package utils

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

func CalculateFormula(formulaExpression string) float64 {
	formulaExpression = strings.Replace(formulaExpression, " ", "", -1)
	return calculatePostfix(infix2ToPostfix(formulaExpression))
}

// (12.3+0.1)*2.0+2
// 12.30.1+2.0*2+
// 后缀式计算
func calculatePostfix(postfix []string) float64 {
	stack := Stack{}
	fixLen := len(postfix)
	for i := 0; i < fixLen; i++ {
		nextChar := postfix[i]
		// 数字：直接压栈
		if _, err := strconv.ParseFloat(nextChar, 64); err == nil {
			stack.Push(nextChar)
		} else {

			switch nextChar {
			case "√":
				// 操作符：取出数字计算值，再将结果压栈
				num1, _ := strconv.ParseFloat(stack.Pop(), 64)
				stack.Push(fmt.Sprintf("%v", math.Sqrt(num1)))
			case "²":
				// 操作符：取出数字计算值，再将结果压栈
				num1, _ := strconv.ParseFloat(stack.Pop(), 64)
				stack.Push(fmt.Sprintf("%v", math.Pow(num1, 2)))
			case "+":
				// 操作符：取出两个数字计算值，再将结果压栈
				num1, _ := strconv.ParseFloat(stack.Pop(), 64)
				num2, _ := strconv.ParseFloat(stack.Pop(), 64)
				stack.Push(fmt.Sprintf("%v", num2+num1))
			case "-":
				// 操作符：取出两个数字计算值，再将结果压栈
				num1, _ := strconv.ParseFloat(stack.Pop(), 64)
				num2, _ := strconv.ParseFloat(stack.Pop(), 64)
				stack.Push(fmt.Sprintf("%v", num2-num1))
			case "*":
				// 操作符：取出两个数字计算值，再将结果压栈
				num1, _ := strconv.ParseFloat(stack.Pop(), 64)
				num2, _ := strconv.ParseFloat(stack.Pop(), 64)
				stack.Push(fmt.Sprintf("%v", num2*num1))
			case "/":
				// 操作符：取出两个数字计算值，再将结果压栈
				num1, _ := strconv.ParseFloat(stack.Pop(), 64)
				num2, _ := strconv.ParseFloat(stack.Pop(), 64)
				stack.Push(fmt.Sprintf("%v", num2/num1))
			}
		}
	}
	result, _ := strconv.ParseFloat(stack.Top(), 64)
	return result
}

// 中缀表达式转后缀表达式
func infix2ToPostfix(expStr string) []string {
	stack := Stack{}
	postfix := make([]string, 0)
	exp := []rune(expStr)
	expLen := len(exp)

	// 遍历整个表达式
	for i := 0; i < expLen; i++ {

		char := string(exp[i])

		switch char {
		case " ":
			continue
		case "(":
			// 左括号直接入栈
			stack.Push("(")
		case ")":
			// 右括号则弹出元素直到遇到左括号
			for !stack.IsEmpty() {
				preChar := stack.Top()
				if preChar == "(" {
					stack.Pop() // 弹出 "("
					break
				}
				postfix = append(postfix, preChar)
				stack.Pop()
			}

			// 数字则直接输出
		case "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", ".":
			j := i
			digit := ""
			for ; j < expLen && (unicode.IsDigit(rune(exp[j])) || "." == string(exp[j])); j++ {
				digit += string(exp[j])
			}
			postfix = append(postfix, digit)
			i = j - 1 // i 向前跨越一个整数，由于执行了一步多余的 j++，需要减 1

		default:
			// 操作符：遇到高优先级的运算符，不断弹出，直到遇见更低优先级运算符
			for !stack.IsEmpty() {
				top := stack.Top()
				if top == "(" || isLower(top, char) {
					break
				}
				postfix = append(postfix, top)
				stack.Pop()
			}
			// 低优先级的运算符入栈
			stack.Push(char)
		}
	}

	// 栈不空则全部输出
	for !stack.IsEmpty() {
		postfix = append(postfix, stack.Pop())
	}

	return postfix
}

// 比较运算符栈栈顶 top 和新运算符 newTop 的优先级高低
func isLower(top string, newTop string) bool {
	// 注意 a + b + c 的后缀表达式是 ab + c +，不是 abc + +

	//优先级定义
	operatorPriority := map[string]uint16{
		"+": 0,
		"-": 0,
		"*": 1,
		"/": 1,
		"√": 3,
		"²": 3,
		"(": 5,
	}
	Priority := operatorPriority[newTop] > operatorPriority[top]

	return Priority

	//switch top {
	//case "+", "-":
	//	if newTop == "*" || newTop == "/" {
	//		return true
	//	}
	//case "(":
	//	return true
	//}
	//return false
}

type Stack struct {
	data [1024]string
	top  int
}

func (s *Stack) Push(d string) {
	s.data[s.top] = d
	s.top++
}

func (s *Stack) Pop() (d string) {
	if s.top == 0 {
		//err = fmt.Errorf("stack is empty")
	}
	s.top--
	d = s.data[s.top]
	return
}

func (s *Stack) Top() (d string) {
	if s.top == 0 {
		//err = fmt.Errorf("stack is empty")
	}
	d = s.data[s.top-1]
	return
}

func (s *Stack) IsEmpty() bool {
	return s.top == 0
}