// 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 token defines constants representing the lexical tokens of the Go
// programming language and basic operations on tokens (printing, predicates).
package token

import (
	"strconv"
	"unicode"
	"unicode/utf8"
)

// Token is the set of lexical tokens of the Go programming language.
type Token int

// The list of tokens.
const (
	// Special tokens
	ILLEGAL Token = iota
	EOF
	COMMENT

	literal_beg
	// Identifiers and basic type literals
	// (these tokens stand for classes of literals)
	IDENT  // main
	INT    // 12345
	FLOAT  // 123.45
	IMAG   // 123.45i
	CHAR   // 'a'
	STRING // "abc"
	literal_end

	operator_beg

	QUESTION
	NIL_COALESCE // ??

	// Operators and delimiters
	ADD // +
	SUB // -
	MUL // *
	QUO // /
	REM // %
	POW // **

	AND     // &
	OR      // |
	XOR     // ^
	SHL     // <<
	SHR     // >>
	AND_NOT // &^

	ADD_ASSIGN // +=
	SUB_ASSIGN // -=
	MUL_ASSIGN // *=
	QUO_ASSIGN // /=
	REM_ASSIGN // %=

	AND_ASSIGN     // &=
	OR_ASSIGN      // |=
	XOR_ASSIGN     // ^=
	SHL_ASSIGN     // <<=
	SHR_ASSIGN     // >>=
	AND_NOT_ASSIGN // &^=

	LAND  // &&
	LOR   // ||
	ARROW // <-
	INC   // ++
	DEC   // --

	EQL    // ==
	LSS    // <
	GTR    // >
	ASSIGN // =
	NOT    // !

	NEQ       // !=
	LEQ       // <=
	GEQ       // >=
	DEFINE    // :=
	ELLIPSIS  // ...
	RANGEOP   // ..
	RANGEOPEQ // ..=

	LPAREN // (
	LBRACK // [
	LBRACE // {
	COMMA  // ,
	PERIOD // .

	RPAREN    // )
	RBRACK    // ]
	RBRACE    // }
	SEMICOLON // ;
	COLON     // :
	operator_end

	keyword_beg
	// Keywords
	OR_BREAK
	OR_CONTINUE
	OR_RETURN
	BREAK
	CASE
	CHAN
	CONST
	CONTINUE

	DEFAULT
	DEFER
	ELSE
	FALLTHROUGH
	FOR

	FUNC
	GO
	GOTO
	IF
	IMPORT
	SOME
	ERR
	OK
	NONE

	INTERFACE
	MAP
	SET
	PACKAGE
	RANGE
	RETURN
	MUT
	IN
	PUB
	GUARD

	SELECT
	STRUCT
	ENUM
	SWITCH
	MATCH
	DUMP
	AT_LINE
	AT_COLUMN
	TYPE
	VAR
	LET
	WHERE
	keyword_end

	additional_beg
	// additional tokens, handled in an ad-hoc manner
	TILDE
	additional_end
)

var tokens = [...]string{
	ILLEGAL: "ILLEGAL",

	EOF:     "EOF",
	COMMENT: "COMMENT",

	IDENT:  "IDENT",
	INT:    "INT",
	FLOAT:  "FLOAT",
	IMAG:   "IMAG",
	CHAR:   "CHAR",
	STRING: "STRING",

	QUESTION:     "?",
	NIL_COALESCE: "??",

	ADD: "+",
	SUB: "-",
	MUL: "*",
	POW: "**",
	QUO: "/",
	REM: "%",

	AND:     "&",
	OR:      "|",
	XOR:     "^",
	SHL:     "<<",
	SHR:     ">>",
	AND_NOT: "&^",

	ADD_ASSIGN: "+=",
	SUB_ASSIGN: "-=",
	MUL_ASSIGN: "*=",
	QUO_ASSIGN: "/=",
	REM_ASSIGN: "%=",

	AND_ASSIGN:     "&=",
	OR_ASSIGN:      "|=",
	XOR_ASSIGN:     "^=",
	SHL_ASSIGN:     "<<=",
	SHR_ASSIGN:     ">>=",
	AND_NOT_ASSIGN: "&^=",

	LAND:  "&&",
	LOR:   "||",
	ARROW: "<-",
	INC:   "++",
	DEC:   "--",

	EQL:    "==",
	LSS:    "<",
	GTR:    ">",
	ASSIGN: "=",
	NOT:    "!",

	NEQ:       "!=",
	LEQ:       "<=",
	GEQ:       ">=",
	DEFINE:    ":=",
	ELLIPSIS:  "...",
	RANGEOP:   "..",
	RANGEOPEQ: "..=",

	LPAREN: "(",
	LBRACK: "[",
	LBRACE: "{",
	COMMA:  ",",
	PERIOD: ".",

	RPAREN:    ")",
	RBRACK:    "]",
	RBRACE:    "}",
	SEMICOLON: ";",
	COLON:     ":",

	OR_BREAK:    "or_break",
	OR_CONTINUE: "or_continue",
	OR_RETURN:   "or_return",
	BREAK:       "break",
	CASE:        "case",
	CHAN:        "chan",
	CONST:       "const",
	CONTINUE:    "continue",

	DEFAULT:     "default",
	DEFER:       "defer",
	ELSE:        "else",
	FALLTHROUGH: "fallthrough",
	FOR:         "for",

	FUNC:   "func",
	GO:     "go",
	GOTO:   "goto",
	IF:     "if",
	IMPORT: "import",
	SOME:   "Some",
	ERR:    "Err",
	OK:     "Ok",
	NONE:   "None",
	LET:    "let",

	INTERFACE: "interface",
	MUT:       "mut",
	IN:        "in",
	PUB:       "pub",
	MAP:       "map",
	SET:       "set",
	PACKAGE:   "package",
	RANGE:     "range",
	RETURN:    "return",
	GUARD:     "guard",

	SELECT: "select",
	STRUCT: "struct",
	ENUM:   "enum",
	SWITCH: "switch",
	MATCH:  "match",
	DUMP:   "dump",
	TYPE:   "type",
	VAR:    "var",
	WHERE:  "where",

	AT_LINE:   "@LINE",
	AT_COLUMN: "@COLUMN",

	TILDE: "~",
}

// String returns the string corresponding to the token tok.
// For operators, delimiters, and keywords the string is the actual
// token character sequence (e.g., for the token [ADD], the string is
// "+"). For all other tokens the string corresponds to the token
// constant name (e.g. for the token [IDENT], the string is "IDENT").
func (tok Token) String() string {
	s := ""
	if 0 <= tok && tok < Token(len(tokens)) {
		s = tokens[tok]
	}
	if s == "" {
		s = "token(" + strconv.Itoa(int(tok)) + ")"
	}
	return s
}

// A set of constants for precedence-based expression parsing.
// Non-operators have lowest precedence, followed by operators
// starting with precedence 1 up to unary operators. The highest
// precedence serves as "catch-all" precedence for selector,
// indexing, and other operator and delimiter tokens.
const (
	LowestPrec  = 0 // non-operators
	UnaryPrec   = 6
	HighestPrec = 7
)

// Precedence returns the operator precedence of the binary
// operator op. If op is not a binary operator, the result
// is LowestPrecedence.
func (op Token) Precedence() int {
	switch op {
	case NIL_COALESCE:
		return 1
	case LOR:
		return 1
	case LAND:
		return 2
	case IN:
		return 3
	case EQL, NEQ, LSS, LEQ, GTR, GEQ:
		return 4
	case RANGEOP, RANGEOPEQ:
		return 5
	case ADD, SUB, OR, XOR:
		return 6
	case MUL, QUO, REM, SHL, SHR, AND, AND_NOT:
		return 7
	case POW:
		return 8
	}
	return LowestPrec
}

var keywords map[string]Token

func init() {
	keywords = make(map[string]Token, keyword_end-(keyword_beg+1))
	for i := keyword_beg + 1; i < keyword_end; i++ {
		keywords[tokens[i]] = i
	}
}

// Lookup maps an identifier to its keyword token or [IDENT] (if not a keyword).
func Lookup(ident string) Token {
	if tok, is_keyword := keywords[ident]; is_keyword {
		return tok
	}
	return IDENT
}

// Predicates

// IsLiteral returns true for tokens corresponding to identifiers
// and basic type literals; it returns false otherwise.
func (tok Token) IsLiteral() bool { return literal_beg < tok && tok < literal_end }

// IsOperator returns true for tokens corresponding to operators and
// delimiters; it returns false otherwise.
func (tok Token) IsOperator() bool {
	return (operator_beg < tok && tok < operator_end) || tok == TILDE
}

// IsKeyword returns true for tokens corresponding to keywords;
// it returns false otherwise.
func (tok Token) IsKeyword() bool { return keyword_beg < tok && tok < keyword_end }

// IsExported reports whether name starts with an upper-case letter.
func IsExported(name string) bool {
	ch, _ := utf8.DecodeRuneInString(name)
	return unicode.IsUpper(ch)
}

// IsKeyword reports whether name is a Go keyword, such as "func" or "return".
func IsKeyword(name string) bool {
	// TODO: opt: use a perfect hash function instead of a global map.
	_, ok := keywords[name]
	return ok
}

// IsIdentifier reports whether name is a Go identifier, that is, a non-empty
// string made up of letters, digits, and underscores, where the first character
// is not a digit. Keywords are not identifiers.
func IsIdentifier(name string) bool {
	if name == "" || IsKeyword(name) {
		return false
	}
	for i, c := range name {
		if !unicode.IsLetter(c) && c != '_' && (i == 0 || !unicode.IsDigit(c)) {
			return false
		}
	}
	return true
}
