#' Table Output
#'
#' @description
#' The `tableOuptut()`/`renderTable()` pair creates a reactive table that is
#' suitable for display small matrices and data frames. The columns are
#' formatted with [xtable::xtable()].
#'
#' See [renderDataTable()] for data frames that are too big to fit on a single
#' page.
#'
#' @param expr An expression that returns an R object that can be used with
#'   [xtable::xtable()].
#' @param striped,hover,bordered Logicals: if `TRUE`, apply the
#'   corresponding Bootstrap table format to the output table.
#' @param spacing The spacing between the rows of the table (`xs`
#'   stands for "extra small", `s` for "small", `m` for "medium"
#'   and `l` for "large").
#' @param width Table width. Must be a valid CSS unit (like "100%", "400px",
#'   "auto") or a number, which will be coerced to a string and
#'   have "px" appended.
#' @param align A string that specifies the column alignment. If equal to
#'   `'l'`, `'c'` or `'r'`, then all columns will be,
#'   respectively, left-, center- or right-aligned. Otherwise, `align`
#'   must have the same number of characters as the resulting table (if
#'   `rownames = TRUE`, this will be equal to `ncol()+1`), with
#'   the *i*-th character specifying the alignment for the
#'   *i*-th column (besides `'l'`, `'c'` and
#'   `'r'`, `'?'` is also permitted - `'?'` is a placeholder
#'   for that particular column, indicating that it should keep its default
#'   alignment). If `NULL`, then all numeric/integer columns (including
#'   the row names, if they are numbers) will be right-aligned and
#'   everything else will be left-aligned (`align = '?'` produces the
#'   same result).
#' @param rownames,colnames Logicals: include rownames? include colnames
#'   (column headers)?
#' @param digits An integer specifying the number of decimal places for
#'   the numeric columns (this will not apply to columns with an integer
#'   class). If `digits` is set to a negative value, then the numeric
#'   columns will be displayed in scientific format with a precision of
#'   `abs(digits)` digits.
#' @param na The string to use in the table cells whose values are missing
#'   (i.e. they either evaluate to `NA` or `NaN`).
#' @param ... Arguments to be passed through to [xtable::xtable()]
#'   and [xtable::print.xtable()].
#' @inheritParams renderUI
#' @param outputArgs A list of arguments to be passed through to the
#'   implicit call to [tableOutput()] when `renderTable` is
#'   used in an interactive R Markdown document.
#' @export
#' @examples
#' ## Only run this example in interactive R sessions
#' if (interactive()) {
#'   # table example
#'   shinyApp(
#'     ui = fluidPage(
#'       fluidRow(
#'         column(12,
#'           tableOutput('table')
#'         )
#'       )
#'     ),
#'     server = function(input, output) {
#'       output$table <- renderTable(iris)
#'     }
#'   )
#' }
renderTable <- function(expr, striped = FALSE, hover = FALSE,
                        bordered = FALSE, spacing = c("s", "xs", "m", "l"),
                        width = "auto", align = NULL,
                        rownames = FALSE, colnames = TRUE,
                        digits = NULL, na = "NA", ...,
                        env = parent.frame(), quoted = FALSE,
                        outputArgs=list())
{
  func <- installExprFunction(expr, "func", env, quoted, label = "renderTable")

  if (!is.function(spacing)) spacing <- match.arg(spacing)

  # A small helper function to create a wrapper for an argument that was
  # passed to renderTable()
  createWrapper <- function(arg) {
    if (is.function(arg)) wrapper <- arg
    else wrapper <- function() arg
    return(wrapper)
  }

  # Create wrappers for most arguments so that functions can also be passed
  # in, rather than only literals (useful for shiny apps)
  stripedWrapper <- createWrapper(striped)
  hoverWrapper <- createWrapper(hover)
  borderedWrapper <- createWrapper(bordered)
  spacingWrapper <- createWrapper(spacing)
  widthWrapper <- createWrapper(width)
  alignWrapper <- createWrapper(align)
  rownamesWrapper <- createWrapper(rownames)
  colnamesWrapper <- createWrapper(colnames)
  digitsWrapper <- createWrapper(digits)
  naWrapper <- createWrapper(na)

  dots <- list(...)  ## used later (but defined here because of scoping)

  createRenderFunction(
    func,
    function(data, session, name, ...) {
      striped <- stripedWrapper()
      hover <- hoverWrapper()
      bordered <- borderedWrapper()
      format <- c(striped = striped, hover = hover, bordered = bordered)
      spacing <- spacingWrapper()
      width <- widthWrapper()
      align <- alignWrapper()
      rownames <- rownamesWrapper()
      colnames <- colnamesWrapper()
      digits <- digitsWrapper()
      na <- naWrapper()

      spacing_choices <- c("s", "xs", "m", "l")
      if (!(spacing %in% spacing_choices)) {
        stop(paste("`spacing` must be one of",
          paste0("'", spacing_choices, "'", collapse=", ")))
      }

      # For css styling
      classNames <- paste0("table shiny-table",
        paste0(" table-", names(format)[format], collapse = "" ),
        paste0(" spacing-", spacing))

      data <- as.data.frame(data)

      # Return NULL if no data is provided
      if (is.null(data) ||
          (is.data.frame(data) && nrow(data) == 0 && ncol(data) == 0))
        return(NULL)

      # Separate the ... args to pass to xtable() vs print.xtable()
      xtable_argnames <- setdiff(names(formals(xtable)), c("x", "..."))
      xtable_args <- dots[intersect(names(dots), xtable_argnames)]
      non_xtable_args <- dots[setdiff(names(dots), xtable_argnames)]

      # By default, numbers are right-aligned and everything else is left-aligned.
      defaultAlignment <- function(col) {
        if (is.numeric(col)) "r" else "l"
      }

      # Figure out column alignment
      ## Case 1: default alignment
      if (is.null(align) || align == "?") {
        names <- defaultAlignment(attr(data, "row.names"))
        cols <- paste(vapply(data, defaultAlignment, character(1)), collapse = "")
        cols <- paste0(names, cols)
      } else {
        ## Case 2: user-specified alignment
        num_cols <- if (rownames) nchar(align) else nchar(align)+1
        valid <- !grepl("[^lcr\\?]", align)
        if (num_cols == ncol(data)+1 && valid) {
          cols <- if (rownames) align else paste0("r", align)
          defaults <- grep("\\?", strsplit(cols,"")[[1]])
          if (length(defaults) != 0) {
            vals <- vapply(data[,defaults-1], defaultAlignment, character(1))
            for (i in seq_len(length(defaults))) {
              substr(cols, defaults[i], defaults[i]) <- vals[i]
            }
          }
        } else if (nchar(align) == 1 && valid) {
          cols <- paste0(rep(align, ncol(data)+1), collapse="")
        } else {
          stop("`align` must contain only the characters `l`, `c`, `r` and/or `?` and",
            "have length either equal to 1 or to the total number of columns")
        }
      }

      # Call xtable with its (updated) args
      xtable_args <- c(xtable_args, align = cols, digits = digits)
      xtable_res <- do.call(xtable, c(list(data), xtable_args))

      # Set up print args
      print_args <- list(
        x = xtable_res,
        type = 'html',
        include.rownames = {
          if ("include.rownames" %in% names(dots)) dots$include.rownames
          else rownames
        },
        include.colnames = {
          if ("include.colnames" %in% names(dots)) dots$include.colnames
          else colnames
        },
        NA.string = {
          if ("NA.string" %in% names(dots)) dots$NA.string
          else na
        },
        html.table.attributes =
          paste0({
            if ("html.table.attributes" %in% names(dots)) dots$html.table.attributes
            else ""
          }, " ",
            "class = '", htmlEscape(classNames, TRUE), "' ",
            "style = 'width:", validateCssUnit(width), ";'"),
        comment = {
          if ("comment" %in% names(dots)) dots$comment
          else FALSE
        }
      )

      print_args <- c(print_args, non_xtable_args)
      print_args <- print_args[unique(names(print_args))]

      # Capture the raw html table returned by print.xtable(), and store it in
      # a variable for further processing
      tab <- paste(utils::capture.output(do.call(print, print_args)),collapse = "\n")

      # Add extra class to cells with NA value, to be able to style them separately
      tab <- gsub(paste(">", na, "<"), paste(" class='NA'>", na, "<"), tab)

      # All further processing concerns the table headers, so we don't need to run
      # any of this if colnames=FALSE
      if (colnames) {
        # Make sure that the final html table has a proper header (not included
        # in the print.xtable() default)
        tab <- sub("<tr>", "<thead> <tr>", tab)
        tab <- sub("</tr>", "</tr> </thead> <tbody>", tab)
        tab <- sub("</table>$", "</tbody> </table>", tab)

        # Update the `cols` string (which stores the alignment of each column) so
        # that it only includes the alignment for the table variables (and not
        # for the row.names)
        cols <- if (rownames) cols else substr(cols, 2, nchar(cols))

        # Create a vector whose i-th entry corresponds to the i-th table variable
        # alignment (substituting "l" by "left", "c" by "center" and "r" by "right")
        cols <- strsplit(cols, "")[[1]]
        cols[cols == "l"] <- "left"
        cols[cols == "r"] <- "right"
        cols[cols == "c"] <- "center"

        # Align each header accordingly (this guarantees that each header and its
        # corresponding column have the same alignment)
        for (i in seq_len(length(cols))) {
          tab <- sub("<th>", paste0("<th style='text-align: ", cols[i], ";'>"), tab)
        }
      }
      return(tab)
    },
    tableOutput, outputArgs
  )
}