// 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.

// Package token is variant of the stdlib package token with types FileSet and
// Token removed.
package token // import "modernc.org/token"

import (
	"fmt"
	"sort"
)

// -----------------------------------------------------------------------------
// 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 (byte count)
}

// IsValid reports whether 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 (measured in bytes),
// first add the respective file to the current file set using 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

// NoPos is the zero value of Pos; 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 reports whether the position is valid.
func (p Pos) IsValid() bool {
	return p != NoPos
}

// -----------------------------------------------------------------------------
// File

// A File is a handle for a file.  A File has a name, size, and line offset
// table.
//
type File struct {
	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 []int // lines contains the offset of the first character for each line (the first entry is always 0)
	infos []lineInfo
}

// NewFile returns  a new file with a given filename and file size.
//
func NewFile(filename string, size int) *File {
	return &File{name: filename, base: 1, size: size, lines: []int{0}}
}

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

// MergeLine merges a line with the following line. It is akin to replacing
// the newline character at the end of the line with a space (to not change the
// remaining offsets). To obtain the line number, consult e.g. Position.Line.
// MergeLine will panic if given an invalid line number.
//
func (f *File) MergeLine(line int) {
	if line <= 0 {
		panic("illegal line number (line numbering starts at 1)")
	}
	if line >= len(f.lines) {
		panic("illegal line number")
	}
	// To merge the line numbered <line> with the line numbered <line+1>,
	// we need to remove the entry in lines corresponding to the line
	// numbered <line+1>. The entry in lines corresponding to the line
	// numbered <line+1> is located at index <line>, since indices in lines
	// are 0-based and line numbers are 1-based.
	copy(f.lines[line:], f.lines[line+1:])
	f.lines = f.lines[:len(f.lines)-1]
}

// SetLines sets the line offsets for a file and reports whether it succeeded.
// 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.
// Callers must not mutate the provided slice after SetLines returns.
//
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.lines = lines
	return true
}

// SetLinesForContent sets the line offsets for the given file content.
// It ignores position-altering //line comments.
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.lines = lines
}

// 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) {
	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})
	}
}

// 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 {
	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
}

// unpack returns the filename and line and column number for a file offset.
// If adjusted is set, unpack will return the filename and line information
// possibly adjusted by //line comments; otherwise those comments are ignored.
//
func (f *File) unpack(offset int, adjusted bool) (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 adjusted && 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, adjusted bool) (pos Position) {
	offset := int(p) - f.base
	pos.Offset = offset
	pos.Filename, pos.Line, pos.Column = f.unpack(offset, adjusted)
	return
}

// PositionFor returns the Position value for the given file position p.
// If adjusted is set, the position may be adjusted by position-altering
// //line comments; otherwise those comments are ignored.
// p must be a Pos value in f or NoPos.
//
func (f *File) PositionFor(p Pos, adjusted bool) (pos Position) {
	if p != NoPos {
		if int(p) < f.base || int(p) > f.base+f.size {
			panic("illegal Pos value")
		}
		pos = f.position(p, adjusted)
	}
	return
}

// Position returns the Position value for the given file position p.
// Calling f.Position(p) is equivalent to calling f.PositionFor(p, true).
//
func (f *File) Position(p Pos) (pos Position) {
	return f.PositionFor(p, true)
}

// -----------------------------------------------------------------------------
// 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
}