<?php

class SVGChartBuilder {
  private $options = [
    'width' => 800,
    'height' => 250,
    'lineColor' => '#000',
    'labelColor' => '#000',
    'smoothed' => false,
    'fontSize' => 15
  ];

  private $width;
  private $height;
  private $output;
  private $xMin;
  private $xMax;
  private $xRange;
  private $yMin;
  private $yMax;
  private $yRange;
  private $padding = ['top'=>10, 'right'=>10, 'bottom'=>10, 'left'=>10];

  private function arrayGet($array, $key, $default = NULL)
  {
      return isset($array[$key]) ? $array[$key] : $default;
  }

  private function labelFormat($float, $places, $minPlaces = 0) {
    $value = number_format($float, max($minPlaces, $places));
    // add a trailing space if there's no decimal
    return (strpos($value, '.') === false ? $value . '.' : $value);
  }

  /* Transform data coords to chart coords */
  /* Transform data coords to chart coords */
  private function transformX($x) {
    return round(
      ($x - $this->xMin) / $this->xRange * $this->width
    , 2);
  }
  private function transformY($y) {
    return round(
    // SVG has y axis reversed, 0 is at the top
      ($this->yMax - $y) / $this->yRange * $this->height
    , 2);
  }

  private function getPrecision($value) { // thanks http://stackoverflow.com/a/21788335/5402566
    if (!is_numeric($value)) { return false; }
    $decimal = $value - floor($value); //get the decimal portion of the number
    if ($decimal == 0) { return 0; } //if it's a whole number
    $precision = strlen(trim(number_format($decimal,10),'0')) - 1; //-2 to account for '0.'
    return $precision;
  }

  public function __construct($chartData, $options) {
    $this->setOptions($options);
    $this->setData($chartData);
  }

  public function setOptions($options) {
    $this->options = array_replace($this->options, $options);
    $this->padding['left'] = $this->options['fontSize'] * 5;
    $this->padding['top'] = $this->padding['bottom'] = $this->options['fontSize'];
  }

  public function setData($chartData) {
    // we assume $chartData is sorted by key and keys and values are all numeric
    $previousX = $previousY = null;
    end($chartData);
    $this->xMax = key($chartData);
    reset($chartData);
    $this->xMin = key($chartData);
    $this->xRange = $this->xMax - $this->xMin;
    $count = count($chartData);
    $deltaX = $this->xRange / $count;
    $this->yMin = INF; // so the first comparison sets this to an actual value
    $this->yMax = -INF;
    $averageAbsSlope = 0; // we will add all of them then divide to get an average
    $secants = []; // slope between this point and the previous one
    $tangents = []; // slope across the point

    foreach ($chartData as $x => $y) {
      if ($y < $this->yMin) {
        $this->yMin = $y;
        $yMinX = $x;
      }
      if ($y > $this->yMax) {
        $this->yMax = $y;
        $yMaxX = $x;
      }
      if (!is_null($previousY)) {
        $averageAbsSlope += abs($y - $previousY); // just add up all the Y differences
        $secants[$previousX] = ($y - $previousY) / $deltaX;
      }
      if ($x == $this->xMax) {
        $secants[$x] = ($y - $previousY) / $deltaX;
      }
      $previousY = $y;
      $previousX = $x;
    }
    $this->yRange = $this->yMax - $this->yMin;
    $averageAbsSlope /= $this->yRange * $deltaX; // turn this absolute-deltas total into a slope

    if ($this->options['smoothed']) {
      // take all these slopes and average them with their neighbors
      // unless they change direction, then make them zero
      // also restrict them a bit when they are very different
      $previousSecant = $previousX = null;
      foreach ($secants as $x => $secant) {
        if (!is_null($previousSecant)) {
          $tangents[$x] = ($secant + $previousSecant) / 2;
          if ($secant == 0 || $previousSecant == 0 || $secant * $previousSecant <= 0)
          {
            $tangents[$x] = 0;
          } else {
            if ($tangents[$x] / $previousSecant > 3) {
              $tangents[$x] = 3 * $previousSecant;
            } else if ($tangents[$x] / $secant > 3) {
              $tangents[$x] = 3 * $secant;
            }
          }
        }
        if ($x == $this->xMax) {
          $tangents[$x] = $secant;
        }
        if ($x == $this->xMin) {
          $tangents[$x] = $secant;
        }

        $previousX = $x;
        $previousSecant = $secant;
      }
    }

    /*
    We want the height of the median y-delta to be the same as
    the width of one x-delta, which puts the median slope at
    45 degrees. This improves comprehension.
    http://vis4.net/blog/posts/doing-the-line-charts-right/
    */
    $aspectRatio = max(0.25, min(0.75, 1 / $averageAbsSlope));
    $this->width = $this->options['width'] - $this->padding['left'] - $this->padding['right'];
    if (isset($this->options['height'])) {
      $this->height = $this->options['height'] - $this->padding['top'] - $this->padding['bottom'];
    } else {
      $this->height = floor($aspectRatio * $this->width);
      $this->options['height'] = $this->height + $this->padding['top'] + $this->padding['bottom'];
    }

    $chartPoints = 'M';
    $chartSplines = 'M'.
      $this->transformX($this->xMin).','.
      $this->transformY($chartData[$this->xMin]);
    if ($this->options['smoothed']) {
      foreach ($chartData as $x => $y) {
        $controlX = $deltaX / 3 / sqrt(1 + $tangents[$x]**2);
        $controlY = $tangents[$x] * $controlX;
        if ($x != $this->xMin) {
          $chartSplines .= ' S'.
            $this->transformX($x - $controlX).','.
            $this->transformY($y - $controlY).' '.
            $this->transformX($x).','.
            $this->transformY($y);
        }
      }
    } else {
      foreach ($chartData as $x => $y) {
        $chartPoints .=
          $this->transformX($x).','.
          $this->transformY($y) . ' ';
      }
    }

    $numLabels = 2 + ceil($this->height / $this->options['fontSize'] / 6);
    $labelInterval = $this->yRange / $numLabels;
    $labelModulation = 10 ** (1 + floor(-log($this->yRange / $numLabels, 10)));

    // 0.1 here is a fudge factor so we get multiples of 2.5 a little more often
    if (fmod($labelInterval * $labelModulation, 2.5) < fmod($labelInterval * $labelModulation, 2) + 0.1) {
      $labelModulation /= 2.5;
    } else {
      $labelModulation /= 2;
    }
    $labelInterval = ceil($labelInterval * $labelModulation) / $labelModulation;
    $labelPrecision = $this->getPrecision($labelInterval);

    // Top and bottom grid lines
    $gridLines =
      'M10,0 '.$this->width.',0 '.
      ' M10,'.$this->height.','.$this->width.','.$this->height;

    // Top and bottom grid labels
    $gridText =
      '<text x="'.(0.4 * $this->options['fontSize']).'" y="'.($this->options['fontSize'] * 0.4).'">'.($this->labelFormat($this->yMax, $labelPrecision + 1)).'</text>' .
      '<text x="'.(0.4 * $this->options['fontSize']).'" y="'.($this->options['fontSize'] * 0.4 + $this->height).'">'.($this->labelFormat($this->yMin, $labelPrecision + 1)).'</text>';

    // Main labels and grid lines
    for (
      $labelY = $this->yMin - fmod($this->yMin, $labelInterval) + $labelInterval; // Start at the first "nice" Y value > min
      $labelY < $this->yMax; // Keep going until max
      $labelY += $labelInterval // Add Interval each iteration
    ) {
      $labelHeight = $this->transformY($labelY);
      if ( // label is not too close to the min or max
        $labelHeight < $this->height - 1.5 * $this->options['fontSize'] &&
        $labelHeight > $this->options['fontSize'] * 1.5
      ) {
        $gridText .= '<text	x="-'.(0.25 * $this->options['fontSize']).'" y="'.($labelHeight + $this->options['fontSize'] * 0.4).'">'.$this->labelFormat($labelY, $labelPrecision).'</text>';
        $gridLines .= ' M0,'.$labelHeight.' '.$this->width.','.$labelHeight;
      } else if ( // label is too close
          $labelHeight < $this->height - $this->options['fontSize'] * 0.75 &&
          $labelHeight > $this->options['fontSize'] * 0.75
        ) {
          $gridLines .= ' M'.( // move grid line over when it's very close to the min or max label
            $labelHeight < $this->height - $this->options['fontSize'] / 2 && $labelHeight > $this->options['fontSize'] / 2 ? 0 : $this->options['fontSize'] / 2
          ).','.$labelHeight.' '.$this->width.','.$labelHeight;
        }
    }

    $chartID = rand();
    $this->output = '<?xml version="1.0" standalone="no"?>
<svg viewBox="-'.( $this->padding['left'] ).' -'.( $this->padding['top'] ).' '.( $this->options['width'] ).' '.( $this->options['height'] ).'" width="'.( $this->options['width'] ).'" height="'.( $this->options['height'] ).'" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
  <defs>
    <marker id="SVGChart-markerCircle-'.( $chartID ).'" markerWidth="2" markerHeight="2" refX="1" refY="1" markerUnits="strokeWidth">
      <circle cx="1" cy="1" r="1" style="stroke: none; fill:'.( $this->options['lineColor'] ).';" />
    </marker>
    <linearGradient id="SVGChart-fadeFromNothing-'.( $chartID ).'" x1="0%" y1="0%" x2="100%" y2="0%">
      <stop offset="0.5%" stop-color="'.( $this->options['lineColor'] ).'" stop-opacity="0"></stop>
      <stop offset="5%" stop-color="'.( $this->options['lineColor'] ).'" stop-opacity="1"></stop>
      <stop offset="100%" stop-color="'.( $this->options['lineColor'] ).'" stop-opacity="1"></stop>
    </linearGradient>
    <style type="text/css">
      <![CDATA[ .SVGChart-'.( $chartID ).' .chart__gridLines {
        font-family: sans-serif;
        font-size: '.( $this->options['fontSize'] ).'px;
        fill: '.( $this->options['labelColor'] ).';
        text-anchor: end;
        shape-rendering: crispEdges;
      }

      .SVGChart-'.( $chartID ).' .chart__gridLinePaths {
        fill: none;
        stroke: '.( $this->options['labelColor'] ).';
        stroke-opacity: 0.75;
        stroke-width: 1;
        stroke-dasharray: 2, 2;
      }

      .SVGChart-'.( $chartID ).' .chart__plotLine {
        fill: none;
        stroke-width: '.( $this->options['fontSize'] / 3 ).';
        stroke-linejoin: round;
        stroke-linecap: round;
        stroke: url(#SVGChart-fadeFromNothing-'.( $chartID ).');
        marker-end: url(#SVGChart-markerCircle-'.( $chartID ).');
      }

      ]]>
    </style>
  </defs>
  <g class="SVGChart SVGChart-'.( $chartID ).'">
    <g class="chart__gridLines">
      <path class="chart__gridLinePaths" d="'.( $gridLines ).'" /> '.( $gridText ).'
    </g>
    <g class="chart__plotLine">
      <path d="'.( $this->options['smoothed'] ? $chartSplines : $chartPoints ).'" />
    </g>
  </g>
</svg>';
  }
  public function render() {
    return $this->output;
  }
}