package com.trafficaudit.reportexport.service;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.trafficaudit.dataimport.entity.ImportBatch;
import com.trafficaudit.dataimport.mapper.ImportBatchMapper;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Service;

import javax.annotation.PreDestroy;
import javax.annotation.Resource;
import java.util.Date;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

/**
 * 报表导出异步任务：把耗时十几秒的《生成_道路运输量汇总表》生成挪到后台线程，
 * 前端只拿「任务号 + 进度（步骤/百分比）」，完成后单独下载文件。
 *
 * 目的（2026-09-20 用户上报「点下载要等一会，数据多了会不会卡死」）：
 * 1) 点击后立刻有反馈，不再长时间无响应；
 * 2) 生成过程不占用 HTTP 请求线程，避免多人同时点把容器拖死（工作线程固定 1 个，多余请求显示「排队中」）；
 * 3) 同一报表期 10 分钟内的结果可复用，避免每次重算整本约 4 万格公式。
 *
 * 缓存正确性守卫：只有当「距上次生成不超过 TTL」且「期间没有任何新的数据导入（import_batch 最大 id 未变）」
 * 时才复用；导入即失效，避免把过期报表给用户。前端仍提供「重新生成」强制刷新。
 */
@Slf4j
@Service
public class ReportExportTaskService {

    /** 汇总工作簿导出任务类型 */
    public static final String TYPE_SUMMARY_WORKBOOK = "summaryWorkbook";

    /** 生成结果保留时长：期间可反复下载，过后自动清理 */
    private static final long RESULT_TTL_MS = 30 * 60 * 1000L;
    /** 同一报表期结果复用时长（且期间无新导入时才复用） */
    private static final long CACHE_TTL_MS = 10 * 60 * 1000L;

    @Resource
    private ReportExportService reportService;
    @Resource
    private ImportBatchMapper importBatchMapper;

    private final Map<String, Task> tasks = new ConcurrentHashMap<>();
    /** 同报表期最近一次成功结果：key -> task */
    private final Map<String, Task> cache = new ConcurrentHashMap<>();
    private final ExecutorService pool = Executors.newFixedThreadPool(1, r -> {
        Thread t = new Thread(r, "report-export-task");
        t.setDaemon(true);
        return t;
    });

    /** 一次导出任务（内存态，进程重启即失效） */
    public static class Task {
        private final String id = UUID.randomUUID().toString().replace("-", "");
        private final String type;
        private final String period;
        private final String mode;
        private final Integer toMonth;
        private final long createdAt = System.currentTimeMillis();
        /** 生成时的数据版本（import_batch 最大 id），用于判断缓存是否过期 */
        private final long importVersion;
        private volatile String status = "PENDING"; // PENDING/RUNNING/DONE/FAILED
        private volatile int percent = 0;
        private volatile String step = "排队中";
        private volatile String error;
        private volatile byte[] data;
        private volatile String fileName;
        private volatile boolean fromCache;
        private volatile long finishedAt;

        Task(String type, String period, String mode, Integer toMonth, long importVersion) {
            this.type = type;
            this.period = period;
            this.mode = mode;
            this.toMonth = toMonth;
            this.importVersion = importVersion;
        }

        void progress(int pct, String stepText) {
            if (pct > this.percent) this.percent = Math.min(pct, 99);
            if (stepText != null) this.step = stepText;
        }

        public String getId() { return id; }

        public String getStatus() { return status; }

        public boolean isDone() { return "DONE".equals(status) && data != null; }

        public boolean isFromCache() { return fromCache; }

        public byte[] getData() { return data; }

        public String getFileName() { return fileName; }

        public String getError() { return error; }

        public Map<String, Object> toView() {
            Map<String, Object> m = new LinkedHashMap<>();
            m.put("taskId", id);
            m.put("type", type);
            m.put("period", period);
            m.put("mode", mode);
            m.put("toMonth", toMonth);
            m.put("status", status);
            m.put("percent", "DONE".equals(status) ? 100 : percent);
            m.put("step", step);
            m.put("fromCache", fromCache);
            m.put("fileName", fileName);
            m.put("error", error);
            long end = finishedAt > 0 ? finishedAt : System.currentTimeMillis();
            m.put("elapsedMs", end - createdAt);
            m.put("finishedAt", finishedAt > 0 ? new Date(finishedAt) : null);
            return m;
        }
    }

    /**
     * 提交导出任务。forceRefresh=true 时忽略缓存重新生成；
     * 否则在「同一报表期、10 分钟内、期间无新导入」的前提下直接复用上次结果。
     * 同一报表期已有任务在跑时直接返回该任务，避免重复排队。
     */
    public Task submit(String type, String period, String mode, Integer toMonth, boolean forceRefresh) {
        cleanupExpired();
        String key = cacheKey(type, period, mode, toMonth);
        if (!forceRefresh) {
            Task hit = cache.get(key);
            if (cacheUsable(hit)) {
                hit.fromCache = true;
                log.info("报表导出任务命中缓存：{} {}（生成于 {}）", type, period, new Date(hit.finishedAt));
                return hit;
            }
        }
        Task running = findRunning(key);
        if (running != null) {
            log.info("报表导出任务已在执行，复用进行中的任务：{} {}（{}）", type, period, running.id);
            return running;
        }
        Task task = new Task(type, period, mode, toMonth, importVersion());
        tasks.put(task.id, task);
        pool.submit(() -> run(task));
        return task;
    }

    public Task get(String taskId) {
        if (taskId == null) return null;
        cleanupExpired();
        return tasks.get(taskId);
    }

    private void run(Task t) {
        t.status = "RUNNING";
        t.step = "开始生成";
        long start = System.currentTimeMillis();
        try {
            byte[] data = reportService.exportSummaryWorkbook(t.period, t.mode, t.toMonth, t::progress);
            t.data = data;
            t.fileName = "生成_道路运输量汇总表_" + t.period + ".xlsx";
            t.step = "完成";
            t.status = "DONE";
            t.finishedAt = System.currentTimeMillis();
            cache.put(cacheKey(t.type, t.period, t.mode, t.toMonth), t);
            log.info("报表导出任务完成：{} {} 用时 {} ms，{} 字节", t.type, t.period, t.finishedAt - start, data.length);
        } catch (Throwable e) {
            t.status = "FAILED";
            t.error = e.getMessage() == null ? e.toString() : e.getMessage();
            t.step = "生成失败";
            t.finishedAt = System.currentTimeMillis();
            log.error("报表导出任务失败：{} {}（用时 {} ms）", t.type, t.period, t.finishedAt - start, e);
        }
    }

    private Task findRunning(String key) {
        for (Task t : tasks.values()) {
            if (!key.equals(cacheKey(t.type, t.period, t.mode, t.toMonth))) continue;
            if ("PENDING".equals(t.status) || "RUNNING".equals(t.status)) return t;
        }
        return null;
    }

    private boolean cacheUsable(Task t) {
        if (t == null || !"DONE".equals(t.status) || t.data == null) return false;
        if (System.currentTimeMillis() - t.finishedAt > CACHE_TTL_MS) return false;
        long now = importVersion();
        if (now < 0 || t.importVersion < 0) return false; // 取不到数据版本时不冒风险复用
        return now == t.importVersion;
    }

    /** 数据版本＝import_batch 最大 id：任何一次导入都会让它变化，取不到返回 -1（此时禁用缓存） */
    private long importVersion() {
        try {
            List<Object> v = importBatchMapper.selectObjs(new QueryWrapper<ImportBatch>().select("IFNULL(MAX(id),0)"));
            if (v == null || v.isEmpty() || v.get(0) == null) return 0L;
            return ((Number) v.get(0)).longValue();
        } catch (Exception e) {
            log.warn("读取导入数据版本失败，本次禁用导出缓存：{}", e.getMessage());
            return -1L;
        }
    }

    private String cacheKey(String type, String period, String mode, Integer toMonth) {
        return type + "|" + period + "|" + mode + "|" + (toMonth == null ? "" : toMonth);
    }

    private void cleanupExpired() {
        long now = System.currentTimeMillis();
        for (Iterator<Map.Entry<String, Task>> it = tasks.entrySet().iterator(); it.hasNext(); ) {
            Task t = it.next().getValue();
            if (t.finishedAt > 0 && now - t.finishedAt > RESULT_TTL_MS) it.remove();
        }
        for (Iterator<Map.Entry<String, Task>> it = cache.entrySet().iterator(); it.hasNext(); ) {
            Task t = it.next().getValue();
            if (t.finishedAt <= 0 || now - t.finishedAt > CACHE_TTL_MS) it.remove();
        }
    }

    @PreDestroy
    public void shutdown() {
        pool.shutdownNow();
        try {
            pool.awaitTermination(3, TimeUnit.SECONDS);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }
}