zero: refactor telemetry and controller (#5135)

* zero: refactor controller

* refactor zero telemetry and controller

* wire with connect handler

* cr

internal/zero/telemetry/sessions/activeusers.go

@@ -0,0 +1,80 @@
+package sessions
+
+import (
+	"time"
+
+	"github.com/pomerium/pomerium/pkg/counter"
+)
+
+const (
+	// activeUsersCap is the number of active users we would be able to track.
+	// for counter to work within the 1% error limit, actual number should be 80% of the cap.
+	activeUsersCap = 10_000
+)
+
+// IntervalResetFunc is a function that determines if a counter should be reset
+type IntervalResetFunc func(lastReset time.Time, now time.Time) bool
+
+// ResetMonthlyUTC resets the counter on a monthly interval
+func ResetMonthlyUTC(lastReset time.Time, now time.Time) bool {
+	lastResetUTC := lastReset.UTC()
+	nowUTC := now.UTC()
+	return lastResetUTC.Year() != nowUTC.Year() ||
+		lastResetUTC.Month() != nowUTC.Month()
+}
+
+// ResetDailyUTC resets the counter on a daily interval
+func ResetDailyUTC(lastReset time.Time, now time.Time) bool {
+	lastResetUTC := lastReset.UTC()
+	nowUTC := now.UTC()
+	return lastResetUTC.Year() != nowUTC.Year() ||
+		lastResetUTC.Month() != nowUTC.Month() ||
+		lastResetUTC.Day() != nowUTC.Day()
+}
+
+// ActiveUsersCounter is a counter that resets on a given interval
+type ActiveUsersCounter struct {
+	*counter.Counter
+	lastReset  time.Time
+	needsReset IntervalResetFunc
+}
+
+// NewActiveUsersCounter creates a new active users counter
+func NewActiveUsersCounter(needsReset IntervalResetFunc, now time.Time) *ActiveUsersCounter {
+	return &ActiveUsersCounter{
+		Counter:    counter.New(activeUsersCap),
+		lastReset:  now,
+		needsReset: needsReset,
+	}
+}
+
+// LoadActiveUsersCounter loads an active users counter from a binary state
+func LoadActiveUsersCounter(state []byte, lastReset time.Time, resetFn IntervalResetFunc) (*ActiveUsersCounter, error) {
+	c, err := counter.FromBinary(state)
+	if err != nil {
+		return nil, err
+	}
+	return &ActiveUsersCounter{
+		Counter:    c,
+		lastReset:  lastReset,
+		needsReset: resetFn,
+	}, nil
+}
+
+// Update updates the counter with the current users
+func (c *ActiveUsersCounter) Update(users []string, now time.Time) (current uint, wasReset bool) {
+	if c.needsReset(c.lastReset, now) {
+		c.Counter.Reset()
+		c.lastReset = now
+		wasReset = true
+	}
+	for _, user := range users {
+		c.Mark(user)
+	}
+	return c.Count(), wasReset
+}
+
+// GetLastReset returns the last time the counter was reset
+func (c *ActiveUsersCounter) GetLastReset() time.Time {
+	return c.lastReset
+}