#' @export
makeRLearner.classif.gbm = function() {
  makeRLearnerClassif(
    cl = "classif.gbm",
    package = "gbm",
    par.set = makeParamSet(
      makeDiscreteLearnerParam(id = "distribution", values = c("bernoulli", "adaboost", "huberized", "multinomial")),
      makeIntegerLearnerParam(id = "n.trees", default = 100L, lower = 1L),
      makeIntegerLearnerParam(id = "cv.folds", default = 0L),
      makeIntegerLearnerParam(id = "interaction.depth", default = 1L, lower = 1L),
      makeIntegerLearnerParam(id = "n.minobsinnode", default = 10L, lower = 1L),
      makeNumericLearnerParam(id = "shrinkage", default = 0.001, lower = 0),
      makeNumericLearnerParam(id = "bag.fraction", default = 0.5, lower = 0, upper = 1),
      makeNumericLearnerParam(id = "train.fraction", default = 1, lower = 0, upper = 1),
      makeLogicalLearnerParam(id = "keep.data", default = TRUE, tunable = FALSE),
      makeLogicalLearnerParam(id = "verbose", default = FALSE, tunable = FALSE)
    ),
    properties = c("twoclass", "multiclass", "missings", "numerics", "factors", "prob", "weights", "featimp"),
    par.vals = list(keep.data = FALSE),
    name = "Gradient Boosting Machine",
    short.name = "gbm",
    note = "`keep.data` is set to FALSE to reduce memory requirements. Note on param 'distribution': gbm will select 'bernoulli' by default for 2 classes, and 'multinomial' for
      multiclass problems. The latter is the only setting that works for > 2 classes."
  )
}

#' @export
trainLearner.classif.gbm = function(.learner, .task, .subset, .weights = NULL,  ...) {
  td = getTaskDescription(.task)
  if (length(td$class.levels) == 2L)
    d = getTaskData(.task, .subset, recode.target = "01")
  else
    d = getTaskData(.task, .subset)
  if (is.null(.weights)) {
    f = getTaskFormula(.task)
    gbm::gbm(f, data = d, ...)
  } else  {
    f = getTaskFormula(.task)
    gbm::gbm(f, data = d, weights = .weights, ...)
  }
}

#' @export
predictLearner.classif.gbm = function(.learner, .model, .newdata, ...) {
  td = .model$task.desc
  m = .model$learner.model
  p = gbm::predict.gbm(m, newdata = .newdata, type = "response", n.trees = m$n.trees, single.tree = FALSE, ...)
  if (length(td$class.levels) == 2L) {
    levs = c(td$negative, td$positive)
    if (.learner$predict.type == "prob") {
      y = matrix(0, ncol = 2, nrow = nrow(.newdata))
      colnames(y) = levs
      y[, 1L] = 1-p
      y[, 2L] = p
      return(y)
    } else {
      p = as.factor(ifelse(p > 0.5, levs[2L], levs[1L]))
      names(p) = NULL
      return(p)
    }
  } else {
    p = p[,,1L]
    if (.learner$predict.type == "prob") {
      return(p)
    } else {
      ind = getMaxIndexOfRows(p)
      cns = colnames(p)
      return(factor(cns[ind], levels = cns))
    }
  }
}

#' @export
getFeatureImportanceLearner.classif.gbm = function(.learner, .model, ...) {
  mod = getLearnerModel(.model)
  gbm::relative.influence(mod, mod$n.trees, ...)
}
