package docker

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"syscall"
)

type ChangeType int

const (
	ChangeModify = iota
	ChangeAdd
	ChangeDelete
)

type Change struct {
	Path string
	Kind ChangeType
}

func (change *Change) String() string {
	var kind string
	switch change.Kind {
	case ChangeModify:
		kind = "C"
	case ChangeAdd:
		kind = "A"
	case ChangeDelete:
		kind = "D"
	}
	return fmt.Sprintf("%s %s", kind, change.Path)
}

type FileInfo struct {
	parent   *FileInfo
	name     string
	stat     syscall.Stat_t
	children map[string]*FileInfo
}

func (root *FileInfo) LookUp(path string) *FileInfo {
	parent := root
	if path == "/" {
		return root
	}

	pathElements := strings.Split(path, "/")
	for _, elem := range pathElements {
		if elem != "" {
			child := parent.children[elem]
			if child == nil {
				return nil
			}
			parent = child
		}
	}
	return parent
}

func (info *FileInfo) path() string {
	if info.parent == nil {
		return "/"
	}
	return filepath.Join(info.parent.path(), info.name)
}

func (info *FileInfo) unlink() {
	if info.parent != nil {
		delete(info.parent.children, info.name)
	}
}

func (info *FileInfo) Remove(path string) bool {
	child := info.LookUp(path)
	if child != nil {
		child.unlink()
		return true
	}
	return false
}

func (info *FileInfo) isDir() bool {
	return info.parent == nil || info.stat.Mode&syscall.S_IFDIR == syscall.S_IFDIR
}

func (info *FileInfo) addChanges(oldInfo *FileInfo, changes *[]Change) {
	if oldInfo == nil {
		// add
		change := Change{
			Path: info.path(),
			Kind: ChangeAdd,
		}
		*changes = append(*changes, change)
	}

	// We make a copy so we can modify it to detect additions
	// also, we only recurse on the old dir if the new info is a directory
	// otherwise any previous delete/change is considered recursive
	oldChildren := make(map[string]*FileInfo)
	if oldInfo != nil && info.isDir() {
		for k, v := range oldInfo.children {
			oldChildren[k] = v
		}
	}

	for name, newChild := range info.children {
		oldChild, _ := oldChildren[name]
		if oldChild != nil {
			// change?
			oldStat := &oldChild.stat
			newStat := &newChild.stat
			// Note: We can't compare inode or ctime or blocksize here, because these change
			// when copying a file into a container. However, that is not generally a problem
			// because any content change will change mtime, and any status change should
			// be visible when actually comparing the stat fields. The only time this
			// breaks down is if some code intentionally hides a change by setting
			// back mtime
			oldMtime := syscall.NsecToTimeval(oldStat.Mtim.Nano())
			newMtime := syscall.NsecToTimeval(oldStat.Mtim.Nano())
			if oldStat.Mode != newStat.Mode ||
				oldStat.Uid != newStat.Uid ||
				oldStat.Gid != newStat.Gid ||
				oldStat.Rdev != newStat.Rdev ||
				// Don't look at size for dirs, its not a good measure of change
				(oldStat.Size != newStat.Size && oldStat.Mode&syscall.S_IFDIR != syscall.S_IFDIR) ||
				oldMtime.Sec != newMtime.Sec ||
				oldMtime.Usec != newMtime.Usec {
				change := Change{
					Path: newChild.path(),
					Kind: ChangeModify,
				}
				*changes = append(*changes, change)
			}

			// Remove from copy so we can detect deletions
			delete(oldChildren, name)
		}

		newChild.addChanges(oldChild, changes)
	}
	for _, oldChild := range oldChildren {
		// delete
		change := Change{
			Path: oldChild.path(),
			Kind: ChangeDelete,
		}
		*changes = append(*changes, change)
	}

}

func (info *FileInfo) Changes(oldInfo *FileInfo) []Change {
	var changes []Change

	info.addChanges(oldInfo, &changes)

	return changes
}

func newRootFileInfo() *FileInfo {
	root := &FileInfo{
		name:     "/",
		children: make(map[string]*FileInfo),
	}
	return root
}

func applyLayer(root *FileInfo, layer string) error {
	err := filepath.Walk(layer, func(layerPath string, f os.FileInfo, err error) error {
		if err != nil {
			return err
		}

		// Skip root
		if layerPath == layer {
			return nil
		}

		// rebase path
		relPath, err := filepath.Rel(layer, layerPath)
		if err != nil {
			return err
		}
		relPath = filepath.Join("/", relPath)

		// Skip AUFS metadata
		if matched, err := filepath.Match("/.wh..wh.*", relPath); err != nil || matched {
			if err != nil || !f.IsDir() {
				return err
			}
			return filepath.SkipDir
		}

		var layerStat syscall.Stat_t
		err = syscall.Lstat(layerPath, &layerStat)
		if err != nil {
			return err
		}

		file := filepath.Base(relPath)
		// If there is a whiteout, then the file was removed
		if strings.HasPrefix(file, ".wh.") {
			originalFile := file[len(".wh."):]
			deletePath := filepath.Join(filepath.Dir(relPath), originalFile)

			root.Remove(deletePath)
		} else {
			// Added or changed file
			existing := root.LookUp(relPath)
			if existing != nil {
				// Changed file
				existing.stat = layerStat
				if !existing.isDir() {
					// Changed from dir to non-dir, delete all previous files
					existing.children = make(map[string]*FileInfo)
				}
			} else {
				// Added file
				parent := root.LookUp(filepath.Dir(relPath))
				if parent == nil {
					return fmt.Errorf("collectFileInfo: Unexpectedly no parent for %s", relPath)
				}

				info := &FileInfo{
					name:     filepath.Base(relPath),
					children: make(map[string]*FileInfo),
					parent:   parent,
					stat:     layerStat,
				}

				parent.children[info.name] = info
			}
		}
		return nil
	})
	return err
}

func collectFileInfo(sourceDir string) (*FileInfo, error) {
	root := newRootFileInfo()

	err := filepath.Walk(sourceDir, func(path string, f os.FileInfo, err error) error {
		if err != nil {
			return err
		}

		// Rebase path
		relPath, err := filepath.Rel(sourceDir, path)
		if err != nil {
			return err
		}
		relPath = filepath.Join("/", relPath)

		if relPath == "/" {
			return nil
		}

		parent := root.LookUp(filepath.Dir(relPath))
		if parent == nil {
			return fmt.Errorf("collectFileInfo: Unexpectedly no parent for %s", relPath)
		}

		info := &FileInfo{
			name:     filepath.Base(relPath),
			children: make(map[string]*FileInfo),
			parent:   parent,
		}

		if err := syscall.Lstat(path, &info.stat); err != nil {
			return err
		}

		parent.children[info.name] = info

		return nil
	})
	if err != nil {
		return nil, err
	}
	return root, nil
}

// Compare a directory with an array of layer directories it was based on and
// generate an array of Change objects describing the changes
func ChangesLayers(newDir string, layers []string) ([]Change, error) {
	newRoot, err := collectFileInfo(newDir)
	if err != nil {
		return nil, err
	}
	oldRoot := newRootFileInfo()
	for i := len(layers) - 1; i >= 0; i-- {
		layer := layers[i]
		if err = applyLayer(oldRoot, layer); err != nil {
			return nil, err
		}
	}

	return newRoot.Changes(oldRoot), nil
}

// Compare two directories and generate an array of Change objects describing the changes
func ChangesDirs(newDir, oldDir string) ([]Change, error) {
	oldRoot, err := collectFileInfo(oldDir)
	if err != nil {
		return nil, err
	}
	newRoot, err := collectFileInfo(newDir)
	if err != nil {
		return nil, err
	}

	// Ignore changes in .docker-id
	_ = newRoot.Remove("/.docker-id")
	_ = oldRoot.Remove("/.docker-id")

	return newRoot.Changes(oldRoot), nil
}