import m, { ClosureComponent, Component, Vnode } from "mithril";

const elements: Map<string, Vnode> = new Map();

// Source: https://werxltd.com/wp/2010/05/13/javascript-implementation-of-javas-string-hashcode-method/
function hash(str: string): number {
  let res = 0;
  for (let i = 0; i < str.length; ++i) {
    const c = str.charCodeAt(i);
    res = (res << 5) - res + c;
    res |= 0;
  }
  return res;
}

export function getDatalistId(options: string[]): string {
  const id = "datalist" + options.reduce((acc, cur) => acc ^ hash(cur), 0);
  if (!elements.has(id)) {
    const n = m(
      "datalist",
      { id },
      options.map((o) => m("option", { value: o })),
    );
    elements.set(id, n);
  }
  return id;
}

const component: ClosureComponent = (): Component => {
  return {
    view: () => {
      return [...elements.values()];
    },
    onupdate: () => {
      for (const id of elements.keys()) {
        const used = document.querySelector(`[list='${id}']`);
        if (!used) elements.delete(id);
      }
    },
  };
};

export default component;