"use strict";

const generateID = require("../../generate-id");

const BLOB_INTERNAL = Buffer.from([ 0 ]);
const BLOB_EXTERNAL = Buffer.from([ 1 ]);

module.exports = {
	encode: function (value, _asIndexKey) {
		if (value.length < 256) {
			return {
				value: [
					BLOB_INTERNAL,
					Buffer.from([ value.length ]),
					value
				],
				auxiliaryBlob: undefined
			};
		} else {
			let blobID = generateID();

			return {
				value: [
					BLOB_EXTERNAL,
					blobID
				],
				auxiliaryBlob: {
					key: blobID,
					value: value
				}
			};
		}
	},
	decode: function (buffer, offset) {
		let blobType = buffer.readUInt8(offset);
		
		if (blobType === 0) {
			// Internal blob
			let blobLength = buffer.readUInt8(offset + 1);
			let blobPosition = offset + 2;
			let bytes = buffer.slice(blobPosition, blobPosition + blobLength);

			return {
				bytesRead: 2 + blobLength,
				value: bytes,
				auxiliaryBlob: undefined
			};
		} else if (blobType === 1) {
			// External blob
			let idPosition = offset + 1;

			return {
				bytesRead: 13, // a blob ID is always 12 bytes
				value: undefined,
				auxiliaryBlob: {
					key: buffer.slice(idPosition, idPosition + 12),
					transform: (blob) => blob
				}
			};
		} else {
			throw new Error(`Invalid blob type: ${blobType}`);
		}
	}
};