#!/usr/bin/env Rscript

`%||%` <- function(lhs, rhs) {
  if (is.null(lhs) || is.na(lhs)) rhs else lhs
}

suppressPackageStartupMessages({
  library(jsonlite)
  library(readr)
})

args <- commandArgs(trailingOnly = TRUE)

if (length(args) < 2) {
  stop("Expected arguments: <data_file_path> <params_json>")
}

data_file_path <- args[1]
params_json <- args[2]

if (!file.exists(data_file_path)) {
  stop(sprintf("Data file not found at %s", data_file_path))
}

params <- tryCatch(
  fromJSON(params_json),
  error = function(e) list()
)

target_column <- params$column
if (is.null(target_column) || target_column == "") {
  stop("Parameter 'column' is required for category_frequency.R")
}

top_n <- as.integer(params$top_n %||% 10)
include_missing <- isTRUE(params$include_missing)

data <- tryCatch(
  read_csv(
    file = data_file_path,
    show_col_types = FALSE,
    progress = FALSE,
    locale = locale(encoding = params$encoding %||% "UTF-8")
  ),
  error = function(e) stop(sprintf("Failed to read CSV: %s", e$message))
)

if (!target_column %in% names(data)) {
  stop(sprintf("Column '%s' not found in dataset", target_column))
}

column_vector <- data[[target_column]]

if (!include_missing) {
  column_vector <- column_vector[!is.na(column_vector)]
}

frequency_table <- sort(table(column_vector, useNA = if (include_missing) "always" else "no"), decreasing = TRUE)

freq_df <- head(as.data.frame(frequency_table, stringsAsFactors = FALSE), top_n)
names(freq_df) <- c("value", "count")

output <- list(
  message = sprintf("Top %s frequency distribution for '%s'.", top_n, target_column),
  analyzed_column = target_column,
  top_n = top_n,
  include_missing = include_missing,
  frequencies = freq_df
)

cat(
  toJSON(
    output,
    pretty = TRUE,
    auto_unbox = TRUE,
    na = "null",
    dataframe = "rows"
  )
)