#'Function to Split Dimension
#'
#'@author Nuria Perez-Zanon, \email{nuria.perez@bsc.es}
#'
#'@description This function split a dimension in two. The user can select the 
#'dimension to split and provide indices indicating how to split that dimension 
#'or dates and the frequency expected (monthly or by day, month and year). The 
#'user can also provide a numeric frequency indicating the length of each division.
#'
#'@param data A 's2dv_cube' object
#'@param split_dim A character string indicating the name of the dimension to 
#'  split.
#'@param indices A vector of numeric indices or dates. If left at NULL, the 
#'  dates provided in the s2dv_cube object (element Dates) will be used.
#'@param freq A character string indicating the frequency: by 'day', 'month' and 
#'  'year' or 'monthly' (by default). 'month' identifies months between 1 and 12 
#'  independently of the year they belong to, while 'monthly' differenciates 
#'  months from different years.
#'@param new_dim_name A character string indicating the name of the new dimension.
#'@param insert_ftime An integer indicating the number of time steps to add at 
#'  the begining of the time series.
#'
#'@details Parameter 'insert_ftime' has been included for the case of using 
#'daily data, requiring split the temporal dimensions by months (or similar) and 
#'the first lead time doesn't correspondt to the 1st day of the month. In this 
#'case, the insert_ftime could be used, to get a final output correctly 
#'organized. E.g.: leadtime 1 is the 2nd of November and the input time series 
#'extend to the 31st of December. When requiring split by month with 
#'\code{inset_ftime = 1}, the 'monthly' dimension of length two will indicate 
#'the month (position 1 for November and position 2 for December), dimension 
#''time' will be length 31. For November, the position 1 and 31 will be NAs, 
#'while from positon 2 to 30 will be filled with the data provided. This allows 
#'to select correctly days trhough time dimension.
#'@import abind
#'@importFrom ClimProjDiags Subset
#'@examples
#'
#'data <- 1 : 20
#'dim(data) <- c(time = 10, lat = 2)
#'data <-list(data = data)
#'class(data) <- 's2dv_cube'
#'indices <- c(rep(1,5), rep(2,5))
#'new_data <- CST_SplitDim(data, indices = indices)
#'time <- c(seq(ISOdate(1903, 1, 1), ISOdate(1903, 1, 4), "days"),
#'          seq(ISOdate(1903, 2, 1), ISOdate(1903, 2, 4), "days"),
#'          seq(ISOdate(1904, 1, 1), ISOdate(1904, 1, 2), "days"))
#'data <- list(data = data$data, Dates = time)
#'class(data) <- 's2dv_cube'
#'new_data <- CST_SplitDim(data, indices = time)
#'dim(new_data$data)
#'new_data <- CST_SplitDim(data, indices = time, freq = 'day')
#'dim(new_data$data)
#'new_data <- CST_SplitDim(data, indices = time, freq = 'month')
#'dim(new_data$data)
#'new_data <- CST_SplitDim(data, indices = time, freq = 'year')
#'dim(new_data$data)
#'@export
CST_SplitDim <- function(data, split_dim = 'time', indices = NULL,
                         freq = 'monthly', new_dim_name = NULL, insert_ftime = NULL) {
  if (!inherits(data, 's2dv_cube')) {
    stop("Parameter 'data' must be of the class 's2dv_cube', ",
         "as output by CSTools::CST_Load.")
  }
  if (!is.null(insert_ftime)) {
    if (!is.numeric(insert_ftime)) {
      stop("Parameter 'insert_ftime' should be an integer.")
    } else {
      if (length(insert_ftime) > 1) {
        warning("Parameter 'insert_ftime' must be of length 1, and only the",
                " first element will be used.")
        insert_ftime <- insert_ftime[1]
      }
      # adding NAs at the begining of the data in ftime dim
      ftimedim <- which(names(dim(data$data)) == 'ftime')
      dims <- dim(data$data)
      dims[ftimedim] <- insert_ftime
      empty_array <- array(NA, dims)
      data$data <- abind(empty_array, data$data, along = ftimedim)
      names(dim(data$data)) <- names(dims)
      # adding dates to Dates for the new NAs introduced
      if ((data$Dates[[1]][2] - data$Dates[[1]][1]) == 1) {
        timefreq <- 'days'
      } else {
        timefreq <- 'months'
        warning("Time frequency of forecast time is considered monthly.")
      }
      start <- data$Dates[[1]]
      dim(start) <- c(ftime = length(start)/dims['sdate'], sdate = dims['sdate'])
      # new <- array(NA, prod(dim(data$data)[c('ftime', 'sdate')]))
      # Pending fix transform to UTC when concatenaiting
      data$Dates$start <- do.call(c, lapply(1:dim(start)[2], function(x) {
                                  seq(start[1,x] - as.difftime(insert_ftime, 
                                  units = timefreq),
                                  start[dim(start)[1],x], by = timefreq, tz = "UTC")}))
    }
  }
  if (is.null(indices)) {
    if (any(split_dim %in% c('ftime', 'time', 'sdate'))) {
      if (is.list(data$Dates)) {
        indices <- data$Dates[[1]]
      } else {
        indices <- data$Dates
      }
      if (any(names(dim(data$data)) %in% 'sdate')) {
        if (!any(names(dim(data$data)) %in% split_dim)) {
          stop("Parameter 'split_dims' must be one of the dimension ",
               "names in parameter 'data'.")
        }
        indices <- indices[1 : dim(data$data)[which(names(dim(data$data)) == split_dim)]]     
      }
    }
  }
  data$data <- SplitDim(data$data, split_dim = split_dim, indices = indices,
                        freq = freq, new_dim_name = new_dim_name)
  return(data)
}
#'Function to Split Dimension
#'
#'@author Nuria Perez-Zanon, \email{nuria.perez@bsc.es}
#'
#'@description This function split a dimension in two. The user can select the 
#'dimension to split and provide indices indicating how to split that dimension 
#'or dates and the frequency expected (monthly or by day, month and year). The 
#'user can also provide a numeric frequency indicating the length of each division.
#'
#'@param data An n-dimensional array with named dimensions.
#'@param split_dim A character string indicating the name of the dimension to 
#'  split.
#'@param indices A vector of numeric indices or dates.
#'@param freq A character string indicating the frequency: by 'day', 'month' and 
#'  'year' or 'monthly' (by default). 'month' identifies months between 1 and 12 
#'  independetly of the year they belong to, while 'monthly' differenciates 
#'  months from different years. Parameter 'freq' can also be numeric indicating 
#'  the length in which to subset the dimension.
#'@param new_dim_name A character string indicating the name of the new 
#'  dimension.
#'@import abind
#'@importFrom ClimProjDiags Subset
#'@examples
#'data <- 1 : 20
#'dim(data) <- c(time = 10, lat = 2)
#'indices <- c(rep(1,5), rep(2,5))
#'new_data <- SplitDim(data, indices = indices)
#'time <- c(seq(ISOdate(1903, 1, 1), ISOdate(1903, 1, 4), "days"),
#'          seq(ISOdate(1903, 2, 1), ISOdate(1903, 2, 4), "days"),
#'          seq(ISOdate(1904, 1, 1), ISOdate(1904, 1, 2), "days"))
#'new_data <- SplitDim(data, indices = time)
#'new_data <- SplitDim(data, indices = time, freq = 'day')
#'new_data <- SplitDim(data, indices = time, freq = 'month')
#'new_data <- SplitDim(data, indices = time, freq = 'year')
#'@export
SplitDim <- function(data, split_dim = 'time', indices, freq = 'monthly',
                     new_dim_name = NULL) {
  # check data
  if (is.null(data)) {
    stop("Parameter 'data' cannot be NULL.")
  }
  if (is.null(dim(data))) {
    dim(data) = c(time = length(data))
  }
  if (is.null(names(dim(data)))) {
    stop("Parameter 'data' must have dimension names.")
  }
  dims <- dim(data)
  # check split_dim
  if (!is.character(split_dim)) {
    stop("Parameter 'split_dim' must be a character.")
  }
  if (length(split_dim) > 1) {
    split_dim <- split_dim[1]
    warning("Parameter 'split_dim' has length greater than ",
            "one and only the first element will be used.")
  }
  if (!any(names(dims) %in% split_dim)) {
    stop("Parameter 'split_dims' must be one of the dimension ",
         "names in parameter 'data'.")
  }
  pos_split <- which(names(dims) == split_dim)
  # check indices and freq
  if (is.null(indices)) {
    if (!is.numeric(freq)) {
      stop("Parameter 'freq' must be a integer number indicating ",
           " the length of each chunk.")
    } else {
      if (!((dims[pos_split] / freq) %% 1 == 0)) {
        stop("Parameter 'freq' must be proportional to the ",
             "length of the 'split_dim' in parameter 'data'.")
      }
      indices <- rep(1 : (dims[pos_split] / freq), freq)
      indices <- sort(indices)
      repited <- sort(unique(indices))
    }
  } else if (is.numeric(indices)) {
    if (!is.null(freq)) {
      if (freq != 'monthly') {
        warning("Parameter 'freq' is not being used since ",
                "parameter 'indices' is numeric.")
      }
    }
    repited <- sort(unique(indices))
  } else {
    # Indices should be Dates and freq character
    if (!is.character(freq)) {
      stop("Parameter 'freq' must be a character indicating ",
           "how to divide the dates provided in parameter 'indices'",
           ", 'monthly', 'anually' or 'daily'.")
    }
    if (!inherits(indices, 'POSIXct')) {
      indices <- try({
        if (is.character(indices)) {
            as.POSIXct(indices)
        } else {
            as.POSIXct(indices)
        }
      })
      if ('try-error' %in% class(indices) | 
        sum(is.na(indices)) == length(indices)) {
        stop("Dates provided in parameter 'indices' must be of class",
             " 'POSIXct' or convertable to 'POSIXct'.")
        }
    }
  }
  if (length(indices) != dims[pos_split]) {
    stop("Parameter 'indices' has different length of parameter ",
         "data in the dimension supplied in 'split_dim'.")
  }
  # check indices as dates:
  if (!is.numeric(indices)) {
    if (freq == 'day') {
      indices <- as.numeric(strftime(indices, format = "%d"))
      repited <- unique(indices)
    } else if (freq == 'month') {
      indices <- as.numeric(strftime(indices, format = "%m"))
      repited <- unique(indices)
    } else if (freq == 'year') {
      indices <- as.numeric(strftime(indices, format = "%Y"))
      repited <- unique(indices)
    } else if (freq == 'monthly' ) {
      indices <- as.numeric(strftime(indices, format = "%m%Y"))
      repited <- unique(indices)
    } else {
      stop("Parameter 'freq' must be numeric or a character: ",
           "by 'day', 'month', 'year' or 'monthly' (for ",
           "distinguishable month).")
    }
  }
  # check new_dim_name
  if (!is.null(new_dim_name)) {
    if (!is.character(new_dim_name)) {
      stop("Parameter 'new_dim_name' must be character string")
    }
    if (length(new_dim_name) > 1) {
      new_dim_name <- new_dim_name[1]
      warning("Parameter 'new_dim_name' has length greater than 1 ",
              "and only the first elemenst is used.")
    }
  }
  max_times <- max(unlist(lapply(repited, 
                          function(x){sum(indices == x)})))
  data <- lapply(repited, function(x) {rebuild(x, data, along = split_dim,
                                       indices = indices, max_times)})
  data <- abind(data, along = length(dims) + 1)
  if (is.character(freq)) {
    names(dim(data)) <- c(names(dims), freq)
  } else {
    names(dim(data)) <- c(names(dims), 'index')
  }
  if (!is.null(new_dim_name)) {
    names(dim(data)) <- c(names(dims), new_dim_name)
  }
  return(data)
}

rebuild <- function(x, data, along, indices, max_times) {
  a <- Subset(data, along = along, indices = which(indices == x))
  pos_dim <- which(names(dim(a)) == along)
  if (dim(a)[pos_dim] != max_times) {
    adding <- max_times - dim(a)[pos_dim]
    new_dims <- dim(a)
    new_dims[pos_dim] <- adding
    extra <- array(NA, dim = new_dims)
    a <- abind(a, extra, along = pos_dim)
    names(dim(a)) <- names(dim(data))
  }
  return(a)
}