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"
)

type fileChanged struct {
	path             string
	fromMode, toMode filemode.FileMode
	fromHash, toHash plumbing.Hash
}

func calcDiff(from, to *object.Tree) ([]fileChanged, error) {

	changes, err := object.DiffTree(from, to)
	if err != nil {
		return nil, fmt.Errorf("could not calculate tree diff: %w", err)
	}

	filesChanged := make([]fileChanged, len(changes))
	for i, change := range changes {
		if from := change.From; from.Name != "" {
			filesChanged[i].path = from.Name
			filesChanged[i].fromMode = from.TreeEntry.Mode
			filesChanged[i].fromHash = from.TreeEntry.Hash
		}
		if to := change.To; to.Name != "" {
			if exPath := filesChanged[i].path; exPath != "" && exPath != to.Name {
				panic(fmt.Sprintf("DiffTree entry changed path from %q to %q", exPath, to.Name))
			}
			filesChanged[i].path = to.Name
			filesChanged[i].toMode = to.TreeEntry.Mode
			filesChanged[i].toHash = to.TreeEntry.Hash
		}
	}
	return filesChanged, nil
}