lua, datetime: calculated attributes for datetimes

* introduced a set of calculated attributes to data object, e.g.:
  - timestamp, seconds, microseconds, minute, or hours

Part of tarantool#5941

src/lua/datetime.lua

@@ -224,6 +224,36 @@ local function interval_serialize(self)
     return { secs = self.secs, nsec = self.nsec }
 end
 
+local datetime_index = function(self, key)
+    local attributes = {
+        timestamp = function(self)
+            return tonumber(self.secs + self.nsec / 1e9)
+        end,
+        nanoseconds = function(self)
+            return tonumber(self.secs * 1e9 + self.nsec)
+        end,
+        microseconds = function(self)
+            return tonumber(self.secs * 1e6 + self.nsec / 1e3)
+        end,
+        milliseconds = function(self)
+            return tonumber(self.secs * 1e3 + self.nsec / 1e6)
+        end,
+        seconds = function(self)
+            return tonumber(self.secs + self.nsec / 1e9)
+        end,
+        minutes = function(self)
+            return tonumber((self.secs + self.nsec / 1e9) / 60 % 60)
+        end,
+        hours = function(self)
+            return tonumber((self.secs + self.nsec / 1e9) / (60 * 60))
+        end,
+        days = function(self)
+            return tonumber((self.secs + self.nsec / 1e9) / (60 * 60)) / 24
+        end,
+    }
+    return attributes[key] ~= nil and attributes[key](self) or nil
+end
+
 local datetime_mt = {
     -- __tostring = datetime_tostring,
     __serialize = datetime_serialize,
@@ -232,23 +262,7 @@ local datetime_mt = {
     __le = datetime_le,
     __sub = datetime_sub,
     __add = datetime_add,
-
-    nanoseconds = function(self)
-        return tonumber(self.secs*NANOS_PER_SEC + self.nsec)
-    end,
-    microseconds = function(self)
-        return tonumber(self.secs*1e6 + self.nsec*1e3)
-    end,
-    seconds = function(self)
-        return tonumber(self.secs + self.nsec*1e3)
-    end,
-    minutes = function(self)
-        return tonumber((self._ticks/(1e6*60))%60)
-    end,
-    hours = function(self)
-        return tonumber(self._ticks/(1e6*60*60))
-    end,
-
+    __index = datetime_index,
 }
 
 local interval_mt = {
@@ -257,6 +271,9 @@ local interval_mt = {
     __eq = datetime_eq,
     __lt = datetime_lt,
     __le = datetime_le,
+    __sub = datetime_sub,
+    __add = datetime_add,
+    __index = datetime_index,
 }
 
 local function datetime_new_raw(secs, nsec, offset)

test/app-tap/datetime.test.lua

@@ -4,7 +4,7 @@ local tap = require('tap')
 local test = tap.test("errno")
 local date = require('datetime')
 
-test:plan(5)
+test:plan(6)
 
 test:test("Simple tests for parser", function(test)
     test:plan(2)
@@ -188,4 +188,19 @@ test:test("Parse iso date - invalid strings", function(test)
     end
 end)
 
+test:test("Parse tiny date into seconds and other parts", function(test)
+    test:plan(9)
+    local str = '19700101 00:00:30.528'
+    local tiny = date(str)
+    test:ok(tiny.secs == 30, ("secs of '%s'"):format(str))
+    test:ok(tiny.nsec == 528000000, ("nsec of '%s'"):format(str))
+    test:ok(tiny.nanoseconds == 30528000000, "nanoseconds")
+    test:ok(tiny.microseconds == 30528000, "microseconds")
+    test:ok(tiny.milliseconds == 30528, "milliseconds")
+    test:ok(tiny.seconds == 30.528, "seconds")
+    test:ok(tiny.timestamp == 30.528, "timestamp")
+    test:ok(tiny.minutes == 0.5088, "minuts")
+    test:ok(tiny.hours == 0.00848, "hours")
+end)
+
 os.exit(test:check() and 0 or 1)