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+<?php
+
+declare(strict_types=1);
+
+/**
+ * Devanagari.php
+ *
+ * @since     2026-04-30
+ * @category  Library
+ * @package   Unicode
+ * @author    Nicola Asuni <info@tecnick.com>
+ * @copyright 2011-2026 Nicola Asuni - Tecnick.com LTD
+ * @license   https://www.gnu.org/copyleft/lesser.html GNU-LGPL v3 (see LICENSE)
+ * @link      https://github.com/tecnickcom/tc-lib-unicode
+ *
+ * This file is part of tc-lib-unicode software library.
+ */
+
+namespace Com\Tecnick\Unicode\Substitution;
+
+use Com\Tecnick\Unicode\Data\Devanagari as DevanagariData;
+
+/**
+ * Com\Tecnick\Unicode\Substitution\Devanagari
+ *
+ * Repositions Devanagari left-positional matras (vowel signs with Indic
+ * Positional Category "Left", such as U+093F VOWEL SIGN I) to precede their
+ * base consonant cluster in the codepoint array.
+ *
+ * In Unicode logical order a left matra is stored after the consonant (or
+ * conjunct cluster) it modifies. For PDF glyph streams the matra glyph must
+ * appear before the consonant, so each left matra is moved to immediately
+ * before the cluster that precedes it.
+ *
+ * A consonant cluster is: base_consonant (VIRAMA base_consonant)*
+ * Only base consonants in the range U+0915–U+0939 and U+0958–U+095F are
+ * recognised as cluster heads. Orphaned matras (no preceding consonant) and
+ * unknown codepoints are left unchanged.
+ *
+ * @since     2026-04-30
+ * @category  Library
+ * @package   Unicode
+ * @author    Nicola Asuni <info@tecnick.com>
+ * @copyright 2011-2026 Nicola Asuni - Tecnick.com LTD
+ * @license   https://www.gnu.org/copyleft/lesser.html GNU-LGPL v3 (see LICENSE)
+ * @link      https://github.com/tecnickcom/tc-lib-unicode
+ */
+final class Devanagari
+{
+    /**
+     * Transformed codepoint array.
+     *
+     * @var list<int>
+     */
+    private array $ordarr;
+
+    /**
+     * @param array<int, int> $ordarr Array of Unicode codepoints.
+     */
+    public function __construct(array $ordarr)
+    {
+        $this->ordarr = array_values($ordarr);
+        $this->process();
+    }
+
+    /**
+     * Returns the transformed codepoint array.
+     *
+     * @return list<int>
+     */
+    public function getOrdarr(): array
+    {
+        return $this->ordarr;
+    }
+
+    /**
+     * Iterates over the codepoint array and repositions left matras that
+     * follow a consonant cluster.
+     */
+    private function process(): void
+    {
+        $len = count($this->ordarr);
+        $result = [];
+        $idx = 0;
+        while ($idx < $len) {
+            $cp = $this->ordarr[$idx] ?? null;
+            if ($cp === null) {
+                ++$idx;
+                continue;
+            }
+
+            if ($this->isBaseConsonant($cp)) {
+                $idx = $this->processConsonantCluster($idx, $len, $result);
+                continue;
+            }
+
+            $result[] = $cp;
+            ++$idx;
+        }
+
+        $this->ordarr = array_values($result);
+    }
+
+    /**
+     * Collects the full conjunct cluster starting at $idx, then checks
+     * whether the next codepoint is a left matra. If so, emits the matra
+     * first and the cluster second; otherwise emits the cluster as-is.
+     *
+     * @param int             $idx    Current index in $this->ordarr.
+     * @param int             $len    Length of $this->ordarr.
+     * @param list<int> $result Result accumulator (passed by reference).
+     *
+     * @return int Updated index after all consumed codepoints.
+     */
+    private function processConsonantCluster(int $idx, int $len, array &$result): int
+    {
+        $cluster = $this->collectCluster($idx, $len);
+        $endIdx = $idx + count($cluster);
+
+        if ($endIdx < $len) {
+            $matra = $this->ordarr[$endIdx] ?? null;
+            if ($matra !== null && $this->isLeftMatra($matra)) {
+                $result[] = $matra;
+                foreach ($cluster as $codepoint) {
+                    $result[] = $codepoint;
+                }
+
+                return $endIdx + 1;
+            }
+        }
+
+        foreach ($cluster as $codepoint) {
+            $result[] = $codepoint;
+        }
+
+        return $endIdx;
+    }
+
+    /**
+     * Collects the full conjunct cluster: base_consonant (VIRAMA base_consonant)*
+     *
+     * @param int $idx Starting index of the cluster head.
+     * @param int $len Length of $this->ordarr.
+     *
+     * @return list<int> Collected cluster codepoints.
+     */
+    private function collectCluster(int $idx, int $len): array
+    {
+        $first = $this->ordarr[$idx] ?? null;
+        if ($first === null) {
+            return [];
+        }
+
+        $cluster = [$first];
+        $pos = $idx + 1;
+        while (($pos + 1) < $len) {
+            $virama = $this->ordarr[$pos] ?? null;
+            $baseConsonant = $this->ordarr[$pos + 1] ?? null;
+            assert($baseConsonant !== null, 'Expected Devanagari base consonant after virama candidate');
+            if ($virama !== DevanagariData::VIRAMA || !$this->isBaseConsonant($baseConsonant)) {
+                break;
+            }
+
+            $cluster[] = $virama;
+            $cluster[] = $baseConsonant;
+            $pos += 2;
+        }
+
+        return $cluster;
+    }
+
+    /**
+     * Returns true when $codepoint is a Devanagari base consonant.
+     */
+    private function isBaseConsonant(int $codepoint): bool
+    {
+        return $this->isInStandardRange($codepoint) || $this->isInExtendedRange($codepoint);
+    }
+
+    /**
+     * Returns true when $codepoint is in the standard consonant range
+     * U+0915–U+0939.
+     */
+    private function isInStandardRange(int $codepoint): bool
+    {
+        return $codepoint >= DevanagariData::BASE_CONSONANT_FIRST && $codepoint <= DevanagariData::BASE_CONSONANT_LAST;
+    }
+
+    /**
+     * Returns true when $codepoint is in the extended consonant range
+     * U+0958–U+095F.
+     */
+    private function isInExtendedRange(int $codepoint): bool
+    {
+        return (
+            $codepoint >= DevanagariData::BASE_CONSONANT_EXT_FIRST
+            && $codepoint <= DevanagariData::BASE_CONSONANT_EXT_LAST
+        );
+    }
+
+    /**
+     * Returns true when $codepoint is a Devanagari left matra.
+     */
+    private function isLeftMatra(int $codepoint): bool
+    {
+        return array_key_exists($codepoint, DevanagariData::LEFT_MATRAS);
+    }
+}