import process from "node:process";

const REQUIRED = [
  "AGENTS24_API_KEY",
  "AGENTS24_AGENTS",
  "AGENTS24_INTEGRATION_ID",
  "SESSION_COOKIE_SECRET",
] as const;

function required(name: (typeof REQUIRED)[number]): string {
  const value = String(process.env[name] || "").trim();
  if (!value) throw new Error(`${name} is required.`);
  return value;
}

type RuntimeTarget = "draft" | "published";
type ConfiguredAgent = ({ agentId: string; agentAlias?: never } | { agentAlias: string; agentId?: never }) & { agentVersionId?: string };

function agentsConfig(): {
  agents: ConfiguredAgent[];
  impliedRuntimeTarget?: RuntimeTarget;
} {
  let value: unknown;
  try { value = JSON.parse(required("AGENTS24_AGENTS")); } catch { throw new Error("AGENTS24_AGENTS must be valid JSON."); }
  if (!Array.isArray(value) || value.length < 1 || value.length > 50) throw new Error("AGENTS24_AGENTS must contain between one and 50 Agents.");

  const impliedTargets = new Set<RuntimeTarget>();
  const agents = value.map((item): ConfiguredAgent => {
    if (!item || typeof item !== "object" || Array.isArray(item)) throw new Error("AGENTS24_AGENTS entries must be objects.");
    const record = item as Record<string, unknown>;
    const agentId = String(record.agentId || "").trim();
    const agentAlias = String(record.agentAlias || "").trim();
    const agentVersion = String(record.agentVersion ?? "").trim().toLowerCase();
    const legacyAgentVersionId = String(record.agentVersionId ?? "").trim();
    if (Boolean(agentId) === Boolean(agentAlias)) throw new Error("Each AGENTS24_AGENTS entry requires exactly one of agentId or agentAlias.");
    if (agentAlias && !/^[a-z][a-z0-9]*(?:-[a-z0-9]+)*$/.test(agentAlias)) throw new Error("Each agentAlias must be lowercase kebab-case.");
    if (agentVersion && legacyAgentVersionId) throw new Error("Use either agentVersion or legacy agentVersionId, not both.");

    if (agentVersion && !/^(?:draft|latest|v[1-9]\d*|[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12})$/i.test(agentVersion)) {
      throw new Error("Each AGENTS24_AGENTS agentVersion must be draft, latest, a published label such as v1, or a UUID.");
    }
    if (legacyAgentVersionId && !/^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i.test(legacyAgentVersionId)) {
      throw new Error("Each legacy agentVersionId must be a UUID.");
    }
    const selector = agentVersion || legacyAgentVersionId;
    if (selector === "draft") impliedTargets.add("draft");
    else if (selector) impliedTargets.add("published");

    const agentVersionId = selector && !["draft", "latest"].includes(selector) ? selector : undefined;
    return agentAlias
      ? { agentAlias, ...(agentVersionId ? { agentVersionId } : {}) }
      : { agentId, ...(agentVersionId ? { agentVersionId } : {}) };
  });
  const selectors = agents.map((agent) => "agentAlias" in agent ? `alias:${agent.agentAlias}` : `id:${agent.agentId}`);
  if (new Set(selectors).size !== agents.length) throw new Error("AGENTS24_AGENTS must contain unique selectors.");
  if (impliedTargets.size > 1) throw new Error("AGENTS24_AGENTS cannot mix draft selectors with latest or pinned published selectors.");
  return { agents, impliedRuntimeTarget: impliedTargets.values().next().value };
}

export function readServerEnvironment() {
  const parsedAgents = agentsConfig();
  const explicitRuntimeTarget = String(process.env.AGENTS24_RUNTIME_TARGET || "").trim() || undefined;
  if (explicitRuntimeTarget && !["draft", "published"].includes(explicitRuntimeTarget)) throw new Error("AGENTS24_RUNTIME_TARGET must be draft or published.");
  if (explicitRuntimeTarget && parsedAgents.impliedRuntimeTarget && explicitRuntimeTarget !== parsedAgents.impliedRuntimeTarget) {
    throw new Error("AGENTS24_RUNTIME_TARGET conflicts with the configured agentVersion selectors.");
  }

  const env = {
    ...Object.fromEntries(REQUIRED.map((name) => [name, required(name)])) as Record<(typeof REQUIRED)[number], string>,
    AGENTS24_BASE_URL: String(process.env.AGENTS24_BASE_URL || "https://api.agents24.dev").trim(),
    AGENTS24_AGENTS: parsedAgents.agents,
    AGENTS24_RUNTIME_TARGET: explicitRuntimeTarget || parsedAgents.impliedRuntimeTarget,
    AGENTS24_INTEGRATION_NAME: String(process.env.AGENTS24_INTEGRATION_NAME || "").trim() || undefined,
    PORT: Number(process.env.PORT || 3001),
  };

  if (!Number.isInteger(env.PORT) || env.PORT < 1 || env.PORT > 65535) throw new Error("PORT must be a valid port.");
  if (env.SESSION_COOKIE_SECRET.length < 32) throw new Error("SESSION_COOKIE_SECRET must contain at least 32 characters.");
  return env;
}

let environment: ReturnType<typeof readServerEnvironment> | undefined;
export function getServerEnvironment() {
  return environment ??= readServerEnvironment();
}