From 27a82681f10f81dcf3fc91b6be3b71232a8a88bc Mon Sep 17 00:00:00 2001
From: Hau Nguyen <hauvipapro@gmail.com>
Date: Fri, 25 Nov 2022 01:17:35 +0700
Subject: [PATCH] feat: simple format file (without actually format)

check go file -> parse ast -> ignore generated
---
 internal/cli/action.go        |  5 ++-
 internal/imports/check.go     | 37 +++++++++++++++++
 internal/imports/formatter.go | 75 ++++++++++++++++++++++++++++++++---
 3 files changed, 110 insertions(+), 7 deletions(-)
 create mode 100644 internal/imports/check.go

diff --git a/internal/cli/action.go b/internal/cli/action.go
index 86504fb..becb516 100644
--- a/internal/cli/action.go
+++ b/internal/cli/action.go
@@ -46,8 +46,9 @@ func (a *action) Run(c *cli.Context) error {
 		imports.FormatterWithDiff(a.flags.diff),
 	)
 
-	if err := f.Format(c.Args().Slice()...); err != nil {
-		return fmt.Errorf("imports formatter: failed to format %v: %w", c.Args().Slice(), err)
+	args := c.Args().Slice()
+	if err := f.Format(args...); err != nil {
+		return fmt.Errorf("imports formatter: failed to format %v: %w", args, err)
 	}
 
 	return nil
diff --git a/internal/imports/check.go b/internal/imports/check.go
new file mode 100644
index 0000000..8b71762
--- /dev/null
+++ b/internal/imports/check.go
@@ -0,0 +1,37 @@
+package imports
+
+import (
+	"go/ast"
+	"regexp"
+	"strings"
+)
+
+var reGoGenerated = regexp.MustCompile(`^// Code generated .* DO NOT EDIT\.$`)
+
+// Copy from https://github.com/mvdan/gofumpt
+func isGoFile(name string) bool {
+	// Hidden files are ignored
+	if strings.HasPrefix(name, ".") {
+		return false
+	}
+
+	return strings.HasSuffix(name, ".go")
+}
+
+// Copy from https://github.com/mvdan/gofumpt
+func isGoGenerated(file *ast.File) bool {
+	for _, cg := range file.Comments {
+		// Ignore if package ... is on top
+		if cg.Pos() > file.Package {
+			return false
+		}
+
+		for _, line := range cg.List {
+			if reGoGenerated.MatchString(line.Text) {
+				return true
+			}
+		}
+	}
+
+	return false
+}
diff --git a/internal/imports/formatter.go b/internal/imports/formatter.go
index 0d3b9d8..488e6bd 100644
--- a/internal/imports/formatter.go
+++ b/internal/imports/formatter.go
@@ -1,5 +1,16 @@
 package imports
 
+import (
+	"errors"
+	"fmt"
+	"go/parser"
+	"go/token"
+	"os"
+	"path/filepath"
+)
+
+var ErrEmptyPaths = errors.New("empty paths")
+
 type Formatter struct {
 	isList  bool
 	isWrite bool
@@ -7,16 +18,70 @@ type Formatter struct {
 }
 
 func NewFormmater(opts ...FormatterOptionFn) *Formatter {
-	f := &Formatter{}
+	ft := &Formatter{}
 
 	for _, opt := range opts {
-		opt(f)
+		opt(ft)
 	}
 
-	return f
+	return ft
 }
 
-// Accept a list of files or directories aka fsNames
-func (f *Formatter) Format(fsNames ...string) error {
+// Accept a list of files or directories
+func (ft *Formatter) Format(paths ...string) error {
+	if len(paths) == 0 {
+		return ErrEmptyPaths
+	}
+
+	// Logic switch case copy from goimports, gofumpt
+	for _, path := range paths {
+		switch dir, err := os.Stat(path); {
+		case err != nil:
+			return fmt.Errorf("os: failed to stat: [%s] %w", path, err)
+		case dir.IsDir():
+			if err := ft.formatDir(path); err != nil {
+				return err
+			}
+		default:
+			if err := ft.formatFile(path); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
+func (ft *Formatter) formatDir(path string) error {
+	return nil
+}
+
+func (ft *Formatter) formatFile(path string) error {
+	// Check go file
+	if !isGoFile(filepath.Base(path)) {
+		return nil
+	}
+
+	pathBytes, err := os.ReadFile(path)
+	if err != nil {
+		return fmt.Errorf("os: failed to read file: [%s] %w", path, err)
+	}
+
+	// Parse ast
+	fset := token.NewFileSet()
+
+	parserMode := parser.Mode(0)
+	parserMode |= parser.ParseComments
+
+	pathASTFile, err := parser.ParseFile(fset, path, pathBytes, parserMode)
+	if err != nil {
+		return fmt.Errorf("parser: failed to parse file [%s]: %w", path, err)
+	}
+
+	// Ignore generated file
+	if isGoGenerated(pathASTFile) {
+		return nil
+	}
+
 	return nil
 }