making map inset with ggplot

gginset.R

library(sf)
library(tidyverse)
library(patchwork)
nc = st_read(system.file("shape/nc.shp", package="sf"))
box <- nc %>% st_bbox()
minify_box <- function(bbox, ratio = 0.5){
  if(class(bbox) != "bbox"){
    stop("bbox must be a bbox object")
  }
  if(class(ratio) != "numeric" ){
    stop("ratio must be numeric")
  }
  if(!(ratio > 0 & ratio < 1)){
    stop("ratio must be between 0 and 1")
  }
  xrange = bbox[["xmax"]] - bbox[["xmin"]]
  yrange = bbox[["ymax"]] - bbox[["ymin"]]
  xportion = xrange*ratio
  yportion = yrange*ratio
  xoffset = (xrange - xportion)/2
  yoffset = (yrange - yportion)/2
  xmin = bbox[["xmin"]] + xoffset
  xmax = bbox[["xmin"]] + xrange - xoffset
  ymin = bbox[["ymin"]] + yoffset
  ymax = bbox[["ymin"]] + yrange - yoffset
  bbox[["xmin"]] = xmin
  bbox[["xmax"]] = xmax
  bbox[["ymin"]] = ymin
  bbox[["ymax"]] = ymax
  return(bbox)
}

minified_box <- minify_box(box,.1) %>% st_as_sfc()
p <- ggplot(nc) +
  geom_sf()
pyrange = layer_scales(p)$y$range$range
yexpand = diff(pyrange) * 0.05
pxrange = layer_scales(p)$x$range$range
xexpand = diff(pxrange) * 0.05
bbox <- minified_box %>% st_bbox()
p1 <- p +
  geom_sf(data = minified_box,fill = NA,color = "red") + 
  geom_segment(aes(x = bbox[["xmax"]],y = bbox[["ymin"]],xend = pxrange[2]+xexpand,yend = pyrange[1]-yexpand),color = "red") +
  geom_segment(aes(x = bbox[["xmax"]],y = bbox[["ymax"]],xend = pxrange[2]+xexpand,yend = pyrange[2]+yexpand),color = "red") +
  theme(plot.margin = margin(0,0,0,0)) + 
  coord_sf(xlim = pxrange,ylim = pyrange)
p2 <- p + 
  coord_sf(xlim = c(bbox[["xmin"]],bbox[["xmax"]]),ylim = c(bbox[["ymin"]],bbox[["ymax"]]),,label_graticule  = "SE") + 
  theme(panel.border = element_rect(colour = "red", fill=NA, size=1),plot.margin = margin(0,0,0,0))
p1+p2