#' Interpolate Values
#'
#' @description This is the core function within the package for areal weighted
#'     interpolation. It validates both data sources before interpolating one or more
#'     listed values from the source data into the target data.
#'
#' @usage aw_interpolate(.data, tid, source, sid, weight = "sum", output = "sf", extensive,
#'     intensive)
#'
#' @details Areal weighted interpolation can be used for generating demographic
#'     estimates for overlapping but incongruent polygon features. It assumes that
#'     individual members of a population are evenly dispersed within the source features
#'     (an assumption not likely to hold in the real world). It also functions best
#'     when data are in a projected coordinate system, like the UTM coordinate system.
#'
#' @param .data A \code{sf} object that data should be interpolated to (this is referred
#'     to as the \code{target} elsewhere in the package).
#' @param tid A unique identification number within \code{target}
#' @param source A \code{sf} object with data to be interpolated
#' @param sid A unique identification number within \code{source}
#' @param weight For \code{"extensive"} interpolations, should be either \code{"total"} or
#'     \code{"sum"}. For \code{"intensive"} interpolations, should be \code{"sum"}. For mixed
#'     interpolations, this will only impact the calculation of the extensive variables.
#' @param output One of either \code{"sf"} or \code{"tibble"}
#' @param extensive A vector of quoted variable names to be treated as spatially extensive
#'     (e.g. population counts); optional if \code{intensive} is specified
#' @param intensive A vector of quoted variable names to be treated as spatially intensive
#'     (e.g. population density); optional if \code{extensive} is specified
#'
#' @return A \code{sf} object or a \code{tibble} with the value or values interpolated into
#'     the \code{target} data.
#'
#' @seealso \link{c}
#'
#' @examples
#' aw_interpolate(ar_stl_wards, tid = WARD, source = ar_stl_race, sid = GEOID, weight = "sum",
#'     output = "sf", extensive = "TOTAL_E")
#'
#' aw_interpolate(ar_stl_wards, tid = WARD, source = ar_stl_asthma, sid = GEOID, weight = "sum",
#'     output = "tibble", intensive = "ASTHMA")
#'
#' @importFrom dplyr as_tibble
#' @importFrom dplyr left_join
#' @importFrom dplyr rename
#' @importFrom dplyr select
#' @importFrom glue glue
#' @importFrom rlang enquo
#' @importFrom rlang quo
#' @importFrom rlang quo_name
#' @importFrom rlang sym
#' @importFrom sf st_geometry
#'
#' @export
aw_interpolate <- function(.data, tid, source, sid, weight = "sum", output = "sf", extensive, intensive){

  # save parameters to list
  paramList <- as.list(match.call())

  # check for missing parameters
  if (missing(.data)) {
    stop("A sf object containing target data must be specified for the '.data' argument.")
  }

  if (missing(tid)) {
    stop("A variable name must be specified for the 'tid' argument.")
  }

  if (missing(source)) {
    stop("A sf object must be specified for the 'source' argument.")
  }

  if (missing(sid)) {
    stop("A variable name must be specified for the 'sid' argument.")
  }

  # determine extensive and intensive
  if (missing(extensive) & missing(intensive)){
    stop("Either 'extensive' or 'intenstive' must be specified with an accompanying list of variables to interpolate.")
  }

  if (missing(intensive) & !missing(extensive)){
    type <- "extensive"
  } else if (!missing(intensive) & missing(extensive)){
    type <- "intensive"
  } else if (!missing(intensive) & !missing(extensive)){
    type <- "mixed"
  }

  # check for misspecified parameters
  if (weight %in% c("sum", "total") == FALSE){
    stop(glue::glue("The given weight type '{var}' is not valid. 'weight' must be either 'sum' or 'total'.",
                    var = weight))
  }

  if (type == "intensive" & weight == "total"){
    stop("Spatially intensive interpolations should be caclulated using 'sum' for 'weight'.")
  }

  if (output %in% c("sf", "tibble") == FALSE){
    stop(glue::glue("The given output type '{var}' is not valid. 'output' must be either 'sf' or 'tibble'.",
                    var = output))
  }

  # nse
  if (!is.character(paramList$sid)) {
    sidQ <- rlang::enquo(sid)
  } else if (is.character(paramList$sid)) {
    sidQ <- rlang::quo(!! rlang::sym(sid))
  }

  sidQN <- rlang::quo_name(rlang::enquo(sid))

  if (!is.character(paramList$tid)) {
    tidQ <- rlang::enquo(tid)
  } else if (is.character(paramList$tid)) {
    tidQ <- rlang::quo(!! rlang::sym(tid))
  }

  tidQN <- rlang::quo_name(rlang::enquo(tid))

  # check variables
  if(!!sidQN %in% colnames(source) == FALSE) {
    stop(glue::glue("Variable '{var}', given for the source ID ('sid'), cannot be found in the given source object.",
                    var = sidQN))
  }

  if(!!tidQN %in% colnames(.data) == FALSE) {
    stop(glue::glue("Variable '{var}', given for the target ID ('tid'), cannot be found in the given target object.",
                    var = tidQN))
  }

  # check for matching tid and sid variable names
  if (tidQN == sidQN){

    # store conflict indicator
    nameConflict <- TRUE

    # store original tid name for later
    tidOrig <- tidQN

    # rename tid to ...tid
    .data <- dplyr::rename(.data, ...tid = !!tidQN)
    tidQN <- "...tid"
    tidQ <- rlang::quo(!! rlang::sym(tidQN))

  } else {

    # store conflict indicator
    nameConflict <- FALSE

  }

  # create variable lists
  if (type == "extensive"){
    vars <- extensive
  } else if (type == "intensive"){
    vars <- intensive
  } else if (type == "mixed"){
    vars <- c(extensive, intensive)
  }

  # validate source and target data
  if (ar_validate(source = source, target = .data, varList = vars, method = "aw") == FALSE){
    stop("Data validation failed. Use ar_validate with verbose = TRUE to identify concerns.")
  }

  # call aw_interpolater
  if ((type == "extensive" | type == "intensive") & length(vars) == 1) {

    # nse
    valueQ <- rlang::quo(!! rlang::sym(vars))

    # interpolate
    data <- aw_interpolate_single(source = source, sid = !!sidQ, value = !!valueQ, target = .data,
                                 tid = !!tidQ, type = type, weight = weight)

  } else if ((type == "extensive" | type == "intensive") & length(vars) > 1) {

    # interpolate
    data <- aw_interpolate_multiple(source = source, sid = !!sidQ, values = vars, target = .data,
                                 tid = !!tidQ, type = type, weight = weight)

  } else if (type == "mixed"){

    # conduct spatially extensive interpolations
    if (length(extensive) == 1){

      # nse
      valueQ <- rlang::quo(!! rlang::sym(extensive))

      # interpolate
      exresults <- aw_interpolate_single(source = source, sid = !!sidQ, value = !!valueQ, target = .data,
                                   tid = !!tidQ, type = "extensive", weight = weight)

    } else if (length(extensive) > 1){

      # interpolate
      exresults <- aw_interpolate_multiple(source = source, sid = !!sidQ, values = extensive, target = .data,
                                      tid = !!tidQ, type = "extensive", weight = weight)

    }

    # conduct spatially intensive interpolations
    if (length(intensive) == 1){

      # nse
      valueQ <- rlang::quo(!! rlang::sym(intensive))

      # interpolate
      inresults <- aw_interpolate_single(source = source, sid = !!sidQ, value = !!valueQ, target = .data,
                                         tid = !!tidQ, type = "intensive", weight = "sum")

    } else if (length(intensive) > 1){

      # interpolate
      inresults <- aw_interpolate_multiple(source = source, sid = !!sidQ, values = intensive, target = .data,
                                           tid = !!tidQ, type = "intensive", weight = "sum")

    }

    # combine spatially extensive and intensive data
    data <- dplyr::left_join(exresults, inresults, by = tidQN)

  }

  # structure output
  if (output == "sf"){

    # left join with target data
    out <- dplyr::left_join(.data, data, by = tidQN)

  } else if (output == "tibble"){

    # left join with target data
    data <- dplyr::left_join(.data, data, by = tidQN)

    # remove geometry
    sf::st_geometry(data) <- NULL

    # convert to tibble
    out <- dplyr::as_tibble(data)

  }

  # rename tid
  if (nameConflict == TRUE){
    out <- dplyr::rename(out, !!tidOrig := !!tidQN)
  }

  # return output
  return(out)

}

# Intermediate Function - Single Value
#
# @description Intermediate function called when there is only one variable to be interpolated.
#     This is used to simplify the code for \code{aw_interpolate}.
#
# @param source A \code{sf} object with data to be interpolated
# @param sid A unique identification number within \code{source}
# @param value A column within \code{source} to be interpolated
# @param target A \code{sf} object that data should be interpolated to
# @param tid A unique identification number within \code{target}
# @param type One of either \code{"extensive"} (if the data are spatially extensive e.g.
#     population counts), \code{"intensive"} (if the data are spatially intensive e.g.
#     population density), or \code{"mixed"} (if the data include both extensive and
#     intensive values). If \code{"extensive"}, the sum is returned for the interpolated
#     value. If \code{"intensive"}, the mean is returned for the interpolated value.
#     If \code{"mixed"}, vectors named \code{"extensive"} and \code{"intensive"} containing
#     the relevant variable names should be specified in the dots.
# @param weight For \code{"extensive"} interpolations; should be either \code{"total"} or
#     \code{"sum"}.
#
# @return A tibble with interpolated data, ready for final merge with \code{target}.
#
aw_interpolate_single <- function(source, sid, value, target, tid, type, weight){

  # save parameters to list
  paramList <- as.list(match.call())

  # nse
  sidQ <- rlang::enquo(sid)
  sidQN <- rlang::quo_name(rlang::enquo(sidQ))

  valueQ <- rlang::enquo(value)
  valueQN <- rlang::quo_name(rlang::enquo(value))

  tidQ <- rlang::enquo(tid)
  tidQN <- rlang::quo_name(rlang::enquo(tidQ))

  # strip source and target dataframes
  sourceS <- aw_strip_df(source, id = sidQN, value = valueQN)
  targetS <- aw_strip_df(target, id = tidQN)

  # interpolate
  out <- aw_interpolater(source = sourceS, sid = !!sidQ, value = !!valueQ, target = targetS,
                         tid = !!tidQ, type = type, weight = weight)

  # return output
  return(out)

}

# Intermediate Function - Multiple Values (iteration)
#
# @description Intermediate function called when are more than one variables to be interpolated.
#     This is used to simplify the code for \code{aw_interpolate}.
#
# @param source A \code{sf} object with data to be interpolated
# @param sid A unique identification number within \code{source}
# @param values A vector of columns within \code{source} to be interpolated
# @param target A \code{sf} object that data should be interpolated to
# @param tid A unique identification number within \code{target}
# @param type One of either \code{"extensive"} (if the data are spatially extensive e.g.
#     population counts), \code{"intensive"} (if the data are spatially intensive e.g.
#     population density), or \code{"mixed"} (if the data include both extensive and
#     intensive values). If \code{"extensive"}, the sum is returned for the interpolated
#     value. If \code{"intensive"}, the mean is returned for the interpolated value.
#     If \code{"mixed"}, vectors named \code{"extensive"} and \code{"intensive"} containing
#     the relevant variable names should be specified in the dots.
# @param weight For \code{"extensive"} interpolations; should be either \code{"total"} or
#     \code{"sum"}.
#
# @importFrom dplyr %>%
# @importFrom dplyr bind_cols
# @importFrom dplyr one_of
# @importFrom dplyr select
# @importFrom purrr imap
# @importFrom purrr map
# @importFrom purrr reduce
# @importFrom rlang enquo
# @importFrom rlang quo_name
#
# @return A tibble with interpolated data, ready for final merge with \code{target}.
#
aw_interpolate_multiple <- function(source, sid, values, target, tid, type, weight){

  # save parameters to list
  paramList <- as.list(match.call())

  # nse
  sidQ <- rlang::enquo(sid)
  sidQN <- rlang::quo_name(rlang::enquo(sidQ))

  tidQ <- rlang::enquo(tid)
  tidQN <- rlang::quo_name(rlang::enquo(tidQ))

  # create column list
  colNames <- c(tidQN, values)

  # strip target dataframe
  targetS <- aw_strip_df(target, id = tidQN)

  # create list of sf objects
  values %>%
    split(values) %>%
    purrr::map(~ aw_strip_df(source, id = !!sidQ, value = .x)) %>%
    purrr::imap(~ aw_interpolater(source = .x, sid = !!sidQ, value = (!! rlang::quo(!! rlang::sym(.y))),
                                  target = targetS, tid = !!tidQ, type = type, weight = weight,
                                  multiple = TRUE)) %>%
    purrr::reduce(.f = dplyr::bind_cols) -> out

  # remove geometry
  sf::st_geometry(targetS) <- NULL

  # combine
  out <- dplyr::bind_cols(targetS, out)

  # return output
  return(out)

}

# Strip dataframe of all non-essential variables
#
# @description \code{aw_strip_df} is called by \code{aw_interpolate}. It
#     strips \code{sf} objects of nonessential variables but keeps
#     variables listed in parameters.
#
# @param .data A \code{sf} object
# @param id A given source id field
# @param value Optional; the variable that estimations will be based on
#
# @return A \code{sf} object with only the \code{id} and, if provided, the
#     \code{value} column as well.
#
aw_strip_df <- function(.data, id, value){

  # save parameters to list
  paramList <- as.list(match.call())

  # nse
  idQ <- rlang::enquo(id)

  # strip variables
  if (missing(value)){

    # strip all but id
    out <- dplyr::select(.data, !!idQ)

  } else {

    # additional nse for value
    valsQ <- rlang::enquo(value)

    # strip all but id and value
    out <- dplyr::select(.data, !!idQ, !!valsQ)

  }

  # return output
  return(out)

}

# Carry Out Interpolation
#
# @description \code{aw_interpolater} performs pipeline of interpolation specific
#     calculations with \code{aw_intersect}, \code{aw_total}, \code{aw_weight},
#     \code{aw_calculate}, and \code{aw_aggregate}. The interpolated total is then
#     verified against the total calculated from the source data using \code{aw_verify}.
#
# @param source A \code{sf} object with data to be interpolated
# @param sid A unique identification number within \code{source}
# @param value A column within \code{source} to be interpolated
# @param target A \code{sf} object that data should be interpolated to
# @param tid A unique identification number within \code{target}
# @param type One of either \code{"extensive"} (if the data are spatially extensive e.g.
#     population counts), \code{"intensive"} (if the data are spatially intensive e.g.
#     population density), or \code{"mixed"} (if the data include both extensive and
#     intensive values). If \code{"extensive"}, the sum is returned for the interpolated
#     value. If \code{"intensive"}, the mean is returned for the interpolated value.
#     If \code{"mixed"}, vectors named \code{"extensive"} and \code{"intensive"} containing
#     the relevant variable names should be specified in the dots.
# @param weight For \code{"extensive"} interpolations; should be either \code{"total"} or
#     \code{"sum"}.
#
# @return A \code{sf} object or tibble with \code{value} interpolated into
#    the \code{target} data.
#
aw_interpolater <- function(source, sid, value, target, tid, type, weight, multiple = FALSE) {

  # save parameters to list
  paramList <- as.list(match.call())

  # nse
  sidQ <- rlang::enquo(sid)

  valueQ <- rlang::enquo(value)
  valueQN <- rlang::quo_name(rlang::enquo(value))

  tidQ <- rlang::enquo(tid)

  # intersect data
  target %>%
    aw_intersect(source = source, areaVar = "...area") -> intersected

  # calculate total value for areal weight
  if (type == "extensive"){

    intersected %>%
      aw_total(source = source, id = !!sidQ, areaVar = "...area", totalVar = "...totalArea",
             type = "extensive", weight = weight) -> totaled

  } else if (type == "intensive"){

    intersected %>%
      aw_total(source = source, id = !!tidQ, areaVar = "...area", totalVar = "...totalArea",
             weight = weight, type = "intensive") -> totaled

  }

  # caclulate areal weight and estimated value; aggregate
  totaled %>%
    aw_weight(areaVar = "...area", totalVar = "...totalArea", areaWeight = "...areaWeight") %>%
    aw_calculate(value = !!valueQ, areaWeight = "...areaWeight") %>%
    aw_aggregate(target = target, tid = !!tidQ, interVar = !!valueQ) -> out

  # remove sf from output
  sf::st_geometry(out) <- NULL

  # fix multiples
  if (multiple == TRUE){
    out <- dplyr::select(out, !!valueQ)
  }

  # return target output
  return(out)

}