Add row shader plugin (#42)

* Add row shader plugin
The row shader plugin shades table rows with two alternating colours.
Config is:
- shade1: first colour to shade the row with (default: #DAE6F2)
- shade2: second colour to shade the alternating row with (default: #BACEE6)
- textColor: text colour to revert to after shading (default: #000)
- x: position where shading starts (default: 72)
- width: width of the shading (default: 449)
- offsetHeader: offset the header height if a header is drawn on each new page (default: false)

* fix bug with offsetHeader config option

plugins/rowshader.js

@@ -0,0 +1,159 @@
+/*jslint node: true, unparam: true, nomen: true */
+'use strict';
+
+var lodash = require('lodash'),
+
+  /**
+   * Plugin constructor. Configuration may take parameters listed below.
+   *
+   * @param {String} shade1 first colour to shade the row with
+   * @param {String} shade2 second colour to shade the alternating row with
+   * @param {String} textColor text colour to revert to after shading
+   * @param {Number} x X position where shading starts
+   * @param {Number} width width of the shading
+   * @param {Boolean} offsetHeader offset the header height if a header is drawn on each new page
+   */
+  PdfTableRowShader = function (conf) {
+    lodash.merge(this, {
+
+      id: 'rowshader',
+
+      /**
+       * The first colour to shade the row with
+       * @var {String}
+       */
+      shade1: null,
+
+      /**
+       * The second colour to shade the alternating row with
+       * @var {String}
+       */
+      shade2: null,
+
+      /**
+       * The text colour to revert to after shading
+       * @var {String}
+       */
+      textColor: null,
+
+      /**
+       * The X position where shading starts
+       * @var {Number}
+       */
+      x: null,
+
+      /**
+       * The width of the shading
+       * @var {Number}
+       */
+      width: null,
+
+      /**
+       * Offset the header height if a header is drawn on each new page
+       * @var {Boolean}
+       */
+      offsetHeader: false,
+
+    }, lodash.clone(conf || {}));
+  };
+
+lodash.assign(PdfTableRowShader.prototype, {
+  /**
+   * Configure plugin by attaching functions to table events
+   *
+   * @param {PdfTable}
+   * @return {void}
+   */
+  configure: function (table) {
+    // setup internal values
+    lodash.merge(this, {
+      _currentRowHeight: 0,
+      _shadingCount: 0,
+      _headerHeight: 0,
+    })
+    // set defaults
+    if (!this.x) this.x = 72;
+    if (!this.shade1) this.shade1 = '#DAE6F2';
+    if (!this.shade2) this.shade2 = '#BACEE6';
+    if (!this.textColor) this.textColor = '#000';
+    if (!this.width) this.width = 449;
+
+    table
+      .onRowAdd(this.onRowAdd.bind(this))
+      .onPageAdded(this.onPageAdded.bind(this))
+      .onHeaderHeightCalculated(this.onHeaderHeightCalculated.bind(this))
+  },
+
+  /**
+   * Draws a background behind the row, unless the page is about to break
+   *
+   * @param {PdfTable} table
+   * @param {row} row about to be added
+   * @return {void}
+   */
+  onRowAdd: function (table, row) {
+    var page = table.pdf.page;
+    // calculate y value where the page will break
+    var pageBreakPoint = page.height - page.margins.bottom - table.bottomMargin;
+
+    this._currentRowHeight = row._renderedContent.height;
+    // check if a page break is about to occur when the row is added
+    // if so return and allow onPageAdded to set the row background
+    if (table.pdf.y > (pageBreakPoint - this._currentRowHeight)) return;
+
+    var shade = this._shadingCount % 2 === 0 ? this.shade1 : this.shade2;
+    // shade the row
+    this.rowShading(table.pdf, this.x, table.pdf.y, this.width, this._currentRowHeight, shade)
+      .fillAndStroke(this.textColor, this.textColor); // revert back to text colour
+
+    this._shadingCount++;
+  },
+
+  /**
+   *  Shade the first row after a page is added
+   *
+   * @param {PdfTable} table
+   * @return {void}
+   */
+  onPageAdded: function (table) {
+    var shade = this._shadingCount % 2 === 0 ? this.shade1 : this.shade2;
+    var y = this.offsetHeader ? table.pdf.y + this._headerHeight : table.pdf.y
+    // shades the first row after a page break
+    this.rowShading(table.pdf, this.x, y, this.width, this._currentRowHeight, shade)
+      .fillAndStroke(this.textColor, this.textColor); // revert back to text colour
+
+    this._shadingCount++;
+  },
+
+  /**
+   * Get the height of the table header
+   *
+   * @param {PdfTable} table
+   * @param {header} header with height calculation
+   * @return {void}
+   */
+  onHeaderHeightCalculated: function (table, header) {
+    this._headerHeight = header._renderedContent.height;
+  },
+
+  /**
+   * Draw a rectangle with the chosen shade of colour
+   *
+   * @param {pdf} pdf document
+   * @param {x} X pos of shading
+   * @param {y} Y pos of shading
+   * @param {w} width of shading
+   * @param {h} height of shading
+   * @param {shade} colour of shading
+   *
+   * @return {pdf}
+   */
+  rowShading: (pdf, x, y, w, h, shade) => {
+    return pdf
+      .rect(x, y, w, h)
+      .fillAndStroke(shade, shade);
+  }
+
+});
+
+module.exports = PdfTableRowShader;