver.java

/*
 * Copyright (c) 2010, SQL Power Group Inc.
 *
 * This file is part of SQL Power Library.
 *
 * SQL Power Library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * SQL Power Library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>. 
 */

package ca.sqlpower.sqlobject;

import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

import ca.sqlpower.object.SPVariableResolver;

/**
 * This {@link SPVariableResolver} resolves variables defined by
 * {@link SQLCheckConstraint}. There is no use of namespaces in these variables
 * because the variables only refer to the {@link SQLObject} the check
 * constraint applies to.
 */
public class SQLCheckConstraintVariableResolver implements SPVariableResolver {

	/**
	 * This enum defines the different check constraint variables that can be
	 * used within a constraint condition.
	 */
	public enum SQLCheckConstraintVariable {
		THIS("this");
		
		private final String variableName;
		
		private SQLCheckConstraintVariable(String variableName) {
			this.variableName = variableName;
		}
		
		public String getVariableName() {
			return variableName;
		}

		/**
		 * Finds the {@link SQLCheckConstraintVariable} given the variable name.
		 * 
		 * @param variableName
		 *            The name of the variable.
		 * @return The found {@link SQLCheckConstraintVariable} that matches with
		 *         the variable name, or null if it does not exist.
		 */
		public static SQLCheckConstraintVariable findVariable(String variableName) {
			if (variableName != null) {
				for (SQLCheckConstraintVariable var : SQLCheckConstraintVariable.values()) {
					if (variableName.equals(var.getVariableName())) {
						return var;
					}
				}
			}
			return null;
		}

		/**
		 * Retrieves the value of a variable given the {@link SQLColumn} it
		 * should resolve from.
		 * 
		 * @param column
		 *            The {@link SQLColumn} which the variable value comes from.
		 * @param variableName
		 *            The name of the variable.
		 * @return The value of the variable.
		 */
		public static Object getVariableValue(
				SQLColumn column, String variableName) {
			SQLCheckConstraintVariable var = findVariable(variableName);
			if (var == null) {
				return null;
			} else {
				switch(var) {
				case THIS:
					return column.getPhysicalName();
				default:
					return null;
				}
			}
		}
	}
	
	private final SQLColumn column;

	/**
	 * Creates a new {@link SQLCheckConstraintVariableResolver} that resolves
	 * variables within a {@link SQLColumn}'s {@link SQLCheckConstraint}s.
	 * 
	 * @param column
	 *            The {@link SQLColumn} that contains the
	 *            {@link SQLCheckConstraint}s to resolve.
	 */
	public SQLCheckConstraintVariableResolver(SQLColumn column) {
		this.column = column;
	}

	/**
	 * Returns the {@link SQLColumn} this
	 * {@link SQLCheckConstraintVariableResolver} resolves for its
	 * {@link SQLCheckConstraint}s.
	 */
	public SQLColumn getColumn() {
		return column;
	}

	public void delete(String key) {
		throw new UnsupportedOperationException("The " + getClass().getName() + 
				" does not support deleting variable values.");
	}

	public String getNamespace() {
		return null;
	}

	public String getUserFriendlyName() {
		return SQLColumn.class.getSimpleName() + 
				" - " + column.getName();
	}

	public Collection<String> keySet(String namespace) {
		if (namespace == null) {
			Set<String> variableNames = new HashSet<String>();
			for (SQLCheckConstraintVariable var : SQLCheckConstraintVariable.values()) {
				variableNames.add(var.getVariableName());
			}
			return variableNames;
		} else {
			return Collections.emptySet();
		}
	}

	public Collection<Object> matches(String key, String partialValue) {
		Object value = resolve(key);
		String stringValue = String.valueOf(value);
		if (stringValue != null && stringValue.startsWith(partialValue)) {
			return Collections.singleton(value);
		} else {
			return Collections.emptySet();
		}
	}

	public Object resolve(String key) {
		return resolve(key, null);
	}

	public Object resolve(String key, Object defaultValue) {
		SQLCheckConstraintVariable variable = 
			SQLCheckConstraintVariable.findVariable(key);
		if (variable == null) {
			return defaultValue;
		} else {
			return SQLCheckConstraintVariable.getVariableValue(
					column, variable.getVariableName());
		}
	}

	public Collection<Object> resolveCollection(String key) {
		Object value = resolve(key);
		if (value == null) {
			return Collections.emptySet();
		} else {
			return Collections.singleton(value);
		}
	}

	public Collection<Object> resolveCollection(String key, Object defaultValue) {
		Object value = resolve(key);
		if (value == null) {
			return Collections.singleton(defaultValue);
		} else {
			return Collections.singleton(value);
		}
	}

	public boolean resolves(String key) {
		return SQLCheckConstraintVariable.findVariable(key) != null;
	}

	public boolean resolvesNamespace(String namespace) {
		return namespace == null;
	}

	public void store(String key, Object value) {
		throw new UnsupportedOperationException("The " + getClass().getName() + 
				" does not support storing variable values.");		
	}

	public void update(String key, Object value) {
		throw new UnsupportedOperationException("The " + getClass().getName() + 
				" does not support storing variable values.");
	}
	
}