Added info on workflows

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Author: AlexRogalskiy

commons/src/main/kotlin/io/nullables/api/playground/commons/utils/NubanValidator.kt

@@ -0,0 +1,44 @@
+package io.nullables.api.playground.commons.utils
+
+/**
+ * NUBAN standards: https://www.cbn.gov.ng/Out/2020/PSMD/REVISED%20STANDARDS%20ON%20NIGERIA%20UNIFORM%20BANK%20ACCOUNT%20NUMBER%20(NUBAN)%20FOR%20BANKS%20AND%20OTHER%20FINANCIAL%20INSTITUTIONS%20.pdf
+ */
+class NubanValidator {
+
+    private companion object {
+        /**
+         *  DMB: Deposit Money Banks
+         */
+        private const val DMB_BANK_CODE_LENGTH = 3
+
+        /**
+         * OFI: Other Financial Institutions
+         */
+        private const val OFI_BANK_CODE_LENGTH = 5
+        private val ALGORITHM = intArrayOf(3, 7, 3, 3, 7, 3, 3, 7, 3, 3, 7, 3, 3, 7, 3)
+    }
+
+    fun validate(bankCode: String, accountNumber: String): Boolean {
+        require(accountNumber.length == 10) { "Account number must be 10 digits long" }
+
+        val formattedBankCode = when (bankCode.length) {
+            DMB_BANK_CODE_LENGTH -> "000$bankCode"
+            OFI_BANK_CODE_LENGTH -> "9$bankCode"
+            else -> throw IllegalArgumentException("Bank code must be 3 or 5 digits")
+        }
+
+        val nubanSerialNumber = accountNumber.take(9)
+        val checkDigit = Character.getNumericValue(accountNumber.last())
+
+        val validatedCheckDigit = 10
+            .minus(
+                (formattedBankCode + nubanSerialNumber)
+                    .mapIndexed { index, char -> Character.getNumericValue(char) * ALGORITHM[index] }
+                    .sum()
+                    .rem(10)
+            )
+            .rem(10)
+
+        return checkDigit == validatedCheckDigit
+    }
+}