library(shiny)
source('barbell.R')


xlim <- c(-10,10)
ylim <- c(-5,15)

function(input, output, session) {

    output$description <- renderUI(list(
        h2("Q: Can you tell whether the barbell will and up in A--B ('heads') or B--A ('tails') position?")))


    observeEvent({ list(input$x, input$l, input$HookeConstant, input$AirResistance, input$omega, input$resetTime) },
    {
        session$userData$currentBarbell = barbell(
            p = 0,
            x = input$x,
            omega = input$omega,
            l = input$l,
            HookeConstant = input$HookeConstant,
            AirResistance = input$AirResistance,
            t = 0)
    })

    out <- eventReactive( input$animation, {
        session$userData$currentBarbell$draw()$evolve()
    })
    
    output$plot <- renderPlot({
        plot(NULL, type=NULL, xlim=xlim, ylim=ylim, xlab='x',
             ylab='y', asp=1)
        out()
    },

    height = 960, width = 960 )

    output$animationSlider <- renderUI(
        sliderInput("animation", label= h3("Animate"),
                    min = 0,
                    max = 1000,
                    value = 0,
                    step = 5,
                    animate =
                        animationOptions(interval = input$frameInterval,
                                         loop = TRUE)
                    )
    )
}