✨ Add Git editor support

Add functionality to act as a Git editor. This is similar to hooks
however this resolves the issue of duplicate message editors.

By taking over the editing capabilities, there are some complexities
with merge and rebase where Git commands can be provided. Comment blocks
also needed to be trimmed to prevent reflow converting the new lines
into commands (which were not understood and failed).

There are likely a number of edge cases not handled (or considered) and
this feature should be used with caution and is experimental.

Implementation allowed for merging the hooks and editor functionality
into reading a file as they were very similar.

README.md

@@ -370,10 +370,56 @@ You can then commit changes with:
 git co
 ```
 
+### Prepare Message Hook
+
+Committed can be installed as a Git prepare message hook. Be aware that any
+existing `prepare-commit-msg` hook will not be replaced and it is necessary to
+remove this hook before installing.
+
+Installation:
+
+```shell
+committed hook --install
+```
+
+Removal:
+
+```shell
+committed hook --uninstall
+```
+
+### Editor
+
+Committed can replace the default Git editor which allows commits to be applied
+using `git commit`. Most of the standard Git command arguments can be used.
+
+```shell
+git config --global core.editor "committed --editor"
+```
+
+This can be removed with:
+
+```shell
+git config --global --unset-all core.editor
+```
+
+There are some limitations related to acting as an editor.
+
+- Comment lines will be truncated to the width of the editor.
+- Interactive rebasing and other operations which require edit commands may have
+  visual issues. The first command may be part of the summary.
+- Author cannot be set. The configured Git author will be used and will be
+  selected using the default Git method (repository followed by global).
+- When amending, subject line may be part of the body.
+- When amending, emoji character or shortcode must be in the existing data set.
+- When amending, summary will be truncated if more than 72 characters.
+- When amending, trailers will be imported into the body.
+
 ### Amend
 
 There are certain limitations when amending commits and it is recommended only
-for use with commits created with Committed. The limitations are:
+for use with commits created with Committed. The limitations share similarities
+with using Git as an editor.
 
 - Emoji character or shortcode must be in the existing data set.
 - Trailers will be imported into the body.

cmd/root.go

@@ -42,6 +42,11 @@ type App struct {
 
 	req  *commit.Request
 	opts commit.Options
+	hook bool
+}
+
+type Options struct {
+	Hook bool
 }
 
 func NewRootCmd(a App) *cobra.Command {
@@ -76,10 +81,12 @@ func NewRootCmd(a App) *cobra.Command {
 	cmd.Flags().StringVarP(&a.opts.SnapshotFile, "snapshot", "", defaultSnapshotFile, "Snapshot file location")
 	cmd.Flags().BoolVarP(&a.opts.DryRun, "dry-run", "", defaultDryRun, "Simulate applying a commit")
 	cmd.Flags().BoolVarP(&a.opts.Amend, "amend", "a", false, "Replace the tip of the current branch by creating a new commit")
-	cmd.Flags().BoolVarP(&a.opts.Hook.Enable, "hook", "", false, "Install and uninstall Git hook")
-	cmd.Flags().StringVarP(&a.opts.Hook.MessageFile, "message-file", "", "", "")
-	cmd.Flags().StringVarP(&a.opts.Hook.Source, "source", "", "", "")
-	cmd.Flags().StringVarP(&a.opts.Hook.SHA, "sha", "", "", "")
+	cmd.Flags().StringVarP(&a.opts.File.MessageFile, "editor", "", "", "")
+	cmd.Flags().BoolVarP(&a.hook, "hook", "", false, "")
+	cmd.Flags().StringVarP(&a.opts.File.MessageFile, "message-file", "", "", "")
+	cmd.Flags().StringVarP(&a.opts.File.Source, "source", "", "", "")
+	cmd.Flags().StringVarP(&a.opts.File.SHA, "sha", "", "", "")
+	cmd.Flags().MarkHidden("editor")
 	cmd.Flags().MarkHidden("hook")
 	cmd.Flags().MarkHidden("message-file")
 	cmd.Flags().MarkHidden("source")
@@ -123,6 +130,8 @@ func NewApp() App {
 }
 
 func (a *App) configure(opts commit.Options) error {
+	a.mode()
+
 	state, err := a.Commiter.Configure(opts)
 	switch {
 	case err == nil:
@@ -158,3 +167,14 @@ func (a *App) apply() error {
 
 	return nil
 }
+
+func (a *App) mode() {
+	switch {
+	case !a.hook && a.opts.File.MessageFile != "":
+		a.opts.Mode = commit.ModeEditor
+	case a.hook:
+		a.opts.Mode = commit.ModeHook
+	default:
+		a.opts.Mode = commit.ModeCommit
+	}
+}

internal/commit/commit.go

@@ -1,11 +1,13 @@
 package commit
 
 import (
+	"bufio"
 	"errors"
 	"fmt"
 	"io"
 	"os"
 	"os/exec"
+	"strings"
 
 	"github.com/mikelorant/committed/internal/config"
 	"github.com/mikelorant/committed/internal/emoji"
@@ -56,11 +58,11 @@ type Options struct {
 	SnapshotFile string
 	DryRun       bool
 	Amend        bool
-	Hook         HookOptions
+	Mode         Mode
+	File         FileOptions
 }
 
-type HookOptions struct {
-	Enable      bool
+type FileOptions struct {
 	MessageFile string
 	Source      string
 	SHA         string
@@ -76,10 +78,19 @@ type Request struct {
 	Author      repository.User
 	Amend       bool
 	DryRun      bool
-	Hook        bool
+	File        bool
 	MessageFile string
 }
 
+type Mode int
+
+const (
+	ModeUnset Mode = iota
+	ModeCommit
+	ModeEditor
+	ModeHook
+)
+
 func New() Commit {
 	return Commit{
 		Emojier:     emoji.New,
@@ -118,16 +129,15 @@ func (c *Commit) Configure(opts Options) (*State, error) {
 		return nil, fmt.Errorf("unable to get snapshot: %w", err)
 	}
 
-	var hook Hook
-
-	if opts.Hook.Enable {
-		hook, err = getHook(c.ReadFiler, opts.Hook)
+	var file File
+	if opts.Mode > ModeCommit {
+		file, err = readFile(c.ReadFiler, opts)
 		if err != nil {
-			return nil, fmt.Errorf("unable to get hook mesage: %w", err)
+			return nil, fmt.Errorf("unable to read message file: %w", err)
 		}
 	}
 
-	if opts.Hook.Enable && opts.Hook.SHA == "HEAD" {
+	if file.Amend {
 		opts.Amend = true
 	}
 
@@ -140,7 +150,7 @@ func (c *Commit) Configure(opts Options) (*State, error) {
 		Config:       cfg,
 		Snapshot:     snap,
 		Options:      opts,
-		Hook:         hook,
+		File:         file,
 	}, nil
 }
 
@@ -156,7 +166,7 @@ func (c *Commit) Apply(req *Request) error {
 		Footer:      req.Footer,
 		Amend:       req.Amend,
 		DryRun:      req.DryRun,
-		Hook:        req.Hook,
+		File:        req.File,
 		MessageFile: req.MessageFile,
 	}
 
@@ -268,19 +278,39 @@ func getEmojis(emojier Emojier, cfg config.Config) *emoji.Set {
 	return emojier(fn)
 }
 
-func getHook(readFile ReadFiler, ho HookOptions) (Hook, error) {
-	msg, err := readFile(ho.MessageFile)
+func readFile(readFile ReadFiler, opts Options) (File, error) {
+	data, err := readFile(opts.File.MessageFile)
 	if err != nil {
-		return Hook{}, fmt.Errorf("unable to read file: %w", err)
+		return File{}, fmt.Errorf("unable to read file: %w", err)
+	}
+
+	msg := string(data)
+
+	f := File{
+		Message: msg,
 	}
 
-	h := Hook{
-		Message: string(msg),
+	if isAmend(msg, opts) {
+		f.Amend = true
 	}
 
-	if ho.SHA == "HEAD" {
-		h.Amend = true
+	return f, nil
+}
+
+func isAmend(msg string, opts Options) bool {
+	if opts.Mode == ModeHook && opts.File.SHA == "HEAD" {
+		return true
+	}
+
+	r := strings.NewReader(msg)
+
+	scanner := bufio.NewScanner(r)
+
+	for scanner.Scan() {
+		if !strings.HasPrefix(scanner.Text(), "#") && strings.TrimSpace(scanner.Text()) != "" {
+			return true
+		}
 	}
 
-	return h, nil
+	return false
 }

internal/commit/commit_test.go

@@ -292,11 +292,12 @@ func TestConfigure(t *testing.T) {
 			},
 		},
 		{
-			name: "hook",
+			name: "file_hook",
 			args: args{
 				opts: commit.Options{
-					Hook: commit.HookOptions{
-						Enable: true,
+					Mode: commit.ModeHook,
+					File: commit.FileOptions{
+						MessageFile: "test",
 					},
 				},
 			},
@@ -306,20 +307,22 @@ func TestConfigure(t *testing.T) {
 					Config:       config.Config{},
 					Emojis:       &emoji.Set{},
 					Options: commit.Options{
-						Hook: commit.HookOptions{
-							Enable: true,
+						Mode: commit.ModeHook,
+						File: commit.FileOptions{
+							MessageFile: "test",
 						},
 					},
 				},
 			},
 		},
 		{
-			name: "hook_sha",
+			name: "file_hook_sha",
 			args: args{
 				opts: commit.Options{
-					Hook: commit.HookOptions{
-						Enable: true,
-						SHA:    "HEAD",
+					Mode: commit.ModeHook,
+					File: commit.FileOptions{
+						MessageFile: "test",
+						SHA:         "HEAD",
 					},
 				},
 			},
@@ -329,13 +332,14 @@ func TestConfigure(t *testing.T) {
 					Config:       config.Config{},
 					Emojis:       &emoji.Set{},
 					Options: commit.Options{
-						Hook: commit.HookOptions{
-							Enable: true,
-							SHA:    "HEAD",
+						Mode: commit.ModeHook,
+						File: commit.FileOptions{
+							MessageFile: "test",
+							SHA:         "HEAD",
 						},
 						Amend: true,
 					},
-					Hook: commit.Hook{
+					File: commit.File{
 						Amend: true,
 					},
 				},
@@ -434,17 +438,15 @@ func TestConfigure(t *testing.T) {
 			},
 		},
 		{
-			name: "hook_error",
+			name: "file_hook_error",
 			args: args{
 				opts: commit.Options{
-					Hook: commit.HookOptions{
-						Enable: true,
-					},
+					Mode: commit.ModeHook,
 				},
 				readFileErr: errMock,
 			},
 			want: want{
-				err: "unable to get hook mesage: unable to read file: error",
+				err: "unable to read message file: unable to read file: error",
 			},
 		},
 	}
@@ -586,31 +588,31 @@ func TestApply(t *testing.T) {
 			},
 		},
 		{
-			name: "hook",
+			name: "file",
 			args: args{
 				req: &commit.Request{
 					Apply: true,
-					Hook:  true,
+					File:  true,
 				},
 			},
 			want: want{
 				cfg: repository.Commit{
-					Hook: true,
+					File: true,
 				},
 			},
 		},
 		{
-			name: "hook_message",
+			name: "file_message",
 			args: args{
 				req: &commit.Request{
 					Apply:       true,
-					Hook:        true,
+					File:        true,
 					MessageFile: "test",
 				},
 			},
 			want: want{
 				cfg: repository.Commit{
-					Hook:        true,
+					File:        true,
 					MessageFile: "test",
 				},
 			},

internal/commit/state.go

@@ -18,7 +18,7 @@ type State struct {
 	Config       config.Config
 	Snapshot     snapshot.Snapshot
 	Options      Options
-	Hook         Hook
+	File         File
 }
 
 type Placeholders struct {
@@ -34,7 +34,7 @@ type Config struct {
 	Authors []repository.User
 }
 
-type Hook struct {
+type File struct {
 	Amend   bool
 	Message string
 }

internal/commit/testdata/comment.golden

@@ -0,0 +1 @@
+# 1234567890123456789012345678901234567890

internal/commit/testdata/comment.input

@@ -0,0 +1 @@
+# 1234567890123456789012345678901234567890