export interface LightMap<K,V> {
    [Symbol.toStringTag]: string;
    has(key: K): boolean;
    get(key: K): V | undefined;
    set(key: K, value: V): this;
    delete(key: K): boolean;
    keys(): Iterable<K>;
}

export class LightMapImpl<K,V> implements LightMap<K,V> {

    [Symbol.toStringTag]: string;

    private readonly record: [K, V][]= [];

    constructor(){ }

    public has(key: K): boolean {
        return this.record
            .map(([_key]) => _key)
            .indexOf(key) >= 0;
    }

    public get(key: K): V | undefined {

        const [ entry ]= this.record
            .filter(([_key]) => _key === key)
            ;

        if( entry === undefined ){
            return undefined;
        }

        return entry[1];

    }

    public set(key: K, value: V) {

        const [ entry ]= this.record
            .filter(([_key]) => _key === key)
            ;

        if( entry === undefined ){

            this.record.push([key, value]);

        }else{

            entry[1]= value;

        }

        return this;

    }

    public delete(key: K): boolean{

        const index= this.record.map(([ key])=> key).indexOf(key);

        if( index < 0 ){
            return false;
        }

        this.record.splice(index, 1);

        return true;

    }

    public keys(): Iterable<K> {
        return this.record.map(([ key ])=> key);
    }

}


export const Polyfill: { new<K,V>(): LightMap<K,V> } = 
    typeof Map !== "undefined" ? Map : LightMapImpl;