//go:build linux

/*
Copyright 2014 The Perkeep Authors

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package fs

import (
	"context"
	"os"
	"strings"
	"sync"
	"time"

	"bazil.org/fuse"
	"bazil.org/fuse/fs"
	"go4.org/syncutil"
	"perkeep.org/pkg/blob"
	"perkeep.org/pkg/search"
)

const versionsRefreshTime = 1 * time.Minute

// versionsDir implements fuse.Node containing all roots. Within this node,
// - a directory permanode is represented with a fuse directory (roVersionsDir)
// - a file permanode is represented with a fuse directory (roFileVersionsDir)
// - a file version is represented with a fuse file (roFileVersion)
// In this way you can navigate to a file at a specific point in time.
// Basically is like `at` magic folder but the path (not the date) goes first.
// It is read-only.
type versionsDir struct {
	fs *CamliFileSystem

	mu        sync.Mutex
	lastQuery time.Time
	m         map[string]blob.Ref // ent name => permanode
	children  map[string]fs.Node  // ent name => child node
}

func (n *versionsDir) isRO() bool {
	return true
}

func (n *versionsDir) dirMode() os.FileMode {
	if n.isRO() {
		return 0500
	}
	return 0700
}

func (n *versionsDir) Attr(ctx context.Context, a *fuse.Attr) error {
	a.Mode = os.ModeDir | n.dirMode()
	a.Uid = uint32(os.Getuid())
	a.Gid = uint32(os.Getgid())
	return nil
}

func (n *versionsDir) ReadDir(ctx context.Context) ([]fuse.Dirent, error) {
	n.mu.Lock()
	defer n.mu.Unlock()
	if err := n.condRefresh(ctx); err != nil {
		return nil, handleEIOorEINTR(err)
	}
	var ents []fuse.Dirent
	for name := range n.m {
		ents = append(ents, fuse.Dirent{Name: name})
	}
	Logger.Printf("fs.versions.ReadDir() -> %v", ents)
	return ents, nil
}

func (n *versionsDir) Lookup(ctx context.Context, name string) (fs.Node, error) {
	Logger.Printf("fs.versions: Lookup(%q)", name)
	n.mu.Lock()
	defer n.mu.Unlock()
	if err := n.condRefresh(ctx); err != nil {
		return nil, handleEIOorEINTR(err)
	}
	br := n.m[name]
	if !br.Valid() {
		return nil, fuse.ENOENT
	}

	nod, ok := n.children[name]

	if ok {
		return nod, nil
	}

	nod = newROVersionsDir(n.fs, br, name)

	n.children[name] = nod

	return nod, nil
}

// requires n.mu is held
func (n *versionsDir) condRefresh(ctx context.Context) error {
	if n.lastQuery.After(time.Now().Add(-versionsRefreshTime)) {
		return nil
	}
	Logger.Printf("fs.versions: querying")

	var rootRes, impRes *search.WithAttrResponse
	var grp syncutil.Group
	grp.Go(func() (err error) {
		rootRes, err = n.fs.client.GetPermanodesWithAttr(ctx, &search.WithAttrRequest{N: 100, Attr: "camliRoot"})
		return
	})
	grp.Go(func() (err error) {
		impRes, err = n.fs.client.GetPermanodesWithAttr(ctx, &search.WithAttrRequest{N: 100, Attr: "camliImportRoot"})
		return
	})
	if err := grp.Err(); err != nil {
		Logger.Printf("fs.versions: GetRecentPermanodes error in ReadDir: %v", err)
		return err
	}

	n.m = make(map[string]blob.Ref)
	if n.children == nil {
		n.children = make(map[string]fs.Node)
	}

	dr := &search.DescribeRequest{
		Depth: 1,
	}
	for _, wi := range rootRes.WithAttr {
		dr.BlobRefs = append(dr.BlobRefs, wi.Permanode)
	}
	for _, wi := range impRes.WithAttr {
		dr.BlobRefs = append(dr.BlobRefs, wi.Permanode)
	}
	if len(dr.BlobRefs) == 0 {
		return nil
	}

	dres, err := n.fs.client.Describe(ctx, dr)
	if err != nil {
		Logger.Printf("Describe failure: %v", err)
		return err
	}

	// Roots
	currentRoots := map[string]bool{}
	for _, wi := range rootRes.WithAttr {
		pn := wi.Permanode
		db := dres.Meta[pn.String()]
		if db != nil && db.Permanode != nil {
			name := db.Permanode.Attr.Get("camliRoot")
			if name != "" {
				currentRoots[name] = true
				n.m[name] = pn
			}
		}
	}

	// Remove any children objects we have mapped that are no
	// longer relevant.
	for name := range n.children {
		if !currentRoots[name] {
			delete(n.children, name)
		}
	}

	// Importers (mapped as roots for now)
	for _, wi := range impRes.WithAttr {
		pn := wi.Permanode
		db := dres.Meta[pn.String()]
		if db != nil && db.Permanode != nil {
			name := db.Permanode.Attr.Get("camliImportRoot")
			if name != "" {
				name = strings.Replace(name, ":", "-", -1)
				name = strings.Replace(name, "/", "-", -1)
				n.m["importer-"+name] = pn
			}
		}
	}

	n.lastQuery = time.Now()
	return nil
}