clock.go

type Clock struct {
        h, m int
}

func (c *Clock) set(h, m int) {
        var dh int
        dh, c.m = c.decompose(m, 60)
        _, c.h = c.decompose(h+dh, 24)
}

func (c Clock) String() string {
        return fmt.Sprintf("%02d:%02d", c.h, c.m)
}

func (c *Clock) Add(m int) *Clock {
        c.set(c.h, c.m+m)
        return c
}

func (c *Clock) decompose(quot int, div int) (h, m int) {
        h = quot / div
        m = quot % div

        if m < 0 {
                m = div + m
                h = h - 1
        }

        return
}

func New(h, m int) *Clock {
        c := new(Clock)
        c.set(h, m)
        return c
}