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package com.enterprisemath.math.lp;

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

import org.apache.commons.lang3.builder.EqualsBuilder;
import org.apache.commons.lang3.builder.HashCodeBuilder;
import org.apache.commons.lang3.builder.ToStringBuilder;

import com.enterprisemath.math.algebra.Vector;
import com.enterprisemath.utils.DomainUtils;
import com.enterprisemath.utils.ValidationUtils;

/**
 * Defines result of the LP (linear programming) problem.
 * Result can be one of the following types:
 * 
 * There is no solution at all
 * There is one optimal solution
 * There are multiple optimal solutions
 * There is no optimal solution as objective function is unbounded and can grow to infinity
 * 
 *
 * @author radek.hecl
 *
 */
public class StandardLPProblemResult {

    /**
     * Builder object.
     */
    public static class Builder {

        /**
         * Value of the objective function.
         */
        private Double value;

        /**
         * Optimal solutions
         */
        private Set solutions = new HashSet();

        /**
         * Sets value of the objective function.
         *
         * @param value objective function value
         * @return this instance
         */
        public Builder setValue(Double value) {
            this.value = value;
            return this;
        }

        /**
         * Sets the optimal solutions.
         *
         * @param solutions optimal solutions
         * @return this instance
         */
        public Builder setSolutions(Set solutions) {
            this.solutions = DomainUtils.softCopySet(solutions);
            return this;
        }

        /**
         * Adds optimal solution into the set.
         *
         * @param solution optimal solution
         * @return this instance
         */
        public Builder addSolution(Vector solution) {
            solutions.add(solution);
            return this;
        }

        /**
         * Builds the result object.
         *
         * @return created object
         */
        public StandardLPProblemResult build() {
            return new StandardLPProblemResult(this);
        }
    }

    /**
     * Value of the objective function.
     */
    private Double value;

    /**
     * Optimal solutions
     */
    private Set solutions = new HashSet();

    /**
     * Creates new instance.
     *
     * @param builder builder object
     */
    public StandardLPProblemResult(Builder builder) {
        value = builder.value;
        solutions = Collections.unmodifiableSet(DomainUtils.softCopySet(builder.solutions));
        guardInvariants();
    }

    /**
     * Guards this object to be consistent. Throws exception if this is not the case.
     */
    private void guardInvariants() {
        ValidationUtils.guardNotNullCollection(solutions, "solutions cannot have null element");
    }

    /**
     * Returns value of the objective function.
     *
     * @return value of the objective function
     */
    public Double getValue() {
        return value;
    }

    /**
     * Returns set of optimal solutions.
     *
     * @return optimal solutions
     */
    public Set getSolutions() {
        return solutions;
    }

    @Override
    public int hashCode() {
        return HashCodeBuilder.reflectionHashCode(this);
    }

    @Override
    public boolean equals(Object obj) {
        return EqualsBuilder.reflectionEquals(this, obj);
    }

    @Override
    public String toString() {
        return ToStringBuilder.reflectionToString(this);
    }

    /**
     * Creates the result.
     *
     * @param value value of objective function
     * @param solutions solutions
     * @return created instance
     */
    public static StandardLPProblemResult create(Double value, Vector... solutions) {
        return new StandardLPProblemResult.Builder().
                setValue(value).
                setSolutions(DomainUtils.createSet(solutions)).
                build();
    }

}