/**
 * ip2region client for nodejs
 *
 * project: https://github.com/lionsoul2014/ip2region
 *
 * @author dongyado<dongyado@gmail.com>
 * @author leeching<leeching.fx@gmail.com>
 * @author dongwei<maledong_github@outlook.com>
 */
const fs = require('fs');

//#region Private Functions
/**
 * Convert ip to long (xxx.xxx.xxx.xxx to a integer)
 *
 * @param {string} ip
 * @return {number} long value
 */
function _ip2long(ip) {
    const arr = ip.split('.');
    if (arr.length !== 4) {
        throw new Error('invalid ip');
    }
    return arr.reduce((val, n, i) => {
        n = Number(n);
        if (!Number.isInteger(n) || n < 0 || n > 255) {
            throw new Error('invalid ip');
        }
        return val + IP_BASE[i] * n;
    }, 0);
}

/**
 * Get long value from buffer with specified offset
 *
 * @param {Buffer} buffer
 * @param {number} offset
 * @return {number} long value
 */
function _getLong(buffer, offset) {
    const val =
        (buffer[offset] & 0x000000ff) |
        ((buffer[offset + 1] << 8) & 0x0000ff00) |
        ((buffer[offset + 2] << 16) & 0x00ff0000) |
        ((buffer[offset + 3] << 24) & 0xff000000);
    return val < 0 ? val >>> 0 : val;
}

//#endregion

//#region Private Variables

// We don't wanna expose a private global settings to
// the public for safety reason.
const _globalInstances = new Map();

const IP_BASE = [16777216, 65536, 256, 1];
const INDEX_BLOCK_LENGTH = 12;
const TOTAL_HEADER_LENGTH = 8192;

// Private Message Symbols for functions
const PrepareHeader = Symbol('#PrepareHeader');
const CalTotalBlocks = Symbol('#CalsTotalBlocks');
const ReadDataSync = Symbol('#ReadDataSync');
const ReadData = Symbol('#ReadData');

//#endregion
class IP2Region {

    //#region Private Functions

    [CalTotalBlocks]() {
        const superBlock = new Buffer(8);
        fs.readSync(this.dbFd, superBlock, 0, 8, 0);
        this.firstIndexPtr = _getLong(superBlock, 0);
        this.lastIndexPtr = _getLong(superBlock, 4);
        this.totalBlocks =
            (this.lastIndexPtr - this.firstIndexPtr) / INDEX_BLOCK_LENGTH + 1;
    }

    [PrepareHeader]() {
        fs.readSync(
            this.dbFd,
            this.headerIndexBuffer,
            0,
            TOTAL_HEADER_LENGTH,
            8
        );

        for (let i = 0; i < TOTAL_HEADER_LENGTH; i += 8) {
            const startIp = _getLong(this.headerIndexBuffer, i);
            const dataPtr = _getLong(this.headerIndexBuffer, i + 4);
            if (dataPtr == 0) break;

            this.headerSip.push(startIp);
            this.headerPtr.push(dataPtr);
            this.headerLen++; // header index size count
        }
    }

    [ReadData](dataPos, callBack) {
        if (dataPos == 0) return callBack(null,null);
        const dataLen = (dataPos >> 24) & 0xff;
        dataPos = dataPos & 0x00ffffff;
        const dataBuffer = new Buffer(dataLen);

        fs.read(this.dbFd, dataBuffer, 0, dataLen, dataPos, (err, result) => {
            if (err) {
                callBack(err, null);
            }
            else {
                const city = _getLong(dataBuffer, 0);
                const region = dataBuffer.toString('utf8', 4, dataLen);
                callBack(null, { city, region });
            }
        });
    }

    [ReadDataSync](dataPos) {
        if (dataPos == 0) return null;
        const dataLen = (dataPos >> 24) & 0xff;
        dataPos = dataPos & 0x00ffffff;
        const dataBuffer = new Buffer(dataLen);

        fs.readSync(this.dbFd, dataBuffer, 0, dataLen, dataPos);

        const city = _getLong(dataBuffer, 0);
        const region = dataBuffer.toString('utf8', 4, dataLen);

        return { city, region };
    }
    //#endregion

    //#region Static Functions

    // Single Instance
    static create(dbPath) {
        let existInstance = _globalInstances.get(dbPath);
        if (existInstance == null) {
            existInstance = new IP2Region({ dbPath: dbPath });
        }
        return existInstance;
    }

    /**
     * For backward compatibility
     */
    static destroy() {
        _globalInstances.forEach(([key, instance]) => {
            instance.destroy();
        });
    }

    //#endregion

    constructor(options = {}) {

        const { dbPath } = options;

        this.dbFd = fs.openSync(dbPath, 'r');

        this.dbPath = dbPath;

        _globalInstances.set(this.dbPath, this);

        this.totalBlocks = this.firstIndexPtr = this.lastIndexPtr = 0;
        this[CalTotalBlocks]();

        this.headerIndexBuffer = new Buffer(TOTAL_HEADER_LENGTH);
        this.headerSip = [];
        this.headerPtr = [];
        this.headerLen = 0;
        this[PrepareHeader]();
    }

    //#region Public Functions
    /**
     * Destroy the current file by closing it.
     */
    destroy() {
        fs.closeSync(this.dbFd);
        _globalInstances.delete(this.dbPath);
    }

    /**
     * Sync of binarySearch.
     * @param {string} ip The IP address to search for.
     * @return {SearchResult} A result something like `{ city: 2163, region: '中国|0|广东省|深圳市|阿里云' }`
     */
    binarySearchSync(ip) {

        ip = _ip2long(ip);

        let low = 0;
        let mid = 0;
        let high = this.totalBlocks;
        let pos = 0;
        let sip = 0;
        const indexBuffer = new Buffer(12);

        // binary search
        while (low <= high) {
            mid = (low + high) >> 1;
            pos = this.firstIndexPtr + mid * INDEX_BLOCK_LENGTH;
            fs.readSync(this.dbFd, indexBuffer, 0, INDEX_BLOCK_LENGTH, pos);
            sip = _getLong(indexBuffer, 0);

            if (ip < sip) {
                high = mid - 1;
            } else {
                sip = _getLong(indexBuffer, 4);
                if (ip > sip) {
                    low = mid + 1;
                } else {
                    sip = _getLong(indexBuffer, 8);
                    break;
                }
            }
        }
        return this[ReadDataSync](sip);
    }

    /**
     * Async of binarySearch.
     * @param {string} ip The IP address to search for.
     * @param {Function} callBack The callBack function with two parameters, if successful,
     * err is null and result is `{ city: 2163, region: '中国|0|广东省|深圳市|阿里云' }`
     */
    binarySearch(ip, callBack) {

        ip = _ip2long(ip);

        let low = 0;
        let mid = 0;
        let high = this.totalBlocks;
        let pos = 0;
        let sip = 0;
        const indexBuffer = new Buffer(12);
        const _self = this;

        // Because `while` is a sync method, we have to convert this to a recursive loop
        // and in each loop we should continue calling `setImmediate` until we found the IP.
        function _innerAsyncWhile() {
            if (low <= high) {
                mid = (low + high) >> 1;
                pos = _self.firstIndexPtr + mid * INDEX_BLOCK_LENGTH;

                // Now async read the file
                fs.read(_self.dbFd, indexBuffer, 0, INDEX_BLOCK_LENGTH, pos, (err) => {

                    if (err) {
                        return callBack(err, null);
                    }

                    sip = _getLong(indexBuffer, 0);

                    if (ip < sip) {
                        high = mid - 1;
                        setImmediate(_innerAsyncWhile);
                    } else {
                        sip = _getLong(indexBuffer, 4);
                        if (ip > sip) {
                            low = mid + 1;
                            setImmediate(_innerAsyncWhile);
                        } else {
                            sip = _getLong(indexBuffer, 8);
                            _self[ReadData](sip, (err, result) => {
                                callBack(err, result);
                            });
                        }
                    }
                });
            }
        }

        // Call this immediately
        _innerAsyncWhile();

    }

    /**
     * Sync of btreeSearch.
     * @param {string} ip The IP address to search for.
     * @return {Function} A result something like `{ city: 2163, region: '中国|0|广东省|深圳市|阿里云' }`
     */
    btreeSearchSync(ip) {

        ip = _ip2long(ip);

        // first search  (in header index)
        let low = 0;
        let mid = 0;
        let high = this.headerLen;
        let sptr = 0;
        let eptr = 0;

        while (low <= high) {
            mid = (low + high) >> 1;

            if (ip == this.headerSip[mid]) {
                if (mid > 0) {
                    sptr = this.headerPtr[mid - 1];
                    eptr = this.headerPtr[mid];
                } else {
                    sptr = this.headerPtr[mid];
                    eptr = this.headerPtr[mid + 1];
                }
                break;
            }

            if (ip < this.headerSip[mid]) {
                if (mid == 0) {
                    sptr = this.headerPtr[mid];
                    eptr = this.headerPtr[mid + 1];
                    break;
                } else if (ip > this.headerSip[mid - 1]) {
                    sptr = this.headerPtr[mid - 1];
                    eptr = this.headerPtr[mid];
                    break;
                }
                high = mid - 1;
            } else {
                if (mid == this.headerLen - 1) {
                    sptr = this.headerPtr[mid - 1];
                    eptr = this.headerPtr[mid];
                    break;
                } else if (ip <= this.headerSip[mid + 1]) {
                    sptr = this.headerPtr[mid];
                    eptr = this.headerPtr[mid + 1];
                    break;
                }
                low = mid + 1;
            }
        }

        // match nothing
        if (sptr == 0) return null;

        // second search (in index)
        const blockLen = eptr - sptr;
        const blockBuffer = new Buffer(blockLen + INDEX_BLOCK_LENGTH);
        fs.readSync(
            this.dbFd,
            blockBuffer,
            0,
            blockLen + INDEX_BLOCK_LENGTH,
            sptr
        );

        low = 0;
        high = blockLen / INDEX_BLOCK_LENGTH;

        let p = 0;
        let sip = 0;

        while (low <= high) {
            mid = (low + high) >> 1;
            p = mid * INDEX_BLOCK_LENGTH;
            sip = _getLong(blockBuffer, p);

            if (ip < sip) {
                high = mid - 1;
            } else {
                sip = _getLong(blockBuffer, p + 4);
                if (ip > sip) {
                    low = mid + 1;
                } else {
                    sip = _getLong(blockBuffer, p + 8);
                    break;
                }
            }
        }
        return this[ReadDataSync](sip);
    }

    /**
    * Async of btreeSearch.
     * @param {string} ip The IP address to search for.
     * @param {Function} callBack The callBack function with two parameters, if successful,
     * err is null and result is `{ city: 2163, region: '中国|0|广东省|深圳市|阿里云' }`
    */
    btreeSearch(ip, callBack) {
        ip = _ip2long(ip);

        // first search  (in header index)
        let low = 0;
        let mid = 0;
        let high = this.headerLen;
        let sptr = 0;
        let eptr = 0;

        while (low <= high) {
            mid = (low + high) >> 1;

            if (ip == this.headerSip[mid]) {
                if (mid > 0) {
                    sptr = this.headerPtr[mid - 1];
                    eptr = this.headerPtr[mid];
                } else {
                    sptr = this.headerPtr[mid];
                    eptr = this.headerPtr[mid + 1];
                }
                break;
            }

            if (ip < this.headerSip[mid]) {
                if (mid == 0) {
                    sptr = this.headerPtr[mid];
                    eptr = this.headerPtr[mid + 1];
                    break;
                } else if (ip > this.headerSip[mid - 1]) {
                    sptr = this.headerPtr[mid - 1];
                    eptr = this.headerPtr[mid];
                    break;
                }
                high = mid - 1;
            } else {
                if (mid == this.headerLen - 1) {
                    sptr = this.headerPtr[mid - 1];
                    eptr = this.headerPtr[mid];
                    break;
                } else if (ip <= this.headerSip[mid + 1]) {
                    sptr = this.headerPtr[mid];
                    eptr = this.headerPtr[mid + 1];
                    break;
                }
                low = mid + 1;
            }
        }

        // match nothing
        if (sptr == 0) return callBack(null, null);

        let p = 0;
        let sip = 0;

        // second search (in index)
        const blockLen = eptr - sptr;
        const blockBuffer = new Buffer(blockLen + INDEX_BLOCK_LENGTH);
        low = 0;
        high = blockLen / INDEX_BLOCK_LENGTH;

        const _self = this;

        function _innerAsyncWhile() {

            if (low <= high) {

                mid = (low + high) >> 1;
                p = mid * INDEX_BLOCK_LENGTH;

                // Use this to call the method itself as
                // an asynchronize step
                fs.read(_self.dbFd, blockBuffer,
                    0,
                    blockLen + INDEX_BLOCK_LENGTH,
                    sptr, (err) => {

                        if (err) {
                            return callBack(err, null);
                        }

                        sip = _getLong(blockBuffer, p);

                        if (ip < sip) {
                            high = mid - 1;
                            setImmediate(_innerAsyncWhile);
                        } else {
                            sip = _getLong(blockBuffer, p + 4);
                            if (ip > sip) {
                                low = mid + 1;
                                setImmediate(_innerAsyncWhile);
                            } else {
                                sip = _getLong(blockBuffer, p + 8);
                                _self[ReadData](sip, (err, result) => {
                                    callBack(err, result);
                                });
                            }
                        }
                    });
            }
            else {
                // If we found nothing, return null
                return callBack(null, null);
            }
        }

        _innerAsyncWhile();
    }

    //#endregion
}

module.exports = IP2Region;