codegenerator

inc/logic/logic.codegenerator.lua

@@ -0,0 +1,60 @@
+--- @section CodeGenerator
+
+CodeGenerator = {}
+
+local SALT     = 27471
+local BASE36   = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+local NAME_LEN = 3
+
+-- Per-position offsets derived from SALT so each character slot
+-- maps to a different region of the 2-char base-36 space.
+local SALTS = {
+  SALT % 36,
+  math.floor(SALT /   36) % 36,
+  math.floor(SALT / 1296) % 36,
+}
+
+--- Encodes a number (0–935) as exactly 2 base-36 characters.
+--- @within CodeGenerator
+function CodeGenerator.encode_pair(n)
+  return BASE36:sub(math.floor(n / 36) + 1, math.floor(n / 36) + 1)
+      .. BASE36:sub(n % 36 + 1,              n % 36 + 1)
+end
+
+--- Decodes 2 base-36 characters back to a number.
+--- @within CodeGenerator
+function CodeGenerator.decode_pair(s)
+  local d1 = BASE36:find(s:sub(1, 1), 1, true) - 1
+  local d2 = BASE36:find(s:sub(2, 2), 1, true) - 1
+  return d1 * 36 + d2
+end
+
+--- Encrypts a player name into a code twice its length.
+--- Each input character (A-Z, value 0-25) is encoded as
+--- c + SALTS[i] * 26, producing 2 base-36 output characters.
+--- @within CodeGenerator
+--- @param text string NAME_LEN-character uppercase player name.
+--- @return string Encrypted code (2 * NAME_LEN base-36 characters).
+function CodeGenerator.encrypt(text)
+  local result = ""
+  for i = 1, NAME_LEN do
+    local c = math.max(0, (string.byte(text, i) or 65) - 65)
+    result = result .. CodeGenerator.encode_pair(c + SALTS[i] * 26)
+  end
+  return result
+end
+
+--- Decrypts a personal code back to the original player name.
+--- @within CodeGenerator
+--- @param encrypted_text string The code to decrypt (2 * NAME_LEN chars).
+--- @return string Original player name, or "???" if the code is invalid.
+function CodeGenerator.decrypt(encrypted_text)
+  local t = encrypted_text:upper()
+  if #t ~= NAME_LEN * 2 then return "???" end
+  local result = ""
+  for i = 1, NAME_LEN do
+    local pair = CodeGenerator.decode_pair(t:sub((i - 1) * 2 + 1, i * 2))
+    result = result .. string.char(pair % 26 + 65)
+  end
+  return result
+end