#' Key glyphs for legends
#'
#' Each geom has an associated function that draws the key when the geom needs
#' to be displayed in a legend. These functions are called `draw_key_*()`, where
#' `*` stands for the name of the respective key glyph. The key glyphs can be
#' customized for individual geoms by providing a geom with the `key_glyph`
#' argument (see [`layer()`] or examples below.)
#'
#' @return A grid grob.
#' @param data A single row data frame containing the scaled aesthetics to
#'   display in this key
#' @param params A list of additional parameters supplied to the geom.
#' @param size Width and height of key in mm.
#' @examples
#' p <- ggplot(economics, aes(date, psavert, color = "savings rate"))
#' # key glyphs can be specified by their name
#' p + geom_line(key_glyph = "timeseries")
#'
#' # key glyphs can be specified via their drawing function
#' p + geom_line(key_glyph = draw_key_rect)
#' @name draw_key
NULL

#' @export
#' @rdname draw_key
draw_key_point <- function(data, params, size) {
  if (is.null(data$shape)) {
    data$shape <- 19
  } else if (is.character(data$shape)) {
    data$shape <- translate_shape_string(data$shape)
  }

  pointsGrob(0.5, 0.5,
    pch = data$shape,
    gp = gpar(
      col = alpha(data$colour %||% "black", data$alpha),
      fill = alpha(data$fill %||% "black", data$alpha),
      fontsize = (data$size %||% 1.5) * .pt + (data$stroke %||% 0.5) * .stroke / 2,
      lwd = (data$stroke %||% 0.5) * .stroke / 2
    )
  )
}

#' @export
#' @rdname draw_key
draw_key_abline <- function(data, params, size) {
  segmentsGrob(0, 0, 1, 1,
    gp = gpar(
      col = alpha(data$colour %||% data$fill %||% "black", data$alpha),
      lwd = (data$size %||% 0.5) * .pt,
      lty = data$linetype %||% 1,
      lineend = "butt"
    )
  )
}

#' @export
#' @rdname draw_key
draw_key_rect <- function(data, params, size) {
  rectGrob(gp = gpar(
    col = NA,
    fill = alpha(data$fill %||% data$colour %||% "grey20", data$alpha),
    lty = data$linetype %||% 1
  ))
}
#' @export
#' @rdname draw_key
draw_key_polygon <- function(data, params, size) {
  if (is.null(data$size)) {
    data$size <- 0.5
  }

  lwd <- min(data$size, min(size) / 4)

  rectGrob(
    width = unit(1, "npc") - unit(lwd, "mm"),
    height = unit(1, "npc") - unit(lwd, "mm"),
    gp = gpar(
      col = data$colour %||% NA,
      fill = alpha(data$fill %||% "grey20", data$alpha),
      lty = data$linetype %||% 1,
      lwd = lwd * .pt,
      linejoin = params$linejoin %||% "mitre",
      # `lineend` is a workaround for Windows and intentionally kept unexposed
      # as an argument. (c.f. https://github.com/tidyverse/ggplot2/issues/3037#issuecomment-457504667)
      lineend = if (identical(params$linejoin, "round")) "round" else "square"
  ))
}

#' @export
#' @rdname draw_key
draw_key_blank <- function(data, params, size) {
  zeroGrob()
}

#' @export
#' @rdname draw_key
draw_key_boxplot <- function(data, params, size) {
  grobTree(
    linesGrob(0.5, c(0.1, 0.25)),
    linesGrob(0.5, c(0.75, 0.9)),
    rectGrob(height = 0.5, width = 0.75),
    linesGrob(c(0.125, 0.875), 0.5),
    gp = gpar(
      col = data$colour %||% "grey20",
      fill = alpha(data$fill %||% "white", data$alpha),
      lwd = (data$size %||% 0.5) * .pt,
      lty = data$linetype %||% 1
    )
  )
}

#' @export
#' @rdname draw_key
draw_key_crossbar <- function(data, params, size) {
  grobTree(
    rectGrob(height = 0.5, width = 0.75),
    linesGrob(c(0.125, 0.875), 0.5),
    gp = gpar(
      col = data$colour %||% "grey20",
      fill = alpha(data$fill %||% "white", data$alpha),
      lwd = (data$size %||% 0.5) * .pt,
      lty = data$linetype %||% 1
    )
  )
}

#' @export
#' @rdname draw_key
draw_key_path <- function(data, params, size) {
  if (is.null(data$linetype)) {
    data$linetype <- 0
  } else {
    data$linetype[is.na(data$linetype)] <- 0
  }

  segmentsGrob(0.1, 0.5, 0.9, 0.5,
    gp = gpar(
      col = alpha(data$colour %||% data$fill %||% "black", data$alpha),
      fill = alpha(params$arrow.fill %||% data$colour
                   %||% data$fill %||% "black", data$alpha),
      lwd = (data$size %||% 0.5) * .pt,
      lty = data$linetype %||% 1,
      lineend = "butt"
    ),
    arrow = params$arrow
  )
}

#' @export
#' @rdname draw_key
draw_key_vpath <- function(data, params, size) {
  segmentsGrob(0.5, 0.1, 0.5, 0.9,
    gp = gpar(
      col = alpha(data$colour %||% data$fill %||% "black", data$alpha),
      lwd = (data$size %||% 0.5) * .pt,
      lty = data$linetype %||% 1,
      lineend = "butt"
    ),
    arrow = params$arrow
  )
}

#' @export
#' @rdname draw_key
draw_key_dotplot <- function(data, params, size) {
  pointsGrob(0.5, 0.5, size = unit(.5, "npc"),
    pch = 21,
    gp = gpar(
      col = alpha(data$colour %||% "black", data$alpha),
      fill = alpha(data$fill %||% "black", data$alpha)
    )
  )
}

#' @export
#' @rdname draw_key
draw_key_pointrange <- function(data, params, size) {
  grobTree(
    draw_key_vpath(data, params, size),
    draw_key_point(transform(data, size = (data$size %||% 1.5) * 4), params)
  )
}

#' @export
#' @rdname draw_key
draw_key_smooth <- function(data, params, size) {
  data$fill <- alpha(data$fill %||% "grey60", data$alpha)
  data$alpha <- 1

  grobTree(
    if (isTRUE(params$se)) rectGrob(gp = gpar(col = NA, fill = data$fill)),
    draw_key_path(data, params)
  )
}

#' @export
#' @rdname draw_key
draw_key_text <- function(data, params, size) {
  if(is.null(data$label)) data$label <- "a"

  textGrob(data$label, 0.5, 0.5,
    rot = data$angle %||% 0,
    gp = gpar(
      col = alpha(data$colour %||% data$fill %||% "black", data$alpha),
      fontfamily = data$family %||% "",
      fontface = data$fontface %||% 1,
      fontsize = (data$size %||% 3.88) * .pt
    )
  )
}

#' @export
#' @rdname draw_key
draw_key_label <- function(data, params, size) {
  grobTree(
    draw_key_rect(data, list()),
    draw_key_text(data, list())
  )
}

#' @export
#' @rdname draw_key
draw_key_vline <- function(data, params, size) {
  segmentsGrob(0.5, 0, 0.5, 1,
    gp = gpar(
      col = alpha(data$colour %||% data$fill %||% "black", data$alpha),
      lwd = (data$size %||% 0.5) * .pt,
      lty = data$linetype %||% 1,
      lineend = "butt"
    )
  )
}

#' @export
#' @rdname draw_key
draw_key_timeseries <- function(data, params, size) {
  if (is.null(data$linetype)) {
    data$linetype <- 0
  } else {
    data$linetype[is.na(data$linetype)] <- 0
  }

  grid::linesGrob(
    x = c(0, 0.4, 0.6, 1),
    y = c(0.1, 0.6, 0.4, 0.9),
    gp = gpar(
      col = alpha(data$colour %||% data$fill %||% "black", data$alpha),
      lwd = (data$size %||% 0.5) * .pt,
      lty = data$linetype %||% 1,
      lineend = "butt"
    )
  )
}