2014 Bitcoin taxes cost basis and income calculations. Uses Libra Tax files as input

tax.js

var argv = require('minimist')(process.argv.slice(2));
var fs = require('fs');
var csvParse = require('csv-parse');
var csvStringify = require('csv-stringify');
var moment = require('moment');

if (argv._.length === 0) {
	console.log('Usage: node tax --year 2014 Libra.csv output.csv');
	process.exit();
}

// first full arg
var input = argv._[0];
// second full arg
var output = argv._[1] || 'output.txt';

var year = argv.year || argv.y;

var error;

error = !input && new Error('No input file specified');

if (error) {
	throw error;
}

// Shared global data model
var data = {
	transactions: [],
	buys: [],
	sells: [],
	generated: [],
	taxables: [],
	delta: 0
}

/**
 * Simple FIFO algorithm matching received coins with spent coins
 */
var firstBuy = (function () {
	// The current index of owned coins
	var index = 0;
	
	return function (sell) {
		var needToSell = -sell.amount;
		var costBasis = 0;
		
		while (needToSell > 0) {
			var buy = data.buys[index];
			if (buy) {
				var buyAmountAvailable = buy.sold ? buy.amount - buy.sold : buy.amount;
				var selling = needToSell > buyAmountAvailable ? buyAmountAvailable : needToSell;
				var buyCostBasis = Math.abs(selling / buyAmountAvailable * buy.totalValue);
				
				buy.sold += selling;
				costBasis += buyCostBasis; 
				needToSell -= selling;
				index++;
			} else {
				console.log('warning, not enough purchases to cover sales!');
				break;
			}

		}
		
		// Taxable event object
		sell.costBasis = costBasis;
		var t = {
			date: moment(sell.date).format('MM-DD-YYYY'),
			amount: sell.amount.toFixed(8),
			proceeds: Math.abs(sell.totalValue).toFixed(2),
			costBasis: sell.costBasis.toFixed(2)
		};
		
		t.delta = (Math.abs(sell.totalValue) - sell.costBasis);
		data.taxables.push(t);
	};
}());

/**
 * Helps caluclate total USD profit/loss from sales
 */
var profitLoss = function (taxable) {
	data.delta += taxable.delta;
};

/**
 * Write taxable events to output CSV
 */
var writeTaxables = function () {
	
	var taxables = [['Description', 'Date', 'Amount', 'Purchase price', 'Proceeds', 'Cost Basis']].concat(data.taxables.map(function (tax) {
		return ['Bitcoin sales', tax.date, tax.amount, 'VARIOUS', tax.proceeds, tax.costBasis];
	}));
	csvStringify(taxables, function (err, data) {
		fs.writeFile(output, data, function (err) {
			if (err) throw err;
			console.log('done');
		});
	});
}

/**
 * Caluclated all mined blocks
 */
var calculateGeneratedIncome = function () {
	var income = {
		btc: 0,
		usd: 0
	};
	
	data.generated.forEach(function (g) {
		income.btc += g.amount;
		income.usd += g.totalValue;
	});
	
	return income;
}

/**
 * Read input CSV and display results
 */
fs.readFile(input, 'utf8', function (err, file) {	
  if (err) throw err;
  importCsv(file, function (data) {
	    data.sells.forEach(firstBuy);
		data.taxables.forEach(profitLoss);
		writeTaxables();
		console.log('Mining income: ', calculateGeneratedIncome());
		console.log('Transaction income (USD): $' + data.delta.toFixed(2));
		//console.log(data.taxables);
  });
});

/**
 * Turns CSV headers into Javascript friendly object field names.  No spaces and camel casing
 */
function objectify(string) {
    return string.split(' ').reduce(function (prev, curr, index) {
		return prev += curr.charAt(0)[index ? 'toUpperCase' : 'toLowerCase']() + curr.slice(1);
	}, '');
}

/**
 * CSV parser to data model
 */
var importCsv = function (file, callback) {
	var fields;
	
	csvParse(file, function (err, output) {
		if (err) throw err;
		
		output.forEach(function (row, index) {
			if (index === 0) {
				// Creates object field names from headers and saves for later
				fields = row.map(objectify);
			} else if (row.length > 1) {
				
				// Unpacks the row into object t using objectify names, above
				var t = row.reduce(function (prev, curr, index) {
					prev[fields[index]] = curr;
					return prev;
				}, {});
				
				// Some post processing
				t.date = new Date(t.date);
				t.amount = parseFloat(t.amount);
				t.spotValue = parseFloat(t.spotValue);
				t.totalValue = parseFloat(t.totalValue);
				
				// Filtering by year or all if unspecified
				if (year ? t.date.getFullYear() === year : true) {
					data.transactions.push(t);
					if (t.taxType === 'sale') {
						data.sells.push(t);
					}
					
					if (t.taxType === 'purchase') {
						t.sold = 0;
						data.buys.push(t);
					}
					
					// These are what p2pool generated (mined) coins tracked by BlockChain look like in Libra Tax CSV
					if (t.destination === 'Blockchain Wallet') {
						data.generated.push(t);
						t.generated = true;
					}
				}
			
			}
		});
		// All done callback
		callback(data);
	});
}