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class TargetNutrientCalculator
# Derive nutrient columns from the NutrientMeasurement table
NUTRIENT_COLUMNS = (NutrientMeasurement.column_names - %w[id measured_on created_at updated_at])
.map!(&:to_sym)
.freeze
# Returns an unsaved NutrientMeasurement with target concentrations (e.g., mg/L)
def self.call
rafts = Raft.includes(:crop).where.not(crop_id: nil)
total = rafts.count
return empty_measurement if total.zero?
sums = Hash.new(0.0)
rafts.each do |raft|
NUTRIENT_COLUMNS.each do |col|
v = raft.crop.public_send(col)
sums[col] += v.to_f if v
end
end
targets = sums.transform_values { |s| s / total }
NutrientMeasurement.new({ measured_on: Date.current }.merge(targets))
end
private
def empty_measurement
NutrientMeasurement.new(
{ measured_on: Date.current }.merge(NUTRIENT_COLUMNS.index_with { 0.0 })
)
end
end
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