fix: resolve critical bugs and refactor code structure

P0 Fixes:
- Fix potential panic in factory.go due to unsafe type assertion
- Fix VIP CIDR mask being lost during parsing (was hardcoded to /32)

P1 Fixes:
- Fix go.mod incorrect indirect dependency markers
- Fix receiveLoop blocking issue preventing graceful shutdown

Refactoring:
- Split state.go into state.go, timer.go, priority.go, history.go
- Split monitor.go into monitor.go and manager.go
- Add IncreasePriority() method for complete priority adjustment
- Fix go vet format string warning in test.go

🤖 Generated with [Qoder][https://qoder.com]

internal/vrrp/history.go

@@ -0,0 +1,95 @@
+package vrrp
+
+import (
+	"fmt"
+	"sync"
+	"time"
+)
+
+// StateTransition represents a single state transition event.
+type StateTransition struct {
+	From      State
+	To        State
+	Timestamp time.Time
+	Reason    string
+}
+
+// StateHistory maintains a bounded history of state transitions.
+type StateHistory struct {
+	transitions []StateTransition
+	maxSize     int
+	mu          sync.RWMutex
+}
+
+// NewStateHistory creates a new StateHistory with the specified maximum size.
+func NewStateHistory(maxSize int) *StateHistory {
+	return &StateHistory{
+		transitions: make([]StateTransition, 0, maxSize),
+		maxSize:     maxSize,
+	}
+}
+
+// Add records a new state transition.
+func (sh *StateHistory) Add(from, to State, reason string) {
+	sh.mu.Lock()
+	defer sh.mu.Unlock()
+
+	transition := StateTransition{
+		From:      from,
+		To:        to,
+		Timestamp: time.Now(),
+		Reason:    reason,
+	}
+
+	sh.transitions = append(sh.transitions, transition)
+
+	// Maintain bounded size using ring buffer style
+	if len(sh.transitions) > sh.maxSize {
+		// Copy to new slice to allow garbage collection of old backing array
+		newTransitions := make([]StateTransition, len(sh.transitions)-1, sh.maxSize)
+		copy(newTransitions, sh.transitions[1:])
+		sh.transitions = newTransitions
+	}
+}
+
+// GetRecent returns the most recent n transitions.
+func (sh *StateHistory) GetRecent(n int) []StateTransition {
+	sh.mu.RLock()
+	defer sh.mu.RUnlock()
+
+	if n > len(sh.transitions) {
+		n = len(sh.transitions)
+	}
+
+	start := len(sh.transitions) - n
+	result := make([]StateTransition, n)
+	copy(result, sh.transitions[start:])
+
+	return result
+}
+
+// Len returns the number of recorded transitions.
+func (sh *StateHistory) Len() int {
+	sh.mu.RLock()
+	defer sh.mu.RUnlock()
+	return len(sh.transitions)
+}
+
+// String returns a formatted string representation of the history.
+func (sh *StateHistory) String() string {
+	sh.mu.RLock()
+	defer sh.mu.RUnlock()
+
+	if len(sh.transitions) == 0 {
+		return "No state transitions"
+	}
+
+	result := "State transition history:\n"
+	for _, t := range sh.transitions {
+		result += fmt.Sprintf("  %s: %s -> %s (%s)\n",
+			t.Timestamp.Format("2006-01-02 15:04:05"),
+			t.From, t.To, t.Reason)
+	}
+
+	return result
+}