#' @title Intraclass Correlation Coefficient (ICC)
#' @name icc
#'
#' @description
#' This function calculates the intraclass-correlation coefficient (ICC) -
#' sometimes also called *variance partition coefficient* (VPC) or
#' *repeatability* - for mixed effects models. The ICC can be calculated for all
#' models supported by [`insight::get_variance()`]. For models fitted with the
#' **brms**-package, `icc()` might fail due to the large variety of
#' models and families supported by the **brms**-package. In such cases, an
#' alternative to the ICC is the `variance_decomposition()`, which is based
#' on the posterior predictive distribution (see 'Details').
#'
#' @param model A (Bayesian) mixed effects model.
#' @param re_formula Formula containing group-level effects to be considered in
#' the prediction. If `NULL` (default), include all group-level effects.
#' Else, for instance for nested models, name a specific group-level effect
#' to calculate the variance decomposition for this group-level. See 'Details'
#' and `?brms::posterior_predict`.
#' @param ci Confidence resp. credible interval level. For `icc()`, `r2()`, and
#' `rmse()`, confidence intervals are based on bootstrapped samples from the
#' ICC, R2 or RMSE value. See `iterations`.
#' @param by_group Logical, if `TRUE`, `icc()` returns the variance components
#' for each random-effects level (if there are multiple levels). See 'Details'.
#' @param iterations Number of bootstrap-replicates when computing confidence
#' intervals for the ICC, R2, RMSE etc.
#' @param ci_method Character string, indicating the bootstrap-method. Should
#' be `NULL` (default), in which case `lme4::bootMer()` is used for bootstrapped
#' confidence intervals. However, if bootstrapped intervals cannot be calculated
#' this way, try `ci_method = "boot"`, which falls back to `boot::boot()`. This
#' may successfully return bootstrapped confidence intervals, but bootstrapped
#' samples may not be appropriate for the multilevel structure of the model.
#' There is also an option `ci_method = "analytical"`, which tries to calculate
#' analytical confidence assuming a chi-squared distribution. However, these
#' intervals are rather inaccurate and often too narrow. It is recommended to
#' calculate bootstrapped confidence intervals for mixed models.
#' @param verbose Toggle warnings and messages.
#' @param null_model Optional, a null model to compute the random effect variances,
#' which is passed to [`insight::get_variance()`]. Usually only required if
#' calculation of r-squared or ICC fails when `null_model` is not specified. If
#' calculating the null model takes longer and you already have fit the null
#' model, you can pass it here, too, to speed up the process.
#' @param ... Arguments passed down to `lme4::bootMer()` or `boot::boot()`
#' for bootstrapped ICC, R2, RMSE etc.; for `variance_decomposition()`,
#' arguments are passed down to `brms::posterior_predict()`.
#'
#' @inheritParams r2_bayes
#' @inheritParams insight::get_variance
#'
#' @return A list with two values, the adjusted ICC and the unadjusted ICC. For
#' `variance_decomposition()`, a list with two values, the decomposed
#' ICC as well as the credible intervals for this ICC.
#'
#' @references
#'  - Hox, J. J. (2010). Multilevel analysis: techniques and applications
#'    (2nd ed). New York: Routledge.
#'  - Nakagawa, S., Johnson, P. C. D., and Schielzeth, H. (2017). The
#'    coefficient of determination R2 and intra-class correlation coefficient
#'    from generalized linear mixed-effects models revisited and expanded.
#'    Journal of The Royal Society Interface, 14(134), 20170213.
#'  - Rabe-Hesketh, S., and Skrondal, A. (2012). Multilevel and longitudinal
#'    modeling using Stata (3rd ed). College Station, Tex: Stata Press
#'    Publication.
#'  - Raudenbush, S. W., and Bryk, A. S. (2002). Hierarchical linear models:
#'    applications and data analysis methods (2nd ed). Thousand Oaks: Sage
#'    Publications.
#'
#' @inheritSection r2_nakagawa Supported models and model families
#'
#' @details
#' ## Interpretation
#' The ICC can be interpreted as "the proportion of the variance explained by
#' the grouping structure in the population". The grouping structure entails
#' that measurements are organized into groups (e.g., test scores in a school
#' can be grouped by classroom if there are multiple classrooms and each
#' classroom was administered the same test) and ICC indexes how strongly
#' measurements in the same group resemble each other. This index goes from 0,
#' if the grouping conveys no information, to 1, if all observations in a group
#' are identical (_Gelman and Hill, 2007, p. 258_). In other word, the ICC -
#' sometimes conceptualized as the measurement repeatability - "can also be
#' interpreted as the expected correlation between two randomly drawn units
#' that are in the same group" _(Hox 2010: 15)_, although this definition might
#' not apply to mixed models with more complex random effects structures. The
#' ICC can help determine whether a mixed model is even necessary: an ICC of
#' zero (or very close to zero) means the observations within clusters are no
#' more similar than observations from different clusters, and setting it as a
#' random factor might not be necessary.
#'
#' ## Difference with R2
#' The coefficient of determination R2 (that can be computed with [`r2()`])
#' quantifies the proportion of variance explained by a statistical model, but
#' its definition in mixed model is complex (hence, different methods to compute
#' a proxy exist). ICC is related to R2 because they are both ratios of
#' variance components. More precisely, R2 is the proportion of the explained
#' variance (of the full model), while the ICC is the proportion of explained
#' variance that can be attributed to the random effects. In simple cases, the
#' ICC corresponds to the difference between the *conditional R2* and the
#' *marginal R2* (see [`r2_nakagawa()`]).
#'
#' ## Calculation
#' The ICC is calculated by dividing the random effect variance,
#' \ifelse{html}{\out{&sigma;<sup>2</sup><sub>i</sub>}}{\eqn{\sigma^2_i}}, by
#' the total variance, i.e. the sum of the random effect variance and the
#' residual variance, \ifelse{html}{\out{&sigma;<sup>2</sup><sub>&epsilon;</sub>}}{\eqn{\sigma^2_\epsilon}}.
#'
#' ## Adjusted and unadjusted ICC
#' `icc()` calculates an adjusted and an unadjusted ICC, which both take all
#' sources of uncertainty (i.e. of *all random effects*) into account. While
#' the *adjusted ICC* only relates to the random effects, the *unadjusted ICC*
#' also takes the fixed effects variances into account, more precisely, the
#' fixed effects variance is added to the denominator of the formula to
#' calculate the ICC (see _Nakagawa et al. 2017_). Typically, the *adjusted*
#' ICC is of interest when the analysis of random effects is of interest.
#' `icc()` returns a meaningful ICC also for more complex random effects
#' structures, like models with random slopes or nested design (more than two
#' levels) and is applicable for models with other distributions than Gaussian.
#' For more details on the computation of the variances, see
#' `?insight::get_variance`.
#'
#' ## ICC for unconditional and conditional models
#' Usually, the ICC is calculated for the null model ("unconditional model").
#' However, according to _Raudenbush and Bryk (2002)_ or
#' _Rabe-Hesketh and Skrondal (2012)_ it is also feasible to compute the
#' ICC for full models with covariates ("conditional models") and compare how
#' much, e.g., a level-2 variable explains the portion of variation in the
#' grouping structure (random intercept).
#'
#' ## ICC for specific group-levels
#' The proportion of variance for specific levels related to the overall model
#' can be computed by setting `by_group = TRUE`. The reported ICC is
#' the variance for each (random effect) group compared to the total
#' variance of the model. For mixed models with a simple random intercept,
#' this is identical to the classical (adjusted) ICC.
#'
#' ## Variance decomposition for brms-models
#' If `model` is of class `brmsfit`, `icc()` might fail due to the large
#' variety of models and families supported by the **brms** package. In such
#' cases, `variance_decomposition()` is an alternative ICC measure. The function
#' calculates a variance decomposition based on the posterior predictive
#' distribution. In this case, first, the draws from the posterior predictive
#' distribution *not conditioned* on group-level terms
#' (`posterior_predict(..., re_formula = NA)`) are calculated as well as draws
#' from this distribution *conditioned* on *all random effects* (by default,
#' unless specified else in `re_formula`) are taken. Then, second, the variances
#' for each of these draws are calculated. The "ICC" is then the ratio between
#' these two variances. This is the recommended way to analyse
#' random-effect-variances for non-Gaussian models. It is then possible to
#' compare variances across models, also by specifying different group-level
#' terms via the `re_formula`-argument.
#'
#' Sometimes, when the variance of the posterior predictive distribution is
#' very large, the variance ratio in the output makes no sense, e.g. because
#' it is negative. In such cases, it might help to use `robust = TRUE`.
#'
#' @examplesIf require("lme4")
#' model <- lme4::lmer(Sepal.Length ~ Petal.Length + (1 | Species), data = iris)
#' icc(model)
#'
#' # ICC for specific group-levels
#' data(sleepstudy, package = "lme4")
#' set.seed(12345)
#' sleepstudy$grp <- sample(1:5, size = 180, replace = TRUE)
#' sleepstudy$subgrp <- NA
#' for (i in 1:5) {
#'   filter_group <- sleepstudy$grp == i
#'   sleepstudy$subgrp[filter_group] <-
#'     sample(1:30, size = sum(filter_group), replace = TRUE)
#' }
#' model <- lme4::lmer(
#'   Reaction ~ Days + (1 | grp / subgrp) + (1 | Subject),
#'   data = sleepstudy
#' )
#' icc(model, by_group = TRUE)
#' @export
icc <- function(
  model,
  by_group = FALSE,
  tolerance = 1e-05,
  ci = NULL,
  iterations = 100,
  ci_method = NULL,
  null_model = NULL,
  approximation = "lognormal",
  model_component = NULL,
  verbose = TRUE,
  ...
) {
  # special handling for smicd::semLme()
  if (inherits(model, "sem") && inherits(model, "lme")) {
    return(model$icc)
  }

  if (insight::is_multivariate(model)) {
    if (inherits(model, "brmsfit")) {
      return(variance_decomposition(model))
    } else {
      if (verbose) {
        insight::format_warning(
          "Multiple response models not yet supported. You may use `performance::variance_decomposition()`."
        )
      }
      return(NULL)
    }
  }

  if (!insight::is_mixed_model(model)) {
    if (verbose) {
      insight::format_warning("`model` has no random effects.")
    }
    return(NULL)
  }

  # calculate random effect variances
  vars <- .compute_random_vars(
    model,
    tolerance = tolerance,
    null_model = null_model,
    approximation = approximation,
    model_component = model_component,
    verbose = verbose
  )

  # return if ICC couldn't be computed
  if (is.null(vars) || all(is.na(vars))) {
    return(vars)
  }

  # Calculate ICC values by groups
  if (isTRUE(by_group)) {
    # with random slopes, icc is inaccurate
    if (!is.null(insight::find_random_slopes(model)) && verbose) {
      insight::format_alert(
        "Model contains random slopes. Cannot compute accurate ICCs by group factors."
      )
    }

    if (!is.null(ci) && !is.na(ci) && verbose) {
      insight::format_alert(
        "Confidence intervals are not yet supported for `by_group = TRUE`."
      )
    }

    # icc per group factor with reference to overall model
    icc_overall <- vars$var.intercept / (vars$var.random + vars$var.residual)

    out <- data.frame(
      Group = names(icc_overall),
      ICC = unname(icc_overall),
      stringsAsFactors = FALSE
    )

    # iccs between groups
    # n_grps <- length(vars$var.intercept)
    # level_combinations <- utils::combn(1:n_grps, m = n_grps - 1, simplify = FALSE)
    # icc_grp <- sapply(
    #   level_combinations,
    #   function(v) {
    #     vars$var.intercept[v[1]] / (vars$var.intercept[v[1]] + vars$var.intercept[v[2]])
    #   }
    # )
    #
    # out2 <- data.frame(
    #   Group1 = group_names[sapply(level_combinations, function(i) i[1])],
    #   Group2 = group_names[sapply(level_combinations, function(i) i[2])],
    #   ICC = unname(icc_grp),
    #   stringsAsFactors = FALSE
    # )

    class(out) <- c("icc_by_group", class(out))
  } else {
    # Calculate ICC values
    icc_adjusted <- vars$var.random / (vars$var.random + vars$var.residual)
    icc_unadjusted <- vars$var.random /
      (vars$var.fixed + vars$var.random + vars$var.residual)

    out <- data.frame(
      ICC_adjusted = icc_adjusted,
      ICC_conditional = icc_unadjusted,
      ICC_unadjusted = icc_unadjusted
    )

    # check if CIs are requested, and compute bootstrapped CIs
    if (!is.null(ci) && !is.na(ci)) {
      # this is experimental!
      if (identical(ci_method, "analytical")) {
        result <- .safe(.analytical_icc_ci(model, ci))
        if (is.null(result)) {
          icc_ci_adjusted <- icc_ci_unadjusted <- NA
        } else {
          icc_ci_adjusted <- result$ICC_adjusted
          icc_ci_unadjusted <- result$ICC_unadjusted
        }
      } else {
        result <- .bootstrap_icc(model, iterations, tolerance, ci_method, ...)
        # CI for adjusted ICC
        icc_ci_adjusted <- as.vector(result$t[, 1])
        icc_ci_adjusted <- icc_ci_adjusted[!is.na(icc_ci_adjusted)]
        # validation check
        if (length(icc_ci_adjusted) > 0) {
          icc_ci_adjusted <- bayestestR::eti(icc_ci_adjusted, ci = ci)
        } else {
          icc_ci_adjusted <- NA
        }
        # CI for unadjusted ICC
        icc_ci_unadjusted <- as.vector(result$t[, 2])
        icc_ci_unadjusted <- icc_ci_unadjusted[!is.na(icc_ci_unadjusted)]
        # validation check
        if (length(icc_ci_unadjusted) > 0) {
          icc_ci_unadjusted <- bayestestR::eti(icc_ci_unadjusted, ci = ci)
        } else {
          icc_ci_unadjusted <- NA
        }
        if ((all(is.na(icc_ci_adjusted)) || all(is.na(icc_ci_unadjusted))) && verbose) {
          insight::format_warning(
            "Could not compute confidence intervals for ICC. Try `ci_method = \"simple\"."
          )
        }
      }
      out_ci <- data.frame(
        ICC_adjusted = c(
          CI_low = icc_ci_adjusted$CI_low,
          CI_high = icc_ci_adjusted$CI_high
        ),
        ICC_conditional = c(
          CI_low = icc_ci_unadjusted$CI_low,
          CI_high = icc_ci_unadjusted$CI_high
        ),
        ICC_unadjusted = c(
          CI_low = icc_ci_unadjusted$CI_low,
          CI_high = icc_ci_unadjusted$CI_high
        )
      )
      out <- rbind(out, out_ci)
      attr(out, "ci") <- ci
    }

    class(out) <- c("icc", "data.frame")
  }
  out
}


#' @rdname icc
#' @export
variance_decomposition <- function(
  model,
  re_formula = NULL,
  robust = TRUE,
  ci = 0.95,
  ...
) {
  if (!inherits(model, "brmsfit")) {
    insight::format_error("Only models from package `brms` are supported.")
  }

  mi <- insight::model_info(model)

  # for multivariate response models, we need a more complicated check...
  if (insight::is_multivariate(model)) {
    resp <- insight::find_response(model)
    is.mixed <- unlist(lapply(resp, function(i) mi[[i]]$is_mixed), use.names = FALSE)
    if (!any(is.mixed)) {
      insight::format_warning("`model` has no random effects.")
      return(NULL)
    }
  } else if (!insight::is_mixed_model(model)) {
    insight::format_warning("`model` has no random effects.")
    return(NULL)
  }

  insight::check_if_installed("brms")

  PPD <- brms::posterior_predict(model, re_formula = re_formula, summary = FALSE, ...)
  var_total <- apply(PPD, MARGIN = 1, FUN = stats::var)

  PPD_0 <- brms::posterior_predict(model, re_formula = NA, summary = FALSE, ...)
  var_rand_intercept <- apply(PPD_0, MARGIN = 1, FUN = stats::var)

  if (robust) {
    fun <- get("median", asNamespace("stats"))
  } else {
    fun <- get("mean", asNamespace("base"))
  }

  var_icc <- var_rand_intercept / var_total
  var_residual <- var_total - var_rand_intercept
  ci_icc <- rev(
    1 -
      stats::quantile(
        var_rand_intercept / var_total,
        probs = c((1 - ci) / 2, (1 + ci) / 2)
      )
  )

  result <- structure(
    class = "icc_decomposed",
    list(
      ICC_decomposed = 1 - fun(var_icc),
      ICC_CI = ci_icc
    )
  )

  attr(result, "var_rand_intercept") <- fun(var_rand_intercept)
  attr(result, "var_residual") <- fun(var_residual)
  attr(result, "var_total") <- fun(var_total)
  attr(result, "ci.var_rand_intercept") <- bayestestR::ci(var_rand_intercept, ci = ci)
  attr(result, "ci.var_residual") <- bayestestR::ci(var_residual, ci = ci)
  attr(result, "ci.var_total") <- bayestestR::ci(var_total, ci = ci)
  attr(result, "ci") <- ci
  attr(result, "re.form") <- re_formula
  attr(result, "ranef") <- model$ranef$group[1]

  # remove data
  attr(attr(result, "ci.var_rand_intercept"), "data") <- NULL
  attr(attr(result, "ci.var_residual"), "data") <- NULL
  attr(attr(result, "ci.var_total"), "data") <- NULL

  result
}


# methods ------------------------------

#' @export
as.data.frame.icc <- function(x, row.names = NULL, optional = FALSE, ...) {
  data.frame(
    ICC_adjusted = x$ICC_adjusted,
    ICC_unadjusted = x$ICC_unadjusted,
    stringsAsFactors = FALSE,
    row.names = row.names,
    optional = optional,
    ...
  )
}


#' @export
print.icc <- function(x, digits = 3, ...) {
  insight::print_color("# Intraclass Correlation Coefficient\n\n", "blue")

  out <- c(
    sprintf("    Adjusted ICC: %.*f", digits, x$ICC_adjusted[1]),
    sprintf("  Unadjusted ICC: %.*f", digits, x$ICC_unadjusted[1])
  )

  # add CI
  if (length(x$ICC_adjusted) == 3) {
    out[1] <- .add_r2_ci_to_print(
      out[1],
      x$ICC_adjusted[2],
      x$ICC_adjusted[3],
      digits = digits
    )
  }
  if (length(x$ICC_unadjusted) == 3) {
    out[2] <- .add_r2_ci_to_print(
      out[2],
      x$ICC_unadjusted[2],
      x$ICC_unadjusted[3],
      digits = digits
    )
  }

  # separate lines for multiple R2
  out <- paste(out, collapse = "\n")

  cat(out)
  cat("\n")
  invisible(x)
}


#' @export
print.icc_by_group <- function(x, digits = 3, ...) {
  insight::print_color("# ICC by Group\n\n", "blue")
  cat(insight::export_table(x, digits = digits))
  invisible(x)
}


#' @export
print.icc_decomposed <- function(x, digits = 2, ...) {
  # print model information
  cat("# Random Effect Variances and ICC\n\n")

  reform <- attr(x, "re.form", exact = TRUE)
  if (is.null(reform)) {
    reform <- "all random effects"
  } else {
    reform <- insight::safe_deparse(reform)
  }

  cat(sprintf("Conditioned on: %s\n\n", reform))

  prob <- attr(x, "ci", exact = TRUE)

  cat(insight::print_color("## Variance Ratio (comparable to ICC)\n", "blue"))

  icc.val <- sprintf("%.*f", digits, x$ICC_decomposed)

  ci.icc.lo <- sprintf("%.*f", digits, x$ICC_CI[1])
  ci.icc.hi <- sprintf("%.*f", digits, x$ICC_CI[2])

  # ICC
  cat(sprintf(
    "Ratio: %s  CI %i%%: [%s %s]\n",
    icc.val,
    as.integer(round(prob * 100)),
    ci.icc.lo,
    ci.icc.hi
  ))

  cat(insight::print_color(
    "\n## Variances of Posterior Predicted Distribution\n",
    "blue"
  ))

  null.model <- sprintf("%.*f", digits, attr(x, "var_rand_intercept", exact = TRUE))

  ci.null <- attr(x, "ci.var_rand_intercept", exact = TRUE)
  ci.null.lo <- sprintf("%.*f", digits, ci.null$CI_low)
  ci.null.hi <- sprintf("%.*f", digits, ci.null$CI_high)

  full.model <- sprintf("%.*f", digits, attr(x, "var_total", exact = TRUE))

  ci.full <- attr(x, "ci.var_total", exact = TRUE)
  ci.full.lo <- sprintf("%.*f", digits, ci.full$CI_low)
  ci.full.hi <- sprintf("%.*f", digits, ci.full$CI_high)

  ml <- max(nchar(null.model), nchar(full.model))
  ml.ci <- max(nchar(ci.full.lo), nchar(ci.null.lo))
  mh.ci <- max(nchar(ci.full.hi), nchar(ci.null.hi))

  # Conditioned on fixed effects
  cat(sprintf(
    "Conditioned on fixed effects: %*s  CI %i%%: [%*s %*s]\n",
    ml,
    null.model,
    as.integer(round(prob * 100)),
    ml.ci,
    ci.null.lo,
    mh.ci,
    ci.null.hi
  ))

  # Conditioned on random effects
  cat(sprintf(
    "Conditioned on rand. effects: %*s  CI %i%%: [%*s %*s]\n",
    ml,
    full.model,
    as.integer(round(prob * 100)),
    ml.ci,
    ci.full.lo,
    mh.ci,
    ci.full.hi
  ))

  cat(insight::print_color("\n## Difference in Variances\n", "red"))

  res <- sprintf("%.*f", digits, attr(x, "var_residual", exact = TRUE))

  ci.res <- attr(x, "ci.var_residual", exact = TRUE)
  ci.res.lo <- sprintf("%.*f", digits, ci.res$CI_low)
  ci.res.hi <- sprintf("%.*f", digits, ci.res$CI_high)

  # ICC
  cat(sprintf(
    "Difference: %s  CI %i%%: [%s %s]\n",
    res,
    as.integer(round(prob * 100)),
    ci.res.lo,
    ci.res.hi
  ))

  invisible(x)
}


# helper -----------------

.compute_random_vars <- function(
  model,
  tolerance,
  components = c("var.fixed", "var.random", "var.residual"),
  name_fun = "icc()",
  name_full = "ICC",
  null_model = NULL,
  model_component = NULL,
  approximation = "lognormal",
  verbose = TRUE
) {
  vars <- tryCatch(
    insight::get_variance(
      model,
      name_fun = name_fun,
      name_full = name_full,
      tolerance = tolerance,
      null_model = null_model,
      approximation = approximation,
      model_component = model_component,
      verbose = verbose
    ),
    error = function(e) {
      if (inherits(e, c("simpleError", "error")) && verbose) {
        insight::print_color(e$message, "red")
        cat("\n")
      }
      NULL
    }
  )

  if (is.null(vars) || all(is.na(vars))) {
    return(NA)
  }

  # check if we have successfully computed all variance components...
  check_elements <- sapply(components, function(.i) !is.null(vars[[.i]]))

  if (!all(check_elements)) {
    return(NA)
  }

  vars
}


# bootstrapping ------------------

# bootstrapping using package "boot"
.boot_icc_fun <- function(data, indices, model, tolerance) {
  d <- data[indices, ] # allows boot to select sample
  fit <- suppressWarnings(suppressMessages(stats::update(model, data = d)))
  vars <- .compute_random_vars(
    fit,
    tolerance,
    verbose = isTRUE(getOption("easystats_errors", FALSE))
  )
  if (is.null(vars) || all(is.na(vars))) {
    return(c(NA, NA))
  }
  c(
    vars$var.random / (vars$var.random + vars$var.residual),
    vars$var.random / (vars$var.fixed + vars$var.random + vars$var.residual)
  )
}


# bootstrapping using "lme4::bootMer"
.boot_icc_fun_lme4 <- function(model) {
  vars <- .compute_random_vars(
    model,
    tolerance = 1e-10,
    verbose = isTRUE(getOption("easystats_errors", FALSE))
  )
  if (is.null(vars) || all(is.na(vars))) {
    return(c(NA, NA))
  }
  c(
    vars$var.random / (vars$var.random + vars$var.residual),
    vars$var.random / (vars$var.fixed + vars$var.random + vars$var.residual)
  )
}


# prepare arguments for "lme4::bootMer"
.do_lme4_bootmer <- function(model, .boot_fun, iterations, dots) {
  insight::check_if_installed(c("lme4", "boot"))
  my_args <- list(
    model,
    .boot_fun,
    nsim = iterations,
    type = "parametric",
    parallel = "no",
    use.u = FALSE,
    ncpus = 1
  )
  # add/overwrite dot-args
  if (!is.null(dots[["use.u"]])) {
    my_args$use.u <- dots[["use.u"]]
  }
  if (!is.null(dots[["re.form"]])) {
    my_args$re.form <- dots[["re.form"]]
  }
  if (!is.null(dots[["type"]])) {
    my_args$type <- dots[["type"]]
    if (my_args$type == "semiparametric") {
      my_args$use.u <- TRUE
    }
  }
  if (!is.null(dots[["parallel"]])) {
    my_args$parallel <- dots[["parallel"]]
  }
  if (!is.null(dots[["ncpus"]])) {
    my_args$ncpus <- dots[["ncpus"]]
  }
  # bootsrap
  do.call(lme4::bootMer, args = my_args)
}


# main function for bootstrapping
.bootstrap_icc <- function(model, iterations, tolerance, ci_method = NULL, ...) {
  if (
    inherits(model, c("merMod", "lmerMod", "glmmTMB")) && !identical(ci_method, "boot")
  ) {
    result <- .do_lme4_bootmer(
      model,
      .boot_icc_fun_lme4,
      iterations,
      dots = list(...)
    )
  } else {
    insight::check_if_installed("boot")
    result <- boot::boot(
      data = insight::get_data(model, verbose = FALSE),
      statistic = .boot_icc_fun,
      R = iterations,
      sim = "ordinary",
      model = model,
      tolerance = tolerance
    )
  }
  result
}


.analytical_icc_ci <- function(model, ci = 0.95, fun = "icc", ...) {
  alpha <- 1 - ci
  n <- insight::n_obs(model)
  df_int <- if (insight::has_intercept(model)) {
    1
  } else {
    0
  }

  model_rank <- tryCatch(
    if (is.null(model$rank)) {
      insight::n_parameters(model) - df_int
    } else {
      model$rank - df_int
    },
    error = function(e) insight::n_parameters(model) - df_int
  )

  if (identical(fun, "icc")) {
    model_icc <- icc(model, ci = NULL, verbose = FALSE, ...)
  } else {
    model_icc <- r2_nakagawa(model, ci = NULL, verbose = FALSE, ...)
  }

  out <- lapply(model_icc, function(.icc) {
    ci_low <- stats::uniroot(
      .pRsq,
      c(0.00001, 0.99999),
      R2_obs = as.vector(.icc),
      p = model_rank,
      nobs = n,
      alpha = 1 - alpha / 2
    )$root

    ci_high <- stats::uniroot(
      .pRsq,
      c(0.00001, 0.99999),
      R2_obs = as.vector(.icc),
      p = model_rank,
      nobs = n,
      alpha = alpha / 2
    )$root

    data.frame(CI_low = ci_low, CI_high = ci_high)
  })

  names(out) <- names(model_icc)
  out
}
