// Package monitor provides a persistent monitor-only mode toggle.
// When active, the EMS continues polling and showing the status page
// but suppresses all actuator calls (Shelly switches, Viessmann API).
// State is stored as a flag file: presence = active, absence = normal.
package monitor

import (
	"os"
	"sync"
)

// Mode is a thread-safe, file-backed monitor-only flag.
type Mode struct {
	mu       sync.RWMutex
	active   bool
	filePath string
}

// New creates a Mode and loads the current state from the flag file.
// If filePath is empty, the mode is in-memory only (not persistent).
func New(filePath string) *Mode {
	m := &Mode{filePath: filePath}
	if filePath != "" {
		_, err := os.Stat(filePath)
		m.active = err == nil // file exists → monitor-only
	}
	return m
}

// IsActive reports whether monitor-only mode is currently enabled.
func (m *Mode) IsActive() bool {
	m.mu.RLock()
	defer m.mu.RUnlock()
	return m.active
}

// Set enables or disables monitor-only mode and persists the change to disk.
func (m *Mode) Set(active bool) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	m.active = active

	if m.filePath == "" {
		return nil // in-memory only
	}

	if active {
		f, err := os.Create(m.filePath)
		if err != nil {
			return err
		}
		return f.Close()
	}

	err := os.Remove(m.filePath)
	if os.IsNotExist(err) {
		return nil
	}
	return err
}