defmodule ArcadiaCloud.Billing do
  @moduledoc """
  Context for cloud cost ingestion: balance snapshots, monthly invoices,
  per-line-item COGS, and resource matching.

  Pipeline:
    BalanceWorker         → cloud_balance_snapshots          (hourly)
    BillingHistoryWorker  → cloud_invoices (headers)          (daily)
    InvoiceIngestWorker   → cloud_cost_lines + resource match (per invoice)

  Phase 1 stops here. Phase 1+ pushes matched cost_lines into skyai-finance
  as expense lines (skyai-internal) or AR (tenant).
  """

  import Ecto.Query, warn: false

  alias ArcadiaCloud.Repo
  alias ArcadiaCloud.Billing.{CloudBalanceSnapshot, CloudInvoice, CloudCostLine}
  alias ArcadiaCloud.Cloud.CloudResource

  # ---- balance --------------------------------------------------------------

  def record_balance(attrs) do
    %CloudBalanceSnapshot{}
    |> CloudBalanceSnapshot.changeset(attrs)
    |> Repo.insert()
  end

  def latest_balance(provider \\ "digitalocean") do
    from(s in CloudBalanceSnapshot,
      where: s.provider == ^provider,
      order_by: [desc: s.generated_at],
      limit: 1
    )
    |> Repo.one()
  end

  # ---- invoices -------------------------------------------------------------

  def upsert_invoice(attrs) do
    provider = attrs[:provider] || attrs["provider"]
    invoice_id = attrs[:provider_invoice_id] || attrs["provider_invoice_id"]

    case Repo.get_by(CloudInvoice, provider: provider, provider_invoice_id: invoice_id) do
      nil ->
        %CloudInvoice{}
        |> CloudInvoice.changeset(attrs)
        |> Repo.insert()

      existing ->
        existing
        |> CloudInvoice.changeset(attrs)
        |> Repo.update()
    end
  end

  def list_invoices_needing_ingest(provider \\ "digitalocean") do
    from(i in CloudInvoice,
      where: i.provider == ^provider and is_nil(i.lines_ingested_at),
      order_by: [desc: i.invoice_period]
    )
    |> Repo.all()
  end

  def mark_invoice_ingested(invoice) do
    now = DateTime.utc_now() |> DateTime.truncate(:second)

    invoice
    |> CloudInvoice.changeset(%{lines_ingested_at: now, csv_fetched_at: now})
    |> Repo.update()
  end

  # ---- cost lines -----------------------------------------------------------

  @doc """
  Replace all cost lines for an invoice in one transaction. CSV is the
  authoritative source for an invoice's content; if we re-fetch, we
  replace not merge.
  """
  def replace_cost_lines(%CloudInvoice{} = invoice, line_attrs_list) when is_list(line_attrs_list) do
    Repo.transaction(fn ->
      Repo.delete_all(from(l in CloudCostLine, where: l.invoice_id == ^invoice.id))

      Enum.each(line_attrs_list, fn attrs ->
        %CloudCostLine{}
        |> CloudCostLine.changeset(Map.put(attrs, :invoice_id, invoice.id))
        |> Repo.insert!()
      end)
    end)
  end

  @doc """
  Match unmatched cost lines for an invoice to cloud_resources by
  (kind, description=name) — case-insensitive. Updates matched_at + resource_id.
  Returns count of newly-matched lines.
  """
  def match_cost_lines_to_resources(%CloudInvoice{id: invoice_id}) do
    unmatched =
      from(l in CloudCostLine,
        where: l.invoice_id == ^invoice_id and is_nil(l.resource_id) and not is_nil(l.kind)
      )
      |> Repo.all()

    now = DateTime.utc_now() |> DateTime.truncate(:second)

    Enum.reduce(unmatched, 0, fn line, acc ->
      case find_resource(line) do
        %CloudResource{id: rid} ->
          line
          |> CloudCostLine.changeset(%{resource_id: rid, matched_at: now})
          |> Repo.update!()

          acc + 1

        nil ->
          acc
      end
    end)
  end

  defp find_resource(%CloudCostLine{kind: kind, description: desc}) when is_binary(desc) do
    name_lower = desc |> extract_name() |> String.downcase()

    from(r in CloudResource,
      where:
        r.kind == ^kind and is_nil(r.deleted_at) and
          fragment("LOWER(?) = ?", r.name, ^name_lower),
      limit: 1
    )
    |> Repo.one()
  end

  defp find_resource(_), do: nil

  # DO CSV description is often "name (size_slug)" or "name-1234 (region) NGB Snapshot".
  # Strip everything after the first " (" — best-effort name extraction.
  defp extract_name(desc) do
    case String.split(desc, " (", parts: 2) do
      [name | _] -> String.trim(name)
      _ -> desc
    end
  end

  def list_cost_lines(opts \\ []) do
    base =
      from(l in CloudCostLine,
        order_by: [desc: l.invoice_period, desc: l.amount_cents]
      )

    base
    |> maybe_filter(:invoice_period, opts[:period])
    |> maybe_filter(:kind, opts[:kind])
    |> maybe_filter(:resource_id, opts[:resource_id])
    |> maybe_limit(opts[:limit])
    |> Repo.all()
  end

  defp maybe_filter(query, _field, nil), do: query

  defp maybe_filter(query, field, value) do
    from(l in query, where: field(l, ^field) == ^value)
  end

  defp maybe_limit(query, nil), do: query
  defp maybe_limit(query, n) when is_integer(n), do: from(q in query, limit: ^n)
end