package process

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

// rotatingFile appends to a log file and rotates it once it exceeds maxSize.
type rotatingFile struct {
	mu      sync.Mutex
	path    string
	maxSize int64
	f       *os.File
	size    int64
}

func newRotatingFile(path string, maxSize int64) (*rotatingFile, error) {
	if maxSize <= 0 {
		maxSize = 10 * 1024 * 1024
	}
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return nil, err
	}
	f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0o644)
	if err != nil {
		return nil, err
	}
	info, err := f.Stat()
	if err != nil {
		_ = f.Close()
		return nil, err
	}
	return &rotatingFile{path: path, maxSize: maxSize, f: f, size: info.Size()}, nil
}

func (r *rotatingFile) Write(p []byte) (int, error) {
	r.mu.Lock()
	defer r.mu.Unlock()

	if r.f == nil {
		f, err := os.OpenFile(r.path, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0o644)
		if err != nil {
			return 0, err
		}
		r.f = f
	}
	if r.size > 0 && r.size+int64(len(p)) > r.maxSize {
		_ = r.f.Close()
		_ = os.Rename(r.path, r.path+".1")
		f, err := os.OpenFile(r.path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o644)
		if err != nil {
			r.f = nil
			return 0, err
		}
		r.f = f
		r.size = 0
	}
	n, err := r.f.Write(p)
	r.size += int64(n)
	return n, err
}

func (r *rotatingFile) Close() error {
	r.mu.Lock()
	defer r.mu.Unlock()
	if r.f != nil {
		err := r.f.Close()
		r.f = nil
		return err
	}
	return nil
}