1 files changed, 90 insertions, 0 deletions
diff --git a/core/command/cmd-diff.go b/core/command/cmd-diff.go
new file mode 100644
index 0000000..120037a
--- /dev/null
+++ b/core/command/cmd-diff.go
@@ -0,0 +1,90 @@
+package command
+
+import (
+	"errors"
+
+	"github.com/isacikgoz/gitbatch/core/git"
+	gogit "gopkg.in/src-d/go-git.v4"
+	"gopkg.in/src-d/go-git.v4/plumbing"
+)
+
+var (
+	diffCmdMode string
+
+	diffCommand       = "diff"
+	diffCmdModeLegacy = "git"
+	diffCmdModeNative = "go-git"
+)
+
+// Diff is a wrapper function for "git diff" command
+// Diff function returns the diff to previous commit detail of the given has
+// of a specific commit
+func Diff(e *git.RepoEntity, hash string) (diff string, err error) {
+	diffCmdMode = diffCmdModeNative
+
+	switch diffCmdMode {
+	case diffCmdModeLegacy:
+		return diffWithGit(e, hash)
+	case diffCmdModeNative:
+		return diffWithGoGit(e, hash)
+	}
+	return diff, errors.New("Unhandled diff operation")
+}
+
+func diffWithGit(e *git.RepoEntity, hash string) (diff string, err error) {
+	return diff, nil
+}
+
+func diffWithGoGit(e *git.RepoEntity, hash string) (diff string, err error) {
+	currentCommitIndex := 0
+	for i, cs := range e.Commits {
+		if cs.Hash == hash {
+			currentCommitIndex = i
+		}
+	}
+	if len(e.Commits)-currentCommitIndex <= 1 {
+		return "there is no diff", nil
+	}
+
+	// maybe we dont need to log the repo again?
+	commits, err := e.Repository.Log(&gogit.LogOptions{
+		From:  plumbing.NewHash(e.Commit.Hash),
+		Order: gogit.LogOrderCommitterTime,
+	})
+	if err != nil {
+		return "", err
+	}
+
+	currentCommit, err := commits.Next()
+	if err != nil {
+		return "", err
+	}
+	currentTree, err := currentCommit.Tree()
+	if err != nil {
+		return diff, err
+	}
+
+	prevCommit, err := commits.Next()
+	if err != nil {
+		return "", err
+	}
+	prevTree, err := prevCommit.Tree()
+	if err != nil {
+		return diff, err
+	}
+
+	changes, err := prevTree.Diff(currentTree)
+	if err != nil {
+		return "", err
+	}
+
+	// here we collect the actual diff
+	for _, c := range changes {
+		patch, err := c.Patch()
+		if err != nil {
+			break
+		}
+		diff = diff + patch.String() + "\n"
+	}
+	return diff, nil
+}