From d1b0d8f87f835988581970955724bbb410dc2d3c Mon Sep 17 00:00:00 2001
From: Justin T <37750742+jtieri@users.noreply.github.com>
Date: Wed, 27 Nov 2019 01:22:36 -0600
Subject: [PATCH] base64 & vl64 encoding implemented

Added the encoders/decoders for FUSE-Base64 & VL64. Shout out to Puomi Wiki for their examples, some of my comments in code are straight from there.
---
 habbgo/utils/encoding/base64.go | 18 ++++++++++
 habbgo/utils/encoding/vl64.go   | 60 +++++++++++++++++++++++++++++++++
 2 files changed, 78 insertions(+)
 create mode 100644 habbgo/utils/encoding/base64.go
 create mode 100644 habbgo/utils/encoding/vl64.go

diff --git a/habbgo/utils/encoding/base64.go b/habbgo/utils/encoding/base64.go
new file mode 100644
index 0000000..634daf2
--- /dev/null
+++ b/habbgo/utils/encoding/base64.go
@@ -0,0 +1,18 @@
+/*
+base64 contains an implementation of the FUSE-Base64 tetrasexagesimal numeric system used in the FUSE v0.2.0 protocol.
+It typically uses two ASCII characters between decimal indexes 64 (@) and 127 (DEL control character) to produce a
+two-character representation of a number between 0 and 4095.
+
+This implementation is a Golang port of the examples from Puomi's wiki for Base64.
+*/
+package encoding
+
+// EncodeB64 takes an integer, encodes it in FUSE-Base64 & returns a slice of bytes that should contain two char's.
+func EncodeB64(i int) []byte {
+	return []byte{byte(i/64 + 64), byte(i%64 + 64)}
+}
+
+// DecodeB64 take a slice of bytes, decodes it from FUSE-Base64 & returns the decoded bytes as an integer.
+func DecodeB64(bytes []byte) int {
+	return 64 * (int(bytes[0]%64) + int(bytes[1]%64))
+}
diff --git a/habbgo/utils/encoding/vl64.go b/habbgo/utils/encoding/vl64.go
new file mode 100644
index 0000000..a78a246
--- /dev/null
+++ b/habbgo/utils/encoding/vl64.go
@@ -0,0 +1,60 @@
+/*
+vl64 contains an implementation of the FUSE mixed radix numeric encoding used by Sulake in HH.
+This implementation is a Golang port of the examples from Puomi's wiki for VL64.
+ */
+package encoding
+
+import "math"
+
+// DecodeVl64 returns a single number from the Vl64 encoded input.
+// Any characters after the length indicated by first char of input will be discarded.
+func DecodeVl64(input []byte) int {
+	length := length(input[0])
+	total := int(input[0]) % 4 // Base4 value
+
+	// Increment all Base64 symbols to the total
+	for inc := 0; inc < length; inc++ {
+		total += (int(input[inc]) - 64) * int(math.Pow(64, float64(inc))/16)
+	}
+
+	if int(input[0]%8) < 4 {
+		return total // Base4 positive
+	}
+
+	return -total // Base4 negative
+}
+
+// EncodeVl64 returns a slice of bytes capable of storing all increments.
+// Removes all @ symbols (padding) after last non-@ before returning.
+func EncodeVl64(input int) []byte {
+	vl64 := make([]byte, 6)              // 32-bit integer causes VL64 to have max length of 6.
+	num := int(math.Abs(float64(input))) // Operate on normalized, positive integer
+	length := 1                          // Length indicator, updated during encode
+
+	var indicator int
+	if input < 0 {
+		indicator = 'D' // positive(+64)
+	} else {
+		indicator = '@' // negative(+68)
+	}
+	vl64[0] = byte(num%4 + indicator) // Base4 char, positive(+64)/negative(+68) indicator
+	num /= 4                          // Base4 processed, prepare for remaining Base64 symbols
+
+	for i := 1; i < 6; i++ {
+		vl64[i] = byte(num%64 + 64) // Base64
+		num /= 64
+
+		if vl64[i] != 64 {
+			length = i + 1 // @ = padding / zero symbol
+		}
+
+	}
+
+	vl64[0] = byte(int(vl64[0]) + length*8) // Base4 char shifted to indicate total length
+	return vl64[:length]                    // Last padding symbols trimmed out
+}
+
+// length returns the total length of the mixed radix number.
+func length(firstChar byte) int {
+	return (int(firstChar) - 64) / 8
+}