rpncalc

package main

import (
    "strconv"
    "strings"

    "fyne.io/fyne"
    "fyne.io/fyne/app"
    "fyne.io/fyne/layout"
    "fyne.io/fyne/widget"
)

type stack []int

func (s *stack) Push(str int) {
    *s = append(*s, str)
}

func (s *stack) Pop() int {
    if s.IsEmpty() {
        return 0
    } else {
        index := len(*s) - 1
        element := (*s)[index]
        *s = (*s)[:index]
        return element
    }
}

func (s *stack) IsEmpty() bool {
    return len(*s) == 0
}

type calc struct {
    equation string
    input    *widget.Entry
    output   *widget.Entry
    window   fyne.Window
}

func (c *calc) loadGUI(app fyne.App, s stack) {
    var selectedOutput []string
    var selectedInput []string
    c.window = app.NewWindow("Calc")
    c.window.SetFixedSize(true)

    c.input = widget.NewEntry()
    c.output = widget.NewEntry()
    c.output.Disable()
    c.output.SetText("Output:")

    c.window.SetContent(fyne.NewContainerWithLayout(layout.NewGridLayout(1),
        c.input,
        c.output,
        fyne.NewContainerWithLayout(layout.NewGridLayout(4),
            widget.NewButton("1", func() {
                selectedInput = []string{c.input.Text, "1"}
                c.input.SetText(strings.Join(selectedInput, ""))
            }),
            widget.NewButton("2", func() {
                selectedInput = []string{c.input.Text, "2"}
                c.input.SetText(strings.Join(selectedInput, ""))
            }),
            widget.NewButton("3", func() {
                selectedInput = []string{c.input.Text, "3"}
                c.input.SetText(strings.Join(selectedInput, ""))
            }),
            widget.NewButton("+", func() {
                selectedInput = []string{c.input.Text, "+"}
                c.input.SetText(strings.Join(selectedInput, ""))
            })),

        fyne.NewContainerWithLayout(layout.NewGridLayout(4),
            widget.NewButton("4", func() {
                selectedInput = []string{c.input.Text, "4"}
                c.input.SetText(strings.Join(selectedInput, ""))
            }),
            widget.NewButton("5", func() {
                selectedInput = []string{c.input.Text, "5"}
                c.input.SetText(strings.Join(selectedInput, ""))
            }),
            widget.NewButton("6", func() {
                selectedInput = []string{c.input.Text, "6"}
                c.input.SetText(strings.Join(selectedInput, ""))
            }),
            widget.NewButton("-", func() {
                selectedInput = []string{c.input.Text, "-"}
                c.input.SetText(strings.Join(selectedInput, ""))
            })),

        fyne.NewContainerWithLayout(layout.NewGridLayout(4),
            widget.NewButton("7", func() {
                selectedInput = []string{c.input.Text, "7"}
                c.input.SetText(strings.Join(selectedInput, ""))
            }),
            widget.NewButton("8", func() {
                selectedInput = []string{c.input.Text, "8"}
                c.input.SetText(strings.Join(selectedInput, ""))
            }),
            widget.NewButton("9", func() {
                selectedInput = []string{c.input.Text, "9"}
                c.input.SetText(strings.Join(selectedInput, ""))
            }),
            widget.NewButton("/", func() {
                selectedInput = []string{c.input.Text, "/"}
                c.input.SetText(strings.Join(selectedInput, ""))
            })),
        fyne.NewContainerWithLayout(layout.NewGridLayout(4),
            widget.NewButton("*", func() {
                selectedInput = []string{c.input.Text, "*"}
                c.input.SetText(strings.Join(selectedInput, ""))
            }),
            widget.NewButton(" ", func() {
                selectedInput = []string{c.input.Text, " "}
                c.input.SetText(strings.Join(selectedInput, ""))
            }),
            widget.NewButton("C", func() {
                c.input.SetText("")
            }),
            widget.NewButton("=", func() {
                c.equation = c.input.Text
                selectedOutput = []string{"Output:", c.calculate(c.equation, s)}
                c.output.SetText(strings.Join(selectedOutput, " "))
            }))))

    c.window.Resize(fyne.NewSize(300, 400))
    c.window.ShowAndRun()
}

func (c *calc) calculate(equation string, s stack) string {
    e := strings.Fields(c.equation)
    for iterations, num := range e {
        if iterations == len(e) {
            break
        }
        if IsLetter(num) {
            switch num {
            case "+":
                p1 := s.Pop()
                p2 := s.Pop()
                s.Push(p1 + p2)
            case "-":
                p1 := s.Pop()
                p2 := s.Pop()
                s.Push(p2 - p1)
            case "*":
                p1 := s.Pop()
                p2 := s.Pop()
                s.Push(p1 * p2)
            case "/":
                p1 := s.Pop()
                p2 := s.Pop()
                s.Push(p2 / p1)
            default:
                c.output.SetText("Output: Error!")
            }
        } else {
            n2, _ := strconv.Atoi(num)
            s.Push(n2)
        }
        //log.Println("stack is", s)
    }
    result := s.Pop()
    resultStr := strconv.Itoa(result)
    return resultStr

}

func IsLetter(v string) bool {
    if _, err := strconv.Atoi(v); err == nil {
        return false
    } else {
        return true
    }
}

func newCalculator() *calc {
    c := &calc{}
    return c
}

func main() {
    var s stack
    c := newCalculator()
    c.loadGUI(app.New(), s)
}