package logger

import (
	"context"
	"fmt"
	"homestead/homestead_gateway/util/config"
	"log/slog"
	"os"
	"path/filepath"
	"time"

	slogmulti "github.com/samber/slog-multi"
)

// New creates a logger identified by id.
// Returns: *slog.Logger, closeFunc, error.
// Call closeFunc() on shutdown to close open files.
func New(id string, cfg config.LogConfig) (*slog.Logger, func() error, error) {
	if cfg.Directory == "" {
		cfg.Directory = "logs"
	}
	if cfg.Rotation <= 0 {
		cfg.Rotation = 7
	}

	console := slog.NewTextHandler(&prefixWriter{inner: os.Stderr, prefix: []byte("[" + id + "] "), startLine: true}, &slog.HandlerOptions{AddSource: true})
	router := newFileRouter(cfg.Directory, cfg.Rotation, id)
	root := slogmulti.Fanout(console, router)

	return slog.New(root), router.CloseFiles, nil
}

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

	totalWritten := 0
	if p.startLine {
		n, err := p.inner.Write(p.prefix)
		totalWritten += n
		if err != nil {
			return totalWritten, err
		}
		p.startLine = false
	}

	n, err := p.inner.Write(b)
	totalWritten += n
	if err != nil {
		return totalWritten, err
	}

	if len(b) > 0 && b[len(b)-1] == '\n' {
		p.startLine = true
	}
	return totalWritten, nil
}

func newFileRouter(baseDir string, rotationDays int, id string) *fileRouter {
	return &fileRouter{
		handlers:      make(map[string]slog.Handler),
		files:         make(map[string]*os.File),
		baseDir:       baseDir,
		rotationDays:  rotationDays,
		id:            id,
		dirTimeLayout: "2006-01-02", // e.g. 2025-11-30
	}
}

//goland:noinspection GoUnusedParameter
func (r *fileRouter) Enabled(ctx context.Context, lvl slog.Level) bool {
	// Conservatively true; actual handler will decide.
	return true
}

func (r *fileRouter) Handle(ctx context.Context, rec slog.Record) error {
	now := time.Now()
	dirName := now.Format(r.dirTimeLayout)
	dirPath := filepath.Join(r.baseDir, dirName)
	filePath := filepath.Join(dirPath, r.id+".log")

	h, err := r.getHandler(dirPath, filePath)
	if err != nil {
		return fmt.Errorf("file router get handler: %w", err)
	}

	return h.Handle(ctx, rec)
}

func (r *fileRouter) WithAttrs(attrs []slog.Attr) slog.Handler {
	return r
}

func (r *fileRouter) WithGroup(name string) slog.Handler {
	return r
}

// getHandler returns a text handler for the given file, creating dir/file and cleaning up old dirs if needed.
func (r *fileRouter) getHandler(dirPath, filePath string) (slog.Handler, error) {
	r.mu.RLock()
	h, ok := r.handlers[filePath]
	r.mu.RUnlock()
	if ok {
		return h, nil
	}

	r.mu.Lock()
	defer r.mu.Unlock()
	if h, ok = r.handlers[filePath]; ok {
		return h, nil
	}

	_, statErr := os.Stat(dirPath)
	dirExisted := statErr == nil

	if err := os.MkdirAll(dirPath, 0o755); err != nil {
		return nil, fmt.Errorf("mkdir %s: %w", dirPath, err)
	}

	if !dirExisted {
		if err := r.cleanupOldDirs(); err != nil {
			// don't fail logging just because cleanup failed; report to stderr and continue.
			_, _ = fmt.Fprintf(os.Stderr, "logger: cleanupOldDirs error: %v\n", err)
		}
	}

	f, err := os.OpenFile(filePath, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o644)
	if err != nil {
		return nil, fmt.Errorf("open log file %s: %w", filePath, err)
	}

	textHandler := slog.NewTextHandler(f, &slog.HandlerOptions{
		AddSource: false,
	})

	r.files[filePath] = f
	r.handlers[filePath] = textHandler
	return textHandler, nil
}

// cleanupOldDirs scans r.baseDir for directories matching the dirTimeLayout and deletes any whose
// day-start time is older than rotationDays from now.
func (r *fileRouter) cleanupOldDirs() error {
	entries, err := os.ReadDir(r.baseDir)
	if err != nil {
		if os.IsNotExist(err) {
			return nil
		}
		return fmt.Errorf("read baseDir: %w", err)
	}

	now := time.Now()
	cutoff := now.AddDate(0, 0, -r.rotationDays)

	for _, e := range entries {
		if !e.IsDir() {
			continue
		}
		name := e.Name()
		t, err := time.ParseInLocation(r.dirTimeLayout, name, time.Local)
		if err != nil {
			continue
		}

		if t.Before(cutoff) {
			path := filepath.Join(r.baseDir, name)

			if err := os.RemoveAll(path); err != nil {
				_, _ = fmt.Fprintf(os.Stderr, "logger: failed to remove old log dir %s: %v\n", path, err)
			}
		}
	}

	return nil
}

// CloseFiles closes open files
func (r *fileRouter) CloseFiles() error {
	r.mu.Lock()
	defer r.mu.Unlock()

	var firstErr error
	for p, f := range r.files {
		if err := f.Close(); err != nil && firstErr == nil {
			firstErr = err
		}
		delete(r.files, p)
		delete(r.handlers, p)
	}
	return firstErr
}