git.go

package main

import (
	"errors"
	"flag"
	"fmt"
	"gopkg.in/src-d/go-git.v4"
	"gopkg.in/src-d/go-git.v4/plumbing"
	"gopkg.in/src-d/go-git.v4/plumbing/object"
	"gopkg.in/src-d/go-git.v4/utils/merkletrie"
	"os"
)

var applyCommit string

func apply() error {
	cm, err := getCurrentCommitObject()
	if err != nil {
		return err
	}

	tree1, err := getTree(cm)
	if err != nil {
		return err
	}

	cm2, err := getPreviousCommitObject(cm)
	tree2, err := getTree(cm2)
	if err != nil {
		return err
	}

	changes, err := tree1.Diff(tree2)
	if err != nil {
		return err
	}
	return printChanges(changes)
}

func printChanges(chng object.Changes) error {
	for _, v := range chng {
		action, err := v.Action()
		if err != nil {
			return err
		}

		switch action {
		case merkletrie.Modify:
			fmt.Println("File Modified: " + v.From.Name)
		case merkletrie.Delete:
			fmt.Println("File Deleted: " + v.From.Name)
		case merkletrie.Insert:
			fmt.Println("File Inserted: " + v.To.Name)
		default:
			return errors.New("Unknown Action on Files")
		}
	}

	return nil
}

func getCurrentCommitObject() (*object.Commit, error) {
	repo, _ := git.PlainOpen(".")
	return repo.CommitObject(plumbing.NewHash(applyCommit))
}

func getPreviousCommitObject(cm *object.Commit) (*object.Commit, error) {
	itr := cm.Parents()
	return itr.Next()
}

func getTree(cm *object.Commit) (*object.Tree, error) {
	return cm.Tree()
}

func main() {
	flag.StringVar(&applyCommit, "commit", "", "commit hash")
	flag.Parse()

	if err := apply(); err != nil {
		fmt.Println(err)
		os.Exit(1)
	}
}