package cluster

import (
	"bufio"
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"
)

type ChangeRecord struct {
	At      time.Time `json:"at"`
	Action  string    `json:"action"`
	Target  string    `json:"target"`
	Details string    `json:"details,omitempty"`
}

func (s *Service) changeHistoryPath() string {
	return filepath.Join(s.DataDir(), "history", "changes.log")
}

func (s *Service) AppendChange(action, target, details string) error {
	if s == nil {
		return nil
	}
	rec := ChangeRecord{
		At:      s.now().UTC(),
		Action:  strings.TrimSpace(action),
		Target:  strings.TrimSpace(target),
		Details: strings.TrimSpace(details),
	}
	if rec.Action == "" {
		return nil
	}
	path := s.changeHistoryPath()
	if err := os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
		return err
	}
	f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o600)
	if err != nil {
		return err
	}
	defer f.Close()
	b, err := json.Marshal(rec)
	if err != nil {
		return err
	}
	_, err = f.Write(append(b, '\n'))
	return err
}

func (s *Service) ListChanges(limit int) ([]ChangeRecord, error) {
	path := s.changeHistoryPath()
	f, err := os.Open(path)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, err
	}
	defer f.Close()
	capHint := 32
	if limit > capHint {
		capHint = limit
	}
	items := make([]ChangeRecord, 0, capHint)
	sc := bufio.NewScanner(f)
	sc.Buffer(make([]byte, 0, 64*1024), 2*1024*1024)
	for sc.Scan() {
		line := strings.TrimSpace(sc.Text())
		if line == "" {
			continue
		}
		var rec ChangeRecord
		if err := json.Unmarshal([]byte(line), &rec); err != nil {
			continue
		}
		items = append(items, rec)
	}
	if err := sc.Err(); err != nil {
		return nil, fmt.Errorf("scan change history: %w", err)
	}
	if limit > 0 && len(items) > limit {
		items = items[len(items)-limit:]
	}
	return items, nil
}