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jBasics is a collection of useful utility classes for Java. This includes helper for XML, mathematic functions, restful web services helper, pattern oriented programming interfaces and more. Currently Java7 and up is supported. Version 1.0 will required at leaset Java8.
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/*
 * Copyright (c) 2009-2015
 * 	IT-Consulting Stephan Schloepke (http://www.schloepke.de/)
 * 	klemm software consulting Mirko Klemm (http://www.klemm-scs.com/)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.jbasics.math.expression.simple;

import org.jbasics.checker.ContractCheck;
import org.jbasics.math.MathFunction;
import org.jbasics.math.expression.simple.impl.SimpleFunctionCallExpression;
import org.jbasics.math.expression.simple.impl.SimpleSymbolExpression;
import org.jbasics.pattern.builder.Builder;
import org.jbasics.pattern.instance.NamedInstance;
import org.jbasics.pattern.strategy.ContextualExecuteStrategy;
import org.jbasics.pattern.strategy.ContextualResolveStrategy;
import org.jbasics.types.builders.MapBuilder;
import org.jbasics.utilities.DataUtilities;

import java.math.BigDecimal;
import java.math.MathContext;
import java.util.Map;

public class SimpleExpressionContext implements ContextualResolveStrategy,
		ContextualExecuteStrategy {
	private final MathContext mathContext;
	private final Map symbols;
	private final Map> functions;
	private final ContextualResolveStrategy additionalSymbolResolver;
	private final ContextualExecuteStrategy additionalFunctionExecutor;
	private final boolean missingSymbolOrFunctionResolvesToNull;

	private SimpleExpressionContext(final MathContext mathContext, final boolean missingSymbolOrFunctionResolvesToNull,
									final Map symbols, final Map mathFunctions,
									final Map> functions,
									final ContextualResolveStrategy additionalSymbolResolver,
									final ContextualExecuteStrategy additionalFunctionExecutor) {
		this.mathContext = ContractCheck.mustNotBeNull(mathContext, "mathContext");
		this.missingSymbolOrFunctionResolvesToNull = missingSymbolOrFunctionResolvesToNull;
		this.symbols = ContractCheck.mustNotBeNull(symbols, "symbols");
		this.functions = ContractCheck.mustNotBeNull(functions, "functions");
		this.additionalSymbolResolver = additionalSymbolResolver;
		this.additionalFunctionExecutor = additionalFunctionExecutor;
	}

	public static ContextBuilder newBuilder() {
		return new ContextBuilder(null);
	}

	public MathContext getMathContext() {
		return this.mathContext;
	}

	public BigDecimal execute(final SimpleFunctionCallExpression functionCallExpression) {
		return execute(functionCallExpression, this);
	}

	@Override
	public BigDecimal execute(final SimpleFunctionCallExpression functionCallExpression, final SimpleExpressionContext context) {
		final ContextualExecuteStrategy function = this.functions
				.get(functionCallExpression.getFunctionName());
		if (function != null) {
			return function.execute(functionCallExpression, context);
		} else if (this.additionalFunctionExecutor != null) {
			return this.additionalFunctionExecutor.execute(functionCallExpression, context);
		} else if (!isMissingSymbolOrFunctionResolvesToNull()) {
			throw new FunctionNotCalledException("Function could not be executed " + functionCallExpression, functionCallExpression);
		} else {
			return null;
		}
	}

	public boolean isMissingSymbolOrFunctionResolvesToNull() {
		return this.missingSymbolOrFunctionResolvesToNull;
	}

	public BigDecimal resolve(final SimpleSymbolExpression symbolExpression) {
		return resolve(symbolExpression, this);
	}

	@Override
	public BigDecimal resolve(final SimpleSymbolExpression symbolExpression, final SimpleExpressionContext context) {
		BigDecimal result = this.symbols.get(symbolExpression.getSymbol());
		if (result == null && this.additionalSymbolResolver != null) {
			result = this.additionalSymbolResolver.resolve(symbolExpression, context);
		}
		if (result == null && !isMissingSymbolOrFunctionResolvesToNull()) {
			throw new SymbolNotFoundException("Cannot find symbol " + symbolExpression.getSymbol(), symbolExpression);
		}
		return result;
	}

	public static class ContextBuilder implements Builder {
		private final boolean subContextBuilder;
		private final MapBuilder symbolsBuilder = new MapBuilder().immutable();
		private final MapBuilder> functionsBuilder = new MapBuilder>()
				.immutable();
		private final MapBuilder mathFunctionBuilder = new MapBuilder().immutable();
		private MathContext mathContext;
		private boolean missingSymbolOrFunctionResolvesToNull;
		private ContextualResolveStrategy additionalSymbolResolver;
		private ContextualExecuteStrategy additionalFunctionExecutor;

		private ContextBuilder(final SimpleExpressionContext parent) {
			this.subContextBuilder = parent != null;
			if (parent != null) {
				this.mathContext = parent.mathContext;
				this.additionalFunctionExecutor = parent;
				this.additionalSymbolResolver = parent;
			}
		}

		public ContextBuilder withMathContext(final MathContext mc) {
			this.mathContext = mc;
			return this;
		}

		public ContextBuilder withMissingSymbolOrFunctionResolvesToNull() {
			this.missingSymbolOrFunctionResolvesToNull = true;
			return this;
		}

		public ContextBuilder withMissingSymbolOrFunctionThrowsException() {
			this.missingSymbolOrFunctionResolvesToNull = false;
			return this;
		}

		public ContextBuilder withAdditionalSymbolResolver(
				final ContextualResolveStrategy additionalSymbolResolver) {
			if (this.subContextBuilder) {
				throw new IllegalStateException("Sub context builder dosn't allow to set additional symbol resolver");
			}
			this.additionalSymbolResolver = additionalSymbolResolver;
			return this;
		}

		public ContextBuilder withAdditionalFunctionExecutor(
				final ContextualExecuteStrategy additionalFunctionExecutor) {
			if (this.subContextBuilder) {
				throw new IllegalStateException("Sub context builder dosn't allow to set additional function executor");
			}
			this.additionalFunctionExecutor = additionalFunctionExecutor;
			return this;
		}

		public ContextBuilder withSymbol(final String name, final BigDecimal value) {
			this.symbolsBuilder.put(name, value);
			return this;
		}

		public ContextBuilder withMathFunction(final MathFunction... functions) {
			for (final MathFunction function : functions) {
				withMathFunction(function);
			}
			return this;
		}

		public ContextBuilder withMathFunction(final MathFunction function) {
			if (ContractCheck.mustNotBeNull(function, "function") instanceof NamedInstance) {
				return withMathFunction(((NamedInstance) function).name(), function);
			} else {
				return withMathFunction(function.getClass().getSimpleName(), function);
			}
		}

		public ContextBuilder withMathFunction(final String name, final MathFunction function) {
			this.mathFunctionBuilder.put(name, function);
			return this;
		}

		public ContextBuilder withFunction(final String name,
										   final ContextualExecuteStrategy strategy) {
			this.functionsBuilder.put(name, strategy);
			return this;
		}

		@Override
		public void reset() {
			this.symbolsBuilder.reset();
			this.functionsBuilder.reset();
			this.mathFunctionBuilder.reset();
		}

		@Override
		public SimpleExpressionContext build() {
			return new SimpleExpressionContext(DataUtilities.coalesce(this.mathContext, MathContext.DECIMAL64), // The math context should never be null here
					this.missingSymbolOrFunctionResolvesToNull, // Either throw exception or return null for expressions with missing functions or symbols
					this.symbolsBuilder.build(), // The map will be immutable and never null
					this.mathFunctionBuilder.build(), // The map will be immutable and never null
					this.functionsBuilder.build(), // The map will be immutable and never null
					this.additionalSymbolResolver, // additional resolver for symbols on root context (sub context uses parent here)
					this.additionalFunctionExecutor // additional function executor for functions on root context (sub context uses parent here)
			);
		}
	}
}