

#' @title Read in a CitizenAir excel file
#' @description Read in a CitizenAir excel file
#' @param file the path to the excel file
#' @param name the name of the file, defaults to the basename of the file
#' @export
#' @return 
#' an object of class \code{citizenair_userdata} which is a list with elements
#' \enumerate{
#' \item{filename: the name of the file}
#' \item{file: the full path to the excel file}
#' \item{time: the timestamp when the data was imported}
#' \item{content: a list where each list element contains the elements meta and data where meta and data are described below}
#' \item{phenomena: all measurement phenomena in the data}
#' }
#' Content element meta is a list containing
#' \enumerate{
#' \item{device: the name of the device}
#' \item{lat: the latitude of the device address}
#' \item{lon: the longitude of the device address}
#' \item{sheet_id: an identifier which is the sequence number of the sheet}
#' \item{sheet: the sheet name which was read in}
#' \item{phenomena: a list containing phenomena measured in the data. Each list element is a character vector with the measurement unit.}
#' }
#' Content element data is a data.frame with the measurements containing
#' \enumerate{
#' \item{datum: the date - in POSIXct format returned by readxl::read_excel when setting that field to date}
#' \item{time: the time - in POSIXct format returned by readxl::read_excel when setting that field to date}
#' \item{several columns, one for each phenomena indicated in the \code{meta} element}
#' }
#' @examples 
#' filename <- system.file(package = "citizenair", "data-raw", "citizenair-example.xls")
#' x <- read_citizenair(filename)
#' meta <- as.data.frame(x, type = "meta")
#' measurements <- as.data.frame(x, type = "measurements")
read_citizenair <- function(file = system.file(package = "citizenair", "data-raw", "test_dummy.xls"), 
                            name = basename(file)){
  file <- path.expand(file)
  result <- list()
  result$filename <- name
  result$file <- file
  result$time <- Sys.time()
  sheets <- readxl::excel_sheets(file)
  result$content <- list()
  for(i in seq_along(sheets)){
    sheet <- sheets[i]
    sheet_details <- read_sheet_info(file, sheet)
    result$content[[sheet]] <- list()
    result$content[[sheet]]$meta <- read_sheet_meta(file, sheet, sheet_details)
    result$content[[sheet]]$meta$sheet_id <- i
    result$content[[sheet]]$meta$phenomena <- read_sheet_units(file, sheet, sheet_details)
    result$content[[sheet]]$data <- read_sheet_measurements(file, sheet, sheet_details)
  }
  result$phenomena <- unique(sort(unlist(lapply(result$content, FUN=function(x) names(x$meta$phenomena)))))
  class(result) <- "citizenair_userdata"
  result
}

#' @title Convert citizen Excel data imported with \code{read_citizenair} to a data.frame
#' @description Convert citizen Excel data imported with \code{read_citizenair} to a data.frame
#' @param x an object of class \code{citizenair_userdata} as returned by \code{\link{read_citizenair}}
#' @param type either 'meta' to get the meta information as a data.frame or 'measurements' to get the measurements data.frame
#' @param row.names not used
#' @param optional not used
#' @param ... not used
#' @export
#' @return a data.frame is returned
#' \enumerate{
#' \item{in case type is meta: contains fields sheet_id, sheet, device, lat, lon, phenomena}
#' \item{in case type is data: contains fields sheet_id, time, date, phenomena, value}
#' }
#' @examples 
#' filename <- system.file(package = "citizenair", "data-raw", "citizenair-example.xls")
#' x <- read_citizenair(filename)
#' meta <- as.data.frame(x, type = "meta")
#' measurements <- as.data.frame(x, type = "measurements")
as.data.frame.citizenair_userdata <- function(x, row.names, optional, ..., type = c("meta", "measurements")){
  type <- match.arg(type)
  if(type == "meta"){
    x <- lapply(x$content, FUN=function(x){
      x <- x$meta
      x$phenomena <- paste(names(x$phenomena), collapse = ", ")
      x$meta[, c("sheet_id", "sheet", "device", "lat", "lon", "phenomena")] 
      x
    })
    x <- rbindlist(x)
  }else if(type == "measurements"){
    x <- lapply(x$content, FUN=function(x){
      meta <- x$meta
      x <- x$data
      measurements <- setdiff(colnames(x), c("datum", "tijd"))
      x$datum <- as.Date(x$datum, tz = "UTC")
      x$datum <- as.POSIXct(x$datum, tz = "UTC")
      if(!all(is.na(x$tijd))){
        idx <- which(!is.na(x$tijd))
        x$datum[idx] <- fasttime::fastPOSIXct(sprintf("%s %s", format(x$datum[idx], "%Y-%m-%d"), format(x$tijd[idx], "%H:%M:%S")), tz = "UTC")
      }
      x <- as.data.table(x)
      x <- data.table::melt.data.table(data = x, id.vars = "datum", measure.vars = measurements, na.rm = TRUE, value.name = "value", variable.name = "phenomena")
      x <- data.table::setnames(x, old = "datum", new = "time")
      x$date <- as.Date(x$time)
      x$sheet_id <- meta$sheet_id
      x <- data.table::setcolorder(x, c("sheet_id", "time", "date", "phenomena", "value"))
      x
    })
    x <- rbindlist(x)
  }
  x
}


read_sheet_info <- function(file, sheet){
  message <- capture.output(
    x <- readxl::read_excel(path = file, sheet = sheet, col_types = "text", range = cellranger::cell_rows(c(NA, 20)), col_names = FALSE),
    type = "message")
  x <- as.matrix(x)
  ## find word meettoestel and look to the text next to the word meettoestel
  meettoestel <- apply(x, MARGIN=1, FUN=function(x) any(grepl(pattern = "meettoestel", x, ignore.case = TRUE)))
  meettoestel_row <- which.min(!meettoestel)
  meettoestel_col <- which.max(grepl(pattern = "meettoestel", x[meettoestel_row, ], ignore.case = TRUE)) + 1
  
  ## find word meetpunt and look to the text next to the word meetpunt
  latlon <- apply(x, MARGIN=1, FUN=function(x) any(grepl(pattern = "meetpunt", x, ignore.case = TRUE)))
  latlon_row <- which.min(!latlon)
  latlon_col <- which.max(grepl(pattern = "meetpunt", x[latlon_row, ], ignore.case = TRUE)) + 1
  
  ## find the location where datum/variabele/tijd are on the same row, these are the headers, 
  ## the units should be one row below that and the data should start 2 rows below that
  data_start <- apply(x, MARGIN=1, FUN=function(x){
    any(grepl(pattern = "datum", x, ignore.case = TRUE)) & 
      any(grepl(pattern = "variabele", x, ignore.case = TRUE)) & 
      any(grepl(pattern = "tijd", x, ignore.case = TRUE))
  })
  data_start_headers <- which.min(!data_start)
  
  ## See how much rows we have - identified by the datum which should always be there
  datum_column  <- grep(pattern = "datum", x[data_start_headers, ], ignore.case = TRUE)
  datums <- readxl::read_excel(path = file, sheet = sheet, col_types = "text", range = cellranger::cell_cols(datum_column), col_names="key")$key
  datums <- datums[-seq_len(data_start_headers + 1)]
  
  ## Find the locations of the columns
  measurements <- readxl::read_excel(path = file, sheet = sheet, col_types = "text", range = cellranger::cell_rows(data_start_headers))
  measurements <- names(measurements)
  measurements_columns <- c(which.min(!tolower(measurements) %in% c("datum", "tijd")), length(measurements))
  measurements_fields <- measurements[measurements_columns[1]:measurements_columns[2]]
  
  ## Return result
  result <- list(meettoestel = c(meettoestel_row, meettoestel_col),
                 latlon = c(latlon_row, latlon_col),
                 data_headers = data_start_headers, 
                 data_start = data_start_headers + 2,
                 measurements_columns = measurements_columns, 
                 measurements_fields = measurements_fields, 
                 data_n = length(datums))
  class(result) <- "citizenair_userdata_excel_locations"
  result
}

read_sheet_meta <- function(file, sheet, sheet_info = read_sheet_info(file, sheet)){
  result <- list()
  result$device <- readxl::read_excel(path = file, sheet = sheet, 
                                      range = cellranger::cell_limits(c(sheet_info$meettoestel[1], sheet_info$meettoestel[2]), c(sheet_info$meettoestel[1], sheet_info$meettoestel[2])), 
                                      col_names = "key",
                                      col_types = "text")$key
  result$gps <- readxl::read_excel(path = file, sheet = sheet, 
                                   range = cellranger::cell_limits(c(sheet_info$latlon[1], sheet_info$latlon[2]), c(sheet_info$latlon[1], sheet_info$latlon[2])), 
                                   col_names = "key",
                                   col_types = "text")$key
  result$latlon <- as.numeric(unlist(strsplit(result$gps, split = ",")))
  result$lat <- head(result$latlon, 1)
  result$lon <- tail(result$latlon, 1)
  result$sheet <- sheet
  result <- result[c("sheet", "device", "lat", "lon")]
  result
}

read_sheet_units <- function(file, sheet, sheet_info = read_sheet_info(file, sheet)){
  units <- readxl::read_excel(path = file, sheet = sheet, 
                              range = cellranger::cell_limits(ul = c(sheet_info$data_headers, sheet_info$measurements_columns[1]), 
                                                              lr = c(sheet_info$data_headers+1, sheet_info$measurements_columns[2])),
                              col_names = TRUE, col_types = "text")
  units <- as.list(units)
  ## remove 'Datum' / 'Tijd'
  units <- units[-which(tolower(names(units)) %in% tolower(c("Datum", "Tijd")))]
  units
}

read_sheet_measurements <- function(file, sheet, sheet_info = read_sheet_info(file, sheet)){
  suppressWarnings(
    message <- capture.output(
      x <-  readxl::read_excel(path = file, sheet = sheet, 
                               range = cellranger::cell_limits(ul = c(sheet_info$data_start, sheet_info$measurements_columns[1]), 
                                                               lr = c(sheet_info$data_start + sheet_info$data_n - 1, sheet_info$measurements_columns[2])),
                               col_names = sheet_info$measurements_fields, guess_max = 10000, 
                               col_types = c("date", "date", rep("numeric", length(sheet_info$measurements_fields) - 2))),
      type = "message"))
  class(x) <- c("data.frame", "citizenair_rawdata")
  idx <- match(c("datum", "tijd"), table = tolower(colnames(x)))
  if(length(idx) != 2){
    stop("Datum + Tijd not present in data")
  }
  x <- data.table::setnames(x, old = colnames(x)[idx], new = c("datum", "tijd"))
  x
}
