// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: BSD-3-Clause

// Package token defines the lexical tokens of Go's Plan 9 assembler (GAsm)
// and the source positions attached to them.  It has no dependencies and is
// shared by the lexer, parser, formatter, linter and language server.
package token

import "strconv"

// Kind classifies a lexical token.
type Kind int

// The token kinds.  The zero value is Illegal so that an uninitialised Token
// is obviously invalid.
const (
	Illegal Kind = iota
	EOF
	Newline
	Comment

	// Literals and names.
	Ident  // instruction mnemonic, label, register or symbol name
	Number // integer or floating-point literal (sign carried separately)
	String // "..."
	Rune   // '.'

	// Punctuation and operators.
	LParen // (
	RParen // )
	Comma  // ,
	Plus   // +
	Minus  // -
	Star   // *
	Slash  // /
	Colon  // :
	Dollar // $
	LAngle // <
	RAngle // >
	LShift // <<
	RShift // >>
	Arrow  // ->
	At     // @
	Hash   // #
)

var kindNames = map[Kind]string{
	Illegal: "ILLEGAL",
	EOF:     "EOF",
	Newline: "NEWLINE",
	Comment: "COMMENT",
	Ident:   "IDENT",
	Number:  "NUMBER",
	String:  "STRING",
	Rune:    "RUNE",
	LParen:  "(",
	RParen:  ")",
	Comma:   ",",
	Plus:    "+",
	Minus:   "-",
	Star:    "*",
	Slash:   "/",
	Colon:   ":",
	Dollar:  "$",
	LAngle:  "<",
	RAngle:  ">",
	LShift:  "<<",
	RShift:  ">>",
	Arrow:   "->",
	At:      "@",
	Hash:    "#",
}

// String returns a human-readable name for the kind.
func (k Kind) String() string {
	if s, ok := kindNames[k]; ok {
		return s
	}
	return "Kind(" + strconv.Itoa(int(k)) + ")"
}

// Position is a byte offset plus one-based line and column within a file.
type Position struct {
	Offset int // byte offset, zero-based
	Line   int // line number, one-based
	Column int // column number, one-based (in runes)
}

// String renders the position as "line:column".
func (p Position) String() string {
	return strconv.Itoa(p.Line) + ":" + strconv.Itoa(p.Column)
}

// IsValid reports whether the position carries a real line number.
func (p Position) IsValid() bool { return p.Line > 0 }

// Token is a single lexical token together with its literal text and span.
type Token struct {
	Kind Kind
	Text string
	Pos  Position // inclusive start
	End  Position // exclusive end
}

// String renders the token for diagnostics and debugging.
func (t Token) String() string {
	return t.Pos.String() + " " + t.Kind.String() + " " + strconv.Quote(t.Text)
}