/**
 * SDK Session 默认 system block 组装逻辑。
 *
 * 关键点（中文）
 * - 面向 `Agent` SDK 的本地会话执行场景。
 * - 注入调用方显式传入的静态 instruction、受托管 plugin system 与显式注册 plugin system。
 * - SDK 不在 system 中注入动态变量；动态上下文应由调用方放入 user message。
 */

import type {
  AgentSessionSystemBlock,
  AgentSessionSystemSessionInfo,
} from "@/types/agent/SessionTypes.js";
import type { BuildSessionSystemBlocksInput } from "@/types/session/SessionSystem.js";

function normalize_system_blocks(
  blocks: AgentSessionSystemBlock[],
): AgentSessionSystemBlock[] {
  if (!Array.isArray(blocks)) return [];
  return blocks
    .map((block) => {
      const content = String(block?.content || "").trim();
      if (!content) return null;
      const source = block.source;
      if (
        source !== "core" &&
        source !== "instruction" &&
        source !== "plugin" &&
        source !== "session"
      ) {
        return null;
      }
      return {
        source,
        name: String(block.name || source).trim() || source,
        content,
      } satisfies AgentSessionSystemBlock;
    })
    .filter((block): block is AgentSessionSystemBlock => Boolean(block));
}

function create_session_info(
  input: Pick<
    BuildSessionSystemBlocksInput,
    "agent_id" | "session_id" | "project_root" | "created_at" | "timezone"
  >,
): AgentSessionSystemSessionInfo {
  const created_at = Number.isFinite(input.created_at) ? input.created_at : 0;
  return {
    agent_id: String(input.agent_id || "").trim(),
    session_id: String(input.session_id || "").trim(),
    project_root: String(input.project_root || "").trim(),
    created_at: new Date(created_at).toISOString(),
    timezone: String(input.timezone || "").trim() || "UTC",
  };
}

function create_session_system_block(
  session: AgentSessionSystemSessionInfo,
): AgentSessionSystemBlock {
  const content = [
    "Current session context:",
    `You are serving agent "${session.agent_id}" in session "${session.session_id}".`,
    `The current project root is "${session.project_root}".`,
    `This session was created at ${session.created_at}, with ${session.timezone} as its reference timezone.`,
    "This creation time is a stable reference for the session and does not represent the current time for every run.",
    "If the user message provides a newer current time, a relative time, or other dynamic context, prioritize the dynamic information from the user message.",
  ].join("\n");
  return {
    source: "session",
    name: "context",
    content,
  };
}

/**
 * 解析 SDK session 当前生效的 system blocks。
 */
export async function build_session_system_blocks(
  input: BuildSessionSystemBlocksInput,
): Promise<AgentSessionSystemBlock[]> {
  const agent_id = String(input.agent_id || "").trim();
  const project_root = String(input.project_root || "").trim();
  const session_id = String(input.session_id || "").trim();
  const created_at = Number(input.created_at || 0);
  const timezone = String(input.timezone || "").trim();
  if (!agent_id) {
    throw new Error("build_session_system_blocks requires a non-empty agent_id");
  }
  if (!project_root) {
    throw new Error("build_session_system_blocks requires a non-empty project_root");
  }
  if (!session_id) {
    throw new Error("build_session_system_blocks requires a non-empty session_id");
  }
  if (!Number.isFinite(created_at) || created_at <= 0) {
    throw new Error("build_session_system_blocks requires a valid created_at");
  }
  if (!timezone) {
    throw new Error("build_session_system_blocks requires a non-empty timezone");
  }
  return [
    ...normalize_system_blocks(input.get_instruction_system_blocks()),
    ...normalize_system_blocks(await input.get_managed_plugin_system_blocks()),
    ...normalize_system_blocks(await input.get_plugin_system_blocks()),
    // session block 放在最后，尽量保留前缀 system blocks 的跨 session 缓存命中。
    create_session_system_block(
      create_session_info({
        agent_id,
        project_root,
        session_id,
        created_at,
        timezone,
      }),
    ),
  ];
}