// Package walk walks directories
package walk

import (
	"bytes"
	"fmt"
	"path"
	"sort"
	"strings"
	"sync"
	"time"

	"github.com/ncw/rclone/fs"
	"github.com/ncw/rclone/fs/filter"
	"github.com/ncw/rclone/fs/list"
	"github.com/pkg/errors"
)

// ErrorSkipDir is used as a return value from Walk to indicate that the
// directory named in the call is to be skipped. It is not returned as
// an error by any function.
var ErrorSkipDir = errors.New("skip this directory")

// ErrorCantListR is returned by WalkR if the underlying Fs isn't
// capable of doing a recursive listing.
var ErrorCantListR = errors.New("recursive directory listing not available")

// Func is the type of the function called for directory
// visited by Walk. The path argument contains remote path to the directory.
//
// If there was a problem walking to directory named by path, the
// incoming error will describe the problem and the function can
// decide how to handle that error (and Walk will not descend into
// that directory). If an error is returned, processing stops. The
// sole exception is when the function returns the special value
// ErrorSkipDir. If the function returns ErrorSkipDir, Walk skips the
// directory's contents entirely.
type Func func(path string, entries fs.DirEntries, err error) error

// Walk lists the directory.
//
// If includeAll is not set it will use the filters defined.
//
// If maxLevel is < 0 then it will recurse indefinitely, else it will
// only do maxLevel levels.
//
// It calls fn for each tranche of DirEntries read.
//
// Note that fn will not be called concurrently whereas the directory
// listing will proceed concurrently.
//
// Parent directories are always listed before their children
//
// This is implemented by WalkR if Config.UseRecursiveListing is true
// and f supports it and level > 1, or WalkN otherwise.
//
// NB (f, path) to be replaced by fs.Dir at some point
func Walk(f fs.Fs, path string, includeAll bool, maxLevel int, fn Func) error {
	if (maxLevel < 0 || maxLevel > 1) && fs.Config.UseListR && f.Features().ListR != nil {
		return walkListR(f, path, includeAll, maxLevel, fn)
	}
	return walkListDirSorted(f, path, includeAll, maxLevel, fn)
}

// walkListDirSorted lists the directory.
//
// It implements Walk using non recursive directory listing.
func walkListDirSorted(f fs.Fs, path string, includeAll bool, maxLevel int, fn Func) error {
	return walk(f, path, includeAll, maxLevel, fn, list.DirSorted)
}

// walkListR lists the directory.
//
// It implements Walk using recursive directory listing if
// available, or returns ErrorCantListR if not.
func walkListR(f fs.Fs, path string, includeAll bool, maxLevel int, fn Func) error {
	listR := f.Features().ListR
	if listR == nil {
		return ErrorCantListR
	}
	return walkR(f, path, includeAll, maxLevel, fn, listR)
}

type listDirFunc func(fs fs.Fs, includeAll bool, dir string) (entries fs.DirEntries, err error)

func walk(f fs.Fs, path string, includeAll bool, maxLevel int, fn Func, listDir listDirFunc) error {
	var (
		wg         sync.WaitGroup // sync closing of go routines
		traversing sync.WaitGroup // running directory traversals
		doClose    sync.Once      // close the channel once
		mu         sync.Mutex     // stop fn being called concurrently
	)
	// listJob describe a directory listing that needs to be done
	type listJob struct {
		remote string
		depth  int
	}

	in := make(chan listJob, fs.Config.Checkers)
	errs := make(chan error, 1)
	quit := make(chan struct{})
	closeQuit := func() {
		doClose.Do(func() {
			close(quit)
			go func() {
				for range in {
					traversing.Done()
				}
			}()
		})
	}
	for i := 0; i < fs.Config.Checkers; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			for {
				select {
				case job, ok := <-in:
					if !ok {
						return
					}
					entries, err := listDir(f, includeAll, job.remote)
					var jobs []listJob
					if err == nil && job.depth != 0 {
						entries.ForDir(func(dir fs.Directory) {
							// Recurse for the directory
							jobs = append(jobs, listJob{
								remote: dir.Remote(),
								depth:  job.depth - 1,
							})
						})
					}
					mu.Lock()
					err = fn(job.remote, entries, err)
					mu.Unlock()
					// NB once we have passed entries to fn we mustn't touch it again
					if err != nil && err != ErrorSkipDir {
						traversing.Done()
						fs.CountError(err)
						fs.Errorf(job.remote, "error listing: %v", err)
						closeQuit()
						// Send error to error channel if space
						select {
						case errs <- err:
						default:
						}
						continue
					}
					if err == nil && len(jobs) > 0 {
						traversing.Add(len(jobs))
						go func() {
							// Now we have traversed this directory, send these
							// jobs off for traversal in the background
							for _, newJob := range jobs {
								in <- newJob
							}
						}()
					}
					traversing.Done()
				case <-quit:
					return
				}
			}
		}()
	}
	// Start the process
	traversing.Add(1)
	in <- listJob{
		remote: path,
		depth:  maxLevel - 1,
	}
	traversing.Wait()
	close(in)
	wg.Wait()
	close(errs)
	// return the first error returned or nil
	return <-errs
}

// DirTree is a map of directories to entries
type DirTree map[string]fs.DirEntries

// parentDir finds the parent directory of path
func parentDir(entryPath string) string {
	dirPath := path.Dir(entryPath)
	if dirPath == "." {
		dirPath = ""
	}
	return dirPath
}

// add an entry to the tree
func (dt DirTree) add(entry fs.DirEntry) {
	dirPath := parentDir(entry.Remote())
	dt[dirPath] = append(dt[dirPath], entry)
}

// add a directory entry to the tree
func (dt DirTree) addDir(entry fs.DirEntry) {
	dt.add(entry)
	// create the directory itself if it doesn't exist already
	dirPath := entry.Remote()
	if _, ok := dt[dirPath]; !ok {
		dt[dirPath] = nil
	}
}

// Find returns the DirEntry for filePath or nil if not found
func (dt DirTree) Find(filePath string) (parentPath string, entry fs.DirEntry) {
	parentPath = parentDir(filePath)
	for _, entry := range dt[parentPath] {
		if entry.Remote() == filePath {
			return parentPath, entry
		}
	}
	return parentPath, nil
}

// check that dirPath has a *Dir in its parent
func (dt DirTree) checkParent(root, dirPath string) {
	if dirPath == root {
		return
	}
	parentPath, entry := dt.Find(dirPath)
	if entry != nil {
		return
	}
	dt[parentPath] = append(dt[parentPath], fs.NewDir(dirPath, time.Now()))
	dt.checkParent(root, parentPath)
}

// check every directory in the tree has *Dir in its parent
func (dt DirTree) checkParents(root string) {
	for dirPath := range dt {
		dt.checkParent(root, dirPath)
	}
}

// Sort sorts all the Entries
func (dt DirTree) Sort() {
	for _, entries := range dt {
		sort.Stable(entries)
	}
}

// Dirs returns the directories in sorted order
func (dt DirTree) Dirs() (dirNames []string) {
	for dirPath := range dt {
		dirNames = append(dirNames, dirPath)
	}
	sort.Strings(dirNames)
	return dirNames
}

// Prune remove directories from a directory tree. dirNames contains
// all directories to remove as keys, with true as values. dirNames
// will be modified in the function.
func (dt DirTree) Prune(dirNames map[string]bool) error {
	// We use map[string]bool to avoid recursion (and potential
	// stack exhaustion).

	// First we need delete directories from their parents.
	for dName, remove := range dirNames {
		if !remove {
			// Currently all values should be
			// true, therefore this should not
			// happen. But this makes function
			// more predictable.
			fs.Infof(dName, "Directory in the map for prune, but the value is false")
			continue
		}
		if dName == "" {
			// if dName is root, do nothing (no parent exist)
			continue
		}
		parent := parentDir(dName)
		// It may happen that dt does not have a dName key,
		// since directory was excluded based on a filter. In
		// such case the loop will be skipped.
		for i, entry := range dt[parent] {
			switch x := entry.(type) {
			case fs.Directory:
				if x.Remote() == dName {
					// the slice is not sorted yet
					// to delete item
					// a) replace it with the last one
					dt[parent][i] = dt[parent][len(dt[parent])-1]
					// b) remove last
					dt[parent] = dt[parent][:len(dt[parent])-1]
					// we modify a slice within a loop, but we stop
					// iterating immediately
					break
				}
			case fs.Object:
				// do nothing
			default:
				return errors.Errorf("unknown object type %T", entry)

			}
		}
	}

	for len(dirNames) > 0 {
		// According to golang specs, if new keys were added
		// during range iteration, they may be skipped.
		for dName, remove := range dirNames {
			if !remove {
				fs.Infof(dName, "Directory in the map for prune, but the value is false")
				continue
			}
			// First, add all subdirectories to dirNames.

			// It may happen that dt[dName] does not exist.
			// If so, the loop will be skipped.
			for _, entry := range dt[dName] {
				switch x := entry.(type) {
				case fs.Directory:
					excludeDir := x.Remote()
					dirNames[excludeDir] = true
				case fs.Object:
					// do nothing
				default:
					return errors.Errorf("unknown object type %T", entry)

				}
			}
			// Then remove current directory from DirTree
			delete(dt, dName)
			// and from dirNames
			delete(dirNames, dName)
		}
	}
	return nil
}

// String emits a simple representation of the DirTree
func (dt DirTree) String() string {
	out := new(bytes.Buffer)
	for _, dir := range dt.Dirs() {
		_, _ = fmt.Fprintf(out, "%s/\n", dir)
		for _, entry := range dt[dir] {
			flag := ""
			if _, ok := entry.(fs.Directory); ok {
				flag = "/"
			}
			_, _ = fmt.Fprintf(out, "  %s%s\n", path.Base(entry.Remote()), flag)
		}
	}
	return out.String()
}

func walkRDirTree(f fs.Fs, startPath string, includeAll bool, maxLevel int, listR fs.ListRFn) (DirTree, error) {
	dirs := make(DirTree)
	// Entries can come in arbitrary order. We use toPrune to keep
	// all directories to exclude later.
	toPrune := make(map[string]bool)
	includeDirectory := filter.Active.IncludeDirectory(f)
	var mu sync.Mutex
	err := listR(startPath, func(entries fs.DirEntries) error {
		mu.Lock()
		defer mu.Unlock()
		for _, entry := range entries {
			slashes := strings.Count(entry.Remote(), "/")
			switch x := entry.(type) {
			case fs.Object:
				// Make sure we don't delete excluded files if not required
				if includeAll || filter.Active.IncludeObject(x) {
					if maxLevel < 0 || slashes <= maxLevel-1 {
						dirs.add(x)
					} else {
						// Make sure we include any parent directories of excluded objects
						dirPath := x.Remote()
						for ; slashes > maxLevel-1; slashes-- {
							dirPath = parentDir(dirPath)
						}
						dirs.checkParent(startPath, dirPath)
					}
				} else {
					fs.Debugf(x, "Excluded from sync (and deletion)")
				}
				// Check if we need to prune a directory later.
				if !includeAll && len(filter.Active.Opt.ExcludeFile) > 0 {
					basename := path.Base(x.Remote())
					if basename == filter.Active.Opt.ExcludeFile {
						excludeDir := parentDir(x.Remote())
						toPrune[excludeDir] = true
						fs.Debugf(basename, "Excluded from sync (and deletion) based on exclude file")
					}
				}
			case fs.Directory:
				inc, err := includeDirectory(x.Remote())
				if err != nil {
					return err
				}
				if includeAll || inc {
					if maxLevel < 0 || slashes <= maxLevel-1 {
						if slashes == maxLevel-1 {
							// Just add the object if at maxLevel
							dirs.add(x)
						} else {
							dirs.addDir(x)
						}
					}
				} else {
					fs.Debugf(x, "Excluded from sync (and deletion)")
				}
			default:
				return errors.Errorf("unknown object type %T", entry)
			}
		}
		return nil
	})
	if err != nil {
		return nil, err
	}
	dirs.checkParents(startPath)
	if len(dirs) == 0 {
		dirs[startPath] = nil
	}
	err = dirs.Prune(toPrune)
	if err != nil {
		return nil, err
	}
	dirs.Sort()
	return dirs, nil
}

// Create a DirTree using List
func walkNDirTree(f fs.Fs, path string, includeAll bool, maxLevel int, listDir listDirFunc) (DirTree, error) {
	dirs := make(DirTree)
	fn := func(dirPath string, entries fs.DirEntries, err error) error {
		if err == nil {
			dirs[dirPath] = entries
		}
		return err
	}
	err := walk(f, path, includeAll, maxLevel, fn, listDir)
	if err != nil {
		return nil, err
	}
	return dirs, nil
}

// NewDirTree returns a DirTree filled with the directory listing
// using the parameters supplied.
//
// If includeAll is not set it will use the filters defined.
//
// If maxLevel is < 0 then it will recurse indefinitely, else it will
// only do maxLevel levels.
//
// This is implemented by WalkR if Config.UseRecursiveListing is true
// and f supports it and level > 1, or WalkN otherwise.
//
// NB (f, path) to be replaced by fs.Dir at some point
func NewDirTree(f fs.Fs, path string, includeAll bool, maxLevel int) (DirTree, error) {
	if ListR := f.Features().ListR; (maxLevel < 0 || maxLevel > 1) && fs.Config.UseListR && ListR != nil {
		return walkRDirTree(f, path, includeAll, maxLevel, ListR)
	}
	return walkNDirTree(f, path, includeAll, maxLevel, list.DirSorted)
}

func walkR(f fs.Fs, path string, includeAll bool, maxLevel int, fn Func, listR fs.ListRFn) error {
	dirs, err := walkRDirTree(f, path, includeAll, maxLevel, listR)
	if err != nil {
		return err
	}
	skipping := false
	skipPrefix := ""
	emptyDir := fs.DirEntries{}
	for _, dirPath := range dirs.Dirs() {
		if skipping {
			// Skip over directories as required
			if strings.HasPrefix(dirPath, skipPrefix) {
				continue
			}
			skipping = false
		}
		entries := dirs[dirPath]
		if entries == nil {
			entries = emptyDir
		}
		err = fn(dirPath, entries, nil)
		if err == ErrorSkipDir {
			skipping = true
			skipPrefix = dirPath
			if skipPrefix != "" {
				skipPrefix += "/"
			}
		} else if err != nil {
			return err
		}
	}
	return nil
}

// GetAll runs Walk getting all the results
func GetAll(f fs.Fs, path string, includeAll bool, maxLevel int) (objs []fs.Object, dirs []fs.Directory, err error) {
	err = Walk(f, path, includeAll, maxLevel, func(dirPath string, entries fs.DirEntries, err error) error {
		if err != nil {
			return err
		}
		for _, entry := range entries {
			switch x := entry.(type) {
			case fs.Object:
				objs = append(objs, x)
			case fs.Directory:
				dirs = append(dirs, x)
			}
		}
		return nil
	})
	return
}

// ListRHelper is used in the implementation of ListR to accumulate DirEntries
type ListRHelper struct {
	callback fs.ListRCallback
	entries  fs.DirEntries
}

// NewListRHelper should be called from ListR with the callback passed in
func NewListRHelper(callback fs.ListRCallback) *ListRHelper {
	return &ListRHelper{
		callback: callback,
	}
}

// send sends the stored entries to the callback if there are >= max
// entries.
func (lh *ListRHelper) send(max int) (err error) {
	if len(lh.entries) >= max {
		err = lh.callback(lh.entries)
		lh.entries = lh.entries[:0]
	}
	return err
}

// Add an entry to the stored entries and send them if there are more
// than a certain amount
func (lh *ListRHelper) Add(entry fs.DirEntry) error {
	if entry == nil {
		return nil
	}
	lh.entries = append(lh.entries, entry)
	return lh.send(100)
}

// Flush the stored entries (if any) sending them to the callback
func (lh *ListRHelper) Flush() error {
	return lh.send(1)
}
