suppressPackageStartupMessages({
  library(dplyr)
  library(tidyr)
})

# estimate_naive_vasopressor_mortality_effect() computes the first simple
# mortality comparison for the early vasopressor teaching example.
#
# This function deliberately does NOT adjust for confounding.
# It only compares observed 28-day mortality between eligible patients who did
# and did not receive early vasopressors.
#
# Arguments:
# - icu_data: a data frame or tibble with the columns created by
#   simulate_icu_cohort().
#
# Returns:
# - A named list with four pieces:
#   - eligible_icu_patients: only the target-trial eligible patients.
#   - mortality_risks_by_early_vasopressor: observed 28-day mortality risk in
#     each treatment group.
#   - mortality_effect_estimates: naive risk difference and risk ratio.
#   - baseline_characteristics_by_early_vasopressor: compact baseline means by
#     observed treatment group.
#
# Example REPL use:
#
#   source("R/simulate_icu_cohort.R")
#   icu_data <- simulate_icu_cohort(n_patients = 1000, seed = 20260531)
#   mortality_analysis <- estimate_naive_vasopressor_mortality_effect(icu_data)
#   mortality_analysis$mortality_effect_estimates
#
estimate_naive_vasopressor_mortality_effect <- function(icu_data) {
  eligible_icu_patients <- icu_data |>
    filter(eligible == 1)

  mortality_risks_by_early_vasopressor <- eligible_icu_patients |>
    group_by(early_vasopressor) |>
    summarize(
      patient_count = n(),
      mortality_risk_28d = mean(death_28d),
      .groups = "drop"
    ) |>
    mutate(
      observed_treatment_group = factor(
        early_vasopressor,
        levels = c(0, 1),
        labels = c("No early vasopressor", "Early vasopressor")
      )
    ) |>
    select(observed_treatment_group, patient_count, mortality_risk_28d)

  mortality_risk_early_vasopressor <- mortality_risks_by_early_vasopressor |>
    filter(observed_treatment_group == "Early vasopressor") |>
    pull(mortality_risk_28d)

  mortality_risk_no_early_vasopressor <- mortality_risks_by_early_vasopressor |>
    filter(observed_treatment_group == "No early vasopressor") |>
    pull(mortality_risk_28d)

  mortality_effect_estimates <- tibble(
    estimate = c(
      "Eligible patients",
      "Early vasopressor patients",
      "No early vasopressor patients",
      "28-day mortality risk, early vasopressor",
      "28-day mortality risk, no early vasopressor",
      "Naive risk difference",
      "Naive risk ratio"
    ),
    value = c(
      nrow(eligible_icu_patients),
      sum(eligible_icu_patients$early_vasopressor == 1),
      sum(eligible_icu_patients$early_vasopressor == 0),
      mortality_risk_early_vasopressor,
      mortality_risk_no_early_vasopressor,
      mortality_risk_early_vasopressor - mortality_risk_no_early_vasopressor,
      mortality_risk_early_vasopressor / mortality_risk_no_early_vasopressor
    )
  )

  baseline_characteristics_by_early_vasopressor <- eligible_icu_patients |>
    group_by(early_vasopressor) |>
    summarize(
      mean_age = mean(age),
      mean_sofa_score = mean(sofa_score),
      mean_lactate = mean(lactate),
      mean_map = mean(map),
      .groups = "drop"
    )

  list(
    eligible_icu_patients = eligible_icu_patients,
    mortality_risks_by_early_vasopressor = mortality_risks_by_early_vasopressor,
    mortality_effect_estimates = mortality_effect_estimates,
    baseline_characteristics_by_early_vasopressor = baseline_characteristics_by_early_vasopressor
  )
}