const fs = require('fs');
const path = require('path');
const https = require('https');
const { exec } = require('child_process');
const { EventEmitter } = require('events');

// 批量下载 grb2 气象文件
// 调用方法:
// 在需要使用的地方引入
// const { grb2DownloadManager } = require("手动引导至/schema/downloadGrb2");
// 在需要使用的地方创建实例
// 创建下载管理器实例
// const manager = new grb2DownloadManager()

// 获取下载工具当前状态
// manager.getStatus();

// 相关监听事件钩子
// manager.on('queueUpdated', (status) => {
//     console.log(`队列更新: 还有 ${status.queueLength} 个任务等待下载`);
// });

// manager.on('downloadStarted', (status) => {
//     console.log('下载开始');
// });

// manager.on('taskStarted', (status) => {
//     console.log(`开始下载: ${status.currentTask.fileName}`);
// });

// manager.on('taskProgress', ({ progress, currentTask }) => {
//   console.log(`下载进度: ${currentTask.fileName} - ${progress}%`);
// });

// manager.on('taskCompleted', (status) => {
//     console.log(`任务完成: 成功 ${status.successfulDownloads}/${status.totalTasks}`);
// });

// manager.on('taskFailed', ({ task, error }) => {
//     console.log(`任务失败: ${task.fileName} - ${error}`);
// });

// manager.on('downloadCompleted', (status) => {
//     console.log(`所有下载完成: 成功 ${status.successfulDownloads}, 失败: ${status.failedDownloads}`);
// });

// manager.on('downloadStopped', () => {
//     console.log('下载已停止');
// });

class grb2DownloadManager extends EventEmitter {
    constructor(options = {}) {
        super();
        this.queue = [];
        this.isDownloading = false;
        this.currentDownload = null;
        this.status = {
            state: 'idle', // 'idle', 'downloading', 'completed', 'stopped'
            totalTasks: 0,
            completedTasks: 0,
            successfulDownloads: 0,
            failedDownloads: 0,
            currentTask: null,
            progress: 0,
            queueLength: 0
        };
        this.retryAttempts = options.retryAttempts || 3;
        this.wgrib2Path = options.wgrib2Path || path.join(__dirname, "../wgrib2/wgrib2.exe");
        this.downloadInterval = null;
    }

    // 添加下载任务
    async addTasks(tasks) {
        if (!Array.isArray(tasks)) {
            tasks = [tasks];
        }

        // 检查任务是否已存在或已完成
        const newTasks = [];
        for (const task of tasks) {
            const isInQueue = this.queue.some(q => q.url === task.url);
            const isCompleted = await this.isTaskCompleted(task);

            if (!isInQueue && !isCompleted) {
                newTasks.push(task);
            }
        }

        if (newTasks.length > 0) {
            this.queue.push(...newTasks);
            this.status.totalTasks += newTasks.length;
            this.status.queueLength = this.queue.length;

            this.emit('queueUpdated', this.status);

            if (!this.isDownloading && this.status.state !== 'stopped') {
                this.startDownload();
            }

            return {
                added: newTasks.length,
                message: `添加了 ${newTasks.length} 个新任务到下载队列`
            };
        } else {
            return {
                added: 0,
                message: '没有新任务可添加，所有任务已完成或已在队列中'
            };
        }
    }

    // 检查任务是否已完成
    async isTaskCompleted(task) {
        const filePath = path.join(task.filePath, task.fileName);

        if (!fs.existsSync(filePath)) {
            return false;
        }

        try {
            await this.verifyFileWithWgrib2(filePath);
            return true;
        } catch (error) {
            console.log(error.message);
            return false;
        }
    }

    // 使用wgrib2验证文件
    verifyFileWithWgrib2(filePath) {
        return new Promise((resolve, reject) => {
            exec(`${this.wgrib2Path} "${filePath}"`, (error, stdout, stderr) => {
                if (error) {
                    reject(new Error(`文件验证失败: ${error.message}`));
                } else if (stderr && stderr.trim() !== '') {
                    reject(new Error(`文件验证失败: ${stderr}`));
                } else {
                    resolve();
                }
            });
        });
    }

    // 开始下载
    startDownload() {
        if (this.isDownloading) {
            return { message: '当前已有下载任务在进行中，新任务已加入队列' };
        }

        this.isDownloading = true;
        this.status.state = 'downloading';

        // 使用setImmediate确保异步操作顺序正确
        setImmediate(() => {
            this.processNextTask();
        });

        this.emit('downloadStarted', this.status);
        return { message: '下载已开始' };
    }

    // 处理下一个任务
    async processNextTask() {
        // 检查是否被停止
        if (this.status.state === 'stopped') {
            this.isDownloading = false;
            return;
        }

        if (this.queue.length === 0) {
            this.isDownloading = false;
            this.status.state = 'completed';
            this.emit('downloadCompleted', this.status);
            return;
        }

        const task = this.queue.shift();
        this.status.queueLength = this.queue.length;
        this.status.currentTask = {
            ...task,
            retryCount: 0
        };

        this.emit('taskStarted', this.status);

        await this.downloadTask(task);

        // 处理完成后继续下一个任务
        if (this.isDownloading) {
            setImmediate(() => {
                this.processNextTask();
            });
        }
    }

    // 下载单个任务
    async downloadTask(task, retryCount = 0) {
        const fileDir = task.filePath;
        const filePath = path.join(fileDir, task.fileName);

        // 确保目录存在
        if (!fs.existsSync(fileDir)) {
            fs.mkdirSync(fileDir, { recursive: true });
        }

        // 检查文件是否已存在且有效
        try {
            if (await this.isTaskCompleted(task)) {
                this.status.completedTasks++;
                this.status.successfulDownloads++;
                this.emit('taskSkipped', { ...this.status, task, reason: '文件已存在且有效' });
                return;
            }
        } catch (error) {
            console.log(`文件检查失败: ${error.message}`);
        }

        this.status.currentTask.retryCount = retryCount;
        this.emit('taskProgress', { ...this.status, progress: 0 });

        try {
            await this.downloadFile(task.url, filePath, (progress) => {
                this.status.progress = progress;
                this.emit('taskProgress', { ...this.status, progress });
            });

            // 验证下载的文件
            await this.verifyFileWithWgrib2(filePath);

            this.status.completedTasks++;
            this.status.successfulDownloads++;
            this.emit('taskCompleted', this.status);

        } catch (error) {
            console.error(`下载失败: ${error.message}`);

            if (retryCount < this.retryAttempts) {
                console.log(`尝试重新下载 (${retryCount + 1}/${this.retryAttempts})`);
                this.emit('taskRetry', {
                    ...this.status,
                    task,
                    retryCount: retryCount + 1,
                    maxRetries: this.retryAttempts
                });

                // 等待一段时间后重试
                await new Promise(resolve => setTimeout(resolve, 5000)); // 5秒后重试
                return this.downloadTask(task, retryCount + 1);
            } else {
                this.status.completedTasks++;
                this.status.failedDownloads++;
                this.emit('taskFailed', {
                    ...this.status,
                    task,
                    error: error.message
                });
            }
        }
    }

    // 实际下载文件
    downloadFile(url, filePath, onProgress) {
        return new Promise((resolve, reject) => {
            const file = fs.createWriteStream(filePath);
            let receivedBytes = 0;
            let totalBytes = 0;

            const request = https.get(url, (response) => {
                if (response.statusCode !== 200) {
                    reject(new Error(`服务器返回状态码: ${response.statusCode}`));
                    return;
                }

                totalBytes = parseInt(response.headers['content-length'], 10);
                this.currentDownload = { request, file };

                response.pipe(file);

                response.on('data', (chunk) => {
                    receivedBytes += chunk.length;
                    const progress = totalBytes ? (receivedBytes / totalBytes * 100) : 0;
                    onProgress(Math.round(progress));
                });

                file.on('finish', () => {
                    file.close();
                    this.currentDownload = null;
                    resolve();
                });
            });

            request.on('error', (err) => {
                if (fs.existsSync(filePath)) {
                    fs.unlink(filePath, () => { });
                }
                reject(err);
            });

            file.on('error', (err) => {
                if (fs.existsSync(filePath)) {
                    fs.unlink(filePath, () => { });
                }
                reject(err);
            });

            // 设置超时
            request.setTimeout(30000, () => {
                request.destroy();
                if (fs.existsSync(filePath)) {
                    fs.unlink(filePath, () => { });
                }
                reject(new Error('请求超时'));
            });

            request.end();
        });
    }

    // 停止当前下载
    stopDownload() {
        if (this.currentDownload) {
            this.currentDownload.request.destroy();
            this.currentDownload.file.destroy();
            this.currentDownload = null;
        }

        this.isDownloading = false;
        this.status.state = 'stopped';
        this.emit('downloadStopped', this.status);

        return { message: '下载已停止' };
    }

    // 重置下载状态
    reset() {
        this.stopDownload();
        this.queue = [];
        this.status = {
            state: 'idle',
            totalTasks: 0,
            completedTasks: 0,
            successfulDownloads: 0,
            failedDownloads: 0,
            currentTask: null,
            progress: 0,
            queueLength: 0
        };

        this.emit('reset', this.status);
        return { message: '下载管理器已重置' };
    }

    // 获取当前状态
    getStatus() {
        return this.status;
    }
}

// 使用示例
async function main() {
    const downloadManager = new DownloadManager({
        retryAttempts: 3,
        wgrib2Path: 'wgrib2' // 确保系统已安装wgrib2
    });

    // 监听事件
    downloadManager.on('queueUpdated', (status) => {
        console.log(`队列更新: 还有 ${status.queueLength} 个任务等待下载`);
    });

    downloadManager.on('downloadStarted', (status) => {
        console.log('下载开始');
    });

    downloadManager.on('taskStarted', (status) => {
        console.log(`开始下载: ${status.currentTask.fileName}`);
    });

    downloadManager.on('taskProgress', ({ progress, currentTask }) => {
        console.log(`下载进度: ${currentTask.fileName} - ${progress}%`);
    });

    downloadManager.on('taskCompleted', (status) => {
        console.log(`任务完成: 成功 ${status.successfulDownloads}/${status.totalTasks}`);
    });

    downloadManager.on('taskFailed', ({ task, error }) => {
        console.log(`任务失败: ${task.fileName} - ${error}`);
    });

    downloadManager.on('downloadCompleted', (status) => {
        console.log(`所有下载完成: 成功 ${status.successfulDownloads}, 失败: ${status.failedDownloads}`);
    });

    downloadManager.on('downloadStopped', () => {
        console.log('下载已停止');
    });

    // 添加下载任务
    const tasks = [
        {
            "url": "https://nomads.ncep.noaa.gov/cgi-bin/filter_gfs_0p50.pl?dir=%2Fgfs.20250901%2F18/atmos&file=gfs.t18z.pgrb2full.0p50.f000&all_lev=on&all_var=on&leftlon=0&rightlon=360&toplat=90&bottomlat=-90",
            "filePath": "./model/grb2/gfs.20250901/18/atmos",
            "fileName": "gfs.t18z.pgrb2full.0p50.f000"
        },
        {
            "url": "https://nomads.ncep.noaa.gov/cgi-bin/filter_gfs_0p50.pl?dir=%2Fgfs.20250901%2F18/atmos&file=gfs.t18z.pgrb2full.0p50.f003&all_lev=on&all_var=on&leftlon=0&rightlon=360&toplat=90&bottomlat=-90",
            "filePath": "./model/grb2/gfs.20250901/18/atmos",
            "fileName": "gfs.t18z.pgrb2full.0p50.f003"
        },
        {
            "url": "https://nomads.ncep.noaa.gov/cgi-bin/filter_gfs_0p50.pl?dir=%2Fgfs.20250901%2F18/atmos&file=gfs.t18z.pgrb2full.0p50.f006&all_lev=on&all_var=on&leftlon=0&rightlon=360&toplat=90&bottomlat=-90",
            "filePath": "./model/grb2/gfs.20250901/18/atmos",
            "fileName": "gfs.t18z.pgrb2full.0p50.f006"
        }
    ];

    // 添加任务到下载队列
    console.log((await downloadManager.addTasks(tasks)).message);

    // 模拟中途停止下载
    setTimeout(async () => {
        console.log(downloadManager.stopDownload().message);

        // 模拟重新开始下载
        setTimeout(() => {
            console.log(downloadManager.startDownload().message);
        }, 2000);
    }, 5000);
}

// 如果直接运行此脚本，则执行示例
if (require.main === module) {
    main().catch(console.error);
}

module.exports = { grb2DownloadManager };