feat(serialize): add deterministic data serialization

src/serialize.lua

@@ -0,0 +1,100 @@
+-- Serializes plain data (no functions, no cycles) to a Lua expression that
+-- rebuilds it. Keys are emitted in sorted order so the text is deterministic,
+-- which makes save/load round trips byte-for-byte comparable.
+
+local Serialize = {}
+
+local encodeValue
+local encodeTable
+
+local function encodeString(str)
+  local out = { '"' }
+  for i = 1, #str do
+    local char = str:sub(i, i)
+    local byte = string.byte(char)
+    if char == '"' then out[#out + 1] = '\\"'
+    elseif char == '\\' then out[#out + 1] = '\\\\'
+    elseif char == '\n' then out[#out + 1] = '\\n'
+    elseif char == '\t' then out[#out + 1] = '\\t'
+    elseif byte < 32 or byte > 126 then out[#out + 1] = string.format('\\%d', byte)
+    else out[#out + 1] = char end
+  end
+  out[#out + 1] = '"'
+  return table.concat(out)
+end
+
+local function isArray(tbl)
+  local count = 0
+  for _ in pairs(tbl) do count = count + 1 end
+  return count == #tbl
+end
+
+local function keyLess(a, b)
+  local ta, tb = type(a), type(b)
+  if ta ~= tb then return ta < tb end
+  return a < b
+end
+
+encodeTable = function(tbl, out)
+  out[#out + 1] = "{"
+  if isArray(tbl) then
+    for i = 1, #tbl do
+      if i > 1 then out[#out + 1] = "," end
+      encodeValue(tbl[i], out)
+    end
+  else
+    local keys = {}
+    for k in pairs(tbl) do keys[#keys + 1] = k end
+    table.sort(keys, keyLess)
+    for i, k in ipairs(keys) do
+      if i > 1 then out[#out + 1] = "," end
+      if type(k) == "string" and k:match("^[%a_][%w_]*$") then
+        out[#out + 1] = k .. "="
+      else
+        out[#out + 1] = "["
+        encodeValue(k, out)
+        out[#out + 1] = "]="
+      end
+      encodeValue(tbl[k], out)
+    end
+  end
+  out[#out + 1] = "}"
+end
+
+encodeValue = function(value, out)
+  local kind = type(value)
+  if kind == "nil" then out[#out + 1] = "nil"
+  elseif kind == "boolean" then out[#out + 1] = value and "true" or "false"
+  elseif kind == "number" then
+    if math.type(value) == "integer" then out[#out + 1] = string.format("%d", value)
+    else out[#out + 1] = string.format("%.17g", value) end
+  elseif kind == "string" then out[#out + 1] = encodeString(value)
+  elseif kind == "table" then encodeTable(value, out)
+  else error("cannot serialize type " .. kind) end
+end
+
+function Serialize.encode(value)
+  local out = {}
+  encodeValue(value, out)
+  return "return " .. table.concat(out)
+end
+
+function Serialize.decode(text)
+  local chunk = load(text, "savegame", "t", {})
+  return chunk()
+end
+
+function Serialize.saveFile(path, value)
+  local file = assert(io.open(path, "w"))
+  file:write(Serialize.encode(value))
+  file:close()
+end
+
+function Serialize.loadFile(path)
+  local file = assert(io.open(path, "r"))
+  local text = file:read("a")
+  file:close()
+  return Serialize.decode(text)
+end
+
+return Serialize