mfd-monitor-agent/internal/snapshot/snapshot.go

package snapshot

import (
	"context"
	"sync"
	"time"

	"mfd-monitor-agent/internal/status"
)

// Collector gathers one subsection of HostStatus into the provided snapshot.
type Collector interface {
	// Name returns the stable collector name used in partial snapshot errors.
	Name() string
	// Collect fills its subsection of out and returns an error when that subsection is incomplete.
	Collect(context.Context, *status.HostStatus) error
}

// CollectorFunc adapts a function into a Collector for tests and small collectors.
type CollectorFunc func(context.Context, *status.HostStatus) error

// Name returns a generic collector name for function-backed collectors.
func (fn CollectorFunc) Name() string {
	return "collector"
}

// Collect calls the wrapped function.
func (fn CollectorFunc) Collect(ctx context.Context, out *status.HostStatus) error {
	return fn(ctx, out)
}

// Cache stores the most recent HostStatus snapshot behind a concurrency-safe interface.
type Cache struct {
	collectors []Collector
	version    string
	startedAt  time.Time
	mu         sync.RWMutex
	last       status.HostStatus
	hasLast    bool
}

// NewCache creates an empty snapshot cache using the provided collectors and agent metadata.
func NewCache(collectors []Collector, version string, startedAt time.Time) *Cache {
	return &Cache{collectors: collectors, version: version, startedAt: startedAt}
}

// Collect runs all collectors once and stores the resulting snapshot even when some collectors fail.
func (c *Cache) Collect(ctx context.Context) status.HostStatus {
	out := status.HostStatus{
		Agent: status.AgentInfo{
			Version:        c.version,
			StartedAt:      c.startedAt,
			SnapshotAt:     time.Now().UTC(),
			SnapshotStatus: "ok",
		},
		Processes:    status.ProcessResult{Status: "ok"},
		TCPListeners: status.TCPResult{Status: "ok"},
	}

	for _, collector := range c.collectors {
		if err := collector.Collect(ctx, &out); err != nil {
			out.Agent.SnapshotStatus = "partial"
			out.Errors = append(out.Errors, status.StatusError{
				Collector: collector.Name(),
				Message:   err.Error(),
			})
		}
	}

	c.mu.Lock()
	c.last = out
	c.hasLast = true
	c.mu.Unlock()
	return out
}

// Get returns the latest cached snapshot and whether collection has completed at least once.
func (c *Cache) Get() (status.HostStatus, bool) {
	c.mu.RLock()
	defer c.mu.RUnlock()
	return c.last, c.hasLast
}

// Run collects immediately and then refreshes the cache until ctx is canceled.
func (c *Cache) Run(ctx context.Context, interval time.Duration, timeout time.Duration) {
	c.collectWithTimeout(ctx, timeout)
	ticker := time.NewTicker(interval)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			c.collectWithTimeout(ctx, timeout)
		}
	}
}

// collectWithTimeout runs one collection cycle with an overall deadline.
func (c *Cache) collectWithTimeout(ctx context.Context, timeout time.Duration) {
	collectCtx, cancel := context.WithTimeout(ctx, timeout)
	defer cancel()
	c.Collect(collectCtx)
}