package castorev1

import (
	"bytes"
	"encoding/base64"
	"fmt"

	"google.golang.org/protobuf/proto"
	"lukechampine.com/blake3"
)

// The size of a directory is calculated by summing up the numbers of
// `directories`, `files` and `symlinks`, and for each directory, its size
// field.
func (d *Directory) Size() uint32 {
	var size uint32
	size = uint32(len(d.Files) + len(d.Symlinks))
	for _, d := range d.Directories {
		size += 1 + d.Size
	}
	return size
}

func (d *Directory) Digest() ([]byte, error) {
	b, err := proto.MarshalOptions{
		Deterministic: true,
	}.Marshal(d)

	if err != nil {
		return nil, fmt.Errorf("error while marshalling directory: %w", err)
	}

	h := blake3.New(32, nil)

	_, err = h.Write(b)
	if err != nil {
		return nil, fmt.Errorf("error writing to hasher: %w", err)
	}

	return h.Sum(nil), nil
}

// isValidName checks a name for validity.
// We disallow slashes, null bytes, '.', '..' and the empty string.
// Depending on the context, a *Node message with an empty string as name is
// allowed, but they don't occur inside a Directory message.
func isValidName(n []byte) bool {
	if len(n) == 0 || bytes.Equal(n, []byte("..")) || bytes.Equal(n, []byte{'.'}) || bytes.Contains(n, []byte{'\x00'}) || bytes.Contains(n, []byte{'/'}) {
		return false
	}
	return true
}

// Validate ensures a DirectoryNode has a valid name and correct digest len.
func (n *DirectoryNode) Validate() error {
	if len(n.Digest) != 32 {
		return fmt.Errorf("invalid digest length for %s, expected %d, got %d", n.Name, 32, len(n.Digest))
	}

	if !isValidName(n.Name) {
		return fmt.Errorf("invalid node name: %s", n.Name)
	}

	return nil
}

// Validate ensures a FileNode has a valid name and correct digest len.
func (n *FileNode) Validate() error {
	if len(n.Digest) != 32 {
		return fmt.Errorf("invalid digest length for %s, expected %d, got %d", n.Name, 32, len(n.Digest))
	}

	if !isValidName(n.Name) {
		return fmt.Errorf("invalid node name: %s", n.Name)
	}

	return nil
}

// Validate ensures a SymlinkNode has a valid name and target.
func (n *SymlinkNode) Validate() error {
	if len(n.Target) == 0 || bytes.Contains(n.Target, []byte{0}) {
		return fmt.Errorf("invalid symlink target: %s", n.Target)
	}

	if !isValidName(n.Name) {
		return fmt.Errorf("invalid node name: %s", n.Name)
	}

	return nil
}

// Validate ensures a node is valid, by dispatching to the per-type validation functions.
func (n *Node) Validate() error {
	if node := n.GetDirectory(); node != nil {
		if err := node.Validate(); err != nil {
			return fmt.Errorf("SymlinkNode failed validation: %w", err)
		}
	} else if node := n.GetFile(); node != nil {
		if err := node.Validate(); err != nil {
			return fmt.Errorf("FileNode failed validation: %w", err)
		}
	} else if node := n.GetSymlink(); node != nil {
		if err := node.Validate(); err != nil {
			return fmt.Errorf("SymlinkNode failed validation: %w", err)
		}

	} else {
		// this would only happen if we introduced a new type
		return fmt.Errorf("no specific node found")
	}

	return nil
}

// Validate thecks the Directory message for invalid data, such as:
// - violations of name restrictions
// - invalid digest lengths
// - not properly sorted lists
// - duplicate names in the three lists
func (d *Directory) Validate() error {
	// seenNames contains all seen names so far.
	// We populate this to ensure node names are unique across all three lists.
	seenNames := make(map[string]interface{})

	// We also track the last seen name in each of the three lists,
	// to ensure nodes are sorted by their names.
	var lastDirectoryName, lastFileName, lastSymlinkName []byte

	// helper function to only insert in sorted order.
	// used with the three lists above.
	// Note this consumes a *pointer to* a string,  as it mutates it.
	insertIfGt := func(lastName *[]byte, name []byte) error {
		// update if it's greater than the previous name
		if bytes.Compare(name, *lastName) == 1 {
			*lastName = name
			return nil
		} else {
			return fmt.Errorf("%v is not in sorted order", name)
		}
	}

	// insertOnce inserts into seenNames if the key doesn't exist yet.
	insertOnce := func(name []byte) error {
		encoded := base64.StdEncoding.EncodeToString(name)
		if _, found := seenNames[encoded]; found {
			return fmt.Errorf("duplicate name: %v", string(name))
		}
		seenNames[encoded] = nil
		return nil
	}

	// Loop over all Directories, Files and Symlinks individually,
	// check them for validity, then check for sorting in the current list, and
	// uniqueness across all three lists.
	for _, directoryNode := range d.Directories {
		directoryName := directoryNode.GetName()

		if err := directoryNode.Validate(); err != nil {
			return fmt.Errorf("DirectoryNode %s failed validation: %w", directoryName, err)
		}

		// ensure names are sorted
		if err := insertIfGt(&lastDirectoryName, directoryName); err != nil {
			return err
		}

		// add to seenNames
		if err := insertOnce(directoryName); err != nil {
			return err
		}

	}

	for _, fileNode := range d.Files {
		fileName := fileNode.GetName()

		if err := fileNode.Validate(); err != nil {
			return fmt.Errorf("FileNode %s failed validation: %w", fileName, err)
		}

		// ensure names are sorted
		if err := insertIfGt(&lastFileName, fileName); err != nil {
			return err
		}

		// add to seenNames
		if err := insertOnce(fileName); err != nil {
			return err
		}
	}

	for _, symlinkNode := range d.Symlinks {
		symlinkName := symlinkNode.GetName()

		if err := symlinkNode.Validate(); err != nil {
			return fmt.Errorf("SymlinkNode %s failed validation: %w", symlinkName, err)
		}

		// ensure names are sorted
		if err := insertIfGt(&lastSymlinkName, symlinkName); err != nil {
			return err
		}

		// add to seenNames
		if err := insertOnce(symlinkName); err != nil {
			return err
		}
	}

	return nil
}