'use strict';

module.exports = function createBufferReaderFactory(rules) {
    return function createBufferReader(buffer) {
        let defaultMethods = {
            slice: function readSlice(start, length) {
                return buffer.slice(start, start + length);
            }
        }

        let customMethods = Object.keys(rules).map((ruleName) => {
            let rule = rules[ruleName];
            let readerFunction;

            return {
                key: ruleName,
                value: function(start, length) {
                    let actualLength;

                    if (rule.length != null) {
                        actualLength = rule.length;
                    } else {
                        actualLength = length;
                    }

                    return rule.decode(buffer.slice(start, start + actualLength));
                }
            }
        }).reduce((methods, item) => {
            methods[item.key] = item.value;
            return methods;
        }, {});

        return Object.assign(defaultMethods, customMethods);
    }
};