package dehub

import (
	"fmt"

	"gopkg.in/src-d/go-git.v4/plumbing"
	"gopkg.in/src-d/go-git.v4/plumbing/filemode"
	"gopkg.in/src-d/go-git.v4/plumbing/object"
)

// ChangedFile describes a single file which has been changed in some way
// between two object.Trees. If the From fields are empty then the file was
// created, if the To fields are empty then the file was deleted.
type ChangedFile struct {
	Path             string
	FromMode, ToMode filemode.FileMode
	FromHash, ToHash plumbing.Hash
}

// ChangedFilesBetweenTrees returns the ChangedFile objects which represent the
// difference between the two given trees.
func ChangedFilesBetweenTrees(from, to *object.Tree) ([]ChangedFile, error) {
	changes, err := object.DiffTree(from, to)
	if err != nil {
		return nil, fmt.Errorf("could not calculate tree diff: %w", err)
	}

	changedFiles := make([]ChangedFile, len(changes))
	for i, change := range changes {
		if from := change.From; from.Name != "" {
			changedFiles[i].Path = from.Name
			changedFiles[i].FromMode = from.TreeEntry.Mode
			changedFiles[i].FromHash = from.TreeEntry.Hash
		}
		if to := change.To; to.Name != "" {
			if exPath := changedFiles[i].Path; exPath != "" && exPath != to.Name {
				panic(fmt.Sprintf("unexpected changed path from %q to %q", exPath, to.Name))
			}
			changedFiles[i].Path = to.Name
			changedFiles[i].ToMode = to.TreeEntry.Mode
			changedFiles[i].ToHash = to.TreeEntry.Hash
		}
	}
	return changedFiles, nil
}