Merge pull request #1417 from XRPLF/normalize_currency_code_sample

Add 'Normalize Currency Code' code sample

content/_code-samples/normalize-currency-codes/README.md

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+# Normalize Currency Codes
+
+Convert from a string from either the XRP Ledger's "standard" 3-character or "non-standard" 40-character hexadecimal format into a string for humans to read.

content/_code-samples/normalize-currency-codes/js/normalize-currency-code.js

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+////////////////////////////////////////////////////////////////////////////////
+// Normalize Currency Codes
+// Original authors: Ali (XUMM), nixer89
+// Upstream version: https://github.com/nixer89/xrpl-services-frontend/blob/master/src/app/utils/normalizers.ts
+////////////////////////////////////////////////////////////////////////////////
+// Convert from a string from either the XRP Ledger's "standard" 3-character
+// format, or several possible decodings of the "non-standard" 40-character
+// hexadecimal format into a string for humans to read.
+//
+// This code is intended for use with Node.js.
+////////////////////////////////////////////////////////////////////////////////
+
+function normalizeCurrencyCode(currencyCode, maxLength = 20) {
+    if(!currencyCode) return "";
+
+    if(currencyCode.length === 3 && currencyCode.trim().toLowerCase() !== 'xrp') {
+        // "Standard" currency code
+        return currencyCode.trim()
+    }
+
+    if(currencyCode.match(/^[a-fA-F0-9]{40}$/) && !isNaN(parseInt(currencyCode, 16))) {
+        // Hexadecimal currency code
+        const hex = currencyCode.toString().replace(/(00)+$/g, '')
+        if (hex.startsWith('01')) {
+            // Old demurrage code. https://xrpl.org/demurrage.html
+            return convertDemurrageToUTF8(currencyCode);
+        }
+        if (hex.startsWith('02')) {
+            // XLS-16d NFT Metadata using XLS-15d Concise Transaction Identifier
+            // https://github.com/XRPLF/XRPL-Standards/discussions/37
+            const xlf15d = Buffer.from(hex, 'hex').slice(8).toString('utf-8').slice(0, maxLength).trim()
+            if (xlf15d.match(/[a-zA-Z0-9]{3,}/) && xlf15d.toLowerCase() !== 'xrp') {
+                return xlf15d
+            }
+        }
+        const decodedHex = Buffer.from(hex, 'hex').toString('utf-8').slice(0, maxLength).trim()
+        if (decodedHex.match(/[a-zA-Z0-9]{3,}/) && decodedHex.toLowerCase() !== 'xrp') {
+            // ASCII or UTF-8 encoded alphanumeric code, 3+ characters long
+            return decodedHex
+        }
+    }
+    return "";
+}
+
+function convertDemurrageToUTF8(demurrageCode) {
+
+    let bytes = Buffer.from(demurrageCode, "hex")
+    let code = String.fromCharCode(bytes[1]) + String.fromCharCode(bytes[2]) + String.fromCharCode(bytes[3]);
+    let interest_start = (bytes[4] << 24) + (bytes[5] << 16) + (bytes[6] <<  8) + (bytes[7]);
+    let interest_period = bytes.readDoubleBE(8);
+    const year_seconds = 31536000; // By convention, the XRP Ledger's interest/demurrage rules use a fixed number of seconds per year (31536000), which is not adjusted for leap days or leap seconds
+    let interest_after_year = Math.pow(Math.E, (interest_start+year_seconds - interest_start) / interest_period)
+    let interest = (interest_after_year * 100) - 100;
+
+    return(`${code} (${interest}% pa)`)
+}
+
+console.log("Standard 3-character code (should be 'USD')")
+console.log(normalizeCurrencyCode("USD"))
+
+console.log("Currency code that decodes to XRP, case-insensitive (should be empty string)")
+console.log(normalizeCurrencyCode("xRp"))
+
+console.log("Demurrage code (should be 'XAU (-0.5% pa)')...")
+console.log(normalizeCurrencyCode("0158415500000000C1F76FF6ECB0BAC600000000"))
+
+console.log("XLS-16d code (should be 'Purple moon')")
+console.log(normalizeCurrencyCode("0252000B03B6296F507572706C65206D6F6F6E00"))
+
+console.log("Long-alphanumeric code (should be 'XWORKS')...")
+console.log(normalizeCurrencyCode("58574F524B530000000000000000000000000000"))