/*-
 * ============LICENSE_START=======================================================
 * OPENECOMP - MSO
 * ================================================================================
 * Copyright (C) 2017 AT&T Intellectual Property. All rights reserved.
 * ================================================================================
 * 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.
 * ============LICENSE_END=========================================================
 */

package org.openecomp.mso.bpmn.core;

import java.util.Objects;

import org.camunda.bpm.engine.ProcessEngineException;
import org.camunda.bpm.engine.delegate.DelegateExecution;
import org.camunda.bpm.engine.delegate.Expression;
import org.camunda.bpm.engine.delegate.JavaDelegate;

/**
 * Base class for service tasks.
 */
public abstract class BaseTask implements JavaDelegate {

	/**
	 * Get the value of a required field.  This method throws
	 * MissingInjectedFieldException if the expression is null, and
	 * BadInjectedFieldException if the expression evaluates to a null
	 * value.
	 *
	 * @param expression the expression
	 * @param execution the execution
	 * @param fieldName the field name (for logging and exceptions)
	 * @return the field value
	 */
	protected Object getField(Expression expression,
			DelegateExecution execution, String fieldName) {
		return getFieldImpl(expression, execution, fieldName, false);
	}
	
	/**
	 * Gets the value of an optional field.  There are three conditions
	 * in which this method returns null:
	 * <p>
	 * <ol>
	 * <li> The expression itself is null (i.e. the field is missing
	 * altogether.</li>
	 * <li>The expression evaluates to a null value.</li>
	 * <li>The expression references a single variable which has not
	 * been set.</li>
	 * </ol>
	 * <p>
	 * Examples:<br>
	 * Expression ${x} when x is null: return null<br>
	 * Expression ${x} when x is unset: return null<br>
	 * Expression ${x+y} when x and/or y are unset: exception<br>
	 * 
	 * @param expression the expression
	 * @param execution the execution
	 * @param fieldName the field name (for logging and exceptions)
	 * @return the field value, possibly null
	 */
	protected Object getOptionalField(Expression expression,
			DelegateExecution execution, String fieldName) {
		return getFieldImpl(expression, execution, fieldName, true);
	}
	
	/**
	 * Get the value of a required output variable field. This method
	 * throws MissingInjectedFieldException if the expression is null, and
	 * BadInjectedFieldException if the expression produces a null or
	 * illegal variable name.  Legal variable names contain only letters,
	 * numbers, and the underscore character ('_').
	 *
	 * @param expression the expression
	 * @param execution the execution
	 * @param fieldName the field name (for logging and exceptions)
	 * @return the output variable name
	 */
	protected String getOutputField(Expression expression,
			DelegateExecution execution, String fieldName) {
		Object o = getFieldImpl(expression, execution, fieldName, false);
		if (o instanceof String) {
			String variable = (String) o;
			if (!isLegalVariable(variable)) {
				throw new BadInjectedFieldException(
					fieldName, getTaskName(), "'" + variable
						+ "' is not a legal variable name");
			}
			return variable;
		} else {
			throw new BadInjectedFieldException(
				fieldName, getTaskName(), "expected a variable name string"
					+ ", got object of type " + o.getClass().getName());
		}
	}
	
	/**
	 * Get the value of an optional output variable field. This method
	 * throws BadInjectedFieldException if the expression produces an illegal
	 * variable name.  Legal variable names contain only letters, numbers,
	 * and the underscore character ('_').
	 * 
	 * @param expression the expression
	 * @param execution the execution
	 * @param fieldName the field name (for logging and exceptions)
	 * @return the output variable name, possibly null
	 */
	protected String getOptionalOutputField(Expression expression,
			DelegateExecution execution, String fieldName) {
		Object o = getFieldImpl(expression, execution, fieldName, true);
		if (o instanceof String) {
			String variable = (String) o;
			if (!isLegalVariable(variable)) {
				throw new BadInjectedFieldException(
					fieldName, getTaskName(), "'" + variable
						+ "' is not a legal variable name");
			}
			return variable;
		} else if (o == null) {
			return null;
		} else {
			throw new BadInjectedFieldException(
				fieldName, getTaskName(), "expected a variable name string"
					+ ", got object of type " + o.getClass().getName());
		}
	}

	/**
	 * Get the value of a required string field.  This method throws
	 * MissingInjectedFieldException if the expression is null, and
	 * BadInjectedFieldException if the expression evaluates to a null
	 * value.
	 * <p>
	 * Note: the result is coerced to a string value, if necessary.
	 *
	 * @param expression the expression
	 * @param execution the execution
	 * @param fieldName the field name (for logging and exceptions)
	 * @return the field value
	 */
	protected String getStringField(Expression expression,
			DelegateExecution execution, String fieldName) {
		Object o = getFieldImpl(expression, execution, fieldName, false);
		if (o instanceof String) {
			return (String) o;
		} else {
			throw new BadInjectedFieldException(
				fieldName, getTaskName(), "cannot convert '" + o.toString()
				+ "' to Integer");
		}
	}
	
	/**
	 * Gets the value of an optional string field.  There are three conditions
	 * in which this method returns null:
	 * <p>
	 * <ol>
	 * <li> The expression itself is null (i.e. the field is missing
	 * altogether.</li>
	 * <li>The expression evaluates to a null value.</li>
	 * <li>The expression references a single variable which has not
	 * been set.</li>
	 * </ol>
	 * <p>
	 * Examples:<br>
	 * Expression ${x} when x is null: return null<br>
	 * Expression ${x} when x is unset: return null<br>
	 * Expression ${x+y} when x and/or y are unset: exception<br>
	 * <p>
	 * Note: the result is coerced to a string value, if necessary.
	 * 
	 * @param expression the expression
	 * @param execution the execution
	 * @param fieldName the field name (for logging and exceptions)
	 * @return the field value, possibly null
	 */
	protected String getOptionalStringField(Expression expression,
			DelegateExecution execution, String fieldName) {
		Object o = getFieldImpl(expression, execution, fieldName, true);
		return Objects.toString(o, null);
	}
	
	/**
	 * Get the value of a required integer field. This method throws
	 * MissingInjectedFieldException if the expression is null, and
	 * BadInjectedFieldException if the expression evaluates to a null
	 * value or a value that cannot be coerced to an integer.
	 *
	 * @param expression the expression
	 * @param execution the execution
	 * @param fieldName the field name (for logging and exceptions)
	 * @return the field value
	 */
	protected Integer getIntegerField(Expression expression,
			DelegateExecution execution, String fieldName) {
		Object o = getFieldImpl(expression, execution, fieldName, false);
		if (o instanceof Integer) {
			return (Integer) o;
		} else {
			try {
				return Integer.parseInt(o.toString());
			} catch (NumberFormatException e) {
				throw new BadInjectedFieldException(
					fieldName, getTaskName(), "cannot convert '" + o.toString()
					+ "' to Integer");
			}
		}
	}
	
	/**
	 * Gets the value of an optional integer field.  There are three conditions
	 * in which this method returns null:
	 * <p>
	 * <ol>
	 * <li> The expression itself is null (i.e. the field is missing
	 * altogether.</li>
	 * <li>The expression evaluates to a null value.</li>
	 * <li>The expression references a single variable which has not
	 * been set.</li>
	 * </ol>
	 * <p>
	 * Examples:<br>
	 * Expression ${x} when x is null: return null<br>
	 * Expression ${x} when x is unset: return null<br>
	 * Expression ${x+y} when x and/or y are unset: exception<br>
	 * <p>
	 * Note: the result is coerced to an integer value, if necessary. This
	 * method throws BadInjectedFieldException if the result cannot be coerced
	 * to an integer.
	 * 
	 * @param expression the expression
	 * @param execution the execution
	 * @param fieldName the field name (for logging and exceptions)
	 * @return the field value, possibly null
	 */
	protected Integer getOptionalIntegerField(Expression expression,
			DelegateExecution execution, String fieldName) {
		Object o = getFieldImpl(expression, execution, fieldName, true);
		if (o instanceof Integer) {
			return (Integer) o;
		} else if (o == null) {
			return null;
		} else {
			try {
				return Integer.parseInt(o.toString());
			} catch (NumberFormatException e) {
				throw new BadInjectedFieldException(
					fieldName, getTaskName(), "cannot convert '" + o.toString()
					+ "' to Integer");
			}
		}
	}
	
	/**
	 * Gets the value of an optional long field.  There are three conditions
	 * in which this method returns null:
	 * <p>
	 * <ol>
	 * <li> The expression itself is null (i.e. the field is missing
	 * altogether.</li>
	 * <li>The expression evaluates to a null value.</li>
	 * <li>The expression references a single variable which has not
	 * been set.</li>
	 * </ol>
	 * <p>
	 * Examples:<br>
	 * Expression ${x} when x is null: return null<br>
	 * Expression ${x} when x is unset: return null<br>
	 * Expression ${x+y} when x and/or y are unset: exception<br>
	 * <p>
	 * Note: the result is coerced to a long value, if necessary. This
	 * method throws BadInjectedFieldException if the result cannot be coerced
	 * to a long.
	 * 
	 * @param expression the expression
	 * @param execution the execution
	 * @param fieldName the field name (for logging and exceptions)
	 * @return the field value, possibly null
	 */
	protected Long getOptionalLongField(Expression expression,
			DelegateExecution execution, String fieldName) {
		Object o = getFieldImpl(expression, execution, fieldName, true);
		if (o instanceof Long) {
			return (Long) o;
		} else if (o == null) {
			return null;
		} else {
			try {
				return Long.parseLong(o.toString());
			} catch (NumberFormatException e) {
				throw new BadInjectedFieldException(
					fieldName, getTaskName(), "cannot convert '" + o.toString()
					+ "' to Long");
			}
		}
	}
	
	/**
	 * Get the value of a required long field. This method throws
	 * MissingInjectedFieldException if the expression is null, and
	 * BadInjectedFieldException if the expression evaluates to a null
	 * value or a value that cannot be coerced to a long.
	 *
	 * @param expression the expression
	 * @param execution the execution
	 * @param fieldName the field name (for logging and exceptions)
	 * @return the field value
	 */
	protected Long getLongField(Expression expression,
			DelegateExecution execution, String fieldName) {
		Object o = getFieldImpl(expression, execution, fieldName, false);
		if (o instanceof Long) {
			return (Long) o;
		} else {
			try {
				return Long.parseLong(o.toString());
			} catch (NumberFormatException e) {
				throw new BadInjectedFieldException(
					fieldName, getTaskName(), "cannot convert '" + o.toString()
					+ "' to Long");
			}
		}
	}

	/**
	 * Common implementation for field "getter" methods.
	 * @param expression the expression
	 * @param execution the execution
	 * @param fieldName the field name (for logging and exceptions)
	 * @param optional true if the field is optional
	 * @return the field value, possibly null
	 */
	private Object getFieldImpl(Expression expression,
			DelegateExecution execution, String fieldName, boolean optional) {
		if (expression == null) {
			if (!optional) {
				throw new MissingInjectedFieldException(
					fieldName, getTaskName());
			}
			return null;
		}

		Object value;

		try {
			value = expression.getValue(execution);
		} catch (Exception e) {
			if (!optional) {
				throw new BadInjectedFieldException(
					fieldName, getTaskName(), e.getClass().getSimpleName(), e);
			}

			// At this point, we have an exception that occurred while
			// evaluating an expression for an optional field. A common 
			// problem is that the expression is a simple reference to a
			// variable which has never been set, e.g. the expression is
			// ${x}. The normal activiti behavior is to throw an exception,
			// but we don't like that, so we have the following workaround,
			// which parses the expression text to see if it is a "simple"
			// variable reference, and if so, returns null.  If the
			// expression is anything other than a single variable
			// reference, then an exception is thrown, as it would have
			// been without this workaround.

			// Get the expression text so we can parse it
			String s = expression.getExpressionText();

//			if (isDebugEnabled(execution)) {
//				logDebug(execution, getTaskName() + " field '" + fieldName
//					+ "' expression evaluation failed: " + s);
//			}

			int len = s.length();
			int i = 0;

			// Skip whitespace
			while (i < len && Character.isWhitespace(s.charAt(i))) {
				i++;
			}

			// Next character must be '$'
			if (i == len || s.charAt(i++) != '$') {
				throw new BadInjectedFieldException(
					fieldName, getTaskName(), e.getClass().getSimpleName(), e);
			}

			// Skip whitespace
			while (i < len && Character.isWhitespace(s.charAt(i))) {
				i++;
			}

			// Next character must be '{'
			if (i == len || s.charAt(i++) != '{') {
				throw new BadInjectedFieldException(
					fieldName, getTaskName(), e.getClass().getSimpleName(), e);
			}

			// Skip whitespace
			while (i < len && Character.isWhitespace(s.charAt(i))) {
				i++;
			}

			// Collect the variable name
			StringBuilder variable = new StringBuilder();
			while (i < len && isWordCharacter(s.charAt(i))) {
				variable.append(s.charAt(i));
				i++;
			}

			if (variable.length() == 0) {
				throw new BadInjectedFieldException(
					fieldName, getTaskName(), e.getClass().getSimpleName(), e);
			}

			// Skip whitespace
			while (i < len && Character.isWhitespace(s.charAt(i))) {
				i++;
			}

			// Next character must be '}'
			if (i == len || s.charAt(i++) != '}') {
				throw new BadInjectedFieldException(
					fieldName, getTaskName(), e.getClass().getSimpleName(), e);
			}

			// Skip whitespace
			while (i < len && Character.isWhitespace(s.charAt(i))) {
				i++;
			}

			// Must be at end of string
			if (i != len) {
				throw new BadInjectedFieldException(
					fieldName, getTaskName(), e.getClass().getSimpleName(), e);
			}

//			if (isDebugEnabled(execution)) {
//				logDebug(execution, "Checking if variable '"
//					+ variable.toString() + "' exists");
//			}

			// If the variable exists then the problem was
			// something else...
			if (execution.hasVariable(variable.toString())) {
				throw new BadInjectedFieldException(
					fieldName, getTaskName(), e.getClass().getSimpleName(), e);
			}

			// The variable doesn't exist.

//			if (isDebugEnabled(execution)) {
//				logDebug(execution, "Variable '" + variable.toString()
//					+ "' does not exist [ok]");
//			}

			value = null;
		}

		if (value == null && !optional) {
			throw new BadInjectedFieldException(
				fieldName, getTaskName(), "required field has null value");
		}
	
		return value;
	}
	
	/**
	 * Tests if a character is a "word" character.
	 * @param c the character
	 * @return true if the character is a "word" character.
	 */
	private boolean isWordCharacter(char c) {
		return (Character.isLetterOrDigit(c) || c == '_');
	}
	
	/**
	 * Tests if the specified string is a legal flow variable name.
	 * @param name the string
	 * @return true if the string is a legal flow variable name
	 */
	private boolean isLegalVariable(String name) {
		if (name == null) {
			return false;
		}

		int len = name.length();

		if (len == 0) {
			return false;
		}

		char c = name.charAt(0);

		if (!Character.isLetter(c) && c != '_') {
			return false;
		}

		for (int i = 1; i < len; i++) {
			c = name.charAt(i);
			if (!Character.isLetterOrDigit(c) && c != '_') {
				return false;
			}
		}

		return true;
	}
	
	/**
	 * Returns the name of the task (normally the java class name).
	 * @return the name of the task
	 */
	public String getTaskName() {
		return getClass().getSimpleName();
	}


	/**
	 * Check if shouldFail variable is set to true.
	 * @param execution
	 * @return
	 */
    protected boolean shouldFail(DelegateExecution execution) {
        Boolean shouldFail = (Boolean) execution.getVariable("shouldFail");
        return shouldFail != null && shouldFail;
    }
}