package logging

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

// LogEntry represents one message log record.
type LogEntry struct {
	Timestamp   time.Time `json:"timestamp"`
	Direction   string    `json:"direction"` // "incoming" or "outgoing"
	Platform    string    `json:"platform"`
	ChannelID   string    `json:"channel_id"`
	SenderID    string    `json:"sender_id"`
	SenderName  string    `json:"sender_name"`
	GroupName   string    `json:"group_name,omitempty"`
	Content     string    `json:"content"`
	ContentType string    `json:"content_type"`
	MessageID   string    `json:"message_id,omitempty"`
	Success     bool      `json:"success"`
	Error       string    `json:"error,omitempty"`
}

// LogListener receives log entries as they are written.
type LogListener func(LogEntry)

// Logger writes message logs to per-platform JSONL files.
type Logger struct {
	mu        sync.Mutex
	dir       string
	files     map[string]*os.File
	listeners []LogListener
}

// OnLog registers a listener that is called for every log entry written.
// The listener is called synchronously; avoid heavy work in the callback.
func (l *Logger) OnLog(fn LogListener) {
	l.mu.Lock()
	defer l.mu.Unlock()
	l.listeners = append(l.listeners, fn)
}

// NewLogger creates a Logger, ensuring the log directory exists.
func NewLogger(dir string) (*Logger, error) {
	if err := os.MkdirAll(dir, 0750); err != nil {
		return nil, fmt.Errorf("create log dir: %w", err)
	}
	return &Logger{
		dir:   dir,
		files: make(map[string]*os.File),
	}, nil
}

// Log writes a log entry to the appropriate platform log file.
func (l *Logger) Log(entry LogEntry) error {
	if entry.Timestamp.IsZero() {
		entry.Timestamp = time.Now()
	}

	f, err := l.getOrCreateFile(entry.Platform)
	if err != nil {
		return err
	}

	data, err := json.Marshal(entry)
	if err != nil {
		return fmt.Errorf("marshal log entry: %w", err)
	}

	l.mu.Lock()
	if _, err := f.Write(append(data, '\n')); err != nil {
		l.mu.Unlock()
		return fmt.Errorf("write log: %w", err)
	}
	if err := f.Sync(); err != nil {
		l.mu.Unlock()
		return err
	}
	listeners := make([]LogListener, len(l.listeners))
	copy(listeners, l.listeners)
	l.mu.Unlock()

	// Notify listeners outside the lock.
	for _, fn := range listeners {
		fn(entry)
	}
	return nil
}

// ReadLogs reads the last N log entries for a platform, newest first.
func (l *Logger) ReadLogs(platform string, limit int) ([]LogEntry, error) {
	if limit <= 0 || limit > 1000 {
		limit = 1000
	}

	l.mu.Lock()
	// Flush any pending writes to the file before reading.
	if f, ok := l.files[platform]; ok {
		f.Sync()
	}
	l.mu.Unlock()

	path := filepath.Join(l.dir, platform+".log")
	f, err := os.Open(path)
	if err != nil {
		if os.IsNotExist(err) {
			return []LogEntry{}, nil
		}
		return nil, fmt.Errorf("open log file: %w", err)
	}
	defer f.Close()

	// Read all lines, keep only the last `limit`.
	var lines []string
	scanner := bufio.NewScanner(f)
	scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024)
	for scanner.Scan() {
		lines = append(lines, scanner.Text())
	}
	if err := scanner.Err(); err != nil {
		return nil, fmt.Errorf("read log file: %w", err)
	}

	// Take last N lines and reverse.
	start := len(lines) - limit
	if start < 0 {
		start = 0
	}
	lines = lines[start:]

	entries := make([]LogEntry, 0, len(lines))
	for i := len(lines) - 1; i >= 0; i-- {
		var entry LogEntry
		if err := json.Unmarshal([]byte(lines[i]), &entry); err != nil {
			continue // Skip corrupted lines.
		}
		entries = append(entries, entry)
	}
	return entries, nil
}

// Close closes all open log file handles.
func (l *Logger) Close() error {
	l.mu.Lock()
	defer l.mu.Unlock()
	for _, f := range l.files {
		f.Close()
	}
	l.files = make(map[string]*os.File)
	return nil
}

func (l *Logger) getOrCreateFile(platform string) (*os.File, error) {
	l.mu.Lock()
	defer l.mu.Unlock()

	if f, ok := l.files[platform]; ok {
		return f, nil
	}

	path := filepath.Join(l.dir, platform+".log")
	f, err := os.OpenFile(path, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0640)
	if err != nil {
		return nil, fmt.Errorf("open log file %s: %w", path, err)
	}
	l.files[platform] = f
	return f, nil
}
