import { isError, Semaphore } from "es-toolkit";

import type { Logger } from "../logger";
import type { ProbeStore } from "./store";
import type { CheckResult, ResolvedTargetBase } from "./types";

import { createNoopLogger } from "../logger";
import { errorFailure } from "./expect/failure";
import { checkerRegistry } from "./runner";

const PRUNE_INTERVAL_MS = 3600000;

export class ProbeEngine {
  private abort: AbortController | null = null;
  private lastMatched = new Map<string, boolean>();
  private logger: Logger;
  private pruneTimer: null | ReturnType<typeof setInterval> = null;
  private retentionMs: number;
  private semaphore: Semaphore;
  private store: ProbeStore;
  private targetIds = new Set<string>();
  private targets: ResolvedTargetBase[];

  constructor(
    store: ProbeStore,
    targets: ResolvedTargetBase[],
    maxConcurrentChecks?: number,
    retentionMs?: number,
    logger?: Logger,
  ) {
    this.store = store;
    this.targets = targets;
    this.semaphore = new Semaphore(maxConcurrentChecks ?? 20);
    this.retentionMs = retentionMs ?? 0;
    this.logger = logger ?? createNoopLogger();
    this.refreshCache();
    this.initStateCache();
  }

  start(): void {
    this.abort = new AbortController();
    const signal = this.abort.signal;

    for (const target of this.targets) {
      void this.runLoop(target, signal);
    }

    if (this.retentionMs > 0) {
      this.store.prune(this.retentionMs);
      this.pruneTimer = setInterval(() => {
        this.store.prune(this.retentionMs);
      }, PRUNE_INTERVAL_MS);
    }
  }

  stop(): void {
    this.abort?.abort();
    this.abort = null;
    if (this.pruneTimer) {
      clearInterval(this.pruneTimer);
      this.pruneTimer = null;
    }
  }

  private initStateCache(): void {
    const latestMap = this.store.getLatestChecksMap();
    for (const [id, row] of latestMap) {
      this.lastMatched.set(id, row.matched === 1);
    }
  }

  private logCheckDebug(result: CheckResult): void {
    this.logger.debug({
      durationMs: result.durationMs,
      failureMessage: result.failure?.message ?? null,
      failurePhase: result.failure?.phase ?? null,
      matched: result.matched,
      targetId: result.targetId,
    });
  }

  private logStateChange(result: CheckResult): void {
    const previous = this.lastMatched.get(result.targetId);
    const current = result.matched;

    if (previous === undefined) {
      if (!current) {
        this.logger.warn(
          { durationMs: result.durationMs, failurePhase: result.failure?.phase, targetId: result.targetId },
          `目标首次 DOWN: ${result.targetId}`,
        );
      }
    } else if (previous && !current) {
      this.logger.warn(
        { durationMs: result.durationMs, failurePhase: result.failure?.phase, targetId: result.targetId },
        `目标状态变化 UP → DOWN: ${result.targetId}`,
      );
    } else if (!previous && current) {
      this.logger.info(
        { durationMs: result.durationMs, targetId: result.targetId },
        `目标恢复 DOWN → UP: ${result.targetId}`,
      );
    }

    this.lastMatched.set(result.targetId, current);
  }

  private refreshCache(): void {
    this.targetIds.clear();
    for (const target of this.store.getTargets()) {
      this.targetIds.add(target.id);
    }
  }

  private async runCheck(target: ResolvedTargetBase): Promise<CheckResult> {
    const checker = checkerRegistry.get(target.type);
    const controller = new AbortController();
    const timeoutId = setTimeout(() => controller.abort(), target.timeoutMs);

    try {
      return await checker.execute(target, { signal: controller.signal });
    } finally {
      clearTimeout(timeoutId);
    }
  }

  private async runLoop(target: ResolvedTargetBase, signal: AbortSignal): Promise<void> {
    while (!signal.aborted) {
      const start = performance.now();
      try {
        await this.runOnce(target, signal);
      } catch {
        break;
      }

      const elapsed = performance.now() - start;
      if (elapsed > target.intervalMs) {
        this.logger.warn(
          { elapsed, intervalMs: target.intervalMs, targetId: target.id },
          `拨测超时: ${target.id} 耗时 ${Math.round(elapsed)}ms > 间隔 ${target.intervalMs}ms`,
        );
      }
      const delay = Math.max(0, target.intervalMs - elapsed);
      try {
        await sleep(delay, signal);
      } catch {
        break;
      }
    }
  }

  private async runOnce(target: ResolvedTargetBase, signal?: AbortSignal): Promise<CheckResult> {
    await this.semaphore.acquire();
    if (signal?.aborted) {
      this.semaphore.release();
      throw new DOMException("Aborted", "AbortError");
    }
    try {
      const result = await this.runCheck(target);
      this.writeResult(result);
      this.logStateChange(result);
      this.logCheckDebug(result);
      return result;
    } catch (error) {
      const reason = formatReason(error);
      this.logger.error({ reason, targetId: target.id, targetType: target.type }, `探针执行失败: ${reason}`);
      const errorResult: CheckResult = {
        detail: null,
        durationMs: null,
        failure: errorFailure("internal", "engine", reason),
        matched: false,
        observation: null,
        targetId: target.id,
        timestamp: new Date().toISOString(),
      };
      this.writeResult(errorResult);
      return errorResult;
    } finally {
      this.semaphore.release();
    }
  }

  private writeResult(result: CheckResult): void {
    if (!this.targetIds.has(result.targetId)) return;

    this.store.insertCheckResult({
      durationMs: result.durationMs,
      failure: result.failure,
      matched: result.matched,
      observation: result.observation ?? null,
      targetId: result.targetId,
      timestamp: result.timestamp,
    });
  }
}

function formatReason(reason: unknown): string {
  return isError(reason) ? reason.message : String(reason);
}

function sleep(ms: number, signal: AbortSignal): Promise<void> {
  return new Promise<void>((resolve, reject) => {
    if (signal.aborted) {
      reject(new DOMException("Aborted", "AbortError"));
      return;
    }

    const timer = setTimeout(() => {
      signal.removeEventListener("abort", onAbort);
      resolve();
    }, ms);

    function onAbort() {
      clearTimeout(timer);
      reject(new DOMException("Aborted", "AbortError"));
    }

    signal.addEventListener("abort", onAbort, { once: true });
  });
}