// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package main

import (
	"bytes"
	"flag"
	"fmt"
	"go/ast"
	"go/parser"
	"go/printer"
	"go/scanner"
	"go/token"
	"io"
	"io/ioutil"
	"os"
	"os/exec"
	"path/filepath"
	"runtime/pprof"
	"strings"
)

var (
	// main operation modes
	list        = flag.Bool("l", false, "list files whose formatting differs from gofmt's")
	write       = flag.Bool("w", false, "write result to (source) file instead of stdout")
	rewriteRule = flag.String("r", "", "rewrite rule (e.g., 'a[b:len(a)] -> a[b:]')")
	simplifyAST = flag.Bool("s", false, "simplify code")
	doDiff      = flag.Bool("d", false, "display diffs instead of rewriting files")
	allErrors   = flag.Bool("e", false, "report all errors (not just the first 10 on different lines)")

	// debugging
	cpuprofile = flag.String("cpuprofile", "", "write cpu profile to this file")
)

const (
	tabWidth    = 8
	printerMode = printer.UseSpaces | printer.TabIndent
)

var (
	fileSet    = token.NewFileSet() // per process FileSet
	exitCode   = 0
	rewrite    func(*ast.File) *ast.File
	parserMode parser.Mode
)

func report(err error) {
	scanner.PrintError(os.Stderr, err)
	exitCode = 2
}

func usage() {
	fmt.Fprintf(os.Stderr, "usage: gofmt [flags] [path ...]\n")
	flag.PrintDefaults()
	os.Exit(2)
}

func initParserMode() {
	parserMode = parser.ParseComments
	if *allErrors {
		parserMode |= parser.AllErrors
	}
}

func isGoFile(f os.FileInfo) bool {
	// ignore non-Go files
	name := f.Name()
	return !f.IsDir() && !strings.HasPrefix(name, ".") && strings.HasSuffix(name, ".go")
}

// If in == nil, the source is the contents of the file with the given filename.
func processFile(filename string, in io.Reader, out io.Writer, stdin bool) error {
	if in == nil {
		f, err := os.Open(filename)
		if err != nil {
			return err
		}
		defer f.Close()
		in = f
	}

	src, err := ioutil.ReadAll(in)
	if err != nil {
		return err
	}

	file, sourceAdj, indentAdj, err := parse(fileSet, filename, src, stdin)
	if err != nil {
		return err
	}

	if rewrite != nil {
		if sourceAdj == nil {
			file = rewrite(file)
		} else {
			fmt.Fprintf(os.Stderr, "warning: rewrite ignored for incomplete programs\n")
		}
	}

	ast.SortImports(fileSet, file)

	if *simplifyAST {
		simplify(file)
	}

	res, err := format(fileSet, file, sourceAdj, indentAdj, src, printer.Config{Mode: printerMode, Tabwidth: tabWidth})
	if err != nil {
		return err
	}

	if !bytes.Equal(src, res) {
		// formatting has changed
		if *list {
			fmt.Fprintln(out, filename)
		}
		if *write {
			err = ioutil.WriteFile(filename, res, 0644)
			if err != nil {
				return err
			}
		}
		if *doDiff {
			data, err := diff(src, res)
			if err != nil {
				return fmt.Errorf("computing diff: %s", err)
			}
			fmt.Printf("diff %s gofmt/%s\n", filename, filename)
			out.Write(data)
		}
	}

	if !*list && !*write && !*doDiff {
		_, err = out.Write(res)
	}

	return err
}

func visitFile(path string, f os.FileInfo, err error) error {
	if err == nil && isGoFile(f) {
		err = processFile(path, nil, os.Stdout, false)
	}
	if err != nil {
		report(err)
	}
	return nil
}

func walkDir(path string) {
	filepath.Walk(path, visitFile)
}

func main() {
	// call gofmtMain in a separate function
	// so that it can use defer and have them
	// run before the exit.
	gofmtMain()
	os.Exit(exitCode)
}

func gofmtMain() {
	flag.Usage = usage
	flag.Parse()

	if *cpuprofile != "" {
		f, err := os.Create(*cpuprofile)
		if err != nil {
			fmt.Fprintf(os.Stderr, "creating cpu profile: %s\n", err)
			exitCode = 2
			return
		}
		defer f.Close()
		pprof.StartCPUProfile(f)
		defer pprof.StopCPUProfile()
	}

	initParserMode()
	initRewrite()

	if flag.NArg() == 0 {
		if *write {
			fmt.Fprintln(os.Stderr, "error: cannot use -w with standard input")
			exitCode = 2
			return
		}
		if err := processFile("<standard input>", os.Stdin, os.Stdout, true); err != nil {
			report(err)
		}
		return
	}

	for i := 0; i < flag.NArg(); i++ {
		path := flag.Arg(i)
		switch dir, err := os.Stat(path); {
		case err != nil:
			report(err)
		case dir.IsDir():
			walkDir(path)
		default:
			if err := processFile(path, nil, os.Stdout, false); err != nil {
				report(err)
			}
		}
	}
}

func diff(b1, b2 []byte) (data []byte, err error) {
	f1, err := ioutil.TempFile("", "gofmt")
	if err != nil {
		return
	}
	defer os.Remove(f1.Name())
	defer f1.Close()

	f2, err := ioutil.TempFile("", "gofmt")
	if err != nil {
		return
	}
	defer os.Remove(f2.Name())
	defer f2.Close()

	f1.Write(b1)
	f2.Write(b2)

	data, err = exec.Command("diff", "-u", f1.Name(), f2.Name()).CombinedOutput()
	if len(data) > 0 {
		// diff exits with a non-zero status when the files don't match.
		// Ignore that failure as long as we get output.
		err = nil
	}
	return

}

// ----------------------------------------------------------------------------
// Support functions
//
// The functions parse, format, and isSpace below are identical to the
// respective functions in src/go/format/format.go - keep them in sync!
//
// TODO(gri) Factor out this functionality, eventually.

// parse parses src, which was read from the named file,
// as a Go source file, declaration, or statement list.
func parse(fset *token.FileSet, filename string, src []byte, fragmentOk bool) (
	file *ast.File,
	sourceAdj func(src []byte, indent int) []byte,
	indentAdj int,
	err error,
) {
	// Try as whole source file.
	file, err = parser.ParseFile(fset, filename, src, parserMode)
	// If there's no error, return.  If the error is that the source file didn't begin with a
	// package line and source fragments are ok, fall through to
	// try as a source fragment.  Stop and return on any other error.
	if err == nil || !fragmentOk || !strings.Contains(err.Error(), "expected 'package'") {
		return
	}

	// If this is a declaration list, make it a source file
	// by inserting a package clause.
	// Insert using a ;, not a newline, so that the line numbers
	// in psrc match the ones in src.
	psrc := append([]byte("package p;"), src...)
	file, err = parser.ParseFile(fset, filename, psrc, parserMode)
	if err == nil {
		sourceAdj = func(src []byte, indent int) []byte {
			// Remove the package clause.
			// Gofmt has turned the ; into a \n.
			src = src[indent+len("package p\n"):]
			return bytes.TrimSpace(src)
		}
		return
	}
	// If the error is that the source file didn't begin with a
	// declaration, fall through to try as a statement list.
	// Stop and return on any other error.
	if !strings.Contains(err.Error(), "expected declaration") {
		return
	}

	// If this is a statement list, make it a source file
	// by inserting a package clause and turning the list
	// into a function body.  This handles expressions too.
	// Insert using a ;, not a newline, so that the line numbers
	// in fsrc match the ones in src.
	fsrc := append(append([]byte("package p; func _() {"), src...), '\n', '}')
	file, err = parser.ParseFile(fset, filename, fsrc, parserMode)
	if err == nil {
		sourceAdj = func(src []byte, indent int) []byte {
			// Cap adjusted indent to zero.
			if indent < 0 {
				indent = 0
			}
			// Remove the wrapping.
			// Gofmt has turned the ; into a \n\n.
			// There will be two non-blank lines with indent, hence 2*indent.
			src = src[2*indent+len("package p\n\nfunc _() {"):]
			src = src[:len(src)-(indent+len("\n}\n"))]
			return bytes.TrimSpace(src)
		}
		// Gofmt has also indented the function body one level.
		// Adjust that with indentAdj.
		indentAdj = -1
	}

	// Succeeded, or out of options.
	return
}

// format formats the given package file originally obtained from src
// and adjusts the result based on the original source via sourceAdj
// and indentAdj.
func format(
	fset *token.FileSet,
	file *ast.File,
	sourceAdj func(src []byte, indent int) []byte,
	indentAdj int,
	src []byte,
	cfg printer.Config,
) ([]byte, error) {
	if sourceAdj == nil {
		// Complete source file.
		var buf bytes.Buffer
		err := cfg.Fprint(&buf, fset, file)
		if err != nil {
			return nil, err
		}
		return buf.Bytes(), nil
	}

	// Partial source file.
	// Determine and prepend leading space.
	i, j := 0, 0
	for j < len(src) && isSpace(src[j]) {
		if src[j] == '\n' {
			i = j + 1 // byte offset of last line in leading space
		}
		j++
	}
	var res []byte
	res = append(res, src[:i]...)

	// Determine and prepend indentation of first code line.
	// Spaces are ignored unless there are no tabs,
	// in which case spaces count as one tab.
	indent := 0
	hasSpace := false
	for _, b := range src[i:j] {
		switch b {
		case ' ':
			hasSpace = true
		case '\t':
			indent++
		}
	}
	if indent == 0 && hasSpace {
		indent = 1
	}
	for i := 0; i < indent; i++ {
		res = append(res, '\t')
	}

	// Format the source.
	// Write it without any leading and trailing space.
	cfg.Indent = indent + indentAdj
	var buf bytes.Buffer
	err := cfg.Fprint(&buf, fset, file)
	if err != nil {
		return nil, err
	}
	res = append(res, sourceAdj(buf.Bytes(), cfg.Indent)...)

	// Determine and append trailing space.
	i = len(src)
	for i > 0 && isSpace(src[i-1]) {
		i--
	}
	return append(res, src[i:]...), nil
}

func isSpace(b byte) bool {
	return b == ' ' || b == '\t' || b == '\n' || b == '\r'
}