var util = require("util"),
	stream = require("stream"),
	constants = require("./constants");

// TODO: clear up specs on returning false from a write and emitting a drain event.
// Does this mean if I return false from a write, I should ignore any write requests between that false return and the drain event?
var WritableStreamBuffer = module.exports = function(opts) {
	var that = this;

	stream.Stream.call(this);

	opts = opts || {};
	var initialSize = opts.initialSize || constants.DEFAULT_INITIAL_SIZE;
	var incrementAmount = opts.incrementAmount || constants.DEFAULT_INCREMENT_AMOUNT;

	var buffer = new Buffer(initialSize);
	var size = 0;

	this.writable = true;
	this.readable = false;

	this.size = function() {
		return size;
	};

	this.maxSize = function() {
		return buffer.length;
	};

	this.getContents = function(length) {
		if(!size) return false;

		var data = new Buffer(Math.min(length || size, size));
		buffer.copy(data, 0, 0, data.length);

		if(data.length < size)
			buffer.copy(buffer, 0, data.length);

		size -= data.length;

		return data;
	};

	this.getContentsAsString = function(encoding, length) {
		if(!size) return false;

		var data = buffer.toString(encoding || "utf8", 0, Math.min(length || size, size));
		var dataLength = Buffer.byteLength(data);

		if(dataLength < size)
			buffer.copy(buffer, 0, dataLength);

		size -= dataLength;
		return data;
	};

	var increaseBufferIfNecessary = function(incomingDataSize) {
		if((buffer.length - size) < incomingDataSize) {
			var factor = Math.ceil((incomingDataSize - (buffer.length - size)) / incrementAmount);

			var newBuffer = new Buffer(buffer.length + (incrementAmount * factor));
			buffer.copy(newBuffer, 0, 0, size);
			buffer = newBuffer;
		}
	};

	this.write = function(data, encoding) {
		if(!that.writable) return;

		if(Buffer.isBuffer(data)) {
			increaseBufferIfNecessary(data.length);
			data.copy(buffer, size, 0);
			size += data.length;
		}
		else {
			data = data + "";
			increaseBufferIfNecessary(data.length);
			buffer.write(data, size, encoding || "utf8");
			size += Buffer.byteLength(data);
		}
	};

	this.end = function() {
		var args = Array.prototype.slice.apply(arguments);
		if(args.length) that.write.apply(that, args);
		that.destroy();
	};

	this.destroySoon = this.destroy = function() {
		that.writable = false;
		that.emit("close");
	};
};
util.inherits(WritableStreamBuffer, stream.Stream);