// Copyright (C) 2022 Marius Schellenberger

package fs

import (
	"context"
	"encoding/json"
	"errors"
	"io"
	stdfs "io/fs"
	"math"
	"net/http"
	"os"
	"path"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"github.com/go-logr/logr"
)

type FS struct {
	mu      sync.RWMutex
	log     logr.Logger
	NoCache http.Handler
	src     string
	dst     string
	mdf     *os.File
	jenc    *json.Encoder
	mm      map[string]*Metadata
	prem    map[string]func()
	cancel  func()
}

func NewFS(src, dst, metadata string, log logr.Logger) (fs *FS, err error) {
	if !filepath.IsAbs(src) {
		return nil, errors.New("src path is not absolute")
	}
	if !filepath.IsAbs(dst) {
		return nil, errors.New("dst path is not absolute")
	}
	if !filepath.IsAbs(metadata) {
		return nil, errors.New("metadata path is not absolute")
	}
	if src == dst {
		return nil, errors.New("src and dst path can not be equal")
	}
	mdf, err := os.OpenFile(metadata, os.O_RDWR|os.O_CREATE, 0o640)
	if err != nil {
		return
	}
	fs = &FS{
		log:     log,
		NoCache: http.FileServer(http.Dir(src)),
		src:     src,
		dst:     dst,
		mdf:     mdf,
		mm:      make(map[string]*Metadata),
		prem:    make(map[string]func()),
		jenc:    json.NewEncoder(mdf),
	}
	err = json.NewDecoder(mdf).Decode(&fs.mm)
	if err == io.EOF {
		err = nil
	}
	fs.initMetadata()
	ctx, cancel := context.WithCancel(context.Background())
	fs.cancel = cancel
	go fs.flusher(ctx)
	return fs, err
}

func (fs *FS) initMetadata() {
	log := fs.log
	for k, v := range fs.mm {
		_, err := fs.statDst(k)
		if errors.Is(err, os.ErrNotExist) {
			log.V(2).Info("removing not existing file from metadata", "file", k)
			delete(fs.mm, k)
			continue
		}
		if len(v.Chunks) == 0 {
			log.V(2).Info("removing empty file", "file", k)
			err := fs.RemoveDst(k)
			if err != nil {
				log.Error(err, "error removing empty file", "file", k)
				continue
			}
			delete(fs.mm, k)
			continue
		}
		v.fs = fs
		v.name = k
	}
}

func (fs *FS) Stat(name string) (fi stdfs.FileInfo, err error) {
	fi, _, err = fs.StatWithOffline(name)
	return
}

func (fs *FS) StatWithOffline(name string) (fi stdfs.FileInfo, offline bool, err error) {
	sp, dp := fs.paths(name)
	fi, err = os.Stat(sp)
	if errors.Is(err, os.ErrNotExist) {
		fi, err = os.Stat(dp)
		if err != nil {
			return
		}
		offline = true
	}
	return
}

func (fs *FS) RemoveDst(name string) error {
	_, dp := fs.paths(name)
	return os.Remove(dp)
}

func (fs *FS) statDst(name string) (fi stdfs.FileInfo, err error) {
	_, dp := fs.paths(name)
	return os.Stat(dp)
}

func (fs *FS) CancelPreload(name string) {
	if cancel, ok := fs.prem[name]; ok {
		cancel()
	}
}

func (fs *FS) Preload(name string) {
	file, err := fs.Open(name)
	if err != nil {
		return
	}
	f, ok := file.(*File)
	if !ok {
		return
	}

	if f.md.Preload() {
		fs.log.WithValues("file", name).Error(errors.New("preload is running"), "error starting preload")
		return
	}
	ctx, cancel := context.WithCancel(context.Background())
	fs.prem[name] = cancel
	unlock := func() {
		delete(fs.prem, name)
		f.md.UnlockPreload()
	}
	go f.Preload(ctx, unlock)
}

func skipLog(name string) bool {
	return strings.HasSuffix(name, "index.html") || strings.HasSuffix(name, "favicon.ico")
}

func (fs *FS) paths(name string) (sp string, dp string) {
	p := filepath.FromSlash(path.Clean("/" + name))
	sp = filepath.Join(fs.src, p)
	dp = filepath.Join(fs.dst, p)
	return
}

func (fs *FS) Open(name string) (f http.File, err error) {
	log := fs.log.WithValues("file", name)
	sp, dp := fs.paths(name)
	offline := false
	sf, err := os.Open(sp)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			sf, err = os.Open(dp)
			if err != nil {
				if !skipLog(name) {
					log.Error(err, "error opening source file")
				}
				return
			}
			offline = true
			log.V(2).Info("file offline mode", "path", dp)
		} else {
			log.Error(err, "error opening source file")
			return
		}
	}
	sfi, err := sf.Stat()
	if err != nil {
		sf.Close()
		log.Error(err, "error stat source file")
		return
	}
	if sfi.IsDir() {
		if empty, e := dirEmpty(sf.Name()); empty && e == nil {
			sf.Close()
			sf, err = os.Open(dp)
			offline = true
			log.V(2).Info("dir offline mode", "path", dp)
		}
		return &Dir{f: sf}, err
	}
	md := fs.metadata(name, sfi.Size())
	return &File{
		log:     log,
		f:       sf,
		md:      md,
		offline: offline,
	}, nil
}

func (fs *FS) openCacheFile(name string, size int64) (df *os.File, err error) {
	_, dp := fs.paths(name)
	log := fs.log
	if i := strings.LastIndex(dp, "/"); i > 0 {
		dir := dp[:i]
		_, err = os.Stat(dir)
		if errors.Is(err, os.ErrNotExist) {
			err = os.MkdirAll(dir, 0o755)
			if err != nil {
				log.Error(err, "error creating cache dir", "dir", dp)
				return
			}
		}
	}
	_, err = os.Stat(dp)
	truncate := errors.Is(err, os.ErrNotExist)
	df, err = os.OpenFile(dp, os.O_RDWR|os.O_CREATE, 0o644)
	if err != nil {
		log.Error(err, "error opening cache file")
		return
	}
	if truncate {
		err = df.Truncate(size)
		if err != nil {
			log.Error(err, "error truncating cache file")
			return
		}
		err = df.Sync()
		if err != nil {
			log.Error(err, "error syncing cache file")
			return
		}
	}
	return
}

func (fs *FS) metadata(name string, size int64) (md *Metadata) {
	fs.mu.Lock()
	defer fs.mu.Unlock()
	if md, ok := fs.mm[name]; ok {
		return md
	}
	md = &Metadata{Size: size, fs: fs, name: name}
	fs.mm[name] = md
	return
}

func (fs *FS) CacheStatus(name string) int {
	fs.mu.RLock()
	defer fs.mu.RUnlock()
	if md, ok := fs.mm[name]; ok {
		return int(math.Round(float64(md.Chunks.Size()) / float64(md.Size) * 100))
	}
	return -1
}

func (fs *FS) flusher(ctx context.Context) {
	for {
		select {
		case <-ctx.Done():
			return
		case <-time.After(time.Minute * 5):
		}
		fs.flushMetadata()
	}
}

func (fs *FS) flushMetadata() {
	log := fs.log
	fs.mu.Lock()
	defer fs.mu.Unlock()
	mm := make(map[string]*Metadata)
	for k, v := range fs.mm {
		if v.f != nil || len(v.Chunks) > 0 {
			mm[k] = v
		}
	}
	_, err := fs.mdf.Seek(0, io.SeekStart)
	if err != nil {
		log.Error(err, "failure seeking metadata file")
		return
	}
	err = fs.mdf.Truncate(0)
	if err != nil {
		log.Error(err, "failure truncating metadata file")
		return
	}
	err = fs.jenc.Encode(mm)
	if err != nil {
		log.Error(err, "failure flushing metadata file")
	}
}

func (fs *FS) Close() {
	fs.cancel()
	for _, md := range fs.mm {
		md.f.Sync()
		md.f.Close()
	}
	fs.flushMetadata()
}

func dirEmpty(name string) (bool, error) {
	f, err := os.Open(name)
	if err != nil {
		return false, err
	}
	defer f.Close()
	_, err = f.Readdir(1)
	if err == io.EOF {
		return true, nil
	}
	return false, err
}