library(sf)
library(tidyverse)

## Draft function

#' Function to assign EAA grid to a df of points
#'
#' @param df A data.frame containing two columns with latitude and longitude.
#' @param lat Character. Name of column in \code{df} containing latitude.
#' @param lon Character. Name of column in \code{df} containing longitude.
#' @param crs A Coordinate Reference System. Default: 4326 (wgs84).
#' @param scale Scale of the EAA grid in meters. Default: 1000.
eaa_grid <- function(df, lat, long, crs = 4326, scale = 1000){
  df %>%
    st_as_sf(coords = c(long, lat),
           crs = crs) %>%
    # transform to Lambert
    st_transform(3035) %>%
    # extract coordinates: X, Y
    st_coordinates() %>%
    # transform to df
    as_data_frame() %>%
    # add cell ID
    mutate(cell_id = paste0("1kmE", floor(X/scale), "N", floor(Y/scale))) %>%
    # remove ancillary columns
    select(-X, -Y) %>%
    # add original columns (decimalLatitude, decimalLongitude)
    bind_cols(df)
}

df_test <-
  tibble::tibble(
    decimalLatitude = c(51.333, 51.232, 50.8, 50.543, 51.032),
    decimalLongitude = c(3.112, 3.420, 4.410, 4.891, 4.435)
  )

df_test <- df_test %>%
  eaa_grid(lat = "decimalLatitude", long = "decimalLongitude")

df_test