require "date"
require "bigdecimal"
require "securerandom"

class PracticeTransferExport
  class Invalid < StandardError; end
  MAX_ENTRIES = 500

  def initialize(user:, from:, to:, descriptions: false)
    @user, @from, @to, @descriptions = user, Date.iso8601(from.to_s), Date.iso8601(to.to_s), descriptions
    raise Invalid, "Der Zeitraum ist ungültig." if @from > @to || !(1900..2200).cover?(@from.year) || !(1900..2200).cover?(@to.year)
  rescue Date::Error
    raise Invalid, "Bitte Beginn und Ende des Zeitraums angeben."
  end

  def call
    entries = @user.entries.where(date: @from..@to).order(:id).limit(MAX_ENTRIES + 1).to_a
    raise Invalid, "Höchstens 500 Einträge je Export. Bitte den Zeitraum verkleinern." if entries.length > MAX_ENTRIES
    namespace = @user.with_lock do
      @user.update!(practice_transfer_id: SecureRandom.uuid) if @user.practice_transfer_id.blank?
      @user.practice_transfer_id
    end
    rates = MileageRate.where(year: (@from.year..@to.year)).pluck(:year, :rate_per_km).to_h
    skipped = 0
    rows = entries.flat_map do |entry|
      if entry.start_time.present? && entry.end_time.nil?
        skipped += 1
        next []
      end
      hours, minutes = entry.hours_and_minutes
      total_minutes = hours * 60 + minutes
      common = { source_id: entry.id.to_s, date: entry.date.iso8601, education: entry.praktikums_typ,
        activity: entry.entry_art, duration_minutes: total_minutes,
        description: @descriptions ? entry.beschreibung.to_s.first(4_000) : nil,
        cost_cents: entry.kosten ? (entry.kosten.to_d * 100).round.to_i : nil }
      result = []
      if entry.distance_km.to_i.positive?
        rate = rates[entry.date.year] || BigDecimal("0.42") # Existing source application fallback, not a tax determination.
        result << common.merge(type: "mileage", kilometers: entry.distance_km, rate_cents: (rate.to_d * 100).round.to_i,
          rate_origin: rates.key?(entry.date.year) ? "configured" : "source_default")
      end
      result << common.merge(type: "development") if total_minutes.positive?
      result
    end
    { format: "pcm-professional-transfer-v1", source_namespace: namespace, exported_at: Time.current.iso8601,
      from: @from.iso8601, to: @to.iso8601, skipped_running: skipped, records: rows }
  end
end