/*
 * (c) 1998-2000 The Brookings Institution, All Rights Reserved
 *
 * Permission to use this software and its documentation for non-commercial
 * purposes and without fee is hereby granted, provided this copyright statement
 * is included. Please contact us for permission for redistribution and other uses.
 * 
 * BROOKINGS MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
 * THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
 * TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, 
 * OR NON-INFRINGEMENT. BROOKINGS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY
 * LICENSEE AS A RESULT OF USING THIS SOFTWARE OR ITS DERIVATIVES.
 *
 * _Sugarscape_
 * See _Growing Artificial Societies: Social Science from the Ground Up_
 * Brookings Institution Press, The MIT Press
 * Joshua Epstein
 * jepstein@brook.edu
 * Robert Axtell
 * raxtell@brook.edu
 *
 * Miles Parker
 * mparker@brook.edu

 * http://www.brook.edu/es/dynamics/models/ascape
 * The Brookings Institution
 * Washington, D.C.
 *
 * Alan Lockard
 * alockard@gmu.edu
 */

package edu.brook.sugarscape;

import java.lang.*;

import edu.brook.ascape.model.*;
import edu.brook.ascape.rule.*;
import edu.brook.ascape.util.*;

/**
 * An object to manage the data associated with a potential 
 * or actual exchange.
 *
 * @author Alan Lockard
 * @version 1.0
 **/
public class Exchange {
	
/** 
 * The agent who is trading
 */
    public SpiceAgent self;
/**
 * The agent with whom our self agent is trading
 */
    public SpiceAgent partner; 
/**
 * Price of spice - units of spice / units of sugar
 */
    public float price; 
/**
 * natural log of the price
 */
    public float logPrice;
/**
 * amount of sugar that would change hands
 */
    public float sugarQuantity;
/**
 * amount of spice that would change hands
 */
    public float spiceQuantity;
/**
 * Marginal Rate of Substitution of agent, prior to trading
 */
    public float selfExAnteMRS;
/**
 * Marginal Rate of Substitution of agent's trading partner, 
 * prior to trading
 */
    public float partnerExAnteMRS;
/**
 * anticipated Marginal Rate of Substitution of agent, after trading
 */
    public float selfExPostMRS;
/**
 * anticipated Marginal Rate of Substitution of agent's trading partner, 
 * after trading
 */
    public float partnerExPostMRS;
/**
 * increase in agent's utility resulting from this trade
 */ 
    public float selfGainsFromTrade; 
/**
 * increase in agent's trading partner's utility resulting from this trade
 */ 
    public float partnerGainsFromTrade; 
/**
 * true if agent is giving spice to get sugar
 * false if agent is giving sugar to get spice
 */
    public boolean buyingSugar;
/**
 * How much sugar agent will have if this trade goes through
 */
    public float selfExPostSugar; 
/**
 * How much spice agent will have if this trade goes through
 */
    public float selfExPostSpice; 
/**
 * How much sugar agent's trading partner will have 
 * if this trade goes through
 */
    public float partnerExPostSugar; 
/**
 * How much spice agent's trading partner will have
 * if this trade goes through
 */
    public float partnerExPostSpice; 
/**
 * Flag indicating illegal trades, such as paying more than you have
 */
//    public boolean tradeIsValid; 
    
/**
 * Constructor for this (Exchange) class
 */
    public Exchange (SpiceAgent self, SpiceAgent partner) {
        this.self = self;
        this.partner = partner;
        selfExAnteMRS = self.calculateMRS();
	partnerExAnteMRS = partner.calculateMRS();
	price = self.makeOffer(partner);
	logPrice = (float) Math.log(price);
	if (price > 1) {
	    sugarQuantity = 1.0f;
            spiceQuantity = price;
        }
        else {
	    sugarQuantity = price;
            spiceQuantity = 1.0f;
        }
        buyingSugar = isBuyingSugar();
        if (isBuyingSugar()) {
            selfExPostSugar = self.getSugarStock() + sugarQuantity;
            selfExPostSpice = self.getSpiceStock() - spiceQuantity;
            partnerExPostSugar = partner.getSugarStock() - sugarQuantity;
            partnerExPostSpice = partner.getSpiceStock() + spiceQuantity;
        }
        else {
            selfExPostSugar = self.getSugarStock() - sugarQuantity;
            selfExPostSpice = self.getSpiceStock() + spiceQuantity;
            partnerExPostSugar = partner.getSugarStock() + sugarQuantity;
            partnerExPostSpice = partner.getSpiceStock() - spiceQuantity;
        }
        selfGainsFromTrade = self.calculateUtility(selfExPostSugar, selfExPostSpice)
		                 - self.calculateUtility();
        partnerGainsFromTrade = partner.calculateUtility(partnerExPostSugar, partnerExPostSpice)
				    - partner.calculateUtility();
	selfExPostMRS = self.calculateMRS (selfExPostSugar, selfExPostSpice);
	partnerExPostMRS = partner.calculateMRS (partnerExPostSugar, partnerExPostSpice);
    }

    public Exchange (SpiceAgent self, SpiceAgent partner, float setPrice) {
        this.self = self;
        this.partner = partner;
        selfExAnteMRS = self.calculateMRS();
	partnerExAnteMRS = partner.calculateMRS();
	price = setPrice;
	logPrice = (float) Math.log(price);
	if (price > 1) {
	    sugarQuantity = 1.0f;
            spiceQuantity = price;
        }
        else {
	    sugarQuantity = price;
            spiceQuantity = 1.0f;
        }
        buyingSugar = isBuyingSugar();
        if (isBuyingSugar()) {
            selfExPostSugar = self.getSugarStock() + sugarQuantity;
            selfExPostSpice = self.getSpiceStock() - spiceQuantity;
            partnerExPostSugar = partner.getSugarStock() - sugarQuantity;
            partnerExPostSpice = partner.getSpiceStock() + spiceQuantity;
        }
        else {
            selfExPostSugar = self.getSugarStock() - sugarQuantity;
            selfExPostSpice = self.getSpiceStock() + spiceQuantity;
            partnerExPostSugar = partner.getSugarStock() + sugarQuantity;
            partnerExPostSpice = partner.getSpiceStock() - spiceQuantity;
        }
        selfGainsFromTrade = self.calculateUtility(selfExPostSugar, selfExPostSpice)
		                 - self.calculateUtility();
        partnerGainsFromTrade = partner.calculateUtility(partnerExPostSugar, partnerExPostSpice)
				    - partner.calculateUtility();
	selfExPostMRS = self.calculateMRS (selfExPostSugar, selfExPostSpice);
	partnerExPostMRS = partner.calculateMRS (partnerExPostSugar, partnerExPostSpice);
    }

    public boolean isBuyingSugar() {
//System.out.println(selfExAnteMRS + " > " + partnerExAnteMRS + " = " + (selfExAnteMRS > partnerExAnteMRS));
	return (selfExAnteMRS > partnerExAnteMRS);
    }

    public boolean tradeIsValid() {
//	return (selfExPostSugar > 0) & (selfExPostSpice > 0) & 
//                 (partnerExPostSugar > 0) & (partnerExPostSpice > 0);
//System.out.println("selfGains = " + selfGainsFromTrade + ", partnerGains = " + partnerGainsFromTrade + ", this step = " + ((selfGainsFromTrade >= 0) & (partnerGainsFromTrade >= 0)));
//System.out.println("  sugarQuantity = " + sugarQuantity + ", spiceQuantity = " + spiceQuantity + ", this step = " + ((sugarQuantity > 0) & (spiceQuantity > 0)));
	if (!((selfGainsFromTrade >= 0) & (partnerGainsFromTrade >= 0))) {
	    return false;
	}
	else if (!((sugarQuantity > 0) & (spiceQuantity > 0))) {
	    return false;
	}
	else {
	    return true;
	}
    }
}