#include <map>
#include <cstring>
#include <fstream>
#include <sstream>
#include <iostream>

/* This is just a very simple and inefficient demo of async responses,
 * please do roll your own variant or use a database or Node.js's async
 * features instead of this really bad demo */
struct AsyncFileReader {
private:
    /* The cache we have in memory for this file */
    std::string cache;
    int cacheOffset = 0;

    /* The pending async file read (yes we only support one pending read) */
    std::function<void(std::string_view)> pendingReadCb;

    int fileSize;
    std::ifstream fin;
    uWS::Loop *loop;

public:
    /* Construct a demo async. file reader for fileName */
    AsyncFileReader(std::string fileName) {
        fin.open(fileName, std::ios::binary);

        // get fileSize
        fin.seekg(0, fin.end);
        fileSize = fin.tellg();

        //std::cout << "File size is: " << fileSize << std::endl;

        // cache up 1 mb!
        cache.resize(1024 * 1024);

        //std::cout << "Caching 1 MB at offset = " << 0 << std::endl;
        fin.seekg(0, fin.beg);
        fin.read(cache.data(), cache.length());
        cacheOffset = 0;

        // get loop for thread

        loop = uWS::Loop::defaultLoop();
    }

    /* Returns any data already cached for this offset */
    std::string_view peek(int offset) {
        /* Did we hit the cache? */
        if (offset >= cacheOffset && ((offset - cacheOffset) < cache.length())) {
            /* Cache hit */
            //std::cout << "Cache hit!" << std::endl;
            return std::string_view(cache.data() + offset - cacheOffset, cache.length() - offset + cacheOffset);
        } else {
            /* Cache miss */
            //std::cout << "Cache miss!" << std::endl;
            return std::string_view(nullptr, 0);
        }
    }

    /* Asynchronously request more data at offset */
    void request(int offset, std::function<void(std::string_view)> cb) {

        // std::async this
        //std::cout << "Caching 1 MB at offset = " << offset << std::endl;
        fin.seekg(offset, fin.beg);
        fin.read(cache.data(), cache.length());
        cacheOffset = offset;

        // Loop.defer this
        cb(std::string_view(cache.data(), cache.length()));
    }

    /* Abort any pending async. request */
    void abort() {

    }

    int getFileSize() {
        return fileSize;
    }
};