Add support for styling

Added top level methods on the Writer:
 - addRowWithStyle()
 - addRowsWithStyle()

Added a style builder, to easily create new styles.
Each writer can specify its own default style and all styles will automatically inherit from it.

For now, the style properties supported are:
 - bold
 - italic
 - underline
 - strikethrough
 - font size
 - font name
 - wrap text (alignment)

src/Spout/Writer/AbstractWriter.php

@@ -5,6 +5,7 @@ namespace Box\Spout\Writer;
 use Box\Spout\Common\Exception\IOException;
 use Box\Spout\Common\Exception\InvalidArgumentException;
 use Box\Spout\Writer\Exception\WriterNotOpenedException;
+use Box\Spout\Writer\Style\StyleBuilder;
 
 /**
  * Class AbstractWriter
@@ -26,6 +27,12 @@ abstract class AbstractWriter implements WriterInterface
     /** @var \Box\Spout\Common\Helper\GlobalFunctionsHelper Helper to work with global functions */
     protected $globalFunctionsHelper;
 
+    /** @var Style\Style Style to be applied to the next written row(s) */
+    protected $rowStyle;
+
+    /** @var Style\Style Default row style. Each writer can have its own default style */
+    protected $defaultRowStyle;
+
     /** @var string Content-Type value for the header - to be defined by child class */
     protected static $headerContentType;
 
@@ -39,13 +46,13 @@ abstract class AbstractWriter implements WriterInterface
 
     /**
      * Adds data to the currently openned writer.
-     * The data must be UTF-8 encoded.
      *
      * @param  array $dataRow Array containing data to be streamed.
      *          Example $dataRow = ['data1', 1234, null, '', 'data5'];
+     * @param Style\Style $style Style to be applied to the written row
      * @return void
      */
-    abstract protected function addRowToWriter(array $dataRow);
+    abstract protected function addRowToWriter(array $dataRow, $style);
 
     /**
      * Closes the streamer, preventing any additional writing.
@@ -55,7 +62,16 @@ abstract class AbstractWriter implements WriterInterface
     abstract protected function closeWriter();
 
     /**
-     * @param $globalFunctionsHelper
+     *
+     */
+    public function __construct()
+    {
+        $this->defaultRowStyle = $this->getDefaultRowStyle();
+        $this->resetRowStyleToDefault();
+    }
+
+    /**
+     * @param \Box\Spout\Common\Helper\GlobalFunctionsHelper $globalFunctionsHelper
      * @return AbstractWriter
      */
     public function setGlobalFunctionsHelper($globalFunctionsHelper)
@@ -138,7 +154,6 @@ abstract class AbstractWriter implements WriterInterface
 
     /**
      * Write given data to the output. New data will be appended to end of stream.
-     * The data must be UTF-8 encoded.
      *
      * @param  array $dataRow Array containing data to be streamed.
      *                        If empty, no data is added (i.e. not even as a blank row)
@@ -153,7 +168,7 @@ abstract class AbstractWriter implements WriterInterface
         if ($this->isWriterOpened) {
             // empty $dataRow should not add an empty line
             if (!empty($dataRow)) {
-                $this->addRowToWriter($dataRow);
+                $this->addRowToWriter($dataRow, $this->rowStyle);
             }
         } else {
             throw new WriterNotOpenedException('The writer needs to be opened before adding row.');
@@ -162,9 +177,32 @@ abstract class AbstractWriter implements WriterInterface
         return $this;
     }
 
+    /**
+     * Write given data to the output and apply the given style.
+     * @see addRow
+     *
+     * @param array $dataRow Array of array containing data to be streamed.
+     * @param Style\Style $style Style to be applied to the row.
+     * @return AbstractWriter
+     * @throws \Box\Spout\Common\Exception\InvalidArgumentException If the input param is not valid
+     * @throws \Box\Spout\Writer\Exception\WriterNotOpenedException If this function is called before opening the writer
+     * @throws \Box\Spout\Common\Exception\IOException If unable to write data
+     */
+    public function addRowWithStyle(array $dataRow, $style)
+    {
+        if (!$style instanceof Style\Style) {
+            throw new InvalidArgumentException('The "$style" argument must be a Style instance and cannot be NULL.');
+        }
+
+        $this->setRowStyle($style);
+        $this->addRow($dataRow);
+        $this->resetRowStyleToDefault();
+
+        return $this;
+    }
+
     /**
      * Write given data to the output. New data will be appended to end of stream.
-     * The data must be UTF-8 encoded.
      *
      * @param  array $dataRows Array of array containing data to be streamed.
      *                         If a row is empty, it won't be added (i.e. not even as a blank row)
@@ -193,6 +231,64 @@ abstract class AbstractWriter implements WriterInterface
         return $this;
     }
 
+    /**
+     * Write given data to the output and apply the given style.
+     * @see addRows
+     *
+     * @param array $dataRows Array of array containing data to be streamed.
+     * @param Style\Style $style Style to be applied to the rows.
+     * @return AbstractWriter
+     * @throws \Box\Spout\Common\Exception\InvalidArgumentException If the input param is not valid
+     * @throws \Box\Spout\Writer\Exception\WriterNotOpenedException If this function is called before opening the writer
+     * @throws \Box\Spout\Common\Exception\IOException If unable to write data
+     */
+    public function addRowsWithStyle(array $dataRows, $style)
+    {
+        if (!$style instanceof Style\Style) {
+            throw new InvalidArgumentException('The "$style" argument must be a Style instance and cannot be NULL.');
+        }
+
+        $this->setRowStyle($style);
+        $this->addRows($dataRows);
+        $this->resetRowStyleToDefault();
+
+        return $this;
+    }
+
+    /**
+     * Returns the default style to be applied to rows.
+     * Can be overriden by children to have a custom style.
+     *
+     * @return Style\Style
+     */
+    protected function getDefaultRowStyle()
+    {
+        return (new StyleBuilder())->build();
+    }
+
+    /**
+     * Sets the style to be applied to the next written rows
+     * until it is changed or reset.
+     *
+     * @param Style\Style $style
+     * @return void
+     */
+    private function setRowStyle($style)
+    {
+        // Merge given style with the default one to inherit custom properties
+        $this->rowStyle = $style->mergeWith($this->defaultRowStyle);
+    }
+
+    /**
+     * Resets the style to be applied to the next written rows.
+     *
+     * @return void
+     */
+    private function resetRowStyleToDefault()
+    {
+        $this->rowStyle = $this->defaultRowStyle;
+    }
+
     /**
      * Closes the writer. This will close the streamer as well, preventing new data
      * to be written to the file.

src/Spout/Writer/CSV/Writer.php

@@ -69,10 +69,11 @@ class Writer extends AbstractWriter
      *
      * @param  array $dataRow Array containing data to be written.
      *          Example $dataRow = ['data1', 1234, null, '', 'data5'];
+     * @param \Box\Spout\Writer\Style\Style $style Ignored here since CSV does not support styling.
      * @return void
      * @throws \Box\Spout\Common\Exception\IOException If unable to write data
      */
-    protected function addRowToWriter(array $dataRow)
+    protected function addRowToWriter(array $dataRow, $style)
     {
         $wasWriteSuccessful = $this->globalFunctionsHelper->fputcsv($this->filePointer, $dataRow, $this->fieldDelimiter, $this->fieldEnclosure);
         if ($wasWriteSuccessful === false) {

src/Spout/Writer/Style/Style.php

@@ -0,0 +1,277 @@
+<?php
+
+namespace Box\Spout\Writer\Style;
+
+/**
+ * Class Style
+ * Represents a style to be applied to a cell
+ *
+ * @package Box\Spout\Writer\Style
+ */
+class Style
+{
+    /** Default font values */
+    const DEFAULT_FONT_SIZE = 11;
+    const DEFAULT_FONT_NAME = 'Arial';
+
+    /** @var int|null Style ID */
+    protected $id = null;
+
+    /** @var bool Whether the font should be bold */
+    protected $fontBold = false;
+    /** @var bool Whether the bold property was set */
+    protected $hasSetFontBold = false;
+
+    /** @var bool Whether the font should be italic */
+    protected $fontItalic = false;
+    /** @var bool Whether the italic property was set */
+    protected $hasSetFontItalic = false;
+
+    /** @var bool Whether the font should be underlined */
+    protected $fontUnderline = false;
+    /** @var bool Whether the underline property was set */
+    protected $hasSetFontUnderline = false;
+
+    /** @var bool Whether the font should be struck through */
+    protected $fontStrikeThrough = false;
+    /** @var bool Whether the strikethrough property was set */
+    protected $hasSetFontStrikeThrough = false;
+
+    /** @var int Font size */
+    protected $fontSize = self::DEFAULT_FONT_SIZE;
+    /** @var bool Whether the font size property was set */
+    protected $hasSetFontSize = false;
+
+    /** @var string Font name */
+    protected $fontName = self::DEFAULT_FONT_NAME;
+    /** @var bool Whether the font name property was set */
+    protected $hasSetFontName = false;
+
+    /** @var bool Whether specific font properties should be applied */
+    protected $shouldApplyFont = false;
+
+    /** @var bool Whether the text should wrap in the cell (useful for long or multi-lines text) */
+    protected $shouldWrapText = false;
+    /** @var bool Whether the wrap text property was set */
+    protected $hasSetWrapText = false;
+
+    /**
+     * @return int|null
+     */
+    public function getId()
+    {
+        return $this->id;
+    }
+
+    /**
+     * @param int $id
+     * @return Style
+     */
+    public function setId($id)
+    {
+        $this->id = $id;
+        return $this;
+    }
+
+    /**
+     * @return boolean
+     */
+    public function isFontBold()
+    {
+        return $this->fontBold;
+    }
+
+    /**
+     * @return Style
+     */
+    public function setFontBold()
+    {
+        $this->fontBold = true;
+        $this->hasSetFontBold = true;
+        $this->shouldApplyFont = true;
+        return $this;
+    }
+
+    /**
+     * @return boolean
+     */
+    public function isFontItalic()
+    {
+        return $this->fontItalic;
+    }
+
+    /**
+     * @return Style
+     */
+    public function setFontItalic()
+    {
+        $this->fontItalic = true;
+        $this->hasSetFontItalic = true;
+        $this->shouldApplyFont = true;
+        return $this;
+    }
+
+    /**
+     * @return boolean
+     */
+    public function isFontUnderline()
+    {
+        return $this->fontUnderline;
+    }
+
+    /**
+     * @return Style
+     */
+    public function setFontUnderline()
+    {
+        $this->fontUnderline = true;
+        $this->hasSetFontUnderline = true;
+        $this->shouldApplyFont = true;
+        return $this;
+    }
+
+    /**
+     * @return boolean
+     */
+    public function isFontStrikeThrough()
+    {
+        return $this->fontStrikeThrough;
+    }
+
+    /**
+     * @return Style
+     */
+    public function setFontStrikeThrough()
+    {
+        $this->fontStrikeThrough = true;
+        $this->hasSetFontStrikeThrough = true;
+        $this->shouldApplyFont = true;
+        return $this;
+    }
+
+    /**
+     * @return int
+     */
+    public function getFontSize()
+    {
+        return $this->fontSize;
+    }
+
+    /**
+     * @param int $fontSize Font size, in pixels
+     * @return Style
+     */
+    public function setFontSize($fontSize)
+    {
+        $this->fontSize = $fontSize;
+        $this->hasSetFontSize = true;
+        $this->shouldApplyFont = true;
+        return $this;
+    }
+
+    /**
+     * @return string
+     */
+    public function getFontName()
+    {
+        return $this->fontName;
+    }
+
+    /**
+     * @param string $fontName Name of the font to use
+     * @return Style
+     */
+    public function setFontName($fontName)
+    {
+        $this->fontName = $fontName;
+        $this->hasSetFontName = true;
+        $this->shouldApplyFont = true;
+        return $this;
+    }
+
+    /**
+     * @return boolean
+     */
+    public function shouldWrapText()
+    {
+        return $this->shouldWrapText;
+    }
+
+    /**
+     * @return Style
+     */
+    public function setShouldWrapText()
+    {
+        $this->shouldWrapText = true;
+        $this->hasSetWrapText = true;
+        return $this;
+    }
+
+    /**
+     * @return bool Whether specific font properties should be applied
+     */
+    public function shouldApplyFont()
+    {
+        return $this->shouldApplyFont;
+    }
+
+    /**
+     * Serializes the style for future comparison with other styles.
+     * The ID is excluded from the comparison, as we only care about
+     * actual style properties.
+     *
+     * @return string The serialized style
+     */
+    public function serialize()
+    {
+        // In order to be able to properly compare style, set static ID value
+        $currentId = $this->id;
+        $this->setId(0);
+
+        $serializedStyle = serialize($this);
+
+        $this->setId($currentId);
+
+        return $serializedStyle;
+    }
+
+    /**
+     * Merges the current style with the given style, using the given style as a base. This means that:
+     *   - if current style and base style both have property A set, use current style property's value
+     *   - if current style has property A set but base style does not, use current style property's value
+     *   - if base style has property A set but current style does not, use base style property's value
+     *
+     * @NOTE: This function returns a new style.
+     *
+     * @param Style $baseStyle
+     * @return Style New style corresponding to the merge of the 2 styles
+     */
+    public function mergeWith($baseStyle)
+    {
+        $mergedStyle = clone $this;
+
+        if (!$this->hasSetFontBold && $baseStyle->isFontBold()) {
+            $mergedStyle->setFontBold();
+        }
+        if (!$this->hasSetFontItalic && $baseStyle->isFontItalic()) {
+            $mergedStyle->setFontItalic();
+        }
+        if (!$this->hasSetFontUnderline && $baseStyle->isFontUnderline()) {
+            $mergedStyle->setFontUnderline();
+        }
+        if (!$this->hasSetFontStrikeThrough && $baseStyle->isFontStrikeThrough()) {
+            $mergedStyle->setFontStrikeThrough();
+        }
+        if (!$this->hasSetFontSize && $baseStyle->getFontSize() !== self::DEFAULT_FONT_SIZE) {
+            $mergedStyle->setFontSize($baseStyle->getFontSize());
+        }
+        if (!$this->hasSetFontName && $baseStyle->getFontName() !== self::DEFAULT_FONT_NAME) {
+            $mergedStyle->setFontName($baseStyle->getFontName());
+        }
+        if (!$this->hasSetWrapText && $baseStyle->shouldWrapText()) {
+            $mergedStyle->setShouldWrapText();
+        }
+
+        return $mergedStyle;
+    }
+}

src/Spout/Writer/Style/StyleBuilder.php

@@ -0,0 +1,113 @@
+<?php
+
+namespace Box\Spout\Writer\Style;
+
+/**
+ * Class StyleBuilder
+ * Builder to create new styles
+ *
+ * @package Box\Spout\Writer\Style
+ */
+class StyleBuilder
+{
+    /** @var Style Style to be created */
+    protected $style;
+
+    /**
+     *
+     */
+    public function __construct()
+    {
+        $this->style = new Style();
+    }
+
+    /**
+     * Makes the font bold.
+     *
+     * @return StyleBuilder
+     */
+    public function setFontBold()
+    {
+        $this->style->setFontBold();
+        return $this;
+    }
+
+    /**
+     * Makes the font italic.
+     *
+     * @return StyleBuilder
+     */
+    public function setFontItalic()
+    {
+        $this->style->setFontItalic();
+        return $this;
+    }
+
+    /**
+     * Makes the font underlined.
+     *
+     * @return StyleBuilder
+     */
+    public function setFontUnderline()
+    {
+        $this->style->setFontUnderline();
+        return $this;
+    }
+
+    /**
+     * Makes the font struck through.
+     *
+     * @return StyleBuilder
+     */
+    public function setFontStrikeThrough()
+    {
+        $this->style->setFontStrikeThrough();
+        return $this;
+    }
+
+    /**
+     * Sets the font size.
+     *
+     * @param int $fontSize Font size, in pixels
+     * @return StyleBuilder
+     */
+    public function setFontSize($fontSize)
+    {
+        $this->style->setFontSize($fontSize);
+        return $this;
+    }
+
+    /**
+     * Sets the font name.
+     *
+     * @param string $fontName Name of the font to use
+     * @return StyleBuilder
+     */
+    public function setFontName($fontName)
+    {
+        $this->style->setFontName($fontName);
+        return $this;
+    }
+
+    /**
+     * Makes the text wrap in the cell if it's too long or
+     * on multiple lines.
+     *
+     * @return StyleBuilder
+     */
+    public function setShouldWrapText()
+    {
+        $this->style->setShouldWrapText();
+        return $this;
+    }
+
+    /**
+     * Returns the configured style. The style is cached and can be reused.
+     *
+     * @return Style
+     */
+    public function build()
+    {
+        return $this->style;
+    }
+}

src/Spout/Writer/WriterInterface.php

@@ -40,6 +40,19 @@ interface WriterInterface
      */
     public function addRow(array $dataRow);
 
+    /**
+     * Write given data to the output and apply the given style.
+     * @see addRow
+     *
+     * @param array $dataRow Array of array containing data to be streamed.
+     * @param Style\Style $style Style to be applied to the row.
+     * @return WriterInterface
+     * @throws \Box\Spout\Common\Exception\InvalidArgumentException If the input param is not valid
+     * @throws \Box\Spout\Writer\Exception\WriterNotOpenedException If this function is called before opening the writer
+     * @throws \Box\Spout\Common\Exception\IOException If unable to write data
+     */
+    public function addRowWithStyle(array $dataRow, $style);
+
     /**
      * Write given data to the output. New data will be appended to end of stream.
      *
@@ -55,6 +68,19 @@ interface WriterInterface
      */
     public function addRows(array $dataRows);
 
+    /**
+     * Write given data to the output and apply the given style.
+     * @see addRows
+     *
+     * @param array $dataRows Array of array containing data to be streamed.
+     * @param Style\Style $style Style to be applied to the rows.
+     * @return WriterInterface
+     * @throws \Box\Spout\Common\Exception\InvalidArgumentException If the input param is not valid
+     * @throws \Box\Spout\Writer\Exception\WriterNotOpenedException If this function is called before opening the writer
+     * @throws \Box\Spout\Common\Exception\IOException If unable to write data
+     */
+    public function addRowsWithStyle(array $dataRows, $style);
+
     /**
      * Closes the writer. This will close the streamer as well, preventing new data
      * to be written to the file.

src/Spout/Writer/XLSX/Helper/FileSystemHelper.php

@@ -26,6 +26,7 @@ class FileSystemHelper extends \Box\Spout\Common\Helper\FileSystemHelper
     const CONTENT_TYPES_XML_FILE_NAME = '[Content_Types].xml';
     const WORKBOOK_XML_FILE_NAME = 'workbook.xml';
     const WORKBOOK_RELS_XML_FILE_NAME = 'workbook.xml.rels';
+    const STYLES_XML_FILE_NAME = 'styles.xml';
 
     /** @var string Path to the root folder inside the temp folder where the files to create the XLSX will be stored */
     protected $rootFolder;
@@ -256,6 +257,7 @@ EOD;
     }
 
     $contentTypesXmlFileContents .= <<<EOD
+    <Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.styles+xml" PartName="/xl/styles.xml"/>
     <Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sharedStrings+xml" PartName="/xl/sharedStrings.xml"/>
     <Override ContentType="application/vnd.openxmlformats-package.core-properties+xml" PartName="/docProps/core.xml"/>
     <Override ContentType="application/vnd.openxmlformats-officedocument.extended-properties+xml" PartName="/docProps/app.xml"/>
@@ -312,6 +314,7 @@ EOD;
         $workbookRelsXmlFileContents = <<<EOD
 <?xml version="1.0" encoding="UTF-8"?>
 <Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships">
+    <Relationship Id="rIdStyles" Target="styles.xml" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/styles"/>
     <Relationship Id="rIdSharedStrings" Target="sharedStrings.xml" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/sharedStrings"/>
 
 EOD;
@@ -329,6 +332,20 @@ EOD;
         return $this;
     }
 
+    /**
+     * Creates the "styles.xml" file under the "xl" folder
+     *
+     * @param StyleHelper $styleHelper
+     * @return FileSystemHelper
+     */
+    public function createStylesFile($styleHelper)
+    {
+        $stylesXmlFileContents = $styleHelper->getStylesXMLFileContent();
+        $this->createFileWithContents($this->xlFolder, self::STYLES_XML_FILE_NAME, $stylesXmlFileContents);
+
+        return $this;
+    }
+
     /**
      * Zips the root folder and streams the contents of the zip into the given stream
      *

src/Spout/Writer/XLSX/Helper/StyleHelper.php

@@ -0,0 +1,230 @@
+<?php
+
+namespace Box\Spout\Writer\XLSX\Helper;
+
+/**
+ * Class StyleHelper
+ * This class provides helper functions to manage styles
+ *
+ * @package Box\Spout\Writer\XLSX\Helper
+ */
+class StyleHelper
+{
+    /** @var array [SERIALIZED_STYLE] => [STYLE_ID] mapping table, keeping track of the registered styles */
+    protected $serializedStyleToStyleIdMappingTable = [];
+
+    /** @var array [STYLE_ID] => [STYLE] mapping table, keeping track of the registered styles */
+    protected $styleIdToStyleMappingTable = [];
+
+    /**
+     * @param \Box\Spout\Writer\Style\Style $defaultStyle
+     */
+    public function __construct($defaultStyle)
+    {
+        // This ensures that the default style is the first one to be registered
+        $this->registerStyle($defaultStyle);
+    }
+
+    /**
+     * Registers the given style as a used style.
+     * Duplicate styles won't be registered more than once.
+     *
+     * @param \Box\Spout\Writer\Style\Style $style The style to be registered
+     * @return \Box\Spout\Writer\Style\Style The registered style, updated with an internal ID.
+     */
+    public function registerStyle($style)
+    {
+        $serializedStyle = $style->serialize();
+
+        if (!$this->hasStyleAlreadyBeenRegistered($style)) {
+            $nextStyleId = count($this->serializedStyleToStyleIdMappingTable);
+            $style->setId($nextStyleId);
+
+            $this->serializedStyleToStyleIdMappingTable[$serializedStyle] = $nextStyleId;
+            $this->styleIdToStyleMappingTable[$nextStyleId] = $style;
+        }
+
+        return $this->getStyleFromSerializedStyle($serializedStyle);
+    }
+
+    /**
+     * Returns whether the given style has already been registered.
+     *
+     * @param \Box\Spout\Writer\Style\Style $style
+     * @return bool
+     */
+    protected function hasStyleAlreadyBeenRegistered($style)
+    {
+        $serializedStyle = $style->serialize();
+        return array_key_exists($serializedStyle, $this->serializedStyleToStyleIdMappingTable);
+    }
+
+    /**
+     * Returns the registered style associated to the given serialization.
+     *
+     * @param string $serializedStyle The serialized style from which the actual style should be fetched from
+     * @return \Box\Spout\Writer\Style\Style
+     */
+    protected function getStyleFromSerializedStyle($serializedStyle)
+    {
+        $styleId = $this->serializedStyleToStyleIdMappingTable[$serializedStyle];
+        return $this->styleIdToStyleMappingTable[$styleId];
+    }
+
+    /**
+     * Returns the content of the "styles.xml" file, given a list of styles.
+     * @return string
+     */
+    public function getStylesXMLFileContent()
+    {
+        $content = <<<EOD
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<styleSheet xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main">
+
+EOD;
+
+        $content .= $this->getFontsSectionContent();
+        $content .= $this->getFillsSectionContent();
+        $content .= $this->getBordersSectionContent();
+        $content .= $this->getCellStyleXfsSectionContent();
+        $content .= $this->getCellXfsSectionContent();
+        $content .= $this->getCellStylesSectionContent();
+
+        $content .= <<<EOD
+</styleSheet>
+EOD;
+
+        return $content;
+    }
+
+    /**
+     * Returns the content of the "<fonts>" section.
+     * @return string
+     */
+    protected function getFontsSectionContent()
+    {
+        $content = '    <fonts count="' . count($this->styleIdToStyleMappingTable) . '">' . PHP_EOL;
+
+        foreach ($this->styleIdToStyleMappingTable as $style) {
+            $content .= '        <font>' . PHP_EOL;
+
+            if ($style->isFontBold()) {
+                $content .= '            <b/>' . PHP_EOL;
+            }
+            if ($style->isFontItalic()) {
+                $content .= '            <i/>' . PHP_EOL;
+            }
+            if ($style->isFontUnderline()) {
+                $content .= '            <u/>' . PHP_EOL;
+            }
+            if ($style->isFontStrikeThrough()) {
+                $content .= '            <strike/>' . PHP_EOL;
+            }
+
+            $content .= '            <sz val="' . $style->getFontSize() . '"/>' . PHP_EOL;
+            $content .= '            <name val="' . $style->getFontName() . '"/>' . PHP_EOL;
+            $content .= '        </font>' . PHP_EOL;
+        }
+
+        $content .= '    </fonts>' . PHP_EOL;
+
+        return $content;
+    }
+
+    /**
+     * Returns the content of the "<fills>" section.
+     *
+     * @return string
+     */
+    protected function getFillsSectionContent()
+    {
+        return <<<EOD
+    <fills count="1">
+        <fill>
+            <patternFill patternType="none"/>
+        </fill>
+    </fills>
+
+EOD;
+    }
+
+    /**
+     * Returns the content of the "<borders>" section.
+     *
+     * @return string
+     */
+    protected function getBordersSectionContent()
+    {
+        return <<<EOD
+    <borders count="1">
+        <border>
+            <left/>
+            <right/>
+            <top/>
+            <bottom/>
+            <diagonal/>
+        </border>
+    </borders>
+
+EOD;
+    }
+
+    /**
+     * Returns the content of the "<cellStyleXfs>" section.
+     *
+     * @return string
+     */
+    protected function getCellStyleXfsSectionContent()
+    {
+        return <<<EOD
+    <cellStyleXfs count="1">
+        <xf borderId="0" fillId="0" fontId="0" numFmtId="0"/>
+    </cellStyleXfs>
+
+EOD;
+    }
+
+    /**
+     * Returns the content of the "<cellXfs>" section.
+     * @return string
+     */
+    protected function getCellXfsSectionContent()
+    {
+        $content = '    <cellXfs count="' . count($this->styleIdToStyleMappingTable) . '">' . PHP_EOL;
+
+        foreach ($this->styleIdToStyleMappingTable as $styleId => $style) {
+            $content .= '        <xf numFmtId="0" fontId="' . $styleId . '" fillId="0" borderId="0" xfId="0"';
+
+            if ($style->shouldApplyFont()) {
+                $content .= ' applyFont="1"';
+            }
+
+            if ($style->shouldWrapText()) {
+                $content .= ' applyAlignment="1">' . PHP_EOL;
+                $content .= '            <alignment wrapText="1"/>' . PHP_EOL;
+                $content .= '        </xf>' . PHP_EOL;
+            } else {
+                $content .= '/>' . PHP_EOL;
+            }
+        }
+
+        $content .= '    </cellXfs>' . PHP_EOL;
+
+        return $content;
+    }
+
+    /**
+     * Returns the content of the "<cellStyles>" section.
+     *
+     * @return string
+     */
+    protected function getCellStylesSectionContent()
+    {
+        return <<<EOD
+    <cellStyles count="1">
+        <cellStyle builtinId="0" name="Normal" xfId="0"/>
+    </cellStyles>
+
+EOD;
+    }
+}

src/Spout/Writer/XLSX/Internal/Workbook.php

@@ -5,6 +5,7 @@ namespace Box\Spout\Writer\XLSX\Internal;
 use Box\Spout\Writer\Exception\SheetNotFoundException;
 use Box\Spout\Writer\XLSX\Helper\FileSystemHelper;
 use Box\Spout\Writer\XLSX\Helper\SharedStringsHelper;
+use Box\Spout\Writer\XLSX\Helper\StyleHelper;
 use Box\Spout\Writer\XLSX\Sheet;
 
 /**
@@ -34,19 +35,28 @@ class Workbook
     /** @var \Box\Spout\Writer\XLSX\Helper\SharedStringsHelper Helper to write shared strings */
     protected $sharedStringsHelper;
 
+    /** @var \Box\Spout\Writer\XLSX\Helper\StyleHelper Helper to apply styles */
+    protected $styleHelper;
+
     /** @var Worksheet[] Array containing the workbook's sheets */
     protected $worksheets = [];
 
     /** @var Worksheet The worksheet where data will be written to */
     protected $currentWorksheet;
 
+    protected $styles = [];
+
+
+
+
     /**
      * @param string $tempFolder
      * @param bool $shouldUseInlineStrings
      * @param bool $shouldCreateNewSheetsAutomatically
+     * @param \Box\Spout\Writer\Style\Style $defaultRowStyle
      * @throws \Box\Spout\Common\Exception\IOException If unable to create at least one of the base folders
      */
-    public function __construct($tempFolder, $shouldUseInlineStrings, $shouldCreateNewSheetsAutomatically)
+    public function __construct($tempFolder, $shouldUseInlineStrings, $shouldCreateNewSheetsAutomatically, $defaultRowStyle)
     {
         $this->shouldUseInlineStrings = $shouldUseInlineStrings;
         $this->shouldCreateNewSheetsAutomatically = $shouldCreateNewSheetsAutomatically;
@@ -54,6 +64,8 @@ class Workbook
         $this->fileSystemHelper = new FileSystemHelper($tempFolder);
         $this->fileSystemHelper->createBaseFilesAndFolders();
 
+        $this->styleHelper = new StyleHelper($defaultRowStyle);
+
         // This helper will be shared by all sheets
         $xlFolder = $this->fileSystemHelper->getXlFolder();
         $this->sharedStringsHelper = new SharedStringsHelper($xlFolder);
@@ -164,11 +176,12 @@ class Workbook
      *
      * @param array $dataRow Array containing data to be written.
      *          Example $dataRow = ['data1', 1234, null, '', 'data5'];
+     * @param \Box\Spout\Writer\Style\Style $style Style to be applied to the row.
      * @return void
      * @throws \Box\Spout\Common\Exception\IOException If trying to create a new sheet and unable to open the sheet for writing
      * @throws \Box\Spout\Writer\Exception\WriterException If unable to write data
      */
-    public function addRowToCurrentWorksheet($dataRow)
+    public function addRowToCurrentWorksheet($dataRow, $style)
     {
         $currentWorksheet = $this->getCurrentWorksheet();
         $hasReachedMaxRows = $this->hasCurrentWorkseetReachedMaxRows();
@@ -178,12 +191,15 @@ class Workbook
             // ... continue writing in a new sheet if option set
             if ($this->shouldCreateNewSheetsAutomatically) {
                 $currentWorksheet = $this->addNewSheetAndMakeItCurrent();
-                $currentWorksheet->addRow($dataRow);
+
+                $registeredStyle = $this->styleHelper->registerStyle($style);
+                $currentWorksheet->addRow($dataRow, $registeredStyle);
             } else {
                 // otherwise, do nothing as the data won't be read anyways
             }
         } else {
-            $currentWorksheet->addRow($dataRow);
+            $registeredStyle = $this->styleHelper->registerStyle($style);
+            $currentWorksheet->addRow($dataRow, $registeredStyle);
         }
     }
 
@@ -217,6 +233,7 @@ class Workbook
             ->createContentTypesFile($this->worksheets)
             ->createWorkbookFile($this->worksheets)
             ->createWorkbookRelsFile($this->worksheets)
+            ->createStylesFile($this->styleHelper)
             ->zipRootFolderAndCopyToStream($finalFilePointer);
 
         $this->cleanupTempFolder();

src/Spout/Writer/XLSX/Internal/Worksheet.php

@@ -38,7 +38,7 @@ EOD;
     /** @var Resource Pointer to the sheet data file (e.g. xl/worksheets/sheet1.xml) */
     protected $sheetFilePointer;
 
-    /** @var int */
+    /** @var int Index of the last written row */
     protected $lastWrittenRowIndex = 0;
 
     /**
@@ -118,11 +118,12 @@ EOD;
      *
      * @param array $dataRow Array containing data to be written.
      *          Example $dataRow = ['data1', 1234, null, '', 'data5'];
+     * @param \Box\Spout\Writer\Style\Style $style Style to be applied to the row. NULL means use default style.
      * @return void
      * @throws \Box\Spout\Common\Exception\IOException If the data cannot be written
      * @throws \Box\Spout\Common\Exception\InvalidArgumentException If a cell value's type is not supported
      */
-    public function addRow($dataRow)
+    public function addRow($dataRow, $style)
     {
         $cellNumber = 0;
         $rowIndex = $this->lastWrittenRowIndex + 1;
@@ -133,6 +134,7 @@ EOD;
         foreach($dataRow as $cellValue) {
             $columnIndex = CellHelper::getCellIndexFromColumnIndex($cellNumber);
             $data .= '            <c r="' . $columnIndex . $rowIndex . '"';
+            $data .= ' s="' . $style->getId() . '"';
 
             if (CellHelper::isNonEmptyString($cellValue)) {
                 if ($this->shouldUseInlineStrings) {

src/Spout/Writer/XLSX/Writer.php

@@ -4,6 +4,7 @@ namespace Box\Spout\Writer\XLSX;
 
 use Box\Spout\Writer\AbstractWriter;
 use Box\Spout\Writer\Exception\WriterNotOpenedException;
+use Box\Spout\Writer\Style\StyleBuilder;
 use Box\Spout\Writer\XLSX\Internal\Workbook;
 
 /**
@@ -14,6 +15,10 @@ use Box\Spout\Writer\XLSX\Internal\Workbook;
  */
 class Writer extends AbstractWriter
 {
+    /** Default style font values */
+    const DEFAULT_FONT_SIZE = 12;
+    const DEFAULT_FONT_NAME = 'Calibri';
+
     /** @var string Content-Type value for the header */
     protected static $headerContentType = 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet';
 
@@ -74,7 +79,7 @@ class Writer extends AbstractWriter
     {
         if (!$this->book) {
             $tempFolder = ($this->tempFolder) ? : sys_get_temp_dir();
-            $this->book = new Workbook($tempFolder, $this->shouldUseInlineStrings, $this->shouldCreateNewSheetsAutomatically);
+            $this->book = new Workbook($tempFolder, $this->shouldUseInlineStrings, $this->shouldCreateNewSheetsAutomatically, $this->defaultRowStyle);
             $this->book->addNewSheetAndMakeItCurrent();
         }
     }
@@ -161,14 +166,28 @@ class Writer extends AbstractWriter
      *
      * @param array $dataRow Array containing data to be written.
      *          Example $dataRow = ['data1', 1234, null, '', 'data5'];
+     * @param \Box\Spout\Writer\Style\Style $style Style to be applied to the row.
      * @return void
      * @throws \Box\Spout\Writer\Exception\WriterNotOpenedException If the book is not created yet
      * @throws \Box\Spout\Common\Exception\IOException If unable to write data
      */
-    protected function addRowToWriter(array $dataRow)
+    protected function addRowToWriter(array $dataRow, $style)
     {
         $this->throwIfBookIsNotAvailable();
-        $this->book->addRowToCurrentWorksheet($dataRow);
+        $this->book->addRowToCurrentWorksheet($dataRow, $style);
+    }
+
+    /**
+     * Returns the default style to be applied to rows.
+     *
+     * @return \Box\Spout\Writer\Style\Style
+     */
+    protected function getDefaultRowStyle()
+    {
+        return (new StyleBuilder())
+            ->setFontSize(self::DEFAULT_FONT_SIZE)
+            ->setFontName(self::DEFAULT_FONT_NAME)
+            ->build();
     }
 
     /**