[Space Lua] Implement math.tointeger

Signed-off-by: Matouš Jan Fialka <mjf@mjf.cz>

client/space_lua/stdlib/math.ts

@@ -40,6 +40,27 @@ export const mathApi = new LuaTable({
     }
     return null;
   }),
+
+  /**
+   * If the value x is representable as a Lua integer, returns an
+   * integer with that value. Otherwise returns nil.
+   */
+  tointeger: new LuaBuiltinFunction((_sf, x?: any) => {
+    if (x === undefined || x === null) return null;
+    if (typeof x === "number") {
+      // plain integer
+      if (Number.isInteger(x)) return x;
+      return null;
+    }
+    if (isTaggedFloat(x)) {
+      // float with integer value e.g. 3.0
+      if (Number.isInteger(x.value)) return x.value;
+      return null;
+    }
+    if (typeof x === "bigint") return x;
+    return null;
+  }),
+
   /**
    * When called without arguments, returns a pseudo-random float with
    * uniform distribution in the range [0,1). When called with two

client/space_lua/stdlib/math_test.lua

@@ -171,3 +171,29 @@ do
   assertEquals(f2, 3, "floor(8*0.49)")
   assertEquals(f3, 4, "floor(9*0.5)")
 end
+
+-- math.tointeger
+do
+  -- integers pass through unchanged
+  assertEquals(math.tointeger(0),  0,  "tointeger(0)")
+  assertEquals(math.tointeger(42), 42, "tointeger(42)")
+  assertEquals(math.tointeger(-7), -7, "tointeger(-7)")
+  assertEquals(math.type(math.tointeger(1)), "integer", "tointeger result is integer")
+
+  -- float with whole value yields integer
+  assertEquals(math.tointeger(3.0),  3,  "tointeger(3.0)")
+  assertEquals(math.tointeger(-1.0), -1, "tointeger(-1.0)")
+  assertEquals(math.type(math.tointeger(3.0)), "integer", "tointeger(3.0) type")
+
+  -- float with fractional part yields nil
+  assertEquals(math.tointeger(3.5),  nil, "tointeger(3.5)")
+  assertEquals(math.tointeger(-0.1), nil, "tointeger(-0.1)")
+
+  -- non-numbers yields nil (no error)
+  assertEquals(math.tointeger("3"),  nil, "tointeger(string)")
+  assertEquals(math.tointeger(nil),  nil, "tointeger(nil)")
+
+  -- inf and nan yields nil
+  assertEquals(math.tointeger(1/0),  nil, "tointeger(inf)")
+  assertEquals(math.tointeger(0/0),  nil, "tointeger(nan)")
+end