package main

import (
	"fmt"
	"math"
	"strconv"
	"strings"
	"unicode"
)

// Define all token types
type TokenType int

const (
	EOF TokenType = iota
	Number
	Plus
	Minus
	Multiply
	Divide
	Power
	Sqrt
	LeftParen
	RightParen
)

// Token structure
type Token struct {
	Type  TokenType
	Value string
}

// Function to check if a rune is a space
func isSpace(r rune) bool {
	return unicode.IsSpace(r)
}

// Function to check if a rune is a digit
func isDigit(r rune) bool {
	return unicode.IsDigit(r)
}

// Function to check if a rune is an operator
func isOperator(r rune) bool {
	return strings.ContainsRune("+-*/^", r)
}

// Function to convert an expression string into tokens

func tokenize(expr string) ([]Token, error) {
	var tokens []Token
	for len(expr) > 0 {
		expr = strings.TrimSpace(expr)
		if len(expr) == 0 {
			break
		}
		var t Token
		switch {
		case expr[0] == '+':
			t = Token{Plus, "+"}
			expr = expr[1:]
		case expr[0] == '-':
			t = Token{Minus, "-"}
			expr = expr[1:]
		case expr[0] == '*':
			t = Token{Multiply, "*"}
			expr = expr[1:]
		case expr[0] == '/':
			t = Token{Divide, "/"}
			expr = expr[1:]
		case expr[0] == '(':
			t = Token{LeftParen, "("}
			expr = expr[1:]
		case expr[0] == ')':
			t = Token{RightParen, ")"}
			expr = expr[1:]
		case expr[0] == '^':
			t = Token{Power, "^"}
			expr = expr[1:]
		case strings.HasPrefix(expr, "sqrt"):
			t = Token{Sqrt, "sqrt"}
			expr = expr[len("sqrt"):]
		case isDigit(rune(expr[0])):
			num := strings.TrimLeftFunc(expr, isDigit)
			t = Token{Number, expr[:len(expr)-len(num)]}
			expr = num

		default:
			return nil, fmt.Errorf("Неизвестный символ: %c", expr[0])
		}

		tokens = append(tokens, t)
	}

	return tokens, nil
}

// Function to get the precedence of an operator
func precedence(op TokenType) int {
	switch op {
	case Power:
		return 4
	case Sqrt:
		return 3
	case Multiply, Divide:
		return 2
	case Plus, Minus:
		return 1
	case LeftParen, RightParen:
		return 0
	default:
		return 0
	}
}

// Function to evaluate an expression given its tokens
func eval(tokens []Token) (float64, error) {
	var stack []float64
	var operatorStack []Token

	for _, t := range tokens {
		switch t.Type {
		case Number:
			value, err := strconv.ParseFloat(t.Value, 64)
			if err != nil {
				return 0, err
			}
			stack = append(stack, value)
		case Plus, Minus, Multiply, Divide, Power, Sqrt:
			for len(operatorStack) > 0 && precedence(t.Type) <= precedence(operatorStack[len(operatorStack)-1].Type) {
				var op Token
				op, operatorStack = operatorStack[len(operatorStack)-1], operatorStack[:len(operatorStack)-1]

				if op.Type == Sqrt {
					if len(stack) < 1 {
						return 0, fmt.Errorf("Invalid expression: %s", t.Value)
					}

					value := stack[len(stack)-1]
					if value < 0 {
						return 0, fmt.Errorf("Cannot take square root of a negative number: %v", value)
					}

					stack = stack[:len(stack)-1]
					stack = append(stack, math.Sqrt(value))
				} else {
					if len(stack) < 2 {
						return 0, fmt.Errorf("Invalid expression: %s", t.Value)
					}

					right, left := stack[len(stack)-1], stack[len(stack)-2]
					stack = stack[:len(stack)-2]

					switch op.Type {
					case Plus:
						stack = append(stack, left+right)
					case Minus:
						stack = append(stack, left-right)
					case Multiply:
						stack = append(stack, left*right)
					case Divide:
						stack = append(stack, left/right)
					case Power:
						stack = append(stack, math.Pow(left, right))
					}
				}
			}

			operatorStack = append(operatorStack, t)

		case LeftParen:
			operatorStack = append(operatorStack, t)
		case RightParen:
			for len(operatorStack) > 0 && operatorStack[len(operatorStack)-1].Type != LeftParen {
				var op Token
				op, operatorStack = operatorStack[len(operatorStack)-1], operatorStack[:len(operatorStack)-1]

				if op.Type == Sqrt {
					if len(stack) < 1 {
						return 0, fmt.Errorf("Invalid expression: %s", t.Value)
					}

					value := stack[len(stack)-1]
					if value < 0 {
						return 0, fmt.Errorf("Cannot take square root of a negative number: %v", value)
					}

					stack = stack[:len(stack)-1]
					stack = append(stack, math.Sqrt(value))
				} else {
					if len(stack) < 2 {
						return 0, fmt.Errorf("Invalid expression: %s", t.Value)
					}

					right, left := stack[len(stack)-1], stack[len(stack)-2]
					stack = stack[:len(stack)-2]

					switch op.Type {
					case Plus:
						stack = append(stack, left+right)
					case Minus:
						stack = append(stack, left-right)
					case Multiply:
						stack = append(stack, left*right)
					case Divide:
						stack = append(stack, left/right)
					case Power:
						stack = append(stack, math.Pow(left, right))
					}
				}
			}

			if len(operatorStack) == 0 || operatorStack[len(operatorStack)-1].Type != LeftParen {
				return 0, fmt.Errorf("Mismatched parentheses")
			}

			operatorStack = operatorStack[:len(operatorStack)-1]
		}
	}

	for len(operatorStack) > 0 {
		var op Token
		op, operatorStack = operatorStack[len(operatorStack)-1], operatorStack[:len(operatorStack)-1]

		if op.Type == Sqrt {
			if len(stack) < 1 {
				return 0, fmt.Errorf("Invalid expression: %s", op.Value)
			}

			value := stack[len(stack)-1]
			if value < 0 {
				return 0, fmt.Errorf("Cannot take square root of a negative number: %v", value)
			}

			stack = stack[:len(stack)-1]
			stack = append(stack, math.Sqrt(value))
		} else {
			if len(stack) < 2 {
				return 0, fmt.Errorf("Invalid expression: %s", op.Value)
			}

			right, left := stack[len(stack)-1], stack[len(stack)-2]
			stack = stack[:len(stack)-2]

			switch op.Type {
			case Plus:
				stack = append(stack, left+right)
			case Minus:
				stack = append(stack, left-right)
			case Multiply:
				stack = append(stack, left*right)
			case Divide:
				stack = append(stack, left/right)
			case Power:
				stack = append(stack, math.Pow(left, right))
			}
		}
	}

	if len(stack) != 1 {
		return 0, fmt.Errorf("Invalid expression")
	}

	return stack[0], nil
}

func main() {
	expr := "sqrt(2-3)  + (4 + 1) "
	tokens, err := tokenize(expr)
	if err != nil {
		fmt.Println(err)
		return
	}

	result, err := eval(tokens)
	if err != nil {
		fmt.Println(err)
		return
	}

	fmt.Printf("%s = %v\n", expr, result)
}

перепиши код на rust