ShinyAPP

library(shiny)
library(ggplot2)
library(DT)

## 
## Attaching package: 'DT'

## The following objects are masked from 'package:shiny':
## 
##     dataTableOutput, renderDataTable

# Mortgage calculator function
mortgage_calculator <- function(loan_amount, interest_rate, loan_term, show_position = NULL) {
  # Convert annual interest rate to monthly rate
  monthly_rate <- interest_rate / 12
  total_payments <- loan_term * 12
  
  # Calculate monthly payment using mortgage formula
  monthly_payment <- loan_amount * (monthly_rate * (1 + monthly_rate)^total_payments) / 
    ((1 + monthly_rate)^total_payments - 1)
  
  # Initialize remaining balance array
  remaining_balance <- numeric(total_payments)
  remaining_balance[1] <- loan_amount
  
  # Simulate mortgage payoff process
  for (i in 2:total_payments) {
    interest_payment <- remaining_balance[i - 1] * monthly_rate
    principal_payment <- monthly_payment - interest_payment
    remaining_balance[i] <- max(0, remaining_balance[i - 1] - principal_payment)
    if (remaining_balance[i] == 0) break
  }
  
  # Calculate total interest paid
  total_interest_paid <- sum(monthly_payment * total_payments) - loan_amount
  
  # Prepare results
  result <- list(
    Initial_Loan_Amount = loan_amount,
    Monthly_Payment = round(monthly_payment, 2),
    Total_Interest_Paid = round(total_interest_paid, 2),
    Remaining_Balance = remaining_balance
  )
  
  # Show a subset of remaining balances based on user request
  if (!is.null(show_position)) {
    if (show_position == "start") {
      result$First_10_Months <- head(remaining_balance, 10)
    } else if (show_position == "end") {
      result$Last_10_Months <- tail(remaining_balance, 10)
    }
  }
  
  return(result)
}

# UI for the Shiny app
ui <- fluidPage(
  titlePanel("Mortgage Calculator"),
  
  # Set light grey background color
  tags$style(HTML("body {background-color: #f5f5f5;}")),
  
  sidebarLayout(
    sidebarPanel(
      numericInput("loan_amount", "Loan Amount ($):", value = 30000, min = 1),
      numericInput("interest_rate", "Interest Rate (Annual %):", value = 8, min = 0, max = 100),
      numericInput("loan_term", "Loan Term (Years):", value = 25, min = 1),
      radioButtons("show_position", "Show Remaining Balance:",
                   choices = c("None" = NULL, "Start of Loan" = "start", "End of Loan" = "end"),
                   selected = NULL),
      actionButton("calculate", "Calculate"),
      actionButton("reset", "Reset"),
      br(),
      h4("Visualize Your Mortgage Progress!")
    ),
    
    mainPanel(
      # Display mortgage summary
      h3("Mortgage Summary"),
      verbatimTextOutput("summary_output"),
      br(),
      
      # Display remaining balance chart
      plotOutput("balance_plot"),
      
      # Show remaining balances for specific months
      DT::dataTableOutput("balance_output")
    )
  )
)

# Server logic for the Shiny app
server <- function(input, output, session) {
  
  # Reactive expression to calculate mortgage details
  mortgage_details <- eventReactive(input$calculate, {
    mortgage_calculator(
      loan_amount = input$loan_amount,
      interest_rate = input$interest_rate / 100, # Convert to decimal
      loan_term = input$loan_term,
      show_position = input$show_position
    )
  })
  
  # Reset the input fields when the reset button is clicked
  observeEvent(input$reset, {
    updateNumericInput(session, "loan_amount", value = 30000)
    updateNumericInput(session, "interest_rate", value = 8)
    updateNumericInput(session, "loan_term", value = 25)
    updateRadioButtons(session, "show_position", selected = NULL)
    output$summary_output <- renderPrint({""})
    output$balance_plot <- renderPlot({NULL})
    output$balance_output <- renderDT({NULL})
  })
  
  # Display summary of results
  output$summary_output <- renderPrint({
    details <- mortgage_details()
    cat("Initial Loan Amount: $", details$Initial_Loan_Amount, "\n")
    cat("Monthly Payment: $", details$Monthly_Payment, "\n")
    cat("Total Interest Paid: $", details$Total_Interest_Paid, "\n")
  })
  
  # Display remaining balance chart
  output$balance_plot <- renderPlot({
    details <- mortgage_details()
    remaining_balance <- details$Remaining_Balance
    
    # Create a color gradient for the plot based on the remaining balance
    color_gradient <- colorRampPalette(c("red", "green"))
    
    ggplot(data.frame(Month = 1:length(remaining_balance), Balance = remaining_balance), aes(x = Month, y = Balance)) +
      geom_line(aes(color = Balance), size = 1.5) +
      scale_color_gradientn(colors = color_gradient(100)) +
      labs(title = "Mortgage Remaining Balance Over Time", x = "Month", y = "Remaining Balance ($)") +
      theme_minimal() +
      theme(
        plot.title = element_text(size = 20, face = "bold"),
        axis.title = element_text(size = 14),
        axis.text = element_text(size = 12)
      )
  })
  
  # Display remaining balance details in pages of 10 months each
  output$balance_output <- DT::renderDataTable({
    details <- mortgage_details()
    balance_data <- data.frame(Month = 1:length(details$Remaining_Balance),
                               Remaining_Balance = details$Remaining_Balance)
    
    # Show the table with pagination, 10 months per page
    DT::datatable(balance_data, options = list(
      pageLength = 10,
      scrollY = "400px",
      paging = TRUE
    ))
  })
}

# Run the application
shinyApp(ui = ui, server = server)

Shiny applications not supported in static R Markdown documents