Validate chart_type early and improve the error message

R/argument_validation.R

@@ -0,0 +1,61 @@
+
+#' Validate chart_type argument
+#'
+#' Checks that `chart_type` is a single, non-NULL character string corresponding
+#' to a supported SPC chart type. Intended for internal use only.
+#'
+#' @param chart_type Character scalar specifying chart type.
+#'
+#' @return Invisibly returns TRUE if valid; otherwise errors.
+#'
+#' @keywords internal
+#' @noRd
+
+
+validate_chart_type <- function(chart_type) {
+
+  allowed_chart_types <- c("XMR", "MR", "C", "C'", "P", "P'")
+
+  # NULL check
+  if (is.null(chart_type)) {
+    stop(
+      "chart_type must be provided. Available chart types are: ",
+      paste(allowed_chart_types, collapse = ", "),
+      ".",
+      call. = FALSE
+    )
+  }
+
+  # Length check
+  if (length(chart_type) != 1) {
+    stop(
+      "chart_type must be a single value. ",
+      "Available chart types are: ",
+      paste(allowed_chart_types, collapse = ", "),
+      ".",
+      call. = FALSE
+    )
+  }
+
+  # Type check (defensive)
+  if (!is.character(chart_type)) {
+    stop(
+      "chart_type must be a character string.",
+      call. = FALSE
+    )
+  }
+
+  # Value check
+  if (!chart_type %in% allowed_chart_types) {
+    stop(
+      sprintf(
+        "Invalid chart_type: '%s'. Available chart types are: %s.",
+        chart_type,
+        paste(allowed_chart_types, collapse = ", ")
+      ),
+      call. = FALSE
+    )
+  }
+
+  invisible(TRUE)
+}

R/autospc.R

@@ -28,8 +28,8 @@
 #'  }
 #' @param n Name of column (passed using tidyselect semantics) to use as
 #' denominator for P and P' charts.
-#' @param chart_type The type of chart you wish to plot. Available options are:
-#' "XMR", "MR", "C", "C'", "P", "P'".
+#' @param chart_type The type of chart you wish to plot.Must be a single value.
+#' Available options are: "XMR", "MR", "C", "C'", "P", "P'".
 #' 
 #' ## Algorithm Parameters
 #' Parameters that control behaviour of the algorithm used to re-establish
@@ -249,7 +249,8 @@ autospc <- function(data,
   upper_annotation_sf <- preprocessed_vars$upper_annotation_sf
   lower_annotation_sf <- preprocessed_vars$lower_annotation_sf
 
-
+  validate_chart_type(chart_type)
+
   # Get control limits
   data <- create_SPC_auto_limits_table(
     data,

tests/testthat/test-autospc-chart-type.R

@@ -0,0 +1,13 @@
+test_that("autospc errors informatively for invalid chart_type", {
+
+  expect_error(
+    autospc(
+      ed_attendances_monthly,
+      chart_type = "XmR'",
+      x = month_start,
+      y = att_all
+    ),
+    "Available chart types are"
+  )
+
+})