package engine

import (
	"os"
	"path/filepath"
	"sync"
)

// RingLog keeps last N log lines in memory and optionally writes to file.
type RingLog struct {
	mu    sync.Mutex
	lines []string
	max   int
	file  *os.File
}

// NewRingLog creates a ring buffer logger.
func NewRingLog(maxLines int, dataDir string) *RingLog {
	rl := &RingLog{
		lines: make([]string, 0, maxLines),
		max:   maxLines,
	}
	if dataDir != "" {
		f, err := os.OpenFile(filepath.Join(dataDir, "vpnem.log"),
			os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o644)
		if err == nil {
			rl.file = f
		}
	}
	return rl
}

// Add appends a line.
func (rl *RingLog) Add(line string) {
	rl.mu.Lock()
	defer rl.mu.Unlock()

	if len(rl.lines) >= rl.max {
		rl.lines = rl.lines[1:]
	}
	rl.lines = append(rl.lines, line)

	if rl.file != nil {
		rl.file.WriteString(line + "\n")
	}
}

// Lines returns all current lines.
func (rl *RingLog) Lines() []string {
	rl.mu.Lock()
	defer rl.mu.Unlock()
	cp := make([]string, len(rl.lines))
	copy(cp, rl.lines)
	return cp
}

// Close closes the log file.
func (rl *RingLog) Close() {
	if rl.file != nil {
		rl.file.Close()
	}
}