Group expenses

expenses.js

// * Create expense categories here.

var cats = {
    ALL: "All",
    JC_AND_JS_FUEL: "Jed & Clare's fuel",
    SK_AND_L_FUEL: "Seb's fuel",
    COTTAGE_BREAKFAST: "Cottage breakfast",
    COTTAGE_FOOD: "Cottage food supplies"
}

// * Amount tolerance. Any amounts owing below this threshold are ignored.

var amountTolerance = 5;

// Arrays for holding data structures

var expenses = [];
var members = [];
var paymentPairs = [];

// PaymentPair class

var PaymentPair = function() {
    this.creditor = null;
    this.debtor = null;
    this.amount = 0;
}

// Member class

var Member = function (name) {
    this.name = name;
    this.exemptions = [];
    this.expenditure = 0;
    this.liability = 0;
    this.owes = 0;
}

Member.prototype.addExemption = function (cat) {
    this.exemptions.push({cat:cat});
    console.log(this.name,"is exempt from",cat);
}

Member.prototype.addExpenditure = function (value) {
    this.expenditure += value;
}

Member.prototype.addLiability = function (value) {
    this.liability += value;
    this.owes = this.liability-this.expenditure;
}

Member.prototype.isExempt = function (cat) {
    var isExempt = false;
    this.exemptions.forEach(function (exemption) {
        if ( exemption.cat === cat ) {
            isExempt = true;
        }
    });
    return isExempt;
}

Member.prototype.toString = function () {
    return this.name;
}

// Expense class

var Expense = function (description,cat,amount) {
    this.description = description;
    this.cat = cat;
    this.amount = amount;
    this.owner = null;
    this.participants = [];
    this.costPerParticipant = 0;
}

Expense.prototype.setOwner = function (owner) {
    this.owner = owner;
}

Expense.prototype.addParticipant = function (participant) {
    this.participants.push(participant);
    this.costPerParticipant = this.amount/this.participants.length;
}

// Util functions

function addMember(name) {
    console.log(name);
    var member  = new Member(name);
    members.push(member);
    return member;
}

function addExpense (description,cat,amount) {
    console.log(description,"£"+amount);
    var expense = new Expense(description,cat,amount);
    expenses.push(expense);
    return expense;
}

function addPaymentPair (creditor,debtor,amount) {
    var pair = new PaymentPair();
    pair.creditor = creditor;
    pair.debtor = debtor;
    pair.amount = amount;
    paymentPairs.push(pair);
}

function getBiggestCreditor () {
    var biggestCreditor;
    members.forEach(function (member) {
        if ( !biggestCreditor ) {
            biggestCreditor = member;
        }
        if ( biggestCreditor.owes > member.owes ) {
            biggestCreditor = member;
        }
    });

    if ( biggestCreditor.owes+amountTolerance > 0 ) {
        return null;
    } else {
        return biggestCreditor;
    }
}

function getBiggestDebtor () {
    var biggestDebtor;
    members.forEach(function (member) {
        if ( !biggestDebtor ) {
            biggestDebtor = member;
        }
        if ( biggestDebtor.owes < member.owes ) {
            biggestDebtor = member;
        }
    });
    // if ( biggestDebtor.owes-amountTolerance < 0 ) {
    //     return null;
    // } else {
    //     return biggestDebtor;
    // }
    return biggestDebtor.owes === 0 ? null : biggestDebtor;
}

// * Create members

console.log("\nCreating members");
console.log("----------------");

var seb = addMember("Seb");
var jedClare = addMember("Jed & Clare");
var luke = addMember("Luke");
var jeromeSarah = addMember("Jerome & Sarah");


// * Set exemptions. Members can be excluded from expenses by category.

console.log("\nSetting exemptions");
console.log("------------------");

jedClare.addExemption(cats.SK_AND_L_FUEL);
jeromeSarah.addExemption(cats.SK_AND_L_FUEL);

seb.addExemption(cats.JC_AND_JS_FUEL);
luke.addExemption(cats.JC_AND_JS_FUEL);

jeromeSarah.addExemption(cats.COTTAGE_BREAKFAST);
seb.addExemption(cats.COTTAGE_FOOD);

// * Create expenses. Expenses have a name, category, amount and owner.
// Members are assumed to be equally liable for all expeses unless they are
// specifically excluded from an expenses category.

console.log("\nCreating expenses");
console.log("-----------------");

var expense;

expense = addExpense("Cottage Breakfast Meat",cats.COTTAGE_BREAKFAST,20);
expense.setOwner(jedClare);
expense = addExpense("Petrol",cats.JC_AND_JS_FUEL,40);
expense.setOwner(jedClare);

expense = addExpense("Cottage Breakfast Extras",cats.COTTAGE_BREAKFAST,6);
expense.setOwner(luke);
expense = addExpense("Whisky",cats.ALL,20);
expense.setOwner(luke);

expense = addExpense("Petrol",cats.SK_AND_L_FUEL,50);
expense.setOwner(seb);
expense = addExpense("Cottage food supplies",cats.COTTAGE_FOOD,38);
expense.setOwner(seb);

// * Nothing more to edit blow.

// Calculate expense owner expenditures

expenses.forEach(function (expense) {
    expense.owner.addExpenditure(expense.amount);
});

// Add participants to expenses

console.log("\nExpense detail");
console.log("--------------");

expenses.forEach(function (expense) {
    console.log(expense.description);
    console.log("  Owner",expense.owner.name);
    console.log("  Category",expense.cat);
    console.log("  Amount","£"+expense.amount);
    members.forEach(function (member) {
        if ( !member.isExempt(expense.cat) ) {
            expense.addParticipant(member);
        }
    });
    console.log("  Participants",expense.participants.length,"("+expense.participants.join(",")+")");
    console.log("  Cost per participant","£"+expense.costPerParticipant.toFixed(2));
});

// Calculate member liabilities

console.log("\nMember detail");
console.log("-------------");

expenses.forEach(function (expense) {
    expense.participants.forEach(function (participant) {
        participant.addLiability(expense.costPerParticipant);
    });
});

// Output member detail

var totalExpenditure = 0;
var totalLiability = 0;

members.forEach(function (member) {
    console.log(member.name);
    console.log("  Expenditure","£"+member.expenditure);
    console.log("  Liability","£"+member.liability.toFixed(2));
    totalExpenditure += member.expenditure;
    totalLiability += member.liability;
    console.log("  Owes","£"+member.owes.toFixed(2));

});

// Sanity check stats

console.log("\nStats");
console.log("-----");
console.log("Num expenses",expenses.length);
console.log("Avg expense value","£"+(totalExpenditure/expenses.length).toFixed(2));
console.log("Total spent","£"+totalExpenditure);
//console.log("Total liability","£"+totalLiability.toFixed(2));

// Calculate payments for resolution

var biggestCreditor = getBiggestCreditor();

while ( biggestCreditor !== null ) {
    var biggestDebtor = getBiggestDebtor();
    if ( biggestDebtor === null ) {
        break;
    }
    if ( biggestDebtor.owes > Math.abs(biggestCreditor.owes) ) {
        addPaymentPair(biggestCreditor,biggestDebtor,Math.abs(biggestCreditor.owes));
        biggestDebtor.owes += biggestCreditor.owes;
        biggestCreditor.owes = 0;
    } else {
        addPaymentPair(biggestCreditor,biggestDebtor,biggestDebtor.owes);
        biggestCreditor.owes += biggestDebtor.owes;
        biggestDebtor.owes = 0;
    }
    biggestCreditor = getBiggestCreditor();
}

// Sort payments by creditor name

paymentPairs.sort(function (a,b) {
    var nameA = a.creditor.name.toLowerCase();
    var nameB = b.creditor.name.toLowerCase();
    if ( nameA < nameB ) {
        return -1;
    } else if ( nameA > nameB ) {
        return 1;
    } else {
        return 0;
    }
});

// Output payment instructions

console.log("\nPayments");
console.log("--------");

paymentPairs.forEach(function (pair) {
    console.log(pair.debtor.name,"pays",pair.creditor.name,"£"+Math.round(pair.amount));
});

console.log("\nRemainders");
console.log("----------");
members.forEach(function (member) {
    console.log(member.name,"£"+member.owes);
});