const http = require("http");
const { Pool } = require("pg");

const port = Number(process.env.API_INTERNAL_PORT || 3001);
const serviceName = process.env.SERVICE_NAME || "video-games-api";
const databaseUrl =
  process.env.DATABASE_URL ||
  "postgres://video_games_user:change_me@video-games-db:5432/video_games";

const pool = new Pool({
  connectionString: databaseUrl,
});

function sendJson(response, statusCode, payload) {
  response.writeHead(statusCode, { "Content-Type": "application/json; charset=utf-8" });
  response.end(JSON.stringify(payload));
}

async function runMigrations() {
  await pool.query("CREATE EXTENSION IF NOT EXISTS pgcrypto;");
  await pool.query(`
    CREATE TABLE IF NOT EXISTS brands (
      id BIGSERIAL PRIMARY KEY,
      name TEXT NOT NULL UNIQUE,
      created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
    );
  `);

  await pool.query(`
    CREATE TABLE IF NOT EXISTS consoles (
      id BIGSERIAL PRIMARY KEY,
      brand_id BIGINT NOT NULL REFERENCES brands(id) ON DELETE CASCADE,
      name TEXT NOT NULL,
      created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
      UNIQUE (brand_id, name)
    );
  `);

  await pool.query(`
    CREATE TABLE IF NOT EXISTS games (
      id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
      console_id BIGINT NOT NULL REFERENCES consoles(id) ON DELETE CASCADE,
      title TEXT NOT NULL,
      genre TEXT,
      publisher TEXT,
      release_year INTEGER CHECK (release_year IS NULL OR (release_year >= 1970 AND release_year <= 2100)),
      estimated_value NUMERIC(10,2) CHECK (estimated_value IS NULL OR estimated_value >= 0),
      loaned_to TEXT,
      created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
      updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
    );
  `);

  await pool.query(`
    CREATE OR REPLACE FUNCTION set_updated_at()
    RETURNS TRIGGER AS $$
    BEGIN
      NEW.updated_at = NOW();
      RETURN NEW;
    END;
    $$ LANGUAGE plpgsql;
  `);

  await pool.query(`
    DROP TRIGGER IF EXISTS trg_games_updated_at ON games;
    CREATE TRIGGER trg_games_updated_at
    BEFORE UPDATE ON games
    FOR EACH ROW
    EXECUTE FUNCTION set_updated_at();
  `);
}

async function querySingleValue(sqlText) {
  const result = await pool.query(sqlText);
  return Number(result.rows[0].count || 0);
}

async function getCatalogSummary() {
  const [brands, consoles, games] = await Promise.all([
    querySingleValue("SELECT COUNT(*)::int AS count FROM brands;"),
    querySingleValue("SELECT COUNT(*)::int AS count FROM consoles;"),
    querySingleValue("SELECT COUNT(*)::int AS count FROM games;"),
  ]);

  return { brands, consoles, games };
}

async function getCatalogTree() {
  const result = await pool.query(`
    SELECT
      b.id::int AS brand_id,
      b.name AS brand_name,
      c.id::int AS console_id,
      c.name AS console_name,
      COUNT(g.id)::int AS games_count
    FROM brands b
    LEFT JOIN consoles c ON c.brand_id = b.id
    LEFT JOIN games g ON g.console_id = c.id
    GROUP BY b.id, b.name, c.id, c.name
    ORDER BY b.name ASC, c.name ASC;
  `);

  const brandMap = new Map();
  for (const row of result.rows) {
    if (!brandMap.has(row.brand_id)) {
      brandMap.set(row.brand_id, {
        id: row.brand_id,
        name: row.brand_name,
        consoles: [],
      });
    }

    if (row.console_id) {
      brandMap.get(row.brand_id).consoles.push({
        id: row.console_id,
        name: row.console_name,
        gamesCount: row.games_count,
      });
    }
  }

  return Array.from(brandMap.values());
}

async function handleRequest(request, response) {
  const url = new URL(request.url || "/", `http://${request.headers.host || "localhost"}`);

  if (request.method === "GET" && url.pathname === "/health") {
    try {
      await pool.query("SELECT 1;");
      sendJson(response, 200, {
        status: "ok",
        service: serviceName,
        db: "up",
        timestamp: new Date().toISOString(),
      });
    } catch (error) {
      sendJson(response, 503, {
        status: "degraded",
        service: serviceName,
        db: "down",
        error: error.message,
      });
    }
    return;
  }

  if (request.method === "GET" && url.pathname === "/api/catalog/summary") {
    try {
      const summary = await getCatalogSummary();
      sendJson(response, 200, summary);
    } catch (error) {
      sendJson(response, 500, { status: "error", message: error.message });
    }
    return;
  }

  if (request.method === "GET" && url.pathname === "/api/catalog/tree") {
    try {
      const tree = await getCatalogTree();
      sendJson(response, 200, { brands: tree });
    } catch (error) {
      sendJson(response, 500, { status: "error", message: error.message });
    }
    return;
  }

  sendJson(response, 404, {
    status: "not_found",
    message: "Route not found",
  });
}

async function start() {
  await runMigrations();

  const server = http.createServer((request, response) => {
    handleRequest(request, response).catch((error) => {
      sendJson(response, 500, { status: "error", message: error.message });
    });
  });

  server.listen(port, "0.0.0.0", () => {
    console.log(`${serviceName} listening on port ${port}`);
  });
}

start().catch((error) => {
  console.error("Failed to start API:", error);
  process.exit(1);
});