<?php
/**
 * LineString. A collection of Points representing a line.
 * A line can have more than one segment.
 */
class LineString extends Collection
{
	protected $geom_type = 'LineString';

	/**
	 * Constructor
	 *
	 * @param array $points An array of at least two points with
	 *                      which to build the LineString
	 */
	public function __construct($points = array())
	{
		if (count($points) == 1) {
			throw new Exception("Cannot construct a LineString with a single point");
		}

		// Call the Collection constructor to build the LineString
		parent::__construct($points);
	}

	// The boundary of a linestring is itself
	public function boundary()
	{
		return $this;
	}

	public function startPoint()
	{
		return $this->pointN(1);
	}

	public function endPoint()
	{
		$last_n = $this->numPoints();
		return $this->pointN($last_n);
	}

	public function isClosed()
	{
		return ($this->startPoint()->equals($this->endPoint()));
	}

	public function isRing()
	{
		return ($this->isClosed() && $this->isSimple());
	}

	public function numPoints()
	{
		return $this->numGeometries();
	}

	public function pointN($n)
	{
		return $this->geometryN($n);
	}

	public function dimension()
	{
		if ($this->isEmpty()) return 0;
		return 1;
	}

	public function area()
	{
		return 0;
	}

	public function length()
	{
		if ($this->geos()) {
			return $this->geos()->length();
		}
		$length = 0;
		foreach ($this->getPoints() as $delta => $point) {
			$previous_point = $this->geometryN($delta);
			if ($previous_point) {
				$length += sqrt(pow(($previous_point->getX() - $point->getX()), 2) + pow(($previous_point->getY()- $point->getY()), 2));
			}
		}
		return $length;
	}

	public function greatCircleLength($radius = 6378137)
	{
		$length = 0;
		$points = $this->getPoints();
		for ($i=0; $i<$this->numPoints()-1; $i++) {
			$point = $points[$i];
			$next_point = $points[$i+1];
			if (!is_object($next_point)) {continue;}
			// Great circle method
			$lat1 = deg2rad($point->getY());
			$lat2 = deg2rad($next_point->getY());
			$lon1 = deg2rad($point->getX());
			$lon2 = deg2rad($next_point->getX());
			$dlon = $lon2 - $lon1;
			$length +=
			$radius *
			atan2(
			sqrt(
			  pow(cos($lat2) * sin($dlon), 2) +
				pow(cos($lat1) * sin($lat2) - sin($lat1) * cos($lat2) * cos($dlon), 2)
			  ),
			sin($lat1) * sin($lat2) +
			  cos($lat1) * cos($lat2) * cos($dlon)
			  );
		}
		// Returns length in meters.
		return $length;
	}

	public function haversineLength()
	{
		$degrees = 0;
		$points = $this->getPoints();
		for ($i=0; $i<$this->numPoints()-1; $i++) {
			$point = $points[$i];
			$next_point = $points[$i+1];
			if (!is_object($next_point)) {continue;}
			$degree = rad2deg(
			acos(
			  sin(deg2rad($point->getY())) * sin(deg2rad($next_point->getY())) +
			cos(deg2rad($point->getY())) * cos(deg2rad($next_point->getY())) *
			  cos(deg2rad(abs($point->getX() - $next_point->getX())))
			)
			);
			$degrees += $degree;
		}
		// Returns degrees
		return $degrees;
	}

	public function explode()
	{
		$parts = array();
		$points = $this->getPoints();

		foreach ($points as $i => $point) {
			if (isset($points[$i+1])) {
				$parts[] = new LineString(array($point, $points[$i+1]));
			}
		}
		return $parts;
	}

	public function isSimple()
	{
		if ($this->geos()) {
			return $this->geos()->isSimple();
		}

		$segments = $this->explode();

		foreach ($segments as $i => $segment) {
			foreach ($segments as $j => $check_segment) {
				if ($i != $j) {
					if ($segment->lineSegmentIntersect($check_segment)) {
						return false;
					}
				}
			}
		}
		return true;
	}

	// Utility function to check if any line sigments intersect
	// Derived from http://stackoverflow.com/questions/563198/how-do-you-detect-where-two-line-segments-intersect
	public function lineSegmentIntersect($segment)
	{
		$p0_x = $this->startPoint()->x();
		$p0_y = $this->startPoint()->y();
		$p1_x = $this->endPoint()->x();
		$p1_y = $this->endPoint()->y();
		$p2_x = $segment->startPoint()->x();
		$p2_y = $segment->startPoint()->y();
		$p3_x = $segment->endPoint()->x();
		$p3_y = $segment->endPoint()->y();

		$s1_x = $p1_x - $p0_x;     $s1_y = $p1_y - $p0_y;
		$s2_x = $p3_x - $p2_x;     $s2_y = $p3_y - $p2_y;

		$fps = (-$s2_x * $s1_y) + ($s1_x * $s2_y);
		$fpt = (-$s2_x * $s1_y) + ($s1_x * $s2_y);

		if ($fps == 0 || $fpt == 0) {
			return false;
		}

		$s = (-$s1_y * ($p0_x - $p2_x) + $s1_x * ($p0_y - $p2_y)) / $fps;
		$t = ( $s2_x * ($p0_y - $p2_y) - $s2_y * ($p0_x - $p2_x)) / $fpt;

		if ($s > 0 && $s < 1 && $t > 0 && $t < 1) {
			// Collision detected
			return true;
		}
		return false;
	}
}