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// Copyright 2010 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.

// TODO(gri) consider making this a separate package outside the go directory.

package token

import (

        "fmt"

        "sort"

        "sync"

)

// -----------------------------------------------------------------------------

// Positions

// Position describes an arbitrary source position

// including the file, line, and column location.

// A Position is valid if the line number is > 0.

//

type Position struct {

        Filename string // filename, if any

        Offset   int    // offset, starting at 0

        Line     int    // line number, starting at 1

        Column   int    // column number, starting at 1 (character count)

}

// IsValid returns true if the position is valid.

func (pos *Position) IsValid() bool { return pos.Line > 0 }

// String returns a string in one of several forms:

//

//      file:line:column    valid position with file name

//      line:column         valid position without file name

//      file                invalid position with file name

//      -                   invalid position without file name

//

func (pos Position) String() string {

        s := pos.Filename

        if pos.IsValid() {

                if s != "" {

                        s += ":"

                }

                s += fmt.Sprintf("%d:%d", pos.Line, pos.Column)

        }

        if s == "" {

                s = "-"

        }

        return s

}

// Pos is a compact encoding of a source position within a file set.

// It can be converted into a Position for a more convenient, but much

// larger, representation.

//

// The Pos value for a given file is a number in the range [base, base+size],

// where base and size are specified when adding the file to the file set via

// AddFile.

//

// To create the Pos value for a specific source offset, first add

// the respective file to the current file set (via FileSet.AddFile)

// and then call File.Pos(offset) for that file. Given a Pos value p

// for a specific file set fset, the corresponding Position value is

// obtained by calling fset.Position(p).

//

// Pos values can be compared directly with the usual comparison operators:

// If two Pos values p and q are in the same file, comparing p and q is

// equivalent to comparing the respective source file offsets. If p and q

// are in different files, p < q is true if the file implied by p was added

// to the respective file set before the file implied by q.

//

type Pos int

// The zero value for Pos is NoPos; there is no file and line information

// associated with it, and NoPos().IsValid() is false. NoPos is always

// smaller than any other Pos value. The corresponding Position value

// for NoPos is the zero value for Position.

//

const NoPos Pos = 0

// IsValid returns true if the position is valid.

func (p Pos) IsValid() bool {

        return p != NoPos

}

// -----------------------------------------------------------------------------

// File

// A File is a handle for a file belonging to a FileSet.

// A File has a name, size, and line offset table.

//

type File struct {

        set  *FileSet

        name string // file name as provided to AddFile

        base int    // Pos value range for this file is [base...base+size]

        size int    // file size as provided to AddFile

        // lines and infos are protected by set.mutex

        lines []int

        infos []lineInfo

}

// Name returns the file name of file f as registered with AddFile.

func (f *File) Name() string {

        return f.name

}

// Base returns the base offset of file f as registered with AddFile.

func (f *File) Base() int {

        return f.base

}

// Size returns the size of file f as registered with AddFile.

func (f *File) Size() int {

        return f.size

}

// LineCount returns the number of lines in file f.

func (f *File) LineCount() int {

        f.set.mutex.RLock()

        n := len(f.lines)

        f.set.mutex.RUnlock()

        return n

}

// AddLine adds the line offset for a new line.

// The line offset must be larger than the offset for the previous line

// and smaller than the file size; otherwise the line offset is ignored.

//

func (f *File) AddLine(offset int) {

        f.set.mutex.Lock()

        if i := len(f.lines); (i == 0 || f.lines[i-1] < offset) && offset < f.size {

                f.lines = append(f.lines, offset)

        }

        f.set.mutex.Unlock()

}

// SetLines sets the line offsets for a file and returns true if successful.

// The line offsets are the offsets of the first character of each line;

// for instance for the content "ab\nc\n" the line offsets are {0, 3}.

// An empty file has an empty line offset table.

// Each line offset must be larger than the offset for the previous line

// and smaller than the file size; otherwise SetLines fails and returns

// false.

//

func (f *File) SetLines(lines []int) bool {

        // verify validity of lines table

        size := f.size

        for i, offset := range lines {

                if i > 0 && offset <= lines[i-1] || size <= offset {

                        return false

                }

        }

        // set lines table

        f.set.mutex.Lock()

        f.lines = lines

        f.set.mutex.Unlock()

        return true

}

// SetLinesForContent sets the line offsets for the given file content.

func (f *File) SetLinesForContent(content []byte) {

        var lines []int

        line := 0

        for offset, b := range content {

                if line >= 0 {

                        lines = append(lines, line)

                }

                line = -1

                if b == '\n' {

                        line = offset + 1

                }

        }

        // set lines table

        f.set.mutex.Lock()

        f.lines = lines

        f.set.mutex.Unlock()

}

// A lineInfo object describes alternative file and line number

// information (such as provided via a //line comment in a .go

// file) for a given file offset.

type lineInfo struct {

        // fields are exported to make them accessible to gob

        Offset   int

        Filename string

        Line     int

}

// AddLineInfo adds alternative file and line number information for

// a given file offset. The offset must be larger than the offset for

// the previously added alternative line info and smaller than the

// file size; otherwise the information is ignored.

//

// AddLineInfo is typically used to register alternative position

// information for //line filename:line comments in source files.

//

func (f *File) AddLineInfo(offset int, filename string, line int) {

        f.set.mutex.Lock()

        if i := len(f.infos); i == 0 || f.infos[i-1].Offset < offset && offset < f.size {

                f.infos = append(f.infos, lineInfo{offset, filename, line})

        }

        f.set.mutex.Unlock()

}

// Pos returns the Pos value for the given file offset;

// the offset must be <= f.Size().

// f.Pos(f.Offset(p)) == p.

//

func (f *File) Pos(offset int) Pos {

        if offset > f.size {

                panic("illegal file offset")

        }

        return Pos(f.base + offset)

}

// Offset returns the offset for the given file position p;

// p must be a valid Pos value in that file.

// f.Offset(f.Pos(offset)) == offset.

//

func (f *File) Offset(p Pos) int {

        if int(p) < f.base || int(p) > f.base+f.size {

                panic("illegal Pos value")

        }

        return int(p) - f.base

}

// Line returns the line number for the given file position p;

// p must be a Pos value in that file or NoPos.

//

func (f *File) Line(p Pos) int {

        // TODO(gri) this can be implemented much more efficiently

        return f.Position(p).Line

}

func searchLineInfos(a []lineInfo, x int) int {

        return sort.Search(len(a), func(i int) bool { return a[i].Offset > x }) - 1

}

// info returns the file name, line, and column number for a file offset.

func (f *File) info(offset int) (filename string, line, column int) {

        filename = f.name

        if i := searchInts(f.lines, offset); i >= 0 {

                line, column = i+1, offset-f.lines[i]+1

        }

        if len(f.infos) > 0 {

                // almost no files have extra line infos

                if i := searchLineInfos(f.infos, offset); i >= 0 {

                        alt := &f.infos[i]

                        filename = alt.Filename

                        if i := searchInts(f.lines, alt.Offset); i >= 0 {

                                line += alt.Line - i - 1

                        }

                }

        }

        return

}

func (f *File) position(p Pos) (pos Position) {

        offset := int(p) - f.base

        pos.Offset = offset

        pos.Filename, pos.Line, pos.Column = f.info(offset)

        return

}

// Position returns the Position value for the given file position p;

// p must be a Pos value in that file or NoPos.

//

func (f *File) Position(p Pos) (pos Position) {

        if p != NoPos {

                if int(p) < f.base || int(p) > f.base+f.size {

                        panic("illegal Pos value")

                }

                pos = f.position(p)

        }

        return

}

// -----------------------------------------------------------------------------

// FileSet

// A FileSet represents a set of source files.

// Methods of file sets are synchronized; multiple goroutines

// may invoke them concurrently.

//

type FileSet struct {

        mutex sync.RWMutex // protects the file set

        base  int          // base offset for the next file

        files []*File      // list of files in the order added to the set

        last  *File        // cache of last file looked up

}

// NewFileSet creates a new file set.

func NewFileSet() *FileSet {

        s := new(FileSet)

        s.base = 1 // 0 == NoPos

        return s

}

// Base returns the minimum base offset that must be provided to

// AddFile when adding the next file.

//

func (s *FileSet) Base() int {

        s.mutex.RLock()

        b := s.base

        s.mutex.RUnlock()

        return b

}

// AddFile adds a new file with a given filename, base offset, and file size

// to the file set s and returns the file. Multiple files may have the same

// name. The base offset must not be smaller than the FileSet's Base(), and

// size must not be negative.

//

// Adding the file will set the file set's Base() value to base + size + 1

// as the minimum base value for the next file. The following relationship

// exists between a Pos value p for a given file offset offs:

//

//      int(p) = base + offs

//

// with offs in the range [0, size] and thus p in the range [base, base+size].

// For convenience, File.Pos may be used to create file-specific position

// values from a file offset.

//

func (s *FileSet) AddFile(filename string, base, size int) *File {

        s.mutex.Lock()

        defer s.mutex.Unlock()

        if base < s.base || size < 0 {

                panic("illegal base or size")

        }

        // base >= s.base && size >= 0

        f := &File{s, filename, base, size, []int{0}, nil}

        base += size + 1 // +1 because EOF also has a position

        if base < 0 {

                panic("token.Pos offset overflow (> 2G of source code in file set)")

        }

        // add the file to the file set

        s.base = base

        s.files = append(s.files, f)

        s.last = f

        return f

}

// Iterate calls f for the files in the file set in the order they were added

// until f returns false.

//

func (s *FileSet) Iterate(f func(*File) bool) {

        for i := 0; ; i++ {

                var file *File

                s.mutex.RLock()

                if i < len(s.files) {

                        file = s.files[i]

                }

                s.mutex.RUnlock()

                if file == nil || !f(file) {

                        break

                }

        }

}

func searchFiles(a []*File, x int) int {

        return sort.Search(len(a), func(i int) bool { return a[i].base > x }) - 1

}

func (s *FileSet) file(p Pos) *File {

        // common case: p is in last file

        if f := s.last; f != nil && f.base <= int(p) && int(p) <= f.base+f.size {

                return f

        }

        // p is not in last file - search all files

        if i := searchFiles(s.files, int(p)); i >= 0 {

                f := s.files[i]

                // f.base <= int(p) by definition of searchFiles

                if int(p) <= f.base+f.size {

                        s.last = f

                        return f

                }

        }

        return nil

}

// File returns the file that contains the position p.

// If no such file is found (for instance for p == NoPos),

// the result is nil.

//

func (s *FileSet) File(p Pos) (f *File) {

        if p != NoPos {

                s.mutex.RLock()

                f = s.file(p)

                s.mutex.RUnlock()

        }

        return

}

// Position converts a Pos in the fileset into a general Position.

func (s *FileSet) Position(p Pos) (pos Position) {

        if p != NoPos {

                s.mutex.RLock()

                if f := s.file(p); f != nil {

                        pos = f.position(p)

                }

                s.mutex.RUnlock()

        }

        return

}

// -----------------------------------------------------------------------------

// Helper functions

func searchInts(a []int, x int) int {

        // This function body is a manually inlined version of:

        //

        //   return sort.Search(len(a), func(i int) bool { return a[i] > x }) - 1

        //

        // With better compiler optimizations, this may not be needed in the

        // future, but at the moment this change improves the go/printer

        // benchmark performance by ~30%. This has a direct impact on the

        // speed of gofmt and thus seems worthwhile (2011-04-29).

        // TODO(gri): Remove this when compilers have caught up.

        i, j := 0, len(a)

        for i < j {

                h := i + (j-i)/2 // avoid overflow when computing h

                // i ≤ h < j

                if a[h] <= x {

                        i = h + 1

                } else {

                        j = h

                }

        }

        return i - 1

}