Re-use original palette color when possible

This is to prevent color changing when copy/pasting xls files written by
PhpSpreadsheet to another file.

Closes #218

src/PhpSpreadsheet/Writer/Xls/Workbook.php

@@ -332,21 +332,32 @@ class Workbook extends BIFFwriter
     private function addColor($rgb)
     {
         if (!isset($this->colors[$rgb])) {
-            if (count($this->colors) < 57) {
+            $color =
-                // then we add a custom color altering the palette
-                $colorIndex = 8 + count($this->colors);
-                $this->palette[$colorIndex] =
                 [
                     hexdec(substr($rgb, 0, 2)),
                     hexdec(substr($rgb, 2, 2)),
                     hexdec(substr($rgb, 4)),
                     0,
                 ];
+            $colorIndex = array_search($color, $this->palette);
+            if ($colorIndex) {
+                $this->colors[$rgb] = $colorIndex;
+            } else {
+                if (count($this->colors) == 0) {
+                    $lastColor = 7;
+                } else {
+                    $lastColor = end($this->colors);
+                }
+                if ($lastColor < 57) {
+                    // then we add a custom color altering the palette
+                    $colorIndex = $lastColor + 1;
+                    $this->palette[$colorIndex] = $color;
                     $this->colors[$rgb] = $colorIndex;
                 } else {
                     // no room for more custom colors, just map to black
                     $colorIndex = 0;
                 }
+            }
         } else {
             // fetch already added custom color
             $colorIndex = $this->colors[$rgb];

tests/PhpSpreadsheetTests/Writer/Xls/WorkbookTest.php

@@ -0,0 +1,143 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Writer\Xls\Workbook;
+
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PhpOffice\PhpSpreadsheet\Writer\Xls\Parser;
+use PhpOffice\PhpSpreadsheet\Writer\Xls\Workbook;
+use PHPUnit_Framework_TestCase;
+
+class WorkbookTest extends PHPUnit_Framework_TestCase
+{
+    /**
+     * @var Workbook
+     */
+    private $workbook;
+
+    protected function setUp()
+    {
+        $spreadsheet = new Spreadsheet();
+        $strTotal = 0;
+        $strUnique = 0;
+        $str_table = [];
+        $colors = [];
+        $parser = new Parser();
+
+        $this->workbook = new Workbook($spreadsheet, $strTotal, $strUnique, $str_table, $colors, $parser);
+    }
+
+    /**
+     * @dataProvider providerAddColor
+     *
+     * @param array $testColors
+     * @param array $expectedResult
+     */
+    public function testAddColor(array $testColors, array $expectedResult)
+    {
+        $workbookReflection = new \ReflectionClass(Workbook::class);
+        $methodAddColor = $workbookReflection->getMethod('addColor');
+        $propertyPalette = $workbookReflection->getProperty('palette');
+        $methodAddColor->setAccessible(true);
+        $propertyPalette->setAccessible(true);
+
+        foreach ($testColors as $testColor) {
+            $methodAddColor->invoke($this->workbook, $testColor);
+        }
+
+        $palette = $propertyPalette->getValue($this->workbook);
+
+        $this->assertEquals($expectedResult, $palette);
+    }
+
+    public function providerAddColor()
+    {
+        $this->setUp();
+
+        $workbookReflection = new \ReflectionClass(Workbook::class);
+        $propertyPalette = $workbookReflection->getProperty('palette');
+        $propertyPalette->setAccessible(true);
+
+        $palette = $propertyPalette->getValue($this->workbook);
+
+        $newColor1 = [0x00, 0x00, 0x01, 0x00];
+        $newColor2 = [0x00, 0x00, 0x02, 0x00];
+        $newColor3 = [0x00, 0x00, 0x03, 0x00];
+
+        // Add one new color
+        $paletteTestOne = $palette;
+        $paletteTestOne[8] = $newColor1;
+
+        // Add one new color + one existing color after index 8
+        $paletteTestTwo = $paletteTestOne;
+
+        // Add one new color + one existing color before index 9
+        $paletteTestThree = $paletteTestOne;
+        $paletteTestThree[9] = $palette[8];
+
+        // Add three new color
+        $paletteTestFour = $palette;
+        $paletteTestFour[8] = $newColor1;
+        $paletteTestFour[9] = $newColor2;
+        $paletteTestFour[10] = $newColor3;
+
+        // Add all existing color
+        $colorsAdd = array_map([$this, 'paletteToColor'], $palette);
+        $paletteTestFive = $palette;
+
+        // Add new color after all existing color
+        $colorsAddTwo = array_map([$this, 'paletteToColor'], $palette);
+        array_push($colorsAddTwo, $this->paletteToColor($newColor1));
+        $paletteTestSix = $palette;
+
+        // Add one existing color
+        $paletteTestSeven = $palette;
+
+        // Add two existing color
+        $paletteTestHeight = $palette;
+
+        // Add last existing color and add one new color
+        $keyPalette = array_keys($palette);
+        $last = end($keyPalette);
+        $lastColor = $this->paletteToColor($palette[$last]);
+        $paletteTestNine = $palette;
+
+        return [
+            [[$this->paletteToColor($newColor1)], $paletteTestOne],
+            [[$this->paletteToColor($newColor1), $this->paletteToColor($palette[12])], $paletteTestTwo],
+            [[$this->paletteToColor($newColor1), $this->paletteToColor($palette[8])], $paletteTestThree],
+            [[$this->paletteToColor($newColor1), $this->paletteToColor($newColor2), $this->paletteToColor($newColor3)], $paletteTestFour],
+            [$colorsAdd, $paletteTestFive],
+            [$colorsAddTwo, $paletteTestSix],
+            [[$this->paletteToColor($palette[8])], $paletteTestSeven],
+            [[$this->paletteToColor($palette[25]), $this->paletteToColor($palette[10])], $paletteTestHeight],
+            [[$lastColor, $this->paletteToColor($newColor1)], $paletteTestNine],
+        ];
+    }
+
+    /**
+     * Change palette color to rgb string.
+     *
+     * @param array $palette palette color
+     *
+     * @return string rgb string
+     */
+    private function paletteToColor($palette)
+    {
+        return $this->right('00' . dechex((int) ($palette[0])), 2)
+            . $this->right('00' . dechex((int) ($palette[1])), 2)
+            . $this->right('00' . dechex((int) ($palette[2])), 2);
+    }
+
+    /**
+     * Return n right character in string.
+     *
+     * @param string $value text to get right character
+     * @param int $nbchar number of char at right of string
+     *
+     * @return string
+     */
+    private function right($value, $nbchar)
+    {
+        return mb_substr($value, mb_strlen($value) - $nbchar, $nbchar);
+    }
+}