import { each } from './each';
import { isFunction } from '../base/isFunction';
import { Fn } from '../../types';
import { isDef } from '../base/isDef';

/**
 * todo 不同类型及深度拷贝
 * 避免引用,使用的对象复制
 * @category Object
 * @param target 
 * @returns {T}
 */
type Customizer = (objVal?, srcVal?, key?, obj?, src?) => boolean

export const createAssign = <T extends Fn<any[], string[]>>(getKeys: T) => {
    const defaultCustomizer: Customizer = (_objVal, srcVal) => isDef(srcVal);
    
    // todo 类型
    function assign<T, S1>(obj: T, src1: S1, customizer?: Customizer): T & S1
    function assign<T, S1, S2>(obj: T, src1: S1, src2: S2, customizer?: Customizer): T & S1 & S2
    function assign<T, S1, S2, S3>(obj: T, src1: S1, src2: S2, src3: S3, customizer?: Customizer): T & S1 & S2 & S3
    function assign<T, S1, S2, S3, S4>(obj: T, src1: S1, src2: S2, src3: S3, src4: S4, customizer?: Customizer): T & S1 & S2 & S3 & S4
    function assign<T, S1, S2, S3, S4, S5>(obj: T, src1: S1, src2: S2, src3: S3, src4: S4, src5: S5, customizer?: Customizer): T & S1 & S2 & S3 & S4 & S5
    function assign(...args): any
    function assign(obj, ...sources) {
        let customizer = defaultCustomizer;
        if (isFunction(sources.slice(-1)[0])) {
            customizer = sources.pop();
        }
        each(sources, (src) => {
            const keys = getKeys(src);
            each(keys, k => {
                const objVal = obj[k];
                const srcVal = src[k];
                if (customizer(objVal, srcVal, k, obj, src)) {
                    obj[k] = srcVal;
                }
            });
        });
        return obj;
    }
    return assign;
};