<?php

/**
 * Text Banner Generator
 *
 * Draws a simple gradient banner with the event title, date and place.
 *
 * This class must stay free of WordPress. The single exception is
 * apply_filters(), which lets a site swap the font file. Keeping it
 * WordPress-free is what lets the unit tests run without loading WordPress.
 *
 * @package Aisentic\Media
 */

declare(strict_types=1);

namespace Aisentic\Media;

defined( 'ABSPATH' ) || exit;

/**
 * Draws a text banner PNG using GD.
 */
class Text_Banner_Generator {

	/**
	 * Banner width in pixels.
	 *
	 * @var int
	 */
	public const BANNER_WIDTH = 1920;

	/**
	 * Banner height in pixels.
	 *
	 * @var int
	 */
	public const BANNER_HEIGHT = 640;

	/**
	 * Card width in pixels.
	 *
	 * @var int
	 */
	public const CARD_WIDTH = 1200;

	/**
	 * Card height in pixels.
	 *
	 * @var int
	 */
	public const CARD_HEIGHT = 800;

	/**
	 * Dark gradient pairs. Each entry is [ start_rgb, end_rgb ].
	 *
	 * All are dark enough for white text to stay readable.
	 *
	 * @var array
	 */
	private const PALETTE = [
		[ [ 17, 24, 39 ], [ 55, 65, 81 ] ],
		[ [ 30, 27, 75 ], [ 79, 70, 229 ] ],
		[ [ 12, 74, 110 ], [ 2, 132, 199 ] ],
		[ [ 19, 78, 74 ], [ 13, 148, 136 ] ],
		[ [ 76, 29, 149 ], [ 147, 51, 234 ] ],
		[ [ 127, 29, 29 ], [ 190, 38, 38 ] ],
		[ [ 120, 53, 15 ], [ 194, 110, 6 ] ],
		[ [ 20, 83, 45 ], [ 22, 143, 74 ] ],
	];

	/**
	 * Whether GD with FreeType text support is present.
	 *
	 * @return bool
	 */
	public static function is_available(): bool {
		return extension_loaded( 'gd' )
			&& function_exists( 'imagecreatetruecolor' )
			&& function_exists( 'imagettftext' )
			&& function_exists( 'imagettfbbox' );
	}

	/**
	 * Pick a gradient pair from a seed string.
	 *
	 * The same seed always returns the same pair.
	 *
	 * @param string $seed Seed string, normally the event title.
	 * @return array [ start_rgb, end_rgb ]
	 */
	public static function palette_for( string $seed ): array {
		$index = abs( crc32( $seed ) ) % count( self::PALETTE );

		return self::PALETTE[ $index ];
	}

	/**
	 * Whether the text only uses Latin characters the bundled font can draw.
	 *
	 * Anything above U+024F (Latin Extended-B) is treated as non-Latin.
	 *
	 * @param string $text Text to check.
	 * @return bool
	 */
	public static function is_latin( string $text ): bool {
		return 0 === preg_match( '/[^\x{0000}-\x{024F}]/u', $text );
	}

	/**
	 * Decide which title the picture should show.
	 *
	 * Returns null when the title cannot be drawn and no English fallback
	 * was supplied. The caller then draws a banner with no title.
	 *
	 * @param string      $title        The real event title.
	 * @param string|null $banner_title Optional English title for the picture.
	 * @return string|null
	 */
	public static function display_title( string $title, ?string $banner_title = null ): ?string {
		if ( self::is_latin( $title ) ) {
			return $title;
		}

		$fallback = trim( (string) $banner_title );

		if ( '' !== $fallback && self::is_latin( $fallback ) ) {
			return $fallback;
		}

		return null;
	}

	/**
	 * Draw a banner and write it to a temp PNG file.
	 *
	 * Accepted keys: title, banner_title, date_line, place_line, width,
	 * height, temp_dir.
	 *
	 * @param array $context Drawing context.
	 * @return string|null Absolute path to the PNG, or null on any failure.
	 */
	public static function generate( array $context ): ?string {
		if ( ! self::is_available() ) {
			return null;
		}

		$width  = (int) ( $context['width'] ?? self::BANNER_WIDTH );
		$height = (int) ( $context['height'] ?? self::BANNER_HEIGHT );

		if ( $width < 1 || $height < 1 ) {
			return null;
		}

		$image = imagecreatetruecolor( $width, $height );

		if ( ! $image ) {
			return null;
		}

		[ $start, $end ] = self::palette_for( (string) ( $context['title'] ?? '' ) );
		self::draw_gradient( $image, $width, $height, $start, $end );

		self::draw_text(
			$image,
			$width,
			$height,
			self::display_title( (string) ( $context['title'] ?? '' ), $context['banner_title'] ?? null ),
			trim( (string) ( $context['date_line'] ?? '' ) ),
			trim( (string) ( $context['place_line'] ?? '' ) )
		);

		$path  = self::temp_path( (string) ( $context['temp_dir'] ?? sys_get_temp_dir() ) );
		$saved = imagepng( $image, $path );
		imagedestroy( $image );

		return $saved ? $path : null;
	}

	/**
	 * Absolute path to a bundled font file.
	 *
	 * A site can point this at its own font — for example a Bengali or
	 * Arabic font — through the aisentic_banner_font_path filter.
	 *
	 * @param string $weight Either 'bold' or 'regular'.
	 * @return string
	 */
	public static function font_path( string $weight = 'regular' ): string {
		$file = 'bold' === $weight ? 'DejaVuSans-Bold.ttf' : 'DejaVuSans.ttf';

		// AISENTIC_DIR is __DIR__, which has no trailing slash. Join with an
		// explicit separator so the path is right either way.
		$path = rtrim( AISENTIC_DIR, '/\\' ) . '/assets/fonts/' . $file;

		return (string) apply_filters( 'aisentic_banner_font_path', $path, $weight );
	}

	/**
	 * Find the largest font size at which the title fits the given box.
	 *
	 * Shrinks by 4 pixels at a time. If nothing fits, it returns the
	 * minimum size with the lines cut to $max_lines.
	 *
	 * @param string $font_path  Path to a .ttf file.
	 * @param string $text       Title text.
	 * @param int    $max_width  Maximum line width in pixels.
	 * @param int    $start_size Largest font size to try.
	 * @param int    $min_size   Smallest font size to try.
	 * @param int    $max_lines  Maximum number of lines.
	 * @return array [ 'size' => int, 'lines' => string[] ]
	 */
	public static function fit_title(
		string $font_path,
		string $text,
		int $max_width,
		int $start_size,
		int $min_size,
		int $max_lines
	): array {
		for ( $size = $start_size; $size >= $min_size; $size -= 4 ) {
			$lines = self::wrap( $font_path, $size, $text, $max_width );

			if ( count( $lines ) > $max_lines ) {
				continue;
			}

			$fits = true;

			foreach ( $lines as $line ) {
				if ( self::text_width( $font_path, $size, $line ) > $max_width ) {
					$fits = false;
					break;
				}
			}

			if ( $fits ) {
				return [
					'size'  => $size,
					'lines' => $lines,
				];
			}
		}

		return [
			'size'  => $min_size,
			'lines' => array_slice( self::wrap( $font_path, $min_size, $text, $max_width ), 0, $max_lines ),
		];
	}

	/**
	 * Break text into lines that fit a width.
	 *
	 * A single word longer than the width gets its own line and overflows.
	 *
	 * @param string $font_path Path to a .ttf file.
	 * @param int    $size      Font size.
	 * @param string $text      Text to wrap.
	 * @param int    $max_width Maximum line width.
	 * @return array
	 */
	private static function wrap( string $font_path, int $size, string $text, int $max_width ): array {
		$words = preg_split( '/\s+/u', trim( $text ) );
		$words = is_array( $words ) ? array_filter( $words, 'strlen' ) : [];

		$lines   = [];
		$current = '';

		foreach ( $words as $word ) {
			$candidate = '' === $current ? $word : $current . ' ' . $word;

			if ( '' === $current || self::text_width( $font_path, $size, $candidate ) <= $max_width ) {
				$current = $candidate;
				continue;
			}

			$lines[] = $current;
			$current = $word;
		}

		if ( '' !== $current ) {
			$lines[] = $current;
		}

		return $lines;
	}

	/**
	 * Measure the pixel width of a piece of text.
	 *
	 * @param string $font_path Path to a .ttf file.
	 * @param int    $size      Font size.
	 * @param string $text      Text to measure.
	 * @return int
	 */
	private static function text_width( string $font_path, int $size, string $text ): int {
		$box = imagettfbbox( $size, 0, $font_path, $text );

		if ( ! $box ) {
			return PHP_INT_MAX;
		}

		return (int) abs( $box[2] - $box[0] );
	}

	/**
	 * Write the title, date and place onto the canvas.
	 *
	 * When $title is null the date takes the title's place, so a title the
	 * bundled font cannot draw never turns into empty boxes.
	 *
	 * @param \GdImage    $image  Image resource.
	 * @param int         $width  Canvas width.
	 * @param int         $height Canvas height.
	 * @param string|null $title  Title to draw, or null to skip it.
	 * @param string      $date   Date line.
	 * @param string      $place  Place line.
	 * @return void
	 */
	private static function draw_text(
		\GdImage $image,
		int $width,
		int $height,
		?string $title,
		string $date,
		string $place
	): void {
		$bold    = self::font_path( 'bold' );
		$regular = self::font_path( 'regular' );

		if ( ! file_exists( $bold ) || ! file_exists( $regular ) ) {
			return;
		}

		$white   = imagecolorallocate( $image, 255, 255, 255 );
		$muted   = imagecolorallocate( $image, 226, 232, 240 );
		$padding = (int) round( $width * 0.07 );
		$box     = $width - ( $padding * 2 );

		// When there is no drawable title, the date becomes the headline.
		$headline = null !== $title && '' !== trim( $title ) ? $title : $date;
		$sub_date = $headline === $date ? '' : $date;

		if ( '' === trim( $headline ) ) {
			return;
		}

		$fit = self::fit_title(
			$bold,
			$headline,
			$box,
			(int) round( $height * 0.17 ),
			(int) round( $height * 0.06 ),
			2
		);

		$title_lead = (int) round( $fit['size'] * 1.25 );
		$meta_lines = array_values( array_filter( [ $sub_date, $place ], 'strlen' ) );

		// Tie the small text to the shorter side too, so a tall, narrow card
		// does not push the date line past the right edge.
		$meta_size = self::fit_meta_size(
			$regular,
			$meta_lines,
			$box,
			(int) round( min( $width * 0.032, $height * 0.055 ) )
		);

		$meta_lead  = (int) round( $meta_size * 1.6 );
		$meta_gap   = (int) round( $height * 0.035 );
		$bar_height = max( 4, (int) round( $height * 0.012 ) );
		$bar_gap    = (int) round( $height * 0.05 );

		$block = $bar_height + $bar_gap + ( count( $fit['lines'] ) * $title_lead );

		if ( ! empty( $meta_lines ) ) {
			$block += $meta_gap + ( count( $meta_lines ) * $meta_lead );
		}

		$y = (int) round( ( $height - $block ) / 2 );

		imagefilledrectangle(
			$image,
			$padding,
			$y,
			$padding + (int) round( $width * 0.08 ),
			$y + $bar_height,
			$white
		);

		$y += $bar_height + $bar_gap + $fit['size'];

		foreach ( $fit['lines'] as $line ) {
			imagettftext( $image, $fit['size'], 0, $padding, $y, $white, $bold, $line );
			$y += $title_lead;
		}

		// Back up to the last title baseline, then start the small text below it.
		$y = $y - $title_lead + $meta_gap + $meta_lead;

		foreach ( $meta_lines as $line ) {
			imagettftext( $image, $meta_size, 0, $padding, $y, $muted, $regular, $line );
			$y += $meta_lead;
		}
	}

	/**
	 * Shrink the small text until every line fits the box.
	 *
	 * @param string $font_path  Path to a .ttf file.
	 * @param array  $lines      Lines to measure.
	 * @param int    $max_width  Maximum line width in pixels.
	 * @param int    $start_size Size to start from.
	 * @return int
	 */
	private static function fit_meta_size( string $font_path, array $lines, int $max_width, int $start_size ): int {
		$min_size = max( 10, (int) round( $start_size * 0.6 ) );

		for ( $size = $start_size; $size > $min_size; $size -= 2 ) {
			$fits = true;

			foreach ( $lines as $line ) {
				if ( self::text_width( $font_path, $size, $line ) > $max_width ) {
					$fits = false;
					break;
				}
			}

			if ( $fits ) {
				return $size;
			}
		}

		return $min_size;
	}

	/**
	 * Fill the canvas with a top-to-bottom gradient.
	 *
	 * @param \GdImage $image  Image resource.
	 * @param int      $width  Canvas width.
	 * @param int      $height Canvas height.
	 * @param array    $start  Top colour as [ r, g, b ].
	 * @param array    $end    Bottom colour as [ r, g, b ].
	 * @return void
	 */
	private static function draw_gradient( \GdImage $image, int $width, int $height, array $start, array $end ): void {
		$span = $height > 1 ? $height - 1 : 1;

		for ( $y = 0; $y < $height; $y++ ) {
			$ratio = $y / $span;
			$color = imagecolorallocate(
				$image,
				(int) round( $start[0] + ( $end[0] - $start[0] ) * $ratio ),
				(int) round( $start[1] + ( $end[1] - $start[1] ) * $ratio ),
				(int) round( $start[2] + ( $end[2] - $start[2] ) * $ratio )
			);

			imagefilledrectangle( $image, 0, $y, $width, $y, $color );
		}
	}

	/**
	 * Build an unused temp file path ending in .png.
	 *
	 * @param string $dir Directory to write into.
	 * @return string
	 */
	private static function temp_path( string $dir ): string {
		$dir = '' !== trim( $dir ) ? rtrim( $dir, '/\\' ) : sys_get_temp_dir();

		return $dir . '/aisentic-banner-' . bin2hex( random_bytes( 8 ) ) . '.png';
	}
}