better UI, +windows1251 encoding support

shared/src/commonMain/kotlin/net/sergeych/toread/fb2/Fb2Format.kt

@@ -10,7 +10,7 @@ object Fb2Format {
         val xml = if (looksLikeZip(input) || fileName?.endsWith(".zip", ignoreCase = true) == true) {
             Fb2Zip.extractFb2Xml(input)
         } else {
-            input.decodeToString()
+            Fb2XmlEncoding.decodeXml(input)
         }
         return parseXml(xml)
     }

shared/src/commonMain/kotlin/net/sergeych/toread/fb2/Fb2XmlEncoding.kt

@@ -0,0 +1,103 @@
+package net.sergeych.toread.fb2
+
+internal object Fb2XmlEncoding {
+    private val EncodingPattern = Regex("""encoding\s*=\s*["']([^"']+)["']""", RegexOption.IGNORE_CASE)
+
+    fun decodeXml(bytes: ByteArray): String =
+        when (declaredEncoding(bytes)?.lowercase()) {
+            "windows-1251" -> decodeWindows1251(bytes)
+            else -> bytes.decodeToString()
+        }
+
+    private fun declaredEncoding(bytes: ByteArray): String? {
+        val probe = bytes
+            .copyOfRange(0, minOf(bytes.size, 256))
+            .map { byte ->
+                val value = byte.toInt() and 0xff
+                if (value in 0x20..0x7e || value == '\n'.code || value == '\r'.code || value == '\t'.code) {
+                    value.toChar()
+                } else {
+                    ' '
+                }
+            }
+            .joinToString("")
+        return EncodingPattern.find(probe)?.groupValues?.getOrNull(1)?.trim()
+    }
+
+    private fun decodeWindows1251(bytes: ByteArray): String = buildString(bytes.size) {
+        bytes.forEach { byte ->
+            append(windows1251Char(byte.toInt() and 0xff))
+        }
+    }
+
+    private fun windows1251Char(value: Int): Char =
+        when (value) {
+            in 0x00..0x7f -> value.toChar()
+            0x80 -> '\u0402'
+            0x81 -> '\u0403'
+            0x82 -> '\u201a'
+            0x83 -> '\u0453'
+            0x84 -> '\u201e'
+            0x85 -> '\u2026'
+            0x86 -> '\u2020'
+            0x87 -> '\u2021'
+            0x88 -> '\u20ac'
+            0x89 -> '\u2030'
+            0x8a -> '\u0409'
+            0x8b -> '\u2039'
+            0x8c -> '\u040a'
+            0x8d -> '\u040c'
+            0x8e -> '\u040b'
+            0x8f -> '\u040f'
+            0x90 -> '\u0452'
+            0x91 -> '\u2018'
+            0x92 -> '\u2019'
+            0x93 -> '\u201c'
+            0x94 -> '\u201d'
+            0x95 -> '\u2022'
+            0x96 -> '\u2013'
+            0x97 -> '\u2014'
+            0x98 -> '\uFFFD'
+            0x99 -> '\u2122'
+            0x9a -> '\u0459'
+            0x9b -> '\u203a'
+            0x9c -> '\u045a'
+            0x9d -> '\u045c'
+            0x9e -> '\u045b'
+            0x9f -> '\u045f'
+            0xa0 -> '\u00a0'
+            0xa1 -> '\u040e'
+            0xa2 -> '\u045e'
+            0xa3 -> '\u0408'
+            0xa4 -> '\u00a4'
+            0xa5 -> '\u0490'
+            0xa6 -> '\u00a6'
+            0xa7 -> '\u00a7'
+            0xa8 -> '\u0401'
+            0xa9 -> '\u00a9'
+            0xaa -> '\u0404'
+            0xab -> '\u00ab'
+            0xac -> '\u00ac'
+            0xad -> '\u00ad'
+            0xae -> '\u00ae'
+            0xaf -> '\u0407'
+            0xb0 -> '\u00b0'
+            0xb1 -> '\u00b1'
+            0xb2 -> '\u0406'
+            0xb3 -> '\u0456'
+            0xb4 -> '\u0491'
+            0xb5 -> '\u00b5'
+            0xb6 -> '\u00b6'
+            0xb7 -> '\u00b7'
+            0xb8 -> '\u0451'
+            0xb9 -> '\u2116'
+            0xba -> '\u0454'
+            0xbb -> '\u00bb'
+            0xbc -> '\u0458'
+            0xbd -> '\u0405'
+            0xbe -> '\u0455'
+            0xbf -> '\u0457'
+            in 0xc0..0xff -> (0x0410 + value - 0xc0).toChar()
+            else -> '\uFFFD'
+        }
+}

shared/src/commonMain/kotlin/net/sergeych/toread/fb2/Fb2Zip.kt

@@ -12,7 +12,7 @@ internal object Fb2Zip {
         val entry = entries.firstOrNull { it.name.endsWith(".fb2", ignoreCase = true) }
             ?: entries.firstOrNull { !it.name.endsWith("/") }
             ?: throw Fb2ParseException("ZIP archive does not contain an FB2 entry")
-        return readEntry(zip, entry).decodeToString()
+        return Fb2XmlEncoding.decodeXml(readEntry(zip, entry))
     }
 
     fun createStoredZip(entryName: String, content: ByteArray): ByteArray {

shared/src/commonTest/kotlin/net/sergeych/toread/fb2/Fb2FormatTest.kt

@@ -43,6 +43,31 @@ class Fb2FormatTest {
         assertTrue(zip.copyOfRange(0, 4).contentEquals(byteArrayOf(0x50, 0x4b, 0x03, 0x04)))
     }
 
+    @Test
+    fun parsesWindows1251PlainXml() {
+        val book = Fb2Format.parse(windows1251Xml.encodeWindows1251(), "legacy.fb2")
+
+        assertEquals("Тестовая книга", book.title)
+        assertEquals("Привет, мир.", book.sections.single().paragraphs.single())
+    }
+
+    @Test
+    fun parsesWindows1251StoredZip() {
+        val zip = Fb2Zip.createStoredZip("legacy.fb2", windows1251Xml.encodeWindows1251())
+        val book = Fb2Format.parse(zip, "legacy.fb2.zip")
+
+        assertEquals("Тестовая книга", book.title)
+        assertEquals("Привет, мир.", book.sections.single().paragraphs.single())
+    }
+
+    @Test
+    fun fallsBackToUtf8ForUnknownEncoding() {
+        val xml = sampleXml.replace("encoding=\"UTF-8\"", "encoding=\"KOI8-R\"")
+        val book = Fb2Format.parse(xml.encodeToByteArray(), "unknown.fb2")
+
+        assertEquals("The Test Book", book.title)
+    }
+
     @Test
     fun preservesReadableBlocksAndInlineStyles() {
         val book = Fb2Format.parseXml(richXml)
@@ -108,4 +133,37 @@ class Fb2FormatTest {
           </body>
         </FictionBook>
     """.trimIndent()
+
+    private val windows1251Xml = """
+        <?xml version="1.0" encoding="windows-1251"?>
+        <FictionBook xmlns="http://www.gribuser.ru/xml/fictionbook/2.0" xmlns:xlink="http://www.w3.org/1999/xlink">
+          <description>
+            <title-info>
+              <author><nickname>Автор</nickname></author>
+              <book-title>Тестовая книга</book-title>
+              <lang>ru</lang>
+            </title-info>
+            <document-info>
+              <author><nickname>Toread</nickname></author>
+              <date>2026-05-12</date>
+              <id>legacy</id>
+              <version>1.0</version>
+            </document-info>
+          </description>
+          <body><section><p>Привет, мир.</p></section></body>
+        </FictionBook>
+    """.trimIndent()
+
+    private fun String.encodeWindows1251(): ByteArray =
+        ByteArray(length) { index ->
+            val char = this[index]
+            val value = when {
+                char.code <= 0x7f -> char.code
+                char in 'А'..'я' -> 0xc0 + char.code - 'А'.code
+                char == 'Ё' -> 0xa8
+                char == 'ё' -> 0xb8
+                else -> error("Test character $char is not mapped to windows-1251")
+            }
+            value.toByte()
+        }
 }