Add base32 decoding function

app/src/main/java/com/chameth/yaotp/util/Base32.kt

@@ -0,0 +1,27 @@
+package com.chameth.yaotp.util
+
+private val alphabet = ('A'..'Z') + ('2'..'7') + '='
+
+fun base32Decode(input: String): ByteArray {
+    val values = padToEights(input).toUpperCase().map(alphabet::indexOf)
+    val bytes = ArrayList<Byte>()
+
+    values.chunked(8).forEach { chunk ->
+        // Each chunk of 8 values is mapped on (up to) 5 return bytes:
+        //      [A1   A2   A3   A4   A5] [B1   B2   B3
+        //       B4   B5] [C1   C2   C3   C4   C5] [D1   -- only if C is present
+        //       D2   D3   D4   D5] [E1   E2   E3   E4   -- only if E is present
+        //       E5] [F1   F2   F3   F4   F5] [G1   G2   -- only if F is present
+        //       G3   G4   G5] [H1   H2   H3   H4   H5]  -- only if H is present
+
+        if (chunk[0] != 32) bytes.add(((chunk[0] shl 3) or (chunk[1] ushr 2)).toByte())
+        if (chunk[2] != 32) bytes.add((((chunk[1] and 3) shl 6) or (chunk[2] shl 1) or (chunk[3] ushr 4)).toByte())
+        if (chunk[4] != 32) bytes.add((((chunk[3] and 15) shl 4) or (chunk[4] ushr 1)).toByte())
+        if (chunk[5] != 32) bytes.add((((chunk[4] and 1) shl 7) or (chunk[5] shl 2) or (chunk[6] ushr 3)).toByte())
+        if (chunk[7] != 32) bytes.add((((chunk[6] and 7) shl 5) or chunk[7]).toByte())
+    }
+
+    return bytes.toByteArray()
+}
+
+internal fun padToEights(input: String) = input + "=".repeat((8 - input.length % 8) % 8)

app/src/test/java/com/chameth/yaotp/algos/TestUtils.kt → app/src/test/java/com/chameth/yaotp/TestUtils.kt

@@ -1,3 +1,3 @@
-package com.chameth.yaotp.algos
+package com.chameth.yaotp
 
 fun ByteArray.toHexString() = map { String.format("%02x", it) }.reduce(String::plus)

app/src/test/java/com/chameth/yaotp/algos/HmacTest.kt

@@ -1,5 +1,6 @@
 package com.chameth.yaotp.algos
 
+import com.chameth.yaotp.toHexString
 import com.natpryce.hamkrest.assertion.assert
 import com.natpryce.hamkrest.equalTo
 import org.junit.Test

app/src/test/java/com/chameth/yaotp/algos/HotpTest.kt

@@ -1,5 +1,6 @@
 package com.chameth.yaotp.algos
 
+import com.chameth.yaotp.toHexString
 import com.natpryce.hamkrest.assertion.assert
 import com.natpryce.hamkrest.equalTo
 import org.junit.Test

app/src/test/java/com/chameth/yaotp/algos/TotpTest.kt

@@ -1,5 +1,6 @@
 package com.chameth.yaotp.algos
 
+import com.chameth.yaotp.toHexString
 import com.natpryce.hamkrest.assertion.assert
 import com.natpryce.hamkrest.equalTo
 import org.junit.Test

app/src/test/java/com/chameth/yaotp/util/Base32Test.kt

@@ -0,0 +1,61 @@
+package com.chameth.yaotp.util
+
+import com.chameth.yaotp.toHexString
+import org.junit.Assert.*
+import org.junit.Test
+
+class Base32Test {
+
+    @Test
+    fun testPadToEights_withEmptyString_returnsEmptyString() {
+        assertEquals("", padToEights(""))
+    }
+
+    @Test
+    fun testPadToEights_withMultipleOfEight_doesNotAddPadding() {
+        assertEquals("0123456701234567", padToEights("0123456701234567"))
+    }
+
+    @Test
+    fun testPadToEights_withOddAmounts_padsWithEquals() {
+        assertEquals("012345==", padToEights("012345"))
+        assertEquals("0123====", padToEights("0123"))
+        assertEquals("0=======", padToEights("0"))
+    }
+
+    @Test
+    fun testBase32_withEmptyString() {
+        assertEquals(0, base32Decode("").size)
+        assertEquals(0, base32Decode("====").size)
+        assertEquals(0, base32Decode("========").size)
+    }
+
+    @Test
+    fun testBase32_withAlignedStrings() {
+        assertEquals("00443214c74254b635cf84653a56d9c675be77df", base32Decode("abcdefghijklmnopqrstuvwzyz234567").toHexString())
+        assertEquals("ffffffffff", base32Decode("77777777").toHexString())
+        assertEquals("0000000000", base32Decode("AAAAAAAA").toHexString())
+    }
+
+    @Test
+    fun testBase32_withUnalignedStings() {
+        assertEquals("08", base32Decode("A").toHexString())
+        assertEquals("00", base32Decode("AA").toHexString())
+        assertEquals("0002", base32Decode("AAA").toHexString())
+        assertEquals("fffffffc", base32Decode("777777").toHexString())
+    }
+
+    @Test
+    fun testBase32_withSampleInputs() {
+        assertEquals("28", base32Decode("FA======").toHexString())
+        assertEquals("d6", base32Decode("2Y======").toHexString())
+        assertEquals("d6f8", base32Decode("234A====").toHexString())
+        assertEquals("d6f800", base32Decode("234AA===").toHexString())
+        assertEquals("d6f810", base32Decode("234BA===").toHexString())
+        assertEquals("d6f8110c", base32Decode("234BCDA=").toHexString())
+        assertEquals("d6f8110c80", base32Decode("234BCDEA").toHexString())
+        assertEquals("d6f8110c8530", base32Decode("234BCDEFGA======").toHexString())
+        assertEquals("d6f8110c8536b7c0886429", base32Decode("234BCDEFG234BCDEFE======").toHexString())
+    }
+
+}