#!/usr/bin/env Rscript

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

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

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()
)

read_opts <- list(
  locale = locale(encoding = params$encoding %||% "UTF-8")
)

data <- tryCatch(
  read_csv(
    file = data_file_path,
    show_col_types = FALSE,
    progress = FALSE,
    guess_max = params$guess_max %||% 1000,
    locale = read_opts$locale
  ),
  error = function(e) stop(sprintf("Failed to read CSV: %s", e$message))
)

numeric_columns <- select(data, where(is.numeric))

column_stats <- lapply(numeric_columns, function(column) {
  list(
    count = sum(!is.na(column)),
    mean = mean(column, na.rm = TRUE),
    median = median(column, na.rm = TRUE),
    sd = sd(column, na.rm = TRUE),
    min = min(column, na.rm = TRUE),
    max = max(column, na.rm = TRUE),
    missing = sum(is.na(column))
  )
})

message_text <- if (length(column_stats) > 0) {
  "Descriptive statistics generated successfully."
} else {
  "No numeric columns detected; returning dataset preview only."
}

preview_rows <- head(data, n = min(5, nrow(data)))

output <- list(
  message = message_text,
  numeric_columns = column_stats,
  sample_rows = preview_rows,
  params = params
)

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