import { NextRequest, NextResponse } from "next/server";

import { prisma } from "@/lib/prisma";

type ComponentHealth = {
  status: "ok" | "degraded" | "down";
  message: string;
  meta?: unknown;
};

function normalizePositiveNumber(value: string | undefined, fallback: number) {
  const parsed = Number(value);
  if (!Number.isFinite(parsed) || parsed <= 0) {
    return fallback;
  }

  return parsed;
}

function maybeExposeDetails(req: NextRequest) {
  const expected = process.env.HEALTHCHECK_TOKEN?.trim();
  if (!expected) {
    return false;
  }

  const fromHeader = req.headers.get("authorization")?.trim() || req.headers.get("x-health-token")?.trim();
  const fromQuery = new URL(req.url).searchParams.get("token")?.trim();
  const token = fromHeader || fromQuery;
  if (!token) {
    return false;
  }

  return token === expected || token === `Bearer ${expected}`;
}

function isUp(components: ComponentHealth[]) {
  return components.every((item) => item.status === "ok");
}

export async function GET(req: NextRequest) {
  const checks: Record<string, ComponentHealth> = {};

  try {
    await prisma.$queryRaw`SELECT 1`;
    checks.database = { status: "ok", message: "connected" };
  } catch (error) {
    checks.database = {
      status: "down",
      message: error instanceof Error ? error.message : "Database query failed"
    };
  }

  let retries: ComponentHealth = { status: "ok", message: "campaign retry worker state unavailable" };
  let webhook: ComponentHealth = { status: "ok", message: "webhook events healthy" };
  if (checks.database.status === "ok") {
    const failureThreshold = normalizePositiveNumber(process.env.WEBHOOK_FAILURE_RATE_THRESHOLD_PER_HOUR, 10);
    const staleThresholdMinutes = normalizePositiveNumber(process.env.RETRY_WORKER_STALE_MINUTES, 30);

    const [retryState, webhookFailureCount, disconnectedChannels] = await Promise.all([
      prisma.backgroundJobState.findUnique({
        where: { jobName: "campaign-retry-worker" },
        select: {
          lockedUntil: true,
          lastRunCompletedAt: true,
          lastRunStatus: true,
          lastError: true,
          consecutiveFailures: true
        }
      }),
      prisma.webhookEvent.count({
        where: {
          processStatus: "failed",
          createdAt: {
            gte: new Date(Date.now() - 60 * 60 * 1000)
          }
        }
      }),
      prisma.channel.count({ where: { status: "DISCONNECTED" } })
    ]);

    if (!retryState) {
      retries = {
        status: "degraded",
        message: "retry worker state not initialized"
      };
    } else {
      const staleSince = new Date(Date.now() - staleThresholdMinutes * 60 * 1000);
      const isStaleLastRun = retryState.lastRunCompletedAt && retryState.lastRunCompletedAt < staleSince;
      const shouldBeDown = retryState.lastRunStatus === "failed" && (retryState.consecutiveFailures ?? 0) >= 3;

      if (shouldBeDown) {
        retries = {
          status: "down",
          message: "retry worker in repeated failure state",
          meta: {
            status: retryState.lastRunStatus,
            consecutiveFailures: retryState.consecutiveFailures
          }
        };
      } else if (isStaleLastRun) {
        retries = {
          status: "degraded",
          message: "retry worker hasn't completed a run recently",
          meta: {
            lastRunCompletedAt: retryState.lastRunCompletedAt?.toISOString() ?? null,
            staleMinutes: staleThresholdMinutes
          }
        };
      } else {
        retries = {
          status: "ok",
          message: `retry worker status: ${retryState.lastRunStatus ?? "unknown"}`,
          meta: {
            consecutiveFailures: retryState.consecutiveFailures ?? 0
          }
        };
      }
    }

    if (webhookFailureCount > failureThreshold) {
      webhook = {
        status: "degraded",
        message: `high webhook failure volume: ${webhookFailureCount} in 60m`,
        meta: { count: webhookFailureCount, threshold: failureThreshold }
      };
    } else if (disconnectedChannels > 0) {
      webhook = {
        status: "degraded",
        message: `disconnected channels: ${disconnectedChannels}`,
        meta: { disconnectedChannels }
      };
    }
  } else {
    retries = {
      status: "down",
      message: "skipped due to database not available"
    };
    webhook = {
      status: "down",
      message: "skipped due to database not available"
    };
  }

  checks.retries = retries;
  checks.webhook = webhook;

  const components = Object.entries(checks);
  const overall: "ok" | "degraded" | "down" = isUp([checks.database, checks.retries, checks.webhook]) ? "ok" : checks.database.status === "down" ? "down" : "degraded";
  const exposeDetails = maybeExposeDetails(req);
  const payload = {
    ok: overall !== "down",
    status: overall,
    components: exposeDetails
      ? checks
      : Object.fromEntries(components.map(([name, item]) => [name, { status: item.status, message: item.message }])),
    timestamp: new Date().toISOString()
  };

  return NextResponse.json(payload, { status: overall === "down" ? 503 : 200 });
}