feat(lib): Stole (Js)Unpacker lib from tachiyomi-extensions repo (#1551)

lib/unpacker/build.gradle.kts

@@ -0,0 +1,8 @@
+plugins {
+    `java-library`
+    kotlin("jvm")
+}
+
+dependencies {
+    compileOnly(libs.kotlin.stdlib)
+}

lib/unpacker/src/main/java/eu/kanade/tachiyomi/lib/unpacker/SubstringExtractor.kt

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+package eu.kanade.tachiyomi.lib.unpacker
+
+/*
+ * Copyright (C) The Tachiyomi Open Source Project
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+/**
+ * A helper class to extract substrings efficiently.
+ *
+ * Note that all methods move [startIndex] over the ending delimiter.
+ */
+class SubstringExtractor(private val text: String) {
+    private var startIndex = 0
+
+    fun skipOver(str: String) {
+        val index = text.indexOf(str, startIndex)
+        if (index == -1) return
+        startIndex = index + str.length
+    }
+
+    fun substringBefore(str: String): String {
+        val index = text.indexOf(str, startIndex)
+        if (index == -1) return ""
+        val result = text.substring(startIndex, index)
+        startIndex = index + str.length
+        return result
+    }
+
+    fun substringBetween(left: String, right: String): String {
+        val index = text.indexOf(left, startIndex)
+        if (index == -1) return ""
+        val leftIndex = index + left.length
+        val rightIndex = text.indexOf(right, leftIndex)
+        if (rightIndex == -1) return ""
+        startIndex = rightIndex + right.length
+        return text.substring(leftIndex, rightIndex)
+    }
+}

lib/unpacker/src/main/java/eu/kanade/tachiyomi/lib/unpacker/Unpacker.kt

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+package eu.kanade.tachiyomi.lib.unpacker
+
+/*
+ * Copyright (C) The Tachiyomi Open Source Project
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+/**
+ * Helper class to unpack JavaScript code compressed by [packer](http://dean.edwards.name/packer/).
+ *
+ * Source code of packer can be found [here](https://github.com/evanw/packer/blob/master/packer.js).
+ */
+object Unpacker {
+
+    /**
+     * Unpacks JavaScript code compressed by packer.
+     *
+     * Specify [left] and [right] to unpack only the data between them.
+     *
+     * Note: single quotes `\'` in the data will be replaced with double quotes `"`.
+     */
+    fun unpack(script: String, left: String? = null, right: String? = null): String =
+        unpack(SubstringExtractor(script), left, right)
+
+    /**
+     * Unpacks JavaScript code compressed by packer.
+     *
+     * Specify [left] and [right] to unpack only the data between them.
+     *
+     * Note: single quotes `\'` in the data will be replaced with double quotes `"`.
+     */
+    fun unpack(script: SubstringExtractor, left: String? = null, right: String? = null): String {
+        val packed = script
+            .substringBetween("}('", ".split('|'),0,{}))")
+            .replace("\\'", "\"")
+
+        val parser = SubstringExtractor(packed)
+        val data: String
+        if (left != null && right != null) {
+            data = parser.substringBetween(left, right)
+            parser.skipOver("',")
+        } else {
+            data = parser.substringBefore("',")
+        }
+        if (data.isEmpty()) return ""
+
+        val dictionary = parser.substringBetween("'", "'").split("|")
+        val size = dictionary.size
+
+        return wordRegex.replace(data) {
+            val key = it.value
+            val index = parseRadix62(key)
+            if (index >= size) return@replace key
+            dictionary[index].ifEmpty { key }
+        }
+    }
+
+    private val wordRegex by lazy { Regex("""\w+""") }
+
+    private fun parseRadix62(str: String): Int {
+        var result = 0
+        for (ch in str.toCharArray()) {
+            result = result * 62 + when {
+                ch.code <= '9'.code -> { // 0-9
+                    ch.code - '0'.code
+                }
+
+                ch.code >= 'a'.code -> { // a-z
+                    // ch - 'a' + 10
+                    ch.code - ('a'.code - 10)
+                }
+
+                else -> { // A-Z
+                    // ch - 'A' + 36
+                    ch.code - ('A'.code - 36)
+                }
+            }
+        }
+        return result
+    }
+}