feat: 初始化 git-air AI 代码评审 CLI 工具

新增多模型 LLM 客户端、Git diff 提取与过滤、配置管理及 pre-commit 钩子支持。

internal/git/diff.go

@@ -0,0 +1,101 @@
+package git
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"os/exec"
+	"strings"
+)
+
+var (
+	ErrNotGitRepo = errors.New("当前目录不是 Git 仓库（未找到 .git）")
+	ErrEmptyDiff  = errors.New("没有检测到任何需要评审的代码变更（Diff 为空）")
+)
+
+// IsGitRepo 检查当前工作目录是否在一个 Git 仓库内
+func IsGitRepo(ctx context.Context) bool {
+	cmd := exec.CommandContext(ctx, "git", "rev-parse", "--is-inside-work-tree")
+	err := cmd.Run()
+	return err == nil
+}
+
+// GetRepoRoot 获取当前 Git 仓库的根目录绝对路径
+func GetRepoRoot(ctx context.Context) (string, error) {
+	cmd := exec.CommandContext(ctx, "git", "rev-parse", "--show-toplevel")
+	out, err := cmd.Output()
+	if err != nil {
+		return "", ErrNotGitRepo
+	}
+
+	return strings.TrimSpace(string(out)), nil
+}
+
+const maxDiffSize = 300 * 1024 // 限制最大 300KB Diff，避免打爆上下文与 OOM
+
+// GetDiff 提取并过滤 Git 代码差异
+// args 可传：
+// - 无参数：默认先查暂存区 (git diff --cached)，若暂存区为空则自动查工作区 (git diff)
+// - 自定义参数：如 "HEAD~1"、"main..feature"、"internal/service/chat.go" 等
+func GetDiff(ctx context.Context, args ...string) (string, error) {
+	if !IsGitRepo(ctx) {
+		return "", ErrNotGitRepo
+	}
+
+	var cmdArgs []string
+	if len(args) == 0 {
+		// 1. 默认先提取暂存区代码 (准备 commit 的代码)
+		stagedDiff, err := execGitDiff(ctx, "--cached")
+		if err != nil {
+			return "", err
+		}
+		if strings.TrimSpace(stagedDiff) != "" {
+			return truncateDiffIfNeeded(FilterDiff(stagedDiff)), nil
+		}
+		// 2. 如果暂存区为空，回退提取工作区未暂存的修改
+		cmdArgs = []string{}
+	} else {
+		cmdArgs = args
+	}
+
+	rawDiff, err := execGitDiff(ctx, cmdArgs...)
+	if err != nil {
+		return "", err
+	}
+
+	filteredDiff := FilterDiff(rawDiff)
+	if strings.TrimSpace(filteredDiff) == "" {
+		return "", ErrEmptyDiff
+	}
+
+	return truncateDiffIfNeeded(filteredDiff), nil
+}
+
+func truncateDiffIfNeeded(diff string) string {
+	runes := []rune(diff)
+	if len(runes) > maxDiffSize {
+		runes = runes[:maxDiffSize]
+	}
+	return string(runes) + "\n\n[WARNING: 代码变更量过大，已自动截断前 300KB 内容进行评审]"
+}
+
+// execGitDiff 执行底层的 git diff 命令
+func execGitDiff(ctx context.Context, args ...string) (string, error) {
+	fullArgs := append([]string{"diff"}, args...)
+	cmd := exec.CommandContext(ctx, "git", fullArgs...)
+	var stdout, stderr bytes.Buffer
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+	if err := cmd.Run(); err != nil {
+		if errors.Is(err, exec.ErrNotFound) {
+			return "", errors.New("系统未检测到 git 命令，请确保已安装 Git 并配置到系统 PATH 中")
+		}
+		errMsg := strings.TrimSpace(stderr.String())
+		if errMsg != "" {
+			return "", fmt.Errorf("git diff 执行失败: %s (%w)", errMsg, err)
+		}
+		return "", fmt.Errorf("git diff 执行失败: %w", err)
+	}
+	return stdout.String(), nil
+}