package mdm

import (
	"sync"

	log "github.com/sirupsen/logrus"
)

// ChangeDetector tracks the last observed policy of a Loader so an
// OS-notification-driven caller can ask whether the managed configuration
// actually changed before restarting anything.
type ChangeDetector struct {
	mu     sync.Mutex
	loader *Loader
	prev   *Policy
}

// NewChangeDetector constructs a ChangeDetector seeded with the loader's
// current policy, so only a later change reports as changed.
func NewChangeDetector(loader *Loader) *ChangeDetector {
	return &ChangeDetector{
		loader: loader,
		prev:   loader.Load(),
	}
}

// Changed re-reads the policy, logs the per-key diff, and reports whether it
// diverged from the last observation; the new snapshot becomes the baseline.
func (d *ChangeDetector) Changed() bool {
	d.mu.Lock()
	defer d.mu.Unlock()
	curr := d.loader.Load()
	if policiesEqual(d.prev, curr) {
		return false
	}
	added, removed, changed := diffPolicies(d.prev, curr)
	log.Infof("MDM policy changed: added=%v removed=%v changed=%v", added, removed, changed)
	d.prev = curr
	return true
}

// Current returns the last observed policy snapshot.
func (d *ChangeDetector) Current() *Policy {
	d.mu.Lock()
	defer d.mu.Unlock()
	return d.prev
}