isolate patchid code

1 files changed, 72 insertions, 0 deletions

diff --git a/patchid.go b/patchid.go
new file mode 100644
index 0000000..28c8313
--- /dev/null
+++ b/patchid.go
@@ -0,0 +1,72 @@
+package gitpb
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+
+	"go.wit.com/log"
+)
+
+
+// git show 5b277e7686974d2195586d5f5b82838ee9ddb036 |git patch-id --stable
+// bf86be06af03b1a89ee155b214358362ec76f7b6 5b277e7686974d2195586d5f5b82838ee9ddb036
+// forged patch: "working on ping pong"
+// The --stable flag is an important detail. When you use it, git patch-id outputs two hashes:
+// <stable_patch_id> <unstable_patch_id>
+func (repo *Repo) FindPatchIdByHash(hash string) (string, error) {
+	if hash == "" {
+		return "", log.Errorf("commit hash blank")
+	}
+
+	// 1. Create the command to get the diff for the commit.
+	//    "git show" is the perfect tool for this.
+	cmdShow := exec.Command("git", "show", hash)
+	cmdShow.Dir = repo.GetFullPath()
+
+	// 2. Create the command to calculate the patch-id from stdin.
+	cmdPipeID := exec.Command("git", "patch-id", "--stable")
+	cmdPipeID.Dir = repo.GetFullPath()
+
+	// 3. Connect the output of "git show" to the input of "git patch-id".
+	//    This is the Go equivalent of the shell pipe `|`.
+	pipe, err := cmdShow.StdoutPipe()
+	if err != nil {
+		return "", fmt.Errorf("failed to create pipe: %w", err)
+	}
+	cmdPipeID.Stdin = pipe
+
+	// 4. We need a buffer to capture the final output from git patch-id.
+	var output bytes.Buffer
+	cmdPipeID.Stdout = &output
+
+	// 5. Start the reading command (patch-id) first.
+	if err := cmdPipeID.Start(); err != nil {
+		return "", fmt.Errorf("failed to start git-patch-id: %w", err)
+	}
+
+	// 6. Run the writing command (show). This will block until it's done.
+	if err := cmdShow.Run(); err != nil {
+		return "", fmt.Errorf("failed to run git-show: %w", err)
+	}
+
+	// 7. Wait for the reading command to finish.
+	if err := cmdPipeID.Wait(); err != nil {
+		return "", fmt.Errorf("failed to wait for git-patch-id: %w", err)
+	}
+
+	fields := strings.Fields(output.String())
+	if len(fields) != 2 {
+		return "", fmt.Errorf("git-patch-id produced empty output")
+	}
+
+	if fields[1] != hash {
+		return "", fmt.Errorf("patchid did not match %s != %v", hash, fields)
+	}
+
+	return fields[0], nil
+}