<?php
/**
 * A small PDF writer: pages, Unicode text, shapes, images and links.
 *
 * @package TurtleReport
 */

namespace TurtleReport\Pdf;

use TurtleReport\Support\Text;

defined( 'ABSPATH' ) || exit;

/**
 * Writes A4 PDF documents in pure PHP, so reports can be made on the server
 * by a cron job without a browser, Chrome, wkhtmltopdf or an external service.
 *
 * Coordinates are in points (1/72 inch) from the top-left corner of the page,
 * which keeps layout code readable; they're flipped to PDF's bottom-left
 * origin when written.
 *
 * Text uses embedded, subsetted TrueType fonts (Identity-H encoding with a
 * ToUnicode map, so text can be searched and copied). Images can be JPEG or
 * PNG, including PNG transparency when zlib is available; GD, if installed,
 * converts anything else. Content is compressed when zlib is available and
 * written uncompressed otherwise.
 */
final class Document {

	const WIDTH  = 595.28;
	const HEIGHT = 841.89;

	/**
	 * Fonts: key => [TrueTypeFont, used glyphs (gid => code point)].
	 *
	 * @var array<string,array>
	 */
	private $fonts = array();

	/**
	 * Page content streams.
	 *
	 * @var string[]
	 */
	private $pages = array();

	/**
	 * Link annotations per page: [x, y, w, h, url].
	 *
	 * @var array<int,array[]>
	 */
	private $links = array();

	/**
	 * Images: key => Image::load() result.
	 *
	 * @var array<string,array>
	 */
	private $images = array();

	/**
	 * Images used on each page.
	 *
	 * @var array<int,string[]>
	 */
	private $page_images = array();

	/**
	 * Current page index.
	 *
	 * @var int
	 */
	private $page = -1;

	/**
	 * Document title.
	 *
	 * @var string
	 */
	private $title = '';

	/**
	 * Whether zlib compression is available.
	 *
	 * @var bool
	 */
	private $deflate;

	/**
	 * Constructor.
	 */
	public function __construct() {
		$this->deflate = function_exists( 'gzcompress' ) && function_exists( 'gzuncompress' );
	}

	/**
	 * Registers a font.
	 *
	 * @param string       $key  Name used in text().
	 * @param TrueTypeFont $font Font.
	 * @return void
	 */
	public function add_font( $key, TrueTypeFont $font ) {
		$this->fonts[ $key ] = array( $font, array() );
	}

	/**
	 * The font registered under a key.
	 *
	 * @param string $key Font key.
	 * @return TrueTypeFont
	 * @throws \InvalidArgumentException For an unknown key.
	 */
	public function font( $key ) {
		if ( ! isset( $this->fonts[ $key ] ) ) {
			throw new \InvalidArgumentException( 'Unknown PDF font.' );
		}
		return $this->fonts[ $key ][0];
	}

	/**
	 * Sets the document title.
	 *
	 * @param string $title Title.
	 * @return void
	 */
	public function set_title( $title ) {
		$this->title = (string) $title;
	}

	/**
	 * Starts a new page.
	 *
	 * @return int Page index.
	 */
	public function add_page() {
		$this->pages[]                    = '';
		$this->page                       = count( $this->pages ) - 1;
		$this->links[ $this->page ]       = array();
		$this->page_images[ $this->page ] = array();
		return $this->page;
	}

	/**
	 * Number of pages.
	 *
	 * @return int
	 */
	public function page_count() {
		return count( $this->pages );
	}

	/**
	 * Switches to an existing page, e.g. to add page numbers at the end.
	 *
	 * @param int $index Page index.
	 * @return void
	 */
	public function go_to( $index ) {
		if ( isset( $this->pages[ $index ] ) ) {
			$this->page = (int) $index;
		}
	}

	/**
	 * Appends raw content to the current page.
	 *
	 * @param string $ops PDF operators.
	 * @return void
	 */
	private function out( $ops ) {
		if ( $this->page < 0 ) {
			$this->add_page();
		}
		$this->pages[ $this->page ] .= $ops . "\n";
	}

	/**
	 * Formats a number for PDF output.
	 *
	 * @param float $n Number.
	 * @return string
	 */
	private static function n( $n ) {
		$s = number_format( (float) $n, 2, '.', '' );
		$s = rtrim( rtrim( $s, '0' ), '.' );
		return '' !== $s ? $s : '0';
	}

	/**
	 * Converts "#rrggbb" to PDF colour components.
	 *
	 * @param string $hex Colour.
	 * @return string "r g b"
	 */
	private static function rgb( $hex ) {
		$hex = ltrim( (string) $hex, '#' );
		if ( 3 === strlen( $hex ) ) {
			$hex = $hex[0] . $hex[0] . $hex[1] . $hex[1] . $hex[2] . $hex[2];
		}
		if ( ! preg_match( '/^[0-9a-fA-F]{6}$/', $hex ) ) {
			$hex = '000000';
		}
		return self::n( hexdec( substr( $hex, 0, 2 ) ) / 255 ) . ' ' . self::n( hexdec( substr( $hex, 2, 2 ) ) / 255 ) . ' ' . self::n( hexdec( substr( $hex, 4, 2 ) ) / 255 );
	}

	/**
	 * Mixes a colour with white: 0 keeps it, 1 is white. Used for tints, since
	 * pages are white and this avoids transparency.
	 *
	 * @param string $hex    Colour.
	 * @param float  $amount How much white.
	 * @return string "#rrggbb"
	 */
	public static function tint( $hex, $amount ) {
		$hex = ltrim( (string) $hex, '#' );
		if ( ! preg_match( '/^[0-9a-fA-F]{6}$/', $hex ) ) {
			return '#ffffff';
		}
		$out = '#';
		for ( $i = 0; $i < 3; $i++ ) {
			$v    = hexdec( substr( $hex, 2 * $i, 2 ) );
			$out .= sprintf( '%02x', (int) round( $v + ( 255 - $v ) * max( 0, min( 1, $amount ) ) ) );
		}
		return $out;
	}

	/**
	 * Whether white text is readable on a colour (WCAG relative luminance).
	 *
	 * @param string $hex Background colour.
	 * @return bool
	 */
	public static function is_dark( $hex ) {
		$hex = ltrim( (string) $hex, '#' );
		if ( ! preg_match( '/^[0-9a-fA-F]{6}$/', $hex ) ) {
			return true;
		}
		$lum = 0;
		foreach ( array( 0.2126, 0.7152, 0.0722 ) as $i => $w ) {
			$c    = hexdec( substr( $hex, 2 * $i, 2 ) ) / 255;
			$c    = $c <= 0.03928 ? $c / 12.92 : pow( ( $c + 0.055 ) / 1.055, 2.4 );
			$lum += $w * $c;
		}
		return $lum < 0.4;
	}

	/**
	 * Draws a rectangle, optionally with rounded corners.
	 *
	 * @param float       $x      Left.
	 * @param float       $y      Top.
	 * @param float       $w      Width.
	 * @param float       $h      Height.
	 * @param string|null $fill   Fill colour or null.
	 * @param string|null $stroke Stroke colour or null.
	 * @param float       $radius Corner radius.
	 * @param float       $lw     Line width.
	 * @return void
	 */
	public function rect( $x, $y, $w, $h, $fill = null, $stroke = null, $radius = 0.0, $lw = 0.75 ) {
		if ( $w <= 0 || $h <= 0 || ( null === $fill && null === $stroke ) ) {
			return;
		}
		$ops = 'q ';
		if ( null !== $fill ) {
			$ops .= self::rgb( $fill ) . ' rg ';
		}
		if ( null !== $stroke ) {
			$ops .= self::rgb( $stroke ) . ' RG ' . self::n( $lw ) . ' w ';
		}
		$r  = min( (float) $radius, $w / 2, $h / 2 );
		$by = self::HEIGHT - $y - $h;
		if ( $r <= 0 ) {
			$ops .= self::n( $x ) . ' ' . self::n( $by ) . ' ' . self::n( $w ) . ' ' . self::n( $h ) . ' re ';
		} else {
			$k    = 0.5523 * $r;
			$x1   = $x + $w;
			$y1   = $by + $h;
			$ops .= self::n( $x + $r ) . ' ' . self::n( $by ) . ' m ';
			$ops .= self::n( $x1 - $r ) . ' ' . self::n( $by ) . ' l ';
			$ops .= self::n( $x1 - $r + $k ) . ' ' . self::n( $by ) . ' ' . self::n( $x1 ) . ' ' . self::n( $by + $r - $k ) . ' ' . self::n( $x1 ) . ' ' . self::n( $by + $r ) . ' c ';
			$ops .= self::n( $x1 ) . ' ' . self::n( $y1 - $r ) . ' l ';
			$ops .= self::n( $x1 ) . ' ' . self::n( $y1 - $r + $k ) . ' ' . self::n( $x1 - $r + $k ) . ' ' . self::n( $y1 ) . ' ' . self::n( $x1 - $r ) . ' ' . self::n( $y1 ) . ' c ';
			$ops .= self::n( $x + $r ) . ' ' . self::n( $y1 ) . ' l ';
			$ops .= self::n( $x + $r - $k ) . ' ' . self::n( $y1 ) . ' ' . self::n( $x ) . ' ' . self::n( $y1 - $r + $k ) . ' ' . self::n( $x ) . ' ' . self::n( $y1 - $r ) . ' c ';
			$ops .= self::n( $x ) . ' ' . self::n( $by + $r ) . ' l ';
			$ops .= self::n( $x ) . ' ' . self::n( $by + $r - $k ) . ' ' . self::n( $x + $r - $k ) . ' ' . self::n( $by ) . ' ' . self::n( $x + $r ) . ' ' . self::n( $by ) . ' c h ';
		}
		$ops .= ( null !== $fill && null !== $stroke ? 'B' : ( null !== $fill ? 'f' : 'S' ) ) . ' Q';
		$this->out( $ops );
	}

	/**
	 * Draws a straight line.
	 *
	 * @param float  $x1    Start x.
	 * @param float  $y1    Start y.
	 * @param float  $x2    End x.
	 * @param float  $y2    End y.
	 * @param string $color Colour.
	 * @param float  $lw    Line width.
	 * @param bool   $dash  Dashed.
	 * @return void
	 */
	public function line( $x1, $y1, $x2, $y2, $color, $lw = 0.75, $dash = false ) {
		$this->out( 'q ' . self::rgb( $color ) . ' RG ' . self::n( $lw ) . ' w ' . ( $dash ? '[2 2] 0 d ' : '' ) . self::n( $x1 ) . ' ' . self::n( self::HEIGHT - $y1 ) . ' m ' . self::n( $x2 ) . ' ' . self::n( self::HEIGHT - $y2 ) . ' l S Q' );
	}

	/**
	 * Draws connected line segments, or a filled shape.
	 *
	 * @param array[]     $points Points as [x, y].
	 * @param string|null $stroke Stroke colour.
	 * @param string|null $fill   Fill colour (closes the shape).
	 * @param float       $lw     Line width.
	 * @return void
	 */
	public function path( array $points, $stroke = null, $fill = null, $lw = 1.5 ) {
		if ( count( $points ) < 2 ) {
			return;
		}
		$ops = 'q 1 j 1 J ';
		if ( null !== $stroke ) {
			$ops .= self::rgb( $stroke ) . ' RG ' . self::n( $lw ) . ' w ';
		}
		if ( null !== $fill ) {
			$ops .= self::rgb( $fill ) . ' rg ';
		}
		foreach ( array_values( $points ) as $i => $p ) {
			$ops .= self::n( $p[0] ) . ' ' . self::n( self::HEIGHT - $p[1] ) . ( $i ? ' l ' : ' m ' );
		}
		if ( null !== $fill ) {
			$ops .= 'h ' . ( null !== $stroke ? 'B' : 'f' );
		} else {
			$ops .= 'S';
		}
		$this->out( $ops . ' Q' );
	}

	/**
	 * Draws a filled circle.
	 *
	 * @param float  $cx    Centre x.
	 * @param float  $cy    Centre y.
	 * @param float  $r     Radius.
	 * @param string $color Fill colour.
	 * @return void
	 */
	public function circle( $cx, $cy, $r, $color ) {
		$this->rect( $cx - $r, $cy - $r, 2 * $r, 2 * $r, $color, null, $r );
	}

	/**
	 * Width of text in points.
	 *
	 * @param string $text UTF-8 text.
	 * @param string $font Font key.
	 * @param float  $size Font size.
	 * @return float
	 */
	public function width( $text, $font, $size ) {
		$f = $this->font( $font );
		$w = 0.0;
		foreach ( Text::codepoints( $text ) as $cp ) {
			$w += $f->width( $f->glyph( $cp ) );
		}
		return $w * $size / 1000;
	}

	/**
	 * Writes one line of text.
	 *
	 * @param float  $x     Left (or right/centre point, see $align).
	 * @param float  $y     Baseline.
	 * @param string $text  UTF-8 text.
	 * @param string $font  Font key.
	 * @param float  $size  Font size in points.
	 * @param string $color Colour.
	 * @param string $align left, right or center.
	 * @return float Width written.
	 */
	public function text( $x, $y, $text, $font, $size, $color = '#000000', $align = 'left' ) {
		$text = (string) $text;
		if ( '' === $text ) {
			return 0.0;
		}
		$w = $this->width( $text, $font, $size );
		if ( 'right' === $align ) {
			$x -= $w;
		} elseif ( 'center' === $align ) {
			$x -= $w / 2;
		}
		$f   = $this->font( $font );
		$hex = '';
		foreach ( Text::codepoints( $text ) as $cp ) {
			$gid = $f->glyph( $cp );
			if ( ! isset( $this->fonts[ $font ][1][ $gid ] ) ) {
				$this->fonts[ $font ][1][ $gid ] = $gid ? $cp : 0xFFFD;
			}
			$hex .= sprintf( '%04X', $gid );
		}
		$this->out( 'BT ' . self::rgb( $color ) . ' rg /F' . $this->font_index( $font ) . ' ' . self::n( $size ) . ' Tf ' . self::n( $x ) . ' ' . self::n( self::HEIGHT - $y ) . ' Td <' . $hex . '> Tj ET' );
		return $w;
	}

	/**
	 * Writes text cut to a width, ending with an ellipsis when cut.
	 *
	 * @param float  $x     Left.
	 * @param float  $y     Baseline.
	 * @param string $text  Text.
	 * @param string $font  Font key.
	 * @param float  $size  Size.
	 * @param string $color Colour.
	 * @param float  $max   Most width.
	 * @param string $align Alignment.
	 * @return void
	 */
	public function text_fit( $x, $y, $text, $font, $size, $color, $max, $align = 'left' ) {
		$this->text( $x, $y, $this->fit( $text, $font, $size, $max ), $font, $size, $color, $align );
	}

	/**
	 * Text cut to fit a width.
	 *
	 * @param string $text Text.
	 * @param string $font Font key.
	 * @param float  $size Size.
	 * @param float  $max  Width.
	 * @return string
	 */
	public function fit( $text, $font, $size, $max ) {
		$text = (string) $text;
		if ( $this->width( $text, $font, $size ) <= $max ) {
			return $text;
		}
		$chars = Text::chars( $text );
		$lo    = 0;
		$hi    = count( $chars );
		while ( $lo < $hi ) {
			$mid = (int) ceil( ( $lo + $hi ) / 2 );
			if ( $this->width( implode( '', array_slice( $chars, 0, $mid ) ) . '…', $font, $size ) <= $max ) {
				$lo = $mid;
			} else {
				$hi = $mid - 1;
			}
		}
		return rtrim( implode( '', array_slice( $chars, 0, $lo ) ) ) . '…';
	}

	/**
	 * Breaks text into lines that fit a width.
	 *
	 * @param string $text  Text (may contain line breaks).
	 * @param string $font  Font key.
	 * @param float  $size  Size.
	 * @param float  $width Line width.
	 * @return string[]
	 */
	public function wrap( $text, $font, $size, $width ) {
		$lines = array();
		foreach ( preg_split( '/\r\n|\r|\n/', (string) $text ) as $para ) {
			$words = preg_split( '/[ \t]+/u', trim( $para ) );
			$line  = '';
			foreach ( $words as $word ) {
				if ( '' === $word ) {
					continue;
				}
				$try = '' === $line ? $word : $line . ' ' . $word;
				if ( $this->width( $try, $font, $size ) <= $width ) {
					$line = $try;
					continue;
				}
				if ( '' !== $line ) {
					$lines[] = $line;
				}
				// A single word longer than the line is split by characters.
				while ( $this->width( $word, $font, $size ) > $width ) {
					$chars = Text::chars( $word );
					$take  = 1;
					$count = count( $chars );
					while ( $take < $count && $this->width( implode( '', array_slice( $chars, 0, $take + 1 ) ), $font, $size ) <= $width ) {
						++$take;
					}
					$lines[] = implode( '', array_slice( $chars, 0, $take ) );
					$word    = implode( '', array_slice( $chars, $take ) );
				}
				$line = $word;
			}
			$lines[] = $line;
		}
		return $lines;
	}

	/**
	 * Adds a clickable link area.
	 *
	 * @param float  $x   Left.
	 * @param float  $y   Top.
	 * @param float  $w   Width.
	 * @param float  $h   Height.
	 * @param string $url http(s) URL.
	 * @return void
	 */
	public function link( $x, $y, $w, $h, $url ) {
		if ( preg_match( '#^https?://#i', (string) $url ) && $this->page >= 0 ) {
			$this->links[ $this->page ][] = array( $x, $y, $w, $h, (string) $url );
		}
	}

	/**
	 * Draws an image from a file, keeping its aspect ratio inside a box.
	 *
	 * @param string $path  Image file (JPEG or PNG; others need GD).
	 * @param float  $x     Left.
	 * @param float  $y     Top.
	 * @param float  $max_w Most width.
	 * @param float  $max_h Most height.
	 * @param string $align left, right or center inside the box.
	 * @return float[]|null [width, height] drawn, or null when the image can't be used.
	 */
	public function image( $path, $x, $y, $max_w, $max_h, $align = 'left' ) {
		$key = 'I' . md5( (string) $path );
		if ( ! isset( $this->images[ $key ] ) ) {
			$image = Image::load( (string) $path, $this->deflate );
			if ( ! $image ) {
				return null;
			}
			$this->images[ $key ] = $image;
		}
		$img   = $this->images[ $key ];
		$scale = min( $max_w / $img['w'], $max_h / $img['h'] );
		$w     = $img['w'] * $scale;
		$h     = $img['h'] * $scale;
		if ( 'right' === $align ) {
			$x += $max_w - $w;
		} elseif ( 'center' === $align ) {
			$x += ( $max_w - $w ) / 2;
		}
		$y += ( $max_h - $h ) / 2;
		$this->out( 'q ' . self::n( $w ) . ' 0 0 ' . self::n( $h ) . ' ' . self::n( $x ) . ' ' . self::n( self::HEIGHT - $y - $h ) . ' cm /' . $key . ' Do Q' );
		$this->page_images[ $this->page ][ $key ] = $key;
		return array( $w, $h );
	}

	/**
	 * Index of a font in the resources.
	 *
	 * @param string $key Font key.
	 * @return int
	 */
	private function font_index( $key ) {
		return (int) array_search( $key, array_keys( $this->fonts ), true ) + 1;
	}

	/**
	 * Compresses a stream when possible.
	 *
	 * @param string $data   Data.
	 * @param string $extra  Extra dictionary entries.
	 * @return string Stream object body (without "N 0 obj").
	 */
	private function stream( $data, $extra = '' ) {
		if ( $this->deflate ) {
			$data   = gzcompress( $data, 6 );
			$extra .= ' /Filter /FlateDecode';
		}
		return '<< /Length ' . strlen( $data ) . $extra . " >>\nstream\n" . $data . "\nendstream";
	}

	/**
	 * UTF-16BE hex for one code point.
	 *
	 * @param int $cp Code point.
	 * @return string
	 */
	private static function utf16_hex( $cp ) {
		$cp = (int) $cp;
		if ( $cp > 0xFFFF ) {
			$cp -= 0x10000;
			return sprintf( '%04X%04X', 0xD800 | ( $cp >> 10 ), 0xDC00 | ( $cp & 0x3FF ) );
		}
		return sprintf( '%04X', $cp );
	}

	/**
	 * Text string in a PDF dictionary (UTF-16BE with BOM).
	 *
	 * @param string $text UTF-8 text.
	 * @return string
	 */
	private static function pdf_string( $text ) {
		$hex = 'FEFF';
		foreach ( Text::codepoints( $text ) as $cp ) {
			$hex .= self::utf16_hex( $cp );
		}
		return '<' . $hex . '>';
	}

	/**
	 * Escapes a literal PDF string.
	 *
	 * @param string $s ASCII text.
	 * @return string
	 */
	private static function literal( $s ) {
		return '(' . strtr(
			(string) $s,
			array(
				'\\' => '\\\\',
				'('  => '\\(',
				')'  => '\\)',
				"\r" => '\\r',
				"\n" => '\\n',
			)
		) . ')';
	}

	/**
	 * Builds the PDF file.
	 *
	 * @return string
	 */
	public function output() {
		if ( ! $this->pages ) {
			$this->add_page();
		}
		$objects = array();
		$next    = 3; // 1 = catalog, 2 = pages.
		$alloc   = static function () use ( &$next ) {
			return $next++;
		};

		// Fonts.
		$font_refs = array();
		$i         = 0;
		foreach ( $this->fonts as $key => $pair ) {
			++$i;
			list( $font, $used ) = $pair;
			$used[0]             = isset( $used[0] ) ? $used[0] : 0xFFFD;
			ksort( $used );
			$tag  = '';
			$hash = md5( $key . implode( ',', array_keys( $used ) ) );
			for ( $c = 0; $c < 6; $c++ ) {
				$tag .= chr( 65 + hexdec( $hash[ $c ] ) % 26 );
			}
			$base   = $tag . '+' . $font->name;
			$file   = $font->subset( array_keys( $used ) );
			$o_file = $alloc();
			$o_desc = $alloc();
			$o_cid  = $alloc();
			$o_uni  = $alloc();
			$o_font = $alloc();
			$widths = '';
			foreach ( array_keys( $used ) as $gid ) {
				$widths .= $gid . ' [' . (int) round( $font->width( $gid ) ) . '] ';
			}
			$cmap = "/CIDInit /ProcSet findresource begin\n12 dict begin\nbegincmap\n/CIDSystemInfo << /Registry (Adobe) /Ordering (UCS) /Supplement 0 >> def\n/CMapName /Adobe-Identity-UCS def\n/CMapType 2 def\n1 begincodespacerange\n<0000> <FFFF>\nendcodespacerange\n";
			foreach ( array_chunk( $used, 100, true ) as $chunk ) {
				$cmap .= count( $chunk ) . " beginbfchar\n";
				foreach ( $chunk as $gid => $cp ) {
					$cmap .= sprintf( '<%04X> <%s>', $gid, self::utf16_hex( $cp ) ) . "\n";
				}
				$cmap .= "endbfchar\n";
			}
			$cmap .= "endcmap\nCMapName currentdict /CMap defineresource pop\nend\nend";

			$objects[ $o_file ] = $this->stream( $file, ' /Length1 ' . strlen( $file ) );
			$objects[ $o_desc ] = '<< /Type /FontDescriptor /FontName /' . $base . ' /Flags 32 /FontBBox [' . $font->scale( $font->bbox[0] ) . ' ' . $font->scale( $font->bbox[1] ) . ' ' . $font->scale( $font->bbox[2] ) . ' ' . $font->scale( $font->bbox[3] ) . '] /ItalicAngle ' . self::n( $font->italic_angle ) . ' /Ascent ' . $font->scale( $font->ascent ) . ' /Descent ' . $font->scale( $font->descent ) . ' /CapHeight ' . $font->scale( $font->cap_height ) . ' /StemV ' . ( $font->weight >= 600 ? 120 : 80 ) . ' /FontFile2 ' . $o_file . ' 0 R >>';
			$objects[ $o_cid ]  = '<< /Type /Font /Subtype /CIDFontType2 /BaseFont /' . $base . ' /CIDSystemInfo << /Registry (Adobe) /Ordering (Identity) /Supplement 0 >> /FontDescriptor ' . $o_desc . ' 0 R /DW 600 /W [' . trim( $widths ) . '] /CIDToGIDMap /Identity >>';
			$objects[ $o_uni ]  = $this->stream( $cmap );
			$objects[ $o_font ] = '<< /Type /Font /Subtype /Type0 /BaseFont /' . $base . ' /Encoding /Identity-H /DescendantFonts [' . $o_cid . ' 0 R] /ToUnicode ' . $o_uni . ' 0 R >>';
			$font_refs[ $i ]    = $o_font;
		}

		// Images.
		$image_refs = array();
		foreach ( $this->images as $key => $img ) {
			$smask = '';
			if ( null !== $img['smask'] ) {
				$o_mask             = $alloc();
				$objects[ $o_mask ] = '<< /Type /XObject /Subtype /Image /Width ' . $img['w'] . ' /Height ' . $img['h'] . ' /ColorSpace /DeviceGray /BitsPerComponent 8' . $img['smask_params'] . ' /Length ' . strlen( $img['smask'] ) . " >>\nstream\n" . $img['smask'] . "\nendstream";
				$smask              = ' /SMask ' . $o_mask . ' 0 R';
			}
			$o_img              = $alloc();
			$objects[ $o_img ]  = '<< /Type /XObject /Subtype /Image /Width ' . $img['w'] . ' /Height ' . $img['h'] . ' ' . $img['dict'] . $smask . ' /Length ' . strlen( $img['data'] ) . " >>\nstream\n" . $img['data'] . "\nendstream";
			$image_refs[ $key ] = $o_img;
		}

		$font_res = '';
		foreach ( $font_refs as $n => $ref ) {
			$font_res .= '/F' . $n . ' ' . $ref . ' 0 R ';
		}

		// Pages.
		$kids = array();
		foreach ( $this->pages as $index => $content ) {
			$o_content             = $alloc();
			$o_page                = $alloc();
			$objects[ $o_content ] = $this->stream( $content );
			$xobjects              = '';
			foreach ( $this->page_images[ $index ] as $key ) {
				$xobjects .= '/' . $key . ' ' . $image_refs[ $key ] . ' 0 R ';
			}
			$annots = '';
			foreach ( $this->links[ $index ] as $l ) {
				$o_annot             = $alloc();
				$objects[ $o_annot ] = '<< /Type /Annot /Subtype /Link /Rect [' . self::n( $l[0] ) . ' ' . self::n( self::HEIGHT - $l[1] - $l[3] ) . ' ' . self::n( $l[0] + $l[2] ) . ' ' . self::n( self::HEIGHT - $l[1] ) . '] /Border [0 0 0] /A << /S /URI /URI ' . self::literal( $l[4] ) . ' >> >>';
				$annots             .= $o_annot . ' 0 R ';
			}
			$objects[ $o_page ] = '<< /Type /Page /Parent 2 0 R /MediaBox [0 0 ' . self::n( self::WIDTH ) . ' ' . self::n( self::HEIGHT ) . '] /Resources << /ProcSet [/PDF /Text /ImageB /ImageC /ImageI] /Font << ' . $font_res . '>>' . ( '' !== $xobjects ? ' /XObject << ' . $xobjects . '>>' : '' ) . ' >> /Contents ' . $o_content . ' 0 R' . ( '' !== $annots ? ' /Annots [' . trim( $annots ) . ']' : '' ) . ' >>';
			$kids[]             = $o_page . ' 0 R';
		}
		$objects[1]         = '<< /Type /Catalog /Pages 2 0 R >>';
		$objects[2]         = '<< /Type /Pages /Kids [' . implode( ' ', $kids ) . '] /Count ' . count( $kids ) . ' >>';
		$o_info             = $alloc();
		$objects[ $o_info ] = '<< /Producer (TurtleReport) /CreationDate ' . self::literal( 'D:' . gmdate( 'YmdHis' ) . 'Z' ) . ( '' !== $this->title ? ' /Title ' . self::pdf_string( $this->title ) : '' ) . ' >>';

		ksort( $objects );
		$pdf     = "%PDF-1.4\n%\xE2\xE3\xCF\xD3\n";
		$offsets = array();
		foreach ( $objects as $n => $body ) {
			$offsets[ $n ] = strlen( $pdf );
			$pdf          .= $n . " 0 obj\n" . $body . "\nendobj\n";
		}
		$xref = strlen( $pdf );
		$size = max( array_keys( $objects ) ) + 1;
		$pdf .= "xref\n0 " . $size . "\n0000000000 65535 f \n";
		for ( $n = 1; $n < $size; $n++ ) {
			$pdf .= isset( $offsets[ $n ] ) ? sprintf( "%010d 00000 n \n", $offsets[ $n ] ) : "0000000000 65535 f \n";
		}
		$id   = md5( $pdf );
		$pdf .= "trailer\n<< /Size " . $size . ' /Root 1 0 R /Info ' . $o_info . ' 0 R /ID [<' . $id . '> <' . $id . ">] >>\nstartxref\n" . $xref . "\n%%EOF\n";
		return $pdf;
	}
}