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1<?php
2
3declare(strict_types=1);
4
5namespace Phpdftk\Css\Cascade;
6
7/**
8 * Context needed to resolve relative lengths (em/rem/%/vw/vh/ex/ch/lh/rlh)
9 * to absolute pixels.
10 *
11 * - `parentFontSize` — used when resolving `em` on the `font-size` property
12 *   itself (parent's font-size is the reference).
13 * - `currentFontSize` — used for everything else; the resolved font-size of
14 *   the element being computed. Two-pass cascade: resolve font-size first
15 *   with `parentFontSize`, then resolve other lengths using the result.
16 * - `rootFontSize` — `rem` reference; the document root's font-size.
17 * - `viewportWidth` / `viewportHeight` — `vw` / `vh` references in CSS pixels.
18 * - `percentageBasis` — the basis a `%` length resolves against; depends on
19 *   the property (width: containing-block width; line-height: own font-size,
20 *   etc.). Callers pass per-property as needed.
21 */
22final readonly class LengthContext
23{
24    public function __construct(
25        public float $parentFontSize = 16.0,
26        public float $currentFontSize = 16.0,
27        public float $rootFontSize = 16.0,
28        public float $viewportWidth = 816.0,    // 8.5in × 96 DPI
29        public float $viewportHeight = 1056.0,  // 11in × 96 DPI
30        public float $percentageBasis = 0.0,
31    ) {}
32
33    public function withCurrentFontSize(float $px): self
34    {
35        return new self(
36            $this->parentFontSize,
37            $px,
38            $this->rootFontSize,
39            $this->viewportWidth,
40            $this->viewportHeight,
41            $this->percentageBasis,
42        );
43    }
44
45    public function withPercentageBasis(float $px): self
46    {
47        return new self(
48            $this->parentFontSize,
49            $this->currentFontSize,
50            $this->rootFontSize,
51            $this->viewportWidth,
52            $this->viewportHeight,
53            $px,
54        );
55    }
56}