import { NextRequest, NextResponse } from "next/server";
import { getSessionUser } from "@/lib/session";
import { listTenants } from "@/lib/k8s";
import { listVisibleTenants } from "@/lib/visibility";
import { getTeamInfo, getTeamSpendLogsV2 } from "@/lib/litellm";
import { safeError } from "@/lib/errors";

/**
 * GET /api/usage
 *
 * Customers: tenant resolved server-side from the user's orgId. The
 *            response is filtered by the tenant's `litellmKeyAlias` so
 *            sibling tenants in the same org don't bleed into the total.
 * Platform admins: may pass ?teamId=... to inspect any team. They may
 *                  also pass ?keyAlias=... to scope to a single tenant.
 *
 * Slice 2 note
 * ------------
 * LiteLLM teams are now shared across all tenants of an org. The team's
 * `/team/info` budget is the *company* budget; the per-tenant numbers
 * come from filtering spend logs by `key_alias`. If a tenant has no
 * `litellmKeyAlias` in status (transitional state right after upgrade,
 * before the operator has reconciled), we fall back to team-level
 * filtering — the numbers will be slightly inflated for that one
 * reconcile cycle.
 */
export async function GET(req: NextRequest) {
  const user = await getSessionUser();
  if (!user)
    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });

  let teamId: string | null = null;
  let keyAlias: string | null = null;

  if (user.isPlatform) {
    teamId = req.nextUrl.searchParams.get("teamId") ?? null;
    keyAlias = req.nextUrl.searchParams.get("keyAlias") ?? null;
  }

  // For customers (or admins without explicit params): resolve from
  // the user's *visible* tenants. With Slice 6, a `user`-role member
  // can only see usage for tenants they're assigned to — a non-assigned
  // user defaults to "no active tenant" (404).
  //
  // Owner and platform get the full org-scoped list and pick the first
  // tenant, matching the dashboard's "current instance" semantics.
  if (!teamId) {
    const allTenants = await listTenants();
    const visible = await listVisibleTenants(user, allTenants);
    const orgTenant = visible.find((t) => !!t.status?.litellmTeamId);

    if (!orgTenant?.status?.litellmTeamId) {
      return NextResponse.json(
        { error: "No active tenant found for your organization" },
        { status: 404 }
      );
    }
    teamId = orgTenant.status.litellmTeamId;

    // If the operator has populated the per-tenant key alias, filter by it.
    // Falling back to team-level (no alias) will return the org total, which
    // is acceptable transitionally but means siblings' usage shows up here.
    if (orgTenant.status.litellmKeyAlias) {
      keyAlias = orgTenant.status.litellmKeyAlias;
    }
  }

  // Month param: YYYY-MM, defaults to current month
  const now = new Date();
  const monthParam =
    req.nextUrl.searchParams.get("month") ||
    `${now.getFullYear()}-${String(now.getMonth() + 1).padStart(2, "0")}`;

  const [year, month] = monthParam.split("-").map(Number);
  const startDate = new Date(year, month - 1, 1);
  const endDate = new Date(year, month, 0); // last day of month

  const startStr = startDate.toISOString().split("T")[0];
  const endStr = endDate.toISOString().split("T")[0];

  try {
    const teamInfo = await getTeamInfo(teamId);

    // Fetch all pages from the team. We always query at the team level —
    // LiteLLM's /spend/logs/v2 doesn't filter by key_alias reliably across
    // versions, so we paginate and post-filter in code. For pilot scale
    // this is cheap; if a single team ever exceeds ~10k entries/month we
    // can revisit.
    const allRequests: any[] = [];
    let page = 1;
    while (true) {
      const result = await getTeamSpendLogsV2(
        teamId,
        startStr,
        endStr,
        page,
        100
      );
      allRequests.push(...(result.data || []));
      if (page >= (result.total_pages || 1)) break;
      page++;
    }

    // Apply key_alias post-filter when scoping to a single tenant. Match
    // both `key_alias` (newer LiteLLM) and `metadata.user_api_key_alias`
    // (older builds nest it inside metadata).
    const scoped = keyAlias
      ? allRequests.filter((r) => {
          const alias =
            r.key_alias ??
            r.metadata?.user_api_key_alias ??
            r.api_key_alias ??
            null;
          return alias === keyAlias;
        })
      : allRequests;

    // Aggregate by day
    const byDay: Record<
      string,
      { inputTokens: number; outputTokens: number; spend: number }
    > = {};
    for (const r of scoped) {
      const day = (r.startTime || r.endTime || "").slice(0, 10);
      if (!day) continue;
      if (!byDay[day])
        byDay[day] = { inputTokens: 0, outputTokens: 0, spend: 0 };
      byDay[day].inputTokens += r.prompt_tokens || 0;
      byDay[day].outputTokens += r.completion_tokens || 0;
      byDay[day].spend += r.spend || 0;
    }

    const dailyUsage = Object.entries(byDay)
      .sort(([a], [b]) => a.localeCompare(b))
      .map(([date, d]) => ({ date, ...d }));

    const totalInput = scoped.reduce(
      (s, r) => s + (r.prompt_tokens || 0),
      0
    );
    const totalOutput = scoped.reduce(
      (s, r) => s + (r.completion_tokens || 0),
      0
    );
    const totalSpend = scoped.reduce((s, r) => s + (r.spend || 0), 0);

    return NextResponse.json({
      teamId,
      keyAlias, // null when not filtering — useful for the client to know it sees company-wide data
      month: monthParam,
      currentPeriod: {
        inputTokens: totalInput,
        outputTokens: totalOutput,
        totalSpend,
        requestCount: scoped.length,
      },
      // Budget is always team-level (= company budget). Spend reported
      // here is the team total, not the per-key total — the customer
      // wants to see "how much of our company budget is left", not just
      // "how much has this one tenant cost".
      budget: {
        maxBudget: teamInfo?.team_info?.max_budget ?? null,
        spend: teamInfo?.team_info?.spend ?? 0,
        remaining: teamInfo?.team_info?.max_budget
          ? teamInfo.team_info.max_budget - (teamInfo.team_info.spend ?? 0)
          : null,
      },
      rateLimits: {
        rpm: teamInfo?.team_info?.rpm_limit ?? null,
        tpm: teamInfo?.team_info?.tpm_limit ?? null,
      },
      dailyUsage,
    });
  } catch (e: any) {
    console.error("Usage fetch error:", e.message);
    return NextResponse.json(
      { error: safeError(e, "Failed to fetch usage") },
      { status: 500 }
    );
  }
}