/**
 * @class Lighting computation, based on a traditional FOV for multiple light sources and multiple passes.
 * @param {function} reflectivityCallback Callback to retrieve cell reflectivity (0..1)
 * @param {object} [options]
 * @param {int} [options.passes=1] Number of passes. 1 equals to simple FOV of all light sources, >1 means a *highly simplified* radiosity-like algorithm.
 * @param {int} [options.emissionThreshold=100] Cells with emissivity > threshold will be treated as light source in the next pass.
 * @param {int} [options.range=10] Max light range
 */
ROT.Lighting = function(reflectivityCallback, options) {
	this._reflectivityCallback = reflectivityCallback;
	this._options = {
		passes: 1,
		emissionThreshold: 100,
		range: 10
	};
	this._fov = null;

	this._lights = {};
	this._reflectivityCache = {};
	this._fovCache = {};

	this.setOptions(options);
}

/**
 * Adjust options at runtime
 * @see ROT.Lighting
 * @param {object} [options]
 */
ROT.Lighting.prototype.setOptions = function(options) {
	for (var p in options) { this._options[p] = options[p]; }
	if (options.range) { this.reset(); }
	return this;
}

/**
 * Set the used Field-Of-View algo
 * @param {ROT.FOV} fov
 */
ROT.Lighting.prototype.setFOV = function(fov) {
	this._fov = fov;
	this._fovCache = {};
	return this;
}

/**
 * Set (or remove) a light source
 * @param {int} x
 * @param {int} y
 * @param {null || string || number[3]} color
 */
ROT.Lighting.prototype.setLight = function(x, y, color) {
	var key = x+","+y;

	if (color) {
		this._lights[key] = (typeof(color) == "string" ? ROT.Color.fromString(color) : color);
	} else {
		delete this._lights[key];
	}
	return this;
}

/**
 * Reset the pre-computed topology values. Call whenever the underlying map changes its light-passability.
 */
ROT.Lighting.prototype.reset = function() {
	this._reflectivityCache = {};
	this._fovCache = {};

	return this;
}

/**
 * Compute the lighting
 * @param {function} lightingCallback Will be called with (x, y, color) for every lit cell
 */
ROT.Lighting.prototype.compute = function(lightingCallback) {
	var doneCells = {};
	var emittingCells = {};
	var litCells = {};

	for (var key in this._lights) { /* prepare emitters for first pass */
		var light = this._lights[key];
		if (!(key in emittingCells)) { emittingCells[key] = [0, 0, 0]; }

		ROT.Color.add_(emittingCells[key], light);
	}

	for (var i=0;i<this._options.passes;i++) { /* main loop */
		this._emitLight(emittingCells, litCells, doneCells);
		if (i+1 == this._options.passes) { continue; } /* not for the last pass */
		emittingCells = this._computeEmitters(litCells, doneCells);
	}

	for (var litKey in litCells) { /* let the user know what and how is lit */
		var parts = litKey.split(",");
		var x = parseInt(parts[0]);
		var y = parseInt(parts[1]);
		lightingCallback(x, y, litCells[litKey]);
	}

	return this;
}

/**
 * Compute one iteration from all emitting cells
 * @param {object} emittingCells These emit light
 * @param {object} litCells Add projected light to these
 * @param {object} doneCells These already emitted, forbid them from further calculations
 */
ROT.Lighting.prototype._emitLight = function(emittingCells, litCells, doneCells) {
	for (var key in emittingCells) {
		var parts = key.split(",");
		var x = parseInt(parts[0]);
		var y = parseInt(parts[1]);
		this._emitLightFromCell(x, y, emittingCells[key], litCells);
		doneCells[key] = 1;
	}
	return this;
}

/**
 * Prepare a list of emitters for next pass
 * @param {object} litCells
 * @param {object} doneCells
 * @returns {object}
 */
ROT.Lighting.prototype._computeEmitters = function(litCells, doneCells) {
	var result = {};

	for (var key in litCells) {
		if (key in doneCells) { continue; } /* already emitted */

		var color = litCells[key];

		if (key in this._reflectivityCache) {
			var reflectivity = this._reflectivityCache[key];
		} else {
			var parts = key.split(",");
			var x = parseInt(parts[0]);
			var y = parseInt(parts[1]);
			var reflectivity = this._reflectivityCallback(x, y);
			this._reflectivityCache[key] = reflectivity;
		}

		if (reflectivity == 0) { continue; } /* will not reflect at all */

		/* compute emission color */
		var emission = [];
		var intensity = 0;
		for (var i=0;i<3;i++) {
			var part = Math.round(color[i]*reflectivity);
			emission[i] = part;
			intensity += part;
		}
		if (intensity > this._options.emissionThreshold) { result[key] = emission; }
	}

	return result;
}

/**
 * Compute one iteration from one cell
 * @param {int} x
 * @param {int} y
 * @param {number[]} color
 * @param {object} litCells Cell data to by updated
 */
ROT.Lighting.prototype._emitLightFromCell = function(x, y, color, litCells) {
	var key = x+","+y;
	if (key in this._fovCache) {
		var fov = this._fovCache[key];
	} else {
		var fov = this._updateFOV(x, y);
	}

	for (var fovKey in fov) {
		var formFactor = fov[fovKey];

		if (fovKey in litCells) { /* already lit */
			var result = litCells[fovKey];
		} else { /* newly lit */
			var result = [0, 0, 0];
			litCells[fovKey] = result;
		}

		for (var i=0;i<3;i++) { result[i] += Math.round(color[i]*formFactor); } /* add light color */
	}

	return this;
}

/**
 * Compute FOV ("form factor") for a potential light source at [x,y]
 * @param {int} x
 * @param {int} y
 * @returns {object}
 */
ROT.Lighting.prototype._updateFOV = function(x, y) {
	var key1 = x+","+y;
	var cache = {};
	this._fovCache[key1] = cache;
	var range = this._options.range;
	var cb = function(x, y, r, vis) {
		var key2 = x+","+y;
		var formFactor = vis * (1-r/range);
		if (formFactor == 0) { return; }
		cache[key2] = formFactor;
	}
	this._fov.compute(x, y, range, cb.bind(this));

	return cache;
}