package logger

import (
	"fmt"
	"log"
	"os"
	"time"

	"gorm.io/gorm"
	"radiantwavetech.com/radiantwave/internal/db"
)

// ─── Level ───────────────────────────────────────────────────────────────────

type Level int

const (
	LevelDebug Level = iota
	LevelInfo
	LevelWarning
	LevelError
	LevelFatal
)

func (l Level) String() string {
	return [...]string{"DEBUG", "INFO", "WARNING", "ERROR", "FATAL"}[l]
}

// ─── Internal entry type ──────────────────────────────────────────────────────

type entry struct {
	level     Level
	message   string
	timestamp time.Time
	fatal     bool
}

// ─── Package state ────────────────────────────────────────────────────────────

var (
	SetLevel Level = LevelInfo
	console        = log.New(os.Stderr, "", 0)

	ch   chan entry // unbuffered send is a bug; always buffered
	done chan struct{}
	db_  *gorm.DB
	file *os.File
)

func init() {
	ch = make(chan entry, 4096)
	done = make(chan struct{})
	go drain()
}

// ─── Configuration ────────────────────────────────────────────────────────────

// AddFile attaches or replaces the file backend. Safe to call at any time.
func AddFile(path string) error {
	f, err := os.OpenFile(path, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0o644)
	if err != nil {
		return fmt.Errorf("logger: open file: %w", err)
	}
	// Send a sentinel that carries the new file handle.
	// We do this through the channel so the drain goroutine owns
	// all file state — no mutex needed.
	fileSwapCh <- f
	return nil
}

// AddDatabase attaches or replaces the database backend. Safe to call at any time.
func AddDatabase(d *gorm.DB) {
	dbSwapCh <- d
}

// Close drains remaining entries and shuts down the logger.
// Call this with defer in main().
func Close() {
	close(done)
	<-drainDone // wait for drain goroutine to finish flushing
	if file != nil {
		file.Close()
		file = nil
	}
}

// ─── Swap channels (owned exclusively by drain goroutine) ────────────────────

var (
	fileSwapCh = make(chan *os.File, 1)
	dbSwapCh   = make(chan *gorm.DB, 1)
	drainDone  = make(chan struct{})
)

// ─── Drain goroutine ──────────────────────────────────────────────────────────
//
// This is the ONLY goroutine that touches file, db_, or does DB writes.
// Everything else just sends to ch.

func drain() {
	defer close(drainDone)

	batch := make([]entry, 0, 64)
	ticker := time.NewTicker(250 * time.Millisecond)
	defer ticker.Stop()

	flush := func() {
		if len(batch) == 0 {
			return
		}
		writeBatchToDB(batch)
		batch = batch[:0]
	}

	for {
		select {

		// New log entry
		case e := <-ch:
			writeToFile(e)
			if db_ != nil {
				batch = append(batch, e)
				if len(batch) >= 64 {
					flush()
				}
			}

		// Periodic DB flush so low-volume logs don't sit in the batch forever
		case <-ticker.C:
			flush()

		// Hot-swap the file backend
		case f := <-fileSwapCh:
			if file != nil {
				file.Close()
			}
			file = f

		// Hot-swap the DB backend
		case d := <-dbSwapCh:
			flush() // flush any pending entries to the old db first
			db_ = d
			console.Println("logger: database backend attached")

		// Shutdown: drain what's left, then exit
		case <-done:
			// Pull any entries still sitting in the channel
			for len(ch) > 0 {
				e := <-ch
				writeToFile(e)
				batch = append(batch, e)
			}
			flush()
			return
		}
	}
}

// ─── Writers (called only from drain goroutine) ───────────────────────────────

func writeToFile(e entry) {
	line := formatLine(e)
	if file != nil {
		fmt.Fprintln(file, line)
	}
}

func writeBatchToDB(batch []entry) {
	if db_ == nil || len(batch) == 0 {
		return
	}
	records := make([]db.Log, len(batch))
	for i, e := range batch {
		records[i] = db.Log{
			Timestamp: e.timestamp.UnixMilli(),
			Level:     e.level.String(),
			Message:   e.message,
		}
	}
	// Single INSERT ... VALUES (...), (...), (...) instead of N individual saves.
	if result := db_.CreateInBatches(records, 64); result.Error != nil {
		console.Printf("logger: db batch write failed: %v\n", result.Error)
	}
}

func formatLine(e entry) string {
	return fmt.Sprintf("%s [%s] %s",
		e.timestamp.Format("2006-01-02 15:04:05.000"),
		e.level,
		e.message,
	)
}

// ─── Public API ───────────────────────────────────────────────────────────────

func logMsg(level Level, fatal bool, format string, args ...any) {
	if level == LevelDebug && SetLevel != LevelDebug {
		return
	}
	e := entry{
		level:     level,
		message:   fmt.Sprintf(format, args...),
		timestamp: time.Now(), // captured here, in the caller's goroutine
		fatal:     fatal,
	}

	// Console is synchronous — log.Logger is internally mutex-protected,
	// so this is safe from any goroutine and gives you immediate output.
	console.Println(formatLine(e))

	// Non-blocking send: if the buffer is full, we drop rather than deadlock.
	// 4096 entries of headroom means this should never happen in practice.
	select {
	case ch <- e:
	default:
		console.Println("logger: channel full, entry dropped")
	}

	if fatal {
		// Give the drain goroutine a moment to flush before we exit.
		// Close() is cleaner but Fatal has to exit immediately.
		time.Sleep(150 * time.Millisecond)
		os.Exit(1)
	}
}

func Debug(format string, args ...any)   { logMsg(LevelDebug, false, format, args...) }
func Info(format string, args ...any)    { logMsg(LevelInfo, false, format, args...) }
func Warning(format string, args ...any) { logMsg(LevelWarning, false, format, args...) }
func Error(format string, args ...any)   { logMsg(LevelError, false, format, args...) }
func Fatal(format string, args ...any)   { logMsg(LevelFatal, true, format, args...) }