defmodule Towerops.Reports do
  @moduledoc """
  Context for managing scheduled reports.

  Handles CRUD operations and report generation/delivery.
  """

  import Ecto.Query

  alias Towerops.Alerts
  alias Towerops.Capacity
  alias Towerops.Devices
  alias Towerops.Repo
  alias Towerops.Reports.Report
  alias Towerops.RfLinks

  require Logger

  # -- CRUD --

  def list_reports(organization_id) do
    Report
    |> where(organization_id: ^organization_id)
    |> order_by(desc: :inserted_at)
    |> Repo.all()
  end

  def get_report!(id), do: Repo.get!(Report, id)

  def get_report(id) do
    case Repo.get(Report, id) do
      nil -> {:error, :not_found}
      report -> {:ok, report}
    end
  end

  def create_report(attrs) do
    %Report{}
    |> Report.changeset(attrs)
    |> Repo.insert()
  end

  def update_report(%Report{} = report, attrs) do
    report
    |> Report.changeset(attrs)
    |> Repo.update()
  end

  def delete_report(%Report{} = report) do
    Repo.delete(report)
  end

  def toggle_report(%Report{} = report) do
    update_report(report, %{enabled: !report.enabled})
  end

  # -- Report Generation --

  @doc """
  Generates report data as a CSV string based on report type and scope.
  """
  def generate_csv(%Report{} = report) do
    org_id = report.organization_id
    time_range = parse_time_range(report.scope)

    case report.report_type do
      "uptime_summary" -> generate_uptime_csv(org_id, time_range)
      "alert_history" -> generate_alert_history_csv(org_id, time_range)
      "capacity_trends" -> generate_capacity_csv(org_id)
      "rf_link_health" -> generate_rf_link_csv(org_id)
    end
  end

  defp generate_uptime_csv(org_id, _time_range) do
    devices = Devices.list_organization_devices(org_id)

    header = "Device,IP Address,Status,Last Seen\n"

    rows =
      Enum.map_join(devices, "\n", fn device ->
        status = if device.monitoring_enabled, do: "monitored", else: "unmonitored"
        "#{csv_escape(device.name)},#{device.ip_address},#{status},#{device.updated_at}"
      end)

    {:ok, header <> rows}
  end

  defp generate_alert_history_csv(org_id, _time_range) do
    alerts = Alerts.list_organization_alerts(org_id, 500)

    header = "Alert,Severity,Status,Device,Created At,Resolved At\n"

    rows =
      Enum.map_join(alerts, "\n", fn alert ->
        device_name = if alert.device, do: alert.device.name, else: "-"
        resolved = if alert.resolved_at, do: to_string(alert.resolved_at), else: "-"

        "#{csv_escape(alert.message)},#{alert.severity},#{alert.status},#{csv_escape(device_name)},#{alert.inserted_at},#{resolved}"
      end)

    {:ok, header <> rows}
  end

  defp generate_capacity_csv(org_id) do
    summaries = Capacity.get_organization_capacity_summary(org_id)

    header = "Site,Total Capacity (bps),Throughput (bps),Utilization %\n"

    rows =
      Enum.map_join(summaries, "\n", fn s ->
        "#{csv_escape(s.site_name || "Unknown")},#{s.total_capacity_bps},#{s.total_throughput_bps},#{s.utilization_pct}"
      end)

    {:ok, header <> rows}
  end

  defp generate_rf_link_csv(org_id) do
    links = RfLinks.list_rf_links(org_id)

    header = "Client,MAC,Signal (dBm),SNR (dB),TX Rate,RX Rate,Health,Last Seen\n"

    rows =
      Enum.map_join(links, "\n", fn link ->
        name = link.hostname || link.ip_address || link.mac_address || "-"

        "#{csv_escape(name)},#{link.mac_address},#{link.signal_strength || "-"},#{link.snr || "-"},#{link.tx_rate || "-"},#{link.rx_rate || "-"},#{link.health},#{link.last_seen_at}"
      end)

    {:ok, header <> rows}
  end

  @doc """
  Escapes a value for inclusion in a CSV cell.

  Wraps values containing commas, quotes, or newlines in double-quotes and
  doubles any embedded quotes. `nil` becomes the empty string; non-binary
  non-nil values are coerced via `to_string/1`.
  """
  @spec csv_escape(term()) :: String.t()
  def csv_escape(nil), do: ""

  def csv_escape(value) when is_binary(value) do
    if String.contains?(value, [",", "\"", "\n"]) do
      "\"#{String.replace(value, "\"", "\"\"")}\""
    else
      value
    end
  end

  def csv_escape(value), do: to_string(value)

  @doc """
  Parses the `days` field of a report's scope map into a `%{from, to}` range
  ending at `DateTime.utc_now/0`. Defaults to 7 days when `days` is missing.
  """
  @spec parse_time_range(map()) :: %{from: DateTime.t(), to: DateTime.t()}
  def parse_time_range(scope) when is_map(scope) do
    days = Map.get(scope, "days", 7)
    now = DateTime.utc_now()
    %{from: DateTime.add(now, -days, :day), to: now}
  end

  # -- Schedule Helpers --

  @doc """
  Returns true if a report is due to run based on its schedule.
  """
  def due?(%Report{schedule: %{"type" => "one_time"}} = report) do
    is_nil(report.last_run_at)
  end

  def due?(%Report{schedule: %{"type" => "daily"}} = report) do
    elapsed_since_last_run(report) >= 86_400
  end

  def due?(%Report{schedule: %{"type" => "weekly"}} = report) do
    elapsed_since_last_run(report) >= 604_800
  end

  def due?(%Report{schedule: %{"type" => "monthly"}} = report) do
    elapsed_since_last_run(report) >= 2_592_000
  end

  def due?(_), do: false

  defp elapsed_since_last_run(%{last_run_at: nil}), do: :infinity

  defp elapsed_since_last_run(%{last_run_at: last_run_at}) do
    DateTime.diff(DateTime.utc_now(), last_run_at, :second)
  end

  @doc """
  Marks a report as having been run.
  """
  def mark_run(%Report{} = report, status) do
    update_report(report, %{
      last_run_at: Towerops.Time.now(),
      last_run_status: status
    })
  end
end