// Copyright 2021 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 types

import (
	"errors"
	"go/ast"
	"go/token"
	. "internal/types/errors"
	"strings"
)

// langCompat reports an error if the representation of a numeric
// literal is not compatible with the current language version.
func (check *Checker) langCompat(lit *ast.BasicLit) {
	s := lit.Value
	if len(s) <= 2 || check.allowVersion(check.pkg, lit.Pos(), 1, 13) {
		return
	}
	// len(s) > 2
	if strings.Contains(s, "_") {
		check.error(lit, UnsupportedFeature, "underscores in numeric literals requires go1.13 or later")
		return
	}
	if s[0] != '0' {
		return
	}
	radix := s[1]
	if radix == 'b' || radix == 'B' {
		check.error(lit, UnsupportedFeature, "binary literals requires go1.13 or later")
		return
	}
	if radix == 'o' || radix == 'O' {
		check.error(lit, UnsupportedFeature, "0o/0O-style octal literals requires go1.13 or later")
		return
	}
	if lit.Kind != token.INT && (radix == 'x' || radix == 'X') {
		check.error(lit, UnsupportedFeature, "hexadecimal floating-point literals requires go1.13 or later")
	}
}

// allowVersion reports whether the given package
// is allowed to use version major.minor.
func (check *Checker) allowVersion(pkg *Package, pos token.Pos, major, minor int) bool {
	// We assume that imported packages have all been checked,
	// so we only have to check for the local package.
	if pkg != check.pkg {
		return true
	}

	// If the source file declares its Go version, use that to decide.
	if check.posVers != nil {
		if v, ok := check.posVers[check.fset.File(pos)]; ok && v.major >= 1 {
			return v.major > major || v.major == major && v.minor >= minor
		}
	}

	// Otherwise fall back to the version in the checker.
	ma, mi := check.version.major, check.version.minor
	return ma == 0 && mi == 0 || ma > major || ma == major && mi >= minor
}

type version struct {
	major, minor int
}

var errVersionSyntax = errors.New("invalid Go version syntax")

// parseGoVersion parses a Go version string (such as "go1.12")
// and returns the version, or an error. If s is the empty
// string, the version is 0.0.
func parseGoVersion(s string) (v version, err error) {
	if s == "" {
		return
	}
	if !strings.HasPrefix(s, "go") {
		return version{}, errVersionSyntax
	}
	s = s[len("go"):]
	i := 0
	for ; i < len(s) && '0' <= s[i] && s[i] <= '9'; i++ {
		if i >= 10 || i == 0 && s[i] == '0' {
			return version{}, errVersionSyntax
		}
		v.major = 10*v.major + int(s[i]) - '0'
	}
	if i > 0 && i == len(s) {
		return
	}
	if i == 0 || s[i] != '.' {
		return version{}, errVersionSyntax
	}
	s = s[i+1:]
	if s == "0" {
		// We really should not accept "go1.0",
		// but we didn't reject it from the start
		// and there are now programs that use it.
		// So accept it.
		return
	}
	i = 0
	for ; i < len(s) && '0' <= s[i] && s[i] <= '9'; i++ {
		if i >= 10 || i == 0 && s[i] == '0' {
			return version{}, errVersionSyntax
		}
		v.minor = 10*v.minor + int(s[i]) - '0'
	}
	if i > 0 && i == len(s) {
		return
	}
	return version{}, errVersionSyntax
}

func (v version) equal(u version) bool {
	return v.major == u.major && v.minor == u.minor
}

func (v version) before(u version) bool {
	return v.major < u.major || v.major == u.major && v.minor < u.minor
}

func (v version) after(u version) bool {
	return v.major > u.major || v.major == u.major && v.minor > u.minor
}