// Copyright 2018 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 txtar implements a trivial text-based file archive format.
//
// The goals for the format are:
//
//   - be trivial enough to create and edit by hand.
//   - be able to store trees of text files describing go command test cases.
//   - diff nicely in git history and code reviews.
//
// Non-goals include being a completely general archive format,
// storing binary data, storing file modes, storing special files like
// symbolic links, and so on.
//
// # Txtar format
//
// A txtar archive is zero or more comment lines and then a sequence of file entries.
// Each file entry begins with a file marker line of the form "-- FILENAME --"
// and is followed by zero or more file content lines making up the file data.
// The comment or file content ends at the next file marker line.
// The file marker line must begin with the three-byte sequence "-- "
// and end with the three-byte sequence " --", but the enclosed
// file name can be surrounding by additional white space,
// all of which is stripped.
//
// If the txtar file is missing a trailing newline on the final line,
// parsers should consider a final newline to be present anyway.
//
// There are no possible syntax errors in a txtar archive.
package txtar

import (
	
	
	
	
)

// An Archive is a collection of files.
type Archive struct {
	Comment []byte
	Files   []File
}

// A File is a single file in an archive.
type File struct {
	Name string // name of file ("foo/bar.txt")
	Data []byte // text content of file
}

// Format returns the serialized form of an Archive.
// It is assumed that the Archive data structure is well-formed:
// a.Comment and all a.File[i].Data contain no file marker lines,
// and all a.File[i].Name is non-empty.
func ( *Archive) []byte {
	var  bytes.Buffer
	.Write(fixNL(.Comment))
	for ,  := range .Files {
		fmt.Fprintf(&, "-- %s --\n", .Name)
		.Write(fixNL(.Data))
	}
	return .Bytes()
}

// ParseFile parses the named file as an archive.
func ( string) (*Archive, error) {
	,  := os.ReadFile()
	if  != nil {
		return nil, 
	}
	return Parse(), nil
}

// Parse parses the serialized form of an Archive.
// The returned Archive holds slices of data.
func ( []byte) *Archive {
	 := new(Archive)
	var  string
	.Comment, ,  = findFileMarker()
	for  != "" {
		 := File{, nil}
		.Data, ,  = findFileMarker()
		.Files = append(.Files, )
	}
	return 
}

var (
	newlineMarker = []byte("\n-- ")
	marker        = []byte("-- ")
	markerEnd     = []byte(" --")
)

// findFileMarker finds the next file marker in data,
// extracts the file name, and returns the data before the marker,
// the file name, and the data after the marker.
// If there is no next marker, findFileMarker returns before = fixNL(data), name = "", after = nil.
func findFileMarker( []byte) ( []byte,  string,  []byte) {
	var  int
	for {
		if ,  = isMarker([:]);  != "" {
			return [:], , 
		}
		 := bytes.Index([:], newlineMarker)
		if  < 0 {
			return fixNL(), "", nil
		}
		 +=  + 1 // positioned at start of new possible marker
	}
}

// isMarker checks whether data begins with a file marker line.
// If so, it returns the name from the line and the data after the line.
// Otherwise it returns name == "" with an unspecified after.
func isMarker( []byte) ( string,  []byte) {
	if !bytes.HasPrefix(, marker) {
		return "", nil
	}
	if  := bytes.IndexByte(, '\n');  >= 0 {
		,  = [:], [+1:]
	}
	if !(bytes.HasSuffix(, markerEnd) && len() >= len(marker)+len(markerEnd)) {
		return "", nil
	}
	return strings.TrimSpace(string([len(marker) : len()-len(markerEnd)])), 
}

// If data is empty or ends in \n, fixNL returns data.
// Otherwise fixNL returns a new slice consisting of data with a final \n added.
func fixNL( []byte) []byte {
	if len() == 0 || [len()-1] == '\n' {
		return 
	}
	 := make([]byte, len()+1)
	copy(, )
	[len()] = '\n'
	return 
}