defmodule ArcadiaCloud.Analytics do
  @moduledoc """
  Cost-vs-revenue analytics — the operator's margin view.

  Revenue side: tenant_invoice_lines / tenant_invoices (what tenants owe
  Sky AI, ex-GST).
  COGS side: cloud_cost_lines (what DO bills Sky AI), attributed to a
  tenant/deployment via cloud_resources.

  margin = revenue (ex-GST) - COGS. GST is pass-through, excluded both
  sides.

  Phase 3 runs these queries directly. A monthly_margin_rollup
  materialized view is the optimization for when the dashboard is slow —
  deliberately deferred.
  """

  import Ecto.Query, warn: false

  alias ArcadiaCloud.Repo
  alias ArcadiaCloud.Cloud.CloudResource
  alias ArcadiaCloud.Billing.{CloudCostLine, TenantInvoice, TenantInvoiceLine}
  alias ArcadiaCloud.Deployments.CloudDeployment
  alias ArcadiaCloud.{Catalog, Metering, Quoting, Subscriptions}

  @doc """
  Margin summary for a month. `period` is the first-of-month date.
  Returns overall P&L plus per-tenant and per-deployment breakdowns.
  """
  def margin_summary(%Date{} = period) do
    revenue_overall = total_revenue(period)
    cogs_overall = total_cogs(period)

    %{
      period: period,
      overall: margin_row(revenue_overall, cogs_overall),
      by_tenant: by_tenant(period),
      by_deployment: by_deployment(period)
    }
  end

  # ---- overall --------------------------------------------------------------

  defp total_revenue(period) do
    from(i in TenantInvoice,
      where: i.period_start == ^period,
      select: coalesce(sum(i.subtotal_cents), 0)
    )
    |> Repo.one()
  end

  defp total_cogs(period) do
    from(cl in CloudCostLine,
      where: cl.invoice_period == ^period,
      select: coalesce(sum(cl.amount_cents), 0)
    )
    |> Repo.one()
  end

  # ---- per tenant -----------------------------------------------------------

  defp by_tenant(period) do
    revenue =
      from(i in TenantInvoice,
        where: i.period_start == ^period,
        group_by: i.tenant_id,
        select: {i.tenant_id, sum(i.subtotal_cents)}
      )
      |> Repo.all()
      |> Map.new()

    # A resource's billing tenant is its deployment's tenant if it's in a
    # deployment, else its own tenant_id (skyai-internal infra).
    cogs =
      from(cl in CloudCostLine,
        join: r in CloudResource,
        on: r.id == cl.resource_id,
        left_join: d in CloudDeployment,
        on: d.id == r.deployment_id,
        where: cl.invoice_period == ^period,
        group_by: fragment("COALESCE(?, ?)", d.tenant_id, r.tenant_id),
        select: {fragment("COALESCE(?, ?)", d.tenant_id, r.tenant_id), sum(cl.amount_cents)}
      )
      |> Repo.all()
      |> Enum.reject(fn {tenant_id, _} -> is_nil(tenant_id) end)
      |> Map.new()

    merge_keys(revenue, cogs)
    |> Enum.map(fn tenant_id ->
      Map.put(
        margin_row(Map.get(revenue, tenant_id, 0), Map.get(cogs, tenant_id, 0)),
        :tenant_id,
        tenant_id
      )
    end)
    |> Enum.sort_by(& &1.margin_cents)
  end

  # ---- per deployment -------------------------------------------------------

  defp by_deployment(period) do
    revenue =
      from(l in TenantInvoiceLine,
        join: i in TenantInvoice,
        on: i.id == l.invoice_id,
        where: i.period_start == ^period and not is_nil(l.deployment_id) and l.kind != "tax",
        group_by: l.deployment_id,
        select: {l.deployment_id, sum(l.amount_cents)}
      )
      |> Repo.all()
      |> Map.new()

    cogs =
      from(cl in CloudCostLine,
        join: r in CloudResource,
        on: r.id == cl.resource_id,
        where: cl.invoice_period == ^period and not is_nil(r.deployment_id),
        group_by: r.deployment_id,
        select: {r.deployment_id, sum(cl.amount_cents)}
      )
      |> Repo.all()
      |> Map.new()

    names =
      from(d in CloudDeployment, select: {d.id, d.slug}) |> Repo.all() |> Map.new()

    merge_keys(revenue, cogs)
    |> Enum.map(fn dep_id ->
      margin_row(Map.get(revenue, dep_id, 0), Map.get(cogs, dep_id, 0))
      |> Map.put(:deployment_id, dep_id)
      |> Map.put(:deployment_slug, Map.get(names, dep_id))
    end)
    |> Enum.sort_by(& &1.margin_cents)
  end

  # ---- by kind --------------------------------------------------------------

  @doc "Revenue and COGS broken down by resource kind (separate axes — DO kinds and billing kinds don't 1:1)."
  def by_kind(%Date{} = period) do
    revenue =
      from(l in TenantInvoiceLine,
        join: i in TenantInvoice,
        on: i.id == l.invoice_id,
        where: i.period_start == ^period and not is_nil(l.resource_kind),
        group_by: l.resource_kind,
        select: {l.resource_kind, sum(l.amount_cents)}
      )
      |> Repo.all()
      |> Enum.map(fn {k, v} -> %{kind: k, amount_cents: v} end)

    cogs =
      from(cl in CloudCostLine,
        where: cl.invoice_period == ^period and not is_nil(cl.kind),
        group_by: cl.kind,
        select: {cl.kind, sum(cl.amount_cents)}
      )
      |> Repo.all()
      |> Enum.map(fn {k, v} -> %{kind: k, amount_cents: v} end)

    %{revenue_by_kind: revenue, cogs_by_kind: cogs}
  end

  # ---- live accrual ---------------------------------------------------------

  @doc """
  Current-month unbilled accrual per tenant — runs the quote engine with
  partial metered usage. Answers "what are tenants racking up right now,
  before the month-end rollup".
  """
  def live_accrual do
    today = Date.utc_today()
    month_start = Date.beginning_of_month(today)

    Subscriptions.list_active_subscriptions()
    |> Enum.map(fn sub ->
      deployment = Repo.get(CloudDeployment, sub.deployment_id)
      plan_version = Catalog.get_version(sub.plan_version_id)
      addons = Subscriptions.list_addons(sub.id)
      usage = Metering.usage_for_period(sub.deployment_id, month_start, today)
      quote = Quoting.quote(plan_version, addons, usage: usage)

      %{
        tenant_id: deployment && deployment.tenant_id,
        deployment_id: sub.deployment_id,
        deployment_slug: deployment && deployment.slug,
        accrued_cents: quote.all_in_monthly_cents,
        recurring_cents: quote.recurring.monthly_total_cents,
        overage_cents: quote.overage.monthly_total_cents
      }
    end)
  end

  # ---- helpers --------------------------------------------------------------

  defp margin_row(revenue, cogs) do
    revenue = revenue || 0
    cogs = cogs || 0
    margin = revenue - cogs

    %{
      revenue_cents: revenue,
      cogs_cents: cogs,
      margin_cents: margin,
      margin_pct: if(revenue > 0, do: Float.round(margin / revenue * 100, 1), else: nil)
    }
  end

  defp merge_keys(map_a, map_b) do
    (Map.keys(map_a) ++ Map.keys(map_b)) |> Enum.uniq()
  end
end