feat: cog_balances() core verb (#25)

R/balances.R

@@ -0,0 +1,98 @@
+# R/balances.R
+#
+# Cash and security holdings. A third verb rather than an argument on a money
+# verb because holdings are a STOCK -- a balance at a point in time -- while
+# cog_spending()/cog_revenue() return FLOWS over a fiscal year. The money
+# verbs' whole argument vocabulary (expenditure_concept, revenue_concept,
+# complete=) describes flows and is meaningless here, so this deliberately
+# does NOT route through .verb_spendrev().
+
+#' Cash and security holdings for one or more governments
+#'
+#' Returns Census cash-and-security holdings (`category_type = "balance"`):
+#' fund balances, retirement system holdings and insurance trust balances.
+#'
+#' @section Holdings are not GAAP fund balance:
+#' Census holdings are **gross** -- no liabilities are netted -- so a reserve
+#' ratio built from them overstates what is actually available. They are not
+#' comparable to a GAAP fund balance from an ACFR.
+#'
+#' @param govid Canonical govid(s): a character vector, or a data frame with a
+#'   `canonical_govid` column (e.g. from [cog_gov_search()]).
+#' @param years Integer vector of fiscal years.
+#' @param category Optional character vector of categories to keep. One of
+#'   `"Fund Balances"`, `"Insurance Trust Balances"`,
+#'   `"Retirement System Holdings"`. There is deliberately no `subtype`
+#'   argument: for holdings, `category` is a strict coarsening of
+#'   `balance_subtype` (unlike the money verbs, where the two axes cross), so
+#'   every combination would be either redundant or empty.
+#'   `category = "Fund Balances"` is exactly the `general` family
+#'   (`W01`/`W31`/`W61`). `balance_subtype` is returned, so a finer split is
+#'   one `dplyr::filter()` away.
+#' @param per_capita Divide holdings by population. Note this is a **stock per
+#'   resident** (reserves per person), which is *not* comparable to
+#'   [cog_spending()]'s per-capita figures -- those are a flow per person.
+#' @param adjust_to_year Deflate to this year's dollars (CPI-U).
+#' @param basis Accepted for uniformity with the money verbs, but currently a
+#'   **no-op**: `harmonization_map` carries no balance-code rows, so harmonized
+#'   and raw space are identical for holdings. Reported in
+#'   `provenance$basis_note`.
+#' @param recipe Optional harmonization recipe id (see [cog_recipes()]).
+#'   `"cash_securities_z77_wide"` and `"cash_securities_z78_wide"` bridge the
+#'   wide era to the modern one.
+#'
+#' @return A `tbl_df` with a `provenance` attribute. Amounts are full US
+#'   dollars.
+#' @export
+cog_balances <- function(govid, years, category = NULL,
+                         per_capita = FALSE, adjust_to_year = NULL,
+                         basis = c("harmonized", "raw"), recipe = NULL) {
+  call <- match.call()
+  basis <- match.arg(basis, c("harmonized", "raw"))
+  govid <- .coerce_govid_input(govid)
+  years <- as.integer(years)
+  if (!is.null(adjust_to_year)) adjust_to_year <- as.integer(adjust_to_year)
+
+  con <- .ensure_session()
+  .require_balance_support(con)
+  .check_govids_in_scope(govid)
+
+  basis_note <- paste0(
+    "`basis` has no effect on holdings: harmonization_map carries no ",
+    "balance-code rows, so harmonized and raw space are identical here."
+  )
+
+  sql <- .build_verb_sql("balance_annotated", "balance_subtype",
+                         govid, years, category,
+                         ig_view = NULL, subtype_scope = NULL)
+  result <- tibble::as_tibble(DBI::dbGetQuery(con, sql))
+
+  prov <- .build_provenance(
+    verb = "cog_balances", call = call, govid = govid, years = years,
+    category = category, per_capita = per_capita,
+    adjust_to_year = adjust_to_year, result = result, sql = sql,
+    subtype_col = "balance_subtype",
+    basis = basis, basis_note = basis_note,
+    # Neither concept vocabulary applies to a stock.
+    expenditure_concept = NA_character_,
+    revenue_concept = NA_character_
+  )
+
+  attr(result, "provenance") <- prov
+  result
+}
+
+#' Abort unless the mounted corpus classifies balance codes.
+#'
+#' `balance_subtype` arrived with cog_pipeline #76/#77 without a
+#' schema_version bump, so the check is on the column, not the version.
+#' @noRd
+.require_balance_support <- function(con) {
+  if (.corpus_has_balance_subtype(con)) return(invisible(TRUE))
+  cli::cli_abort(
+    c("This corpus does not classify cash and security holdings.",
+      i = "`summary_categories` has no {.field balance_subtype} column.",
+      i = "Republish from cog_pipeline at #76/#77 or later."),
+    class = "uscogdata_no_balance_support"
+  )
+}