import { StringUtil } from "../StringUtil";

export function snake(str: string): string {
  if (str.length === 0) return str;

  // PREFIX
  // eslint-disable-next-line @typescript-eslint/no-unused-vars
  let prefix: string = "";
  for (let i: number = 0; i < str.length; i++) {
    if (str[i] === "_") prefix += "_";
    else break;
  }
  if (prefix.length !== 0) str = str.substring(prefix.length);

  const out = (s: string) => `${prefix}${s}`;

  // SNAKE CASE
  const items: string[] = str.split("_");
  if (items.length > 1) return out(items.map((s) => s.toLowerCase()).join("_"));

  // CAMEL OR PASCAL CASE
  const indexes: number[] = [];
  for (let i: number = 0; i < str.length; i++) {
    const code: number = str.charCodeAt(i);
    if (65 <= code && code <= 90) indexes.push(i);
  }
  for (let i: number = indexes.length - 1; i > 0; --i) {
    const now: number = indexes[i]!;
    const prev: number = indexes[i - 1]!;
    if (now - prev === 1) indexes.splice(i, 1);
  }
  if (indexes.length !== 0 && indexes[0] === 0) indexes.splice(0, 1);
  if (indexes.length === 0) return str.toLowerCase();

  let ret: string = "";
  for (let i: number = 0; i < indexes.length; i++) {
    const first: number = i === 0 ? 0 : indexes[i - 1]!;
    const last: number = indexes[i]!;

    ret += str.substring(first, last).toLowerCase();
    ret += "_";
  }
  ret += str.substring(indexes[indexes.length - 1]!).toLowerCase();
  return out(ret);
}

export const camel = (str: string): string =>
  unsnake({
    plain: (str) =>
      str.length
        ? str === str.toUpperCase()
          ? str.toLocaleLowerCase()
          : `${str[0]!.toLowerCase()}${str.substring(1)}`
        : str,
    snake: (str, i) =>
      i === 0 ? str.toLowerCase() : StringUtil.capitalize(str.toLowerCase()),
  })(str);

export const pascal = (str: string): string =>
  unsnake({
    plain: (str) =>
      str.length ? `${str[0]!.toUpperCase()}${str.substring(1)}` : str,
    snake: StringUtil.capitalize,
  })(str);

const unsnake =
  (props: {
    plain: (str: string) => string;
    snake: (str: string, index: number) => string;
  }) =>
  (str: string): string => {
    // eslint-disable-next-line @typescript-eslint/no-unused-vars
    let prefix: string = "";
    for (let i: number = 0; i < str.length; i++) {
      if (str[i] === "_") prefix += "_";
      else break;
    }
    if (prefix.length !== 0) str = str.substring(prefix.length);

    const out = (s: string) => `${prefix}${s}`;
    if (str.length === 0) return out("");

    const items: string[] = str.split("_").filter((s) => s.length !== 0);
    return items.length === 0
      ? out("")
      : items.length === 1
        ? out(props.plain(items[0]!))
        : out(items.map(props.snake).join(""));
  };