# ── track_erosion_depth ───────────────────────────────────────────────────────
test_that("track_erosion_depth returns correct structure", {
  data(erosion_profile, package = "soiltillr")
  result <- track_erosion_depth(erosion_profile, "year", "field_id",
                                "erosion_depth_mm")
  expect_s3_class(result, "data.frame")
  expect_true(all(c("year", "field_id", "erosion_depth_mm",
                    "change_mm", "cumulative_loss_mm", "trend") %in% names(result)))
})

test_that("track_erosion_depth first year is baseline with NA change", {
  data(erosion_profile, package = "soiltillr")
  result <- track_erosion_depth(erosion_profile, "year", "field_id",
                                "erosion_depth_mm")
  baselines <- result[result$trend == "baseline", ]
  expect_true(all(is.na(baselines$change_mm)))
})

test_that("track_erosion_depth cumulative is non-decreasing", {
  data(erosion_profile, package = "soiltillr")
  result <- track_erosion_depth(erosion_profile, "year", "field_id",
                                "erosion_depth_mm")
  for (fld in unique(result$field_id)) {
    sub <- result[result$field_id == fld, ]
    sub <- sub[order(sub$year), ]
    expect_true(all(diff(sub$cumulative_loss_mm) >= 0))
  }
})

test_that("track_erosion_depth detects improving trend", {
  df <- data.frame(
    year             = 2020:2022,
    field_id         = rep("A", 3),
    erosion_depth_mm = c(5.0, 3.0, 1.5)
  )
  result <- track_erosion_depth(df, "year", "field_id", "erosion_depth_mm",
                                validate = FALSE)
  expect_true(any(result$trend == "improving"))
})

test_that("track_erosion_depth fails on invalid data", {
  df <- data.frame(
    year             = 2020:2022,
    field_id         = rep("A", 3),
    erosion_depth_mm = c(5, -1, 2)
  )
  expect_error(
    track_erosion_depth(df, "year", "field_id", "erosion_depth_mm"),
    "Data validation failed"
  )
})

# ── estimate_soil_loss ────────────────────────────────────────────────────────
test_that("estimate_soil_loss returns correct structure", {
  data(erosion_profile, package = "soiltillr")
  result <- estimate_soil_loss(erosion_profile, "year", "field_id",
                               "erosion_depth_mm", "bulk_density_g_cm3",
                               slope_col = "slope_pct")
  expect_s3_class(result, "data.frame")
  expect_true(all(c("year", "field_id", "erosion_depth_mm",
                    "estimated_loss_t_ha", "loss_category") %in% names(result)))
})

test_that("estimate_soil_loss values are positive", {
  data(erosion_profile, package = "soiltillr")
  result <- estimate_soil_loss(erosion_profile, "year", "field_id",
                               "erosion_depth_mm", "bulk_density_g_cm3")
  expect_true(all(result$estimated_loss_t_ha > 0))
})

test_that("estimate_soil_loss loss_category is valid", {
  data(erosion_profile, package = "soiltillr")
  result <- estimate_soil_loss(erosion_profile, "year", "field_id",
                               "erosion_depth_mm", "bulk_density_g_cm3")
  valid_cats <- c("tolerable", "moderate", "severe", "very severe")
  expect_true(all(as.character(result$loss_category) %in% valid_cats))
})

test_that("estimate_soil_loss uses default bulk density when col missing", {
  df <- data.frame(
    year             = 2020:2021,
    field_id         = rep("A", 2),
    erosion_depth_mm = c(3.0, 2.5)
  )
  expect_warning(
    result <- estimate_soil_loss(df, "year", "field_id",
                                 "erosion_depth_mm", "bd_missing"),
    "default"
  )
  expect_true(all(result$estimated_loss_t_ha > 0))
})

# ── compare_fields ────────────────────────────────────────────────────────────
test_that("compare_fields returns one row per year", {
  data(erosion_profile, package = "soiltillr")
  result <- compare_fields(erosion_profile, "year", "field_id",
                           "erosion_depth_mm", "organic_matter_pct")
  n_years <- length(unique(erosion_profile$year))
  expect_equal(nrow(result), n_years)
})

test_that("compare_fields includes difference column", {
  data(erosion_profile, package = "soiltillr")
  result <- compare_fields(erosion_profile, "year", "field_id",
                           "erosion_depth_mm", "organic_matter_pct")
  expect_true("erosion_diff_mm" %in% names(result))
})

test_that("compare_fields fails with single field", {
  df <- data.frame(
    year             = 2020:2022,
    field_id         = rep("A", 3),
    erosion_depth_mm = c(3, 2.5, 2),
    om               = c(2.8, 3.0, 3.2)
  )
  expect_error(
    compare_fields(df, "year", "field_id", "erosion_depth_mm", "om"),
    "two fields"
  )
})