const Iconv = require('iconv-lite'),
	Long = require('long');

function readUInt64BE(buffer,offset) {
    const high = buffer.readUInt32BE(offset);
    const low = buffer.readUInt32BE(offset+4);
	return new Long(low,high,true);
}
function readUInt64LE(buffer,offset) {
    const low = buffer.readUInt32LE(offset);
    const high = buffer.readUInt32LE(offset+4);
	return new Long(low,high,true);
}

class Reader {
	constructor(query,buffer) {
		this.query = query;
		this.buffer = buffer;
		this.i = 0;
	}

	offset() {
		return this.i;
	}

	skip(i) {
		this.i += i;
	}

	string(...args) {
        let options = {};
		if(args.length === 0) {
			options = {};
		} else if(args.length === 1) {
			if(typeof args[0] === 'string') options = { delimiter: args[0] };
			else if(typeof args[0] === 'number') options = { length: args[0] };
			else options = args[0];
		}

		options.encoding = options.encoding || this.query.encoding;
		if(options.encoding === 'latin1') options.encoding = 'win1252';

		const start = this.i+0;
		let end = start;
		if(!('length' in options)) {
			// terminated by the delimiter
			let delim = options.delimiter || this.query.delimiter;
			if(typeof delim === 'string') delim = delim.charCodeAt(0);
			while(true) {
				if(end >= this.buffer.length) {
					end = this.buffer.length;
					break;
				}
				if(this.buffer.readUInt8(end) === delim) break;
				end++;
			}
			this.i = end+1;
		} else {
			end = start+options.length;
			if(end >= this.buffer.length) {
				end = this.buffer.length;
			}
			this.i = end;
		}

		let out = this.buffer.slice(start, end);
		const enc = options.encoding;
		if(enc === 'utf8' || enc === 'ucs2' || enc === 'binary') {
			out = out.toString(enc);
		} else {
			out = Iconv.decode(out,enc);
		}
		return out;
	}

	int(bytes) {
		let r = 0;
		if(this.remaining() >= bytes) {
			if(this.query.byteorder === 'be') {
				if(bytes === 1) r = this.buffer.readInt8(this.i);
				else if(bytes === 2) r = this.buffer.readInt16BE(this.i);
				else if(bytes === 4) r = this.buffer.readInt32BE(this.i);
			} else {
				if(bytes === 1) r = this.buffer.readInt8(this.i);
				else if(bytes === 2) r = this.buffer.readInt16LE(this.i);
				else if(bytes === 4) r = this.buffer.readInt32LE(this.i);
			}
		}
		this.i += bytes;
		return r;
	}

	/** @returns {number} */
	uint(bytes) {
		let r = 0;
		if(this.remaining() >= bytes) {
			if(this.query.byteorder === 'be') {
				if(bytes === 1) r = this.buffer.readUInt8(this.i);
				else if(bytes === 2) r = this.buffer.readUInt16BE(this.i);
				else if(bytes === 4) r = this.buffer.readUInt32BE(this.i);
				else if(bytes === 8) r = readUInt64BE(this.buffer,this.i).toString();
			} else {
				if(bytes === 1) r = this.buffer.readUInt8(this.i);
				else if(bytes === 2) r = this.buffer.readUInt16LE(this.i);
				else if(bytes === 4) r = this.buffer.readUInt32LE(this.i);
				else if(bytes === 8) r = readUInt64LE(this.buffer,this.i).toString();
			}
		}
		this.i += bytes;
		return r;
	}

	float() {
		let r = 0;
		if(this.remaining() >= 4) {
			if(this.query.byteorder === 'be') r = this.buffer.readFloatBE(this.i);
			else r = this.buffer.readFloatLE(this.i);
		}
		this.i += 4;
		return r;
	}

	part(bytes) {
		let r;
		if(this.remaining() >= bytes) {
			r = this.buffer.slice(this.i,this.i+bytes);
		} else {
			r = Buffer.from([]);
		}
		this.i += bytes;
		return r;
	}

	remaining() {
		return this.buffer.length-this.i;
	}

	rest() {
		return this.buffer.slice(this.i);
	}

	done() {
		return this.i >= this.buffer.length;
	}
}

module.exports = Reader;