feat: add git hook integration for automatic commit message generation

cmd/hook.go

@@ -0,0 +1,77 @@
+package cmd
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+	"huseynovvusal/gitai/internal/hook"
+)
+
+func NewHookCmd() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "hook",
+		Short: "Manage gitai git hooks",
+		Long:  `Install or uninstall a prepare-commit-msg git hook that automatically generates commit messages using gitai.`,
+	}
+
+	cmd.AddCommand(newHookInstallCmd())
+	cmd.AddCommand(newHookUninstallCmd())
+	cmd.AddCommand(newHookStatusCmd())
+
+	return cmd
+}
+
+func newHookInstallCmd() *cobra.Command {
+	return &cobra.Command{
+		Use:   "install",
+		Short: "Install the prepare-commit-msg hook",
+		Long: `Install a prepare-commit-msg git hook that runs gitai automatically
+when you use "git commit" without the -m flag.
+
+The hook respects existing prepare-commit-msg hooks by appending
+rather than overwriting. Set GITAI_SKIP_HOOK=1 to bypass the hook.`,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			if err := hook.Install(); err != nil {
+				return fmt.Errorf("install hook: %w", err)
+			}
+			fmt.Fprintln(cmd.OutOrStdout(), "gitai hook installed successfully.")
+			fmt.Fprintln(cmd.OutOrStdout(), "Commit messages will be generated automatically when you run 'git commit'.")
+			fmt.Fprintln(cmd.OutOrStdout(), "Set GITAI_SKIP_HOOK=1 to bypass the hook.")
+			return nil
+		},
+	}
+}
+
+func newHookUninstallCmd() *cobra.Command {
+	return &cobra.Command{
+		Use:   "uninstall",
+		Short: "Uninstall the prepare-commit-msg hook",
+		Long:  `Remove the gitai snippet from the prepare-commit-msg hook. Other hook content is preserved.`,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			if err := hook.Uninstall(); err != nil {
+				return fmt.Errorf("uninstall hook: %w", err)
+			}
+			fmt.Fprintln(cmd.OutOrStdout(), "gitai hook uninstalled successfully.")
+			return nil
+		},
+	}
+}
+
+func newHookStatusCmd() *cobra.Command {
+	return &cobra.Command{
+		Use:   "status",
+		Short: "Check if the gitai hook is installed",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			installed, err := hook.IsInstalled()
+			if err != nil {
+				return fmt.Errorf("check hook status: %w", err)
+			}
+			if installed {
+				fmt.Fprintln(cmd.OutOrStdout(), "gitai hook is installed.")
+			} else {
+				fmt.Fprintln(cmd.OutOrStdout(), "gitai hook is not installed.")
+			}
+			return nil
+		},
+	}
+}

cmd/root.go

@@ -16,6 +16,7 @@ func Execute(version string) {
 	}
 	rootCmd.AddCommand(NewSuggestCmd())
 	rootCmd.AddCommand(NewReviewCmd())
+	rootCmd.AddCommand(NewHookCmd())
 	err := rootCmd.Execute()
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)

internal/hook/hook.go

@@ -0,0 +1,178 @@
+package hook
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"huseynovvusal/gitai/internal/git"
+)
+
+const (
+	hookFileName = "prepare-commit-msg"
+	markerBegin  = "# >>> gitai hook >>>"
+	markerEnd    = "# <<< gitai hook <<<"
+)
+
+// hookScript returns the shell snippet that gitai injects into prepare-commit-msg.
+// It skips when a message is already provided (commit -m), on merge commits, or
+// when the GITAI_SKIP_HOOK env var is set.
+func hookScript() string {
+	return fmt.Sprintf(`%s
+# Installed by: gitai hook install
+# This hook runs gitai to generate a commit message when none is provided.
+# Set GITAI_SKIP_HOOK=1 to bypass this hook.
+
+if [ -n "$GITAI_SKIP_HOOK" ]; then
+  exit 0
+fi
+
+COMMIT_MSG_FILE="$1"
+COMMIT_SOURCE="$2"
+
+# Only run when there is no explicit message source (e.g. -m, merge, squash).
+if [ -z "$COMMIT_SOURCE" ]; then
+  if command -v gitai >/dev/null 2>&1; then
+    # Run gitai in hook mode: generate message and write to the commit message file.
+    GITAI_SKIP_HOOK=1 gitai suggest --no-hint 2>/dev/null
+    LAST_MSG=$(git log -1 --pretty=%%B 2>/dev/null)
+    if [ -n "$LAST_MSG" ]; then
+      printf "%%s" "$LAST_MSG" > "$COMMIT_MSG_FILE"
+    fi
+  fi
+fi
+%s
+`, markerBegin, markerEnd)
+}
+
+// Install adds the gitai hook snippet to the prepare-commit-msg hook in the
+// current git repository. If a hook file already exists, the snippet is appended
+// without overwriting the existing content. If a gitai hook is already installed,
+// it returns an error.
+func Install() error {
+	hookPath, err := hookFilePath()
+	if err != nil {
+		return err
+	}
+
+	existing, err := readFileIfExists(hookPath)
+	if err != nil {
+		return fmt.Errorf("failed to read existing hook: %w", err)
+	}
+
+	if strings.Contains(existing, markerBegin) {
+		return errors.New("gitai hook is already installed in this repository")
+	}
+
+	content := existing
+	if content == "" {
+		content = "#!/bin/sh\n"
+	}
+	content += "\n" + hookScript()
+
+	if err := os.MkdirAll(filepath.Dir(hookPath), 0o755); err != nil {
+		return fmt.Errorf("failed to create hooks directory: %w", err)
+	}
+
+	if err := os.WriteFile(hookPath, []byte(content), 0o755); err != nil {
+		return fmt.Errorf("failed to write hook file: %w", err)
+	}
+
+	return nil
+}
+
+// Uninstall removes the gitai hook snippet from the prepare-commit-msg hook.
+// If other content remains, the file is preserved; otherwise it is removed.
+func Uninstall() error {
+	hookPath, err := hookFilePath()
+	if err != nil {
+		return err
+	}
+
+	existing, err := readFileIfExists(hookPath)
+	if err != nil {
+		return fmt.Errorf("failed to read existing hook: %w", err)
+	}
+
+	if !strings.Contains(existing, markerBegin) {
+		return errors.New("gitai hook is not installed in this repository")
+	}
+
+	cleaned := removeSection(existing, markerBegin, markerEnd)
+	cleaned = strings.TrimRight(cleaned, "\n") + "\n"
+
+	// If only the shebang remains, remove the file entirely.
+	trimmed := strings.TrimSpace(cleaned)
+	if trimmed == "#!/bin/sh" || trimmed == "#!/bin/bash" || trimmed == "" {
+		if err := os.Remove(hookPath); err != nil {
+			return fmt.Errorf("failed to remove hook file: %w", err)
+		}
+		return nil
+	}
+
+	if err := os.WriteFile(hookPath, []byte(cleaned), 0o755); err != nil {
+		return fmt.Errorf("failed to write hook file: %w", err)
+	}
+
+	return nil
+}
+
+// IsInstalled checks if the gitai hook is currently installed.
+func IsInstalled() (bool, error) {
+	hookPath, err := hookFilePath()
+	if err != nil {
+		return false, err
+	}
+
+	existing, err := readFileIfExists(hookPath)
+	if err != nil {
+		return false, err
+	}
+
+	return strings.Contains(existing, markerBegin), nil
+}
+
+func hookFilePath() (string, error) {
+	root, err := git.GetGitRoot()
+	if err != nil {
+		return "", fmt.Errorf("not a git repository: %w", err)
+	}
+	return filepath.Join(root, ".git", "hooks", hookFileName), nil
+}
+
+func readFileIfExists(path string) (string, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return "", nil
+		}
+		return "", fmt.Errorf("failed to read file: %w", err)
+	}
+	return string(data), nil
+}
+
+func removeSection(content, beginMarker, endMarker string) string {
+	beginIdx := strings.Index(content, beginMarker)
+	if beginIdx == -1 {
+		return content
+	}
+	endIdx := strings.Index(content, endMarker)
+	if endIdx == -1 {
+		return content
+	}
+	endIdx += len(endMarker)
+
+	// Also consume trailing newline after the end marker.
+	if endIdx < len(content) && content[endIdx] == '\n' {
+		endIdx++
+	}
+
+	// Also consume the leading newline before the begin marker.
+	if beginIdx > 0 && content[beginIdx-1] == '\n' {
+		beginIdx--
+	}
+
+	return content[:beginIdx] + content[endIdx:]
+}