library(sf)
library(dplyr)
library(osmextract)

setwd("")

# ------- Inputs (files expected in your working directory) -------
# Regional .osm.pbf files you have on disk:
pbf_files <- c(
  "us-midwest-latest.osm.pbf",
  "us-south-latest.osm.pbf",
  "us-west-latest.osm.pbf",
  "us-northeast-latest.osm.pbf"
)

# Name each region (used for output layer names)
region_names <- c("Midwest", "South", "West", "Northeast")
stopifnot(length(pbf_files) == length(region_names))

# Highway classes to keep (fixed 'tertiary' typo)
wanted_hw <- c("residential","motorway","trunk","primary",
               "secondary","tertiary","unclassified","living_street")

# SQL WHERE clause for oe_read (quote strings for SQL IN)
in_list <- paste0("('", paste(wanted_hw, collapse = "', '"), "')")
sql <- paste(
  "SELECT geometry, highway FROM 'lines'",
  "WHERE highway IN", in_list
)

# ------- Process each region -------
intersection_list <- vector("list", length(pbf_files))

for (i in seq_along(pbf_files)) {
  pbf <- pbf_files[i]
  reg <- region_names[i]
  message("Reading roads for: ", reg)
  
  # Read filtered road lines from OSM PBF
  roads <- oe_read(pbf, query = sql)
  
  # Persist regional roads to a GeoPackage (one layer per region)
  st_write(roads, "OSM_roads.gpkg",
           layer = paste0(reg, "_roads"),
           delete_layer = TRUE,
           quiet = TRUE)
  
  # Convert linework to vertices and keep only duplicated nodes (intersections)
  intersections <- roads |>
    st_cast("MULTIPOINT") |>
    st_cast("POINT")
  
  # Duplicated compares geometry column; TRUE = appears more than once
  intersections <- intersections[duplicated(intersections$geometry), ]
  
  intersection_list[[i]] <- intersections
  
  rm(roads, intersections); gc()
}

# ------- Combine and write out -------
Intersections <- do.call(rbind, intersection_list)

# Shapefile output to match your original; consider .gpkg for fewer limits
st_write(Intersections, "Intersections.shp",
         driver = "ESRI Shapefile",
         delete_layer = TRUE,
         quiet = TRUE)