col_exists.R

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#  This file is part of the 'rstudio/pointblank' project.
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#  Copyright (c) 2017-2024 pointblank authors
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#  For full copyright and license information, please look at
#  https://rstudio.github.io/pointblank/LICENSE.html
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#' Do one or more columns actually exist?
#'
#' @description
#' 
#' The `col_exists()` validation function, the `expect_col_exists()` expectation
#' function, and the `test_col_exists()` test function all check whether one or
#' more columns exist in the target table. The only requirement is specification
#' of the column names. The validation function can be used directly on a data
#' table or with an *agent* object (technically, a `ptblank_agent` object)
#' whereas the expectation and test functions can only be used with a data
#' table. Each validation step or expectation will operate over a single test
#' unit, which is whether the column exists or not.
#' 
#' @inheritParams col_vals_gt
#' 
#' @return For the validation function, the return value is either a
#'   `ptblank_agent` object or a table object (depending on whether an agent
#'   object or a table was passed to `x`). The expectation function invisibly
#'   returns its input but, in the context of testing data, the function is
#'   called primarily for its potential side-effects (e.g., signaling failure).
#'   The test function returns a logical value.
#' 
#' @section Supported Input Tables:
#' 
#' The types of data tables that are officially supported are:
#' 
#'  - data frames (`data.frame`) and tibbles (`tbl_df`)
#'  - Spark DataFrames (`tbl_spark`)
#'  - the following database tables (`tbl_dbi`):
#'    - *PostgreSQL* tables (using the `RPostgres::Postgres()` as driver)
#'    - *MySQL* tables (with `RMySQL::MySQL()`)
#'    - *Microsoft SQL Server* tables (via **odbc**)
#'    - *BigQuery* tables (using `bigrquery::bigquery()`)
#'    - *DuckDB* tables (through `duckdb::duckdb()`)
#'    - *SQLite* (with `RSQLite::SQLite()`)
#'    
#' Other database tables may work to varying degrees but they haven't been
#' formally tested (so be mindful of this when using unsupported backends with
#' **pointblank**).
#'
#' @section Column Names:
#' 
#' `columns` may be a single column (as symbol `a` or string `"a"`) or a vector
#' of columns (`c(a, b, c)` or `c("a", "b", "c")`). `{tidyselect}` helpers
#' are also supported, such as `contains("date")` and `where(is.double)`. If
#' passing an *external vector* of columns, it should be wrapped in `all_of()`.
#' 
#' When multiple columns are selected by `columns`, the result will be an
#' expansion of validation steps to that number of columns (e.g.,
#' `c(col_a, col_b)` will result in the entry of two validation steps).
#' 
#' Previously, columns could be specified in `vars()`. This continues to work, 
#' but `c()` offers the same capability and supersedes `vars()` in `columns`.
#'
#' @section Actions:
#' 
#' Often, we will want to specify `actions` for the validation. This argument,
#' present in every validation function, takes a specially-crafted list object
#' that is best produced by the [action_levels()] function. Read that function's
#' documentation for the lowdown on how to create reactions to above-threshold
#' failure levels in validation. The basic gist is that you'll want at least a
#' single threshold level (specified as either the fraction of test units
#' failed, or, an absolute value), often using the `warn_at` argument. Using
#' `action_levels(warn_at = 1)` or `action_levels(stop_at = 1)` are good choices
#' depending on the situation (the first produces a warning, the other
#' `stop()`s).
#'
#' @section Labels:
#' 
#' `label` may be a single string or a character vector that matches the number
#' of expanded steps. `label` also supports `{glue}` syntax and exposes the
#' following dynamic variables contextualized to the current step:
#'   
#' - `"{.step}"`: The validation step name
#' - `"{.col}"`: The current column name
#'     
#' The glue context also supports ordinary expressions for further flexibility
#' (e.g., `"{toupper(.step)}"`) as long as they return a length-1 string.
#' 
#' @section Briefs:
#' 
#' Want to describe this validation step in some detail? Keep in mind that this
#' is only useful if `x` is an *agent*. If that's the case, `brief` the agent
#' with some text that fits. Don't worry if you don't want to do it. The
#' *autobrief* protocol is kicked in when `brief = NULL` and a simple brief will
#' then be automatically generated.
#' 
#' @section YAML:
#' 
#' A **pointblank** agent can be written to YAML with [yaml_write()] and the
#' resulting YAML can be used to regenerate an agent (with [yaml_read_agent()])
#' or interrogate the target table (via [yaml_agent_interrogate()]). When
#' `col_exists()` is represented in YAML (under the top-level `steps` key as a
#' list member), the syntax closely follows the signature of the validation
#' function. Here is an example of how a complex call of `col_exists()` as a
#' validation step is expressed in R code and in the corresponding YAML
#' representation.
#' 
#' R statement:
#' 
#' ```r
#' agent %>% 
#'   col_exists(
#'     columns = a,
#'     actions = action_levels(warn_at = 0.1, stop_at = 0.2),
#'     label = "The `col_exists()` step.",
#'     active = FALSE
#'   )
#' ```
#' 
#' YAML representation:
#' 
#' ```yaml
#' steps:
#' - col_exists:
#'     columns: c(a)
#'     actions:
#'       warn_fraction: 0.1
#'       stop_fraction: 0.2
#'     label: The `col_exists()` step.
#'     active: false
#' ```
#' 
#' In practice, both of these will often be shorter as only the `columns`
#' argument requires a value. Arguments with default values won't be written to
#' YAML when using [yaml_write()] (though it is acceptable to include them with
#' their default when generating the YAML by other means). It is also possible
#' to preview the transformation of an agent to YAML without any writing to disk
#' by using the [yaml_agent_string()] function.
#'   
#' @section Examples:
#' 
#' For all examples here, we'll use a simple table with two columns: `a` and
#' `b`.
#' 
#' ```{r}
#' tbl <-
#'   dplyr::tibble(
#'     a = c(5, 7, 6, 5, 8, 7),
#'     b = c(7, 1, 0, 0, 0, 3)
#'   )
#'   
#' tbl
#' ```
#' 
#' We'll use this table with the different function variants.
#' 
#' ## A: Using an `agent` with validation functions and then `interrogate()`
#' 
#' Validate that column `a` exists in the `tbl` table with `col_exists()`.
#' 
#' ```r
#' agent <-
#'   create_agent(tbl = tbl) %>%
#'   col_exists(columns = a) %>%
#'   interrogate()
#' ```
#' 
#' Printing the `agent` in the console shows the validation report in the
#' Viewer. Here is an excerpt of validation report, showing the single entry
#' that corresponds to the validation step demonstrated here.
#' 
#' \if{html}{
#' \out{
#' `r pb_get_image_tag(file = "man_col_exists_1.png")`
#' }
#' }
#' 
#' ## B: Using the validation function directly on the data (no `agent`)
#' 
#' This way of using validation functions acts as a data filter. Data is
#' passed through but should `stop()` if there is a single test unit failing.
#' The behavior of side effects can be customized with the `actions` option.
#' 
#' ```{r}
#' tbl %>% col_exists(columns = a)
#' ```
#' 
#' ## C: Using the expectation function
#' 
#' With the `expect_*()` form, we would typically perform one validation at a
#' time. This is primarily used in **testthat** tests.
#' 
#' ```r
#' expect_col_exists(tbl, columns = a)
#' ```
#' 
#' ## D: Using the test function
#' 
#' With the `test_*()` form, we should get a single logical value returned to
#' us.
#' 
#' ```{r}
#' tbl %>% test_col_exists(columns = a)
#' ```
#' 
#' @family validation functions
#' @section Function ID:
#' 2-29
#' 
#' @name col_exists
NULL

#' @rdname col_exists
#' @import rlang
#' @export
col_exists <- function(
    x,
    columns = NULL,
    actions = NULL,
    step_id = NULL,
    label = NULL,
    brief = NULL,
    active = TRUE
) {

  preconditions <- NULL
  values <- NULL
  
  # Capture the `columns` expression
  columns <- rlang::enquo(columns)
  # Get `columns` as a label
  columns_expr <- as_columns_expr(columns)
  
  # Resolve the columns based on the expression
  ## Only for `col_exists()`: error gracefully if column not found
  columns <- tryCatch(
    expr = resolve_columns(x = x, var_expr = columns, preconditions = NULL,
                           allow_empty = FALSE),
    error = function(cnd) cnd$i %||% cnd
  )
  ## Missing column selection
  if (rlang::is_error(columns)) {
    cnd <- columns
    if (inherits(cnd, "resolve_eval_err")) {
      # Evaluation errors should be rethrown
      rlang::cnd_signal(cnd)
    }
    columns <- NA_character_
  }

  if (is_a_table_object(x)) {
    
    secret_agent <- 
      create_agent(x, label = "::QUIET::") %>%
      col_exists(
        columns = tidyselect::all_of(columns),
        actions = prime_actions(actions),
        label = label,
        brief = brief,
        active = active
      ) %>% 
      interrogate()
    
    return(x)
  }
  
  agent <- x

  if (is.null(brief)) {
    brief <- 
      generate_autobriefs(agent, columns, preconditions, values, "col_exists")
  }
  
  # Normalize any provided `step_id` value(s)
  step_id <- normalize_step_id(step_id, columns, agent)
  
  # Get the next step number for the `validation_set` tibble
  i_o <- get_next_validation_set_row(agent)
  
  # Check `step_id` value(s) against all other `step_id`
  # values in earlier validation steps
  check_step_id_duplicates(step_id, agent)
  
  # Add one or more validation steps based on the
  # length of the `columns` variable
  label <- resolve_label(label, columns)
  for (i in seq_along(columns)) {
    
    agent <-
      create_validation_step(
        agent = agent,
        assertion_type = "col_exists",
        i_o = i_o,
        columns_expr = columns_expr,
        column = columns[i],
        preconditions = NULL,
        actions = covert_actions(actions, agent),
        step_id = step_id[i],
        label = label[[i]],
        brief = brief[i],
        active = active
      )
  }

  agent
}

#' @rdname col_exists
#' @import rlang
#' @export
expect_col_exists <- function(
    object,
    columns,
    threshold = 1
) {

  fn_name <- "expect_col_exists"
  
  vs <- 
    create_agent(tbl = object, label = "::QUIET::") %>%
    col_exists(
      columns = {{ columns }},
      actions = action_levels(notify_at = threshold)
    ) %>%
    interrogate() %>%
    .$validation_set
  
  x <- vs$notify
  
  threshold_type <- get_threshold_type(threshold = threshold)
  
  if (threshold_type == "proportional") {
    failed_amount <- vs$f_failed
  } else {
    failed_amount <- vs$n_failed
  }
  
  # If several validations were performed serially (due to supplying
  # multiple columns)
  if (length(x) > 1 && any(x)) {
    
    # Get the index (step) of the first failure instance
    fail_idx <- which(x)[1]
    
    # Get the correct, single `failed_amount` for the first
    # failure instance
    failed_amount <- failed_amount[fail_idx]
    
    # Redefine `x` as a single TRUE value
    x <- TRUE
    
  } else {
    x <- any(x)
    fail_idx <- 1
  }
  
  if (inherits(vs$capture_stack[[1]]$warning, "simpleWarning")) {
    warning(conditionMessage(vs$capture_stack[[1]]$warning))
  }
  if (inherits(vs$capture_stack[[1]]$error, "simpleError")) {
    stop(conditionMessage(vs$capture_stack[[1]]$error))
  }
  
  act <- testthat::quasi_label(enquo(x), arg = "object")
  
  column_text <- prep_column_text(vs$column[[fail_idx]])
  
  testthat::expect(
    ok = identical(!as.vector(act$val), TRUE),
    failure_message = glue::glue(
      failure_message_gluestring(fn_name = fn_name, lang = "en")
    )
  )
  
  act$val <- object
  
  invisible(act$val)
}

#' @rdname col_exists
#' @import rlang
#' @export
test_col_exists <- function(
    object,
    columns,
    threshold = 1
) {
  
  vs <- 
    create_agent(tbl = object, label = "::QUIET::") %>%
    col_exists(
      columns = {{ columns }},
      actions = action_levels(notify_at = threshold)
    ) %>%
    interrogate() %>%
    .$validation_set

  if (inherits(vs$capture_stack[[1]]$warning, "simpleWarning")) {
    warning(conditionMessage(vs$capture_stack[[1]]$warning))
  }
  if (inherits(vs$capture_stack[[1]]$error, "simpleError")) {
    stop(conditionMessage(vs$capture_stack[[1]]$error))
  }

  all(!vs$notify)
}