[#1210] timers: Add IterationsTicker

It allows specifying duration in blocks and a desired number of handler
calls in that period.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

cmd/neofs-node/reputation/ticker/fixed.go

@@ -0,0 +1,90 @@
+package ticker
+
+import (
+	"fmt"
+	"sync"
+)
+
+// IterationHandler is a callback of a certain block advance.
+type IterationHandler func()
+
+// IterationsTicker represents fixed tick number block timer.
+//
+// It can tick the blocks and perform certain actions
+// on block time intervals.
+type IterationsTicker struct {
+	m sync.Mutex
+
+	curr   uint64
+	period uint64
+
+	times uint64
+
+	h IterationHandler
+}
+
+// NewIterationsTicker creates a new IterationsTicker.
+//
+// It guaranties that handler would be called the
+// specified amount of times in the specified amount
+// of blocks. After the last meaningful Tick IterationsTicker
+// becomes no-op timer.
+//
+// Returns error only if times is greater than totalBlocks.
+func NewIterationsTicker(totalBlocks uint64, times uint64, h IterationHandler) (*IterationsTicker, error) {
+	period := totalBlocks / times
+
+	if period == 0 {
+		return nil, fmt.Errorf("impossible to tick %d times in %d blocks",
+			times, totalBlocks,
+		)
+	}
+
+	var curr uint64
+
+	// try to make handler calls as rare as possible
+	if totalBlocks%times != 0 {
+		extraBlocks := (period+1)*times - totalBlocks
+
+		if period >= extraBlocks {
+			curr = extraBlocks + (period-extraBlocks)/2
+			period++
+		}
+	}
+
+	return &IterationsTicker{
+		curr:   curr,
+		period: period,
+		times:  times,
+		h:      h,
+	}, nil
+}
+
+// Tick ticks one block in the IterationsTicker.
+//
+// Returns `false` if the timer has finished its operations
+// and there will be no more handler calls.
+// Calling Tick after the returned `false` is safe, no-op
+// and also returns `false`.
+func (ft *IterationsTicker) Tick() bool {
+	ft.m.Lock()
+	defer ft.m.Unlock()
+
+	if ft.times == 0 {
+		return false
+	}
+
+	ft.curr++
+
+	if ft.curr%ft.period == 0 {
+		ft.h()
+
+		ft.times--
+
+		if ft.times == 0 {
+			return false
+		}
+	}
+
+	return true
+}