#' Split REDCap repeating instruments table into multiple tables
#'
#' This will take output from a REDCap export and split it into a base table
#' and child tables for each repeating instrument. Metadata
#' is used to determine which fields should be included in each resultant table.
#'
#' @param records Exported project records. May be a \code{data.frame},
#'   \code{response}, or \code{character} vector containing JSON from an API
#'   call.
#' @param metadata Project metadata (the data dictionary). May be a
#'   \code{data.frame}, \code{response}, or \code{character} vector containing
#'   JSON from an API call.
#' @param primary_table_name Name given to the list element for the primary
#'   output table (as described in \emph{README.md}). Ignored if
#'   \code{forms = 'all'}.
#' @param forms Indicate whether to create separate tables for repeating
#'   instruments only or for all forms.
#' @author Paul W. Egeler, M.S., GStat
#' @examples
#' \dontrun{
#' # Using an API call -------------------------------------------------------
#'
#' library(RCurl)
#'
#' # Get the records
#' records <- postForm(
#'   uri = api_url,     # Supply your site-specific URI
#'   token = api_token, # Supply your own API token
#'   content = 'record',
#'   format = 'json',
#'   returnFormat = 'json'
#' )
#'
#' # Get the metadata
#' metadata <- postForm(
#'   uri = api_url,     # Supply your site-specific URI
#'   token = api_token, # Supply your own API token
#'   content = 'metadata',
#'   format = 'json'
#' )
#'
#' # Convert exported JSON strings into a list of data.frames
#' REDCapRITS::REDCap_split(records, metadata)
#'
#' # Using a raw data export -------------------------------------------------
#'
#' # Get the records
#' records <- read.csv("/path/to/data/ExampleProject_DATA_2018-06-03_1700.csv")
#'
#' # Get the metadata
#' metadata <- read.csv(
#' "/path/to/data/ExampleProject_DataDictionary_2018-06-03.csv")
#'
#' # Split the tables
#' REDCapRITS::REDCap_split(records, metadata)
#'
#' # In conjunction with the R export script ---------------------------------
#'
#' # You must set the working directory first since the REDCap data export
#' # script contains relative file references.
#' setwd("/path/to/data/")
#'
#' # Run the data export script supplied by REDCap.
#' # This will create a data.frame of your records called 'data'
#' source("ExampleProject_R_2018-06-03_1700.r")
#'
#' # Get the metadata
#' metadata <- read.csv("ExampleProject_DataDictionary_2018-06-03.csv")
#'
#' # Split the tables
#' REDCapRITS::REDCap_split(data, metadata)
#' }
#' @return A list of \code{"data.frame"}s. The number of tables will differ
#'   depending on the \code{forms} option selected.
#'   \itemize{
#'     \item \code{'repeating'}: one base table and one or more
#'     tables for each repeating instrument.
#'     \item \code{'all'}: a data.frame for each instrument, regardless of
#'     whether it is a repeating instrument or not.
#'   }
#' @include process_user_input.r utils.r
#' @export
REDCap_split <- function(records,
                         metadata,
                         primary_table_name = "",
                         forms = c("repeating", "all")) {

  # Process user input
  records  <- process_user_input(records)
  metadata <-
    as.data.frame(process_user_input(metadata)) # See issue #12

  # Get the variable names in the dataset
  vars_in_data <- names(records)

  # Match arg for forms
  forms <- match.arg(forms)

  # Check to see if there were any repeating instruments
  if (forms == "repeating" &&
      !"redcap_repeat_instrument" %in% vars_in_data) {
    stop("There are no repeating instruments in this dataset.")
  }

  # Remove NAs from `redcap_repeat_instrument` (see issue #12)
  if (any(is.na(records$redcap_repeat_instrument))) {
    records$redcap_repeat_instrument <- ifelse(
      is.na(records$redcap_repeat_instrument),
      "",
      as.character(records$redcap_repeat_instrument)
    )
  }

  # Standardize variable names for metadata
  # names(metadata) <- metadata_names

  # Make sure that no metadata columns are factors
  metadata <-
    rapply(metadata, as.character, classes = "factor", how = "replace")

  # Find the fields and associated form
  fields <- match_fields_to_form(metadata, vars_in_data)

  # Variables to be present in each output table
  universal_fields <- c(
    vars_in_data[1],
    grep(
      "^redcap_(?!(repeat)).*",
      vars_in_data,
      value = TRUE,
      perl = TRUE
    )
  )

  if ("redcap_repeat_instrument" %in% vars_in_data) {
    # Variables to be at the beginning of each repeating instrument
    repeat_instrument_fields <- grep("^redcap_repeat.*",
                                     vars_in_data,
                                     value = TRUE)

    # Identify the subtables in the data
    subtables <- unique(records$redcap_repeat_instrument)
    subtables <- subtables[subtables != ""]

    # Split the table based on instrument
    out <-
      split.data.frame(records, records$redcap_repeat_instrument)
    primary_table_index <- which(names(out) == "")

    if (forms == "repeating" && primary_table_name %in% subtables) {
      warning(
        "The label given to the primary table is already used by a repeating
        instrument. The primary table label will be left blank."
      )
      primary_table_name <- ""
    } else if (primary_table_name > "") {
      names(out)[[primary_table_index]] <- primary_table_name
    }

    # Delete the variables that are not relevant
    for (i in names(out)) {
      if (i == primary_table_name) {
        out_fields <- which(vars_in_data %in% c(universal_fields,
                                                fields[!fields[, 2] %in%
                                                         subtables, 1]))
        out[[primary_table_index]] <-
          out[[primary_table_index]][out_fields]

      } else {
        out_fields <- which(vars_in_data %in% c(universal_fields,
                                                repeat_instrument_fields,
                                                fields[fields[, 2] == i, 1]))
        out[[i]] <- out[[i]][out_fields]

      }

    }

    if (forms == "all") {
      out <- c(split_non_repeating_forms(out[[primary_table_index]],
                                         universal_fields,
                                         fields[!fields[, 2] %in% subtables, ]),
               out[-primary_table_index])

    }

  } else {
    out <- split_non_repeating_forms(records, universal_fields, fields)

  }

  out

}