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
}