import IData from '../interfaces/IData';
import validLetters from './validLetters';
import ISectionData from '../interfaces/ISectionData';

interface IAlphabetSet<T> {
  [key: string]: IData<T>[];
}

interface IEntry<T> {
  title: string;
  data: IData<T>[];
}

const getSectionData<T> = (data: IData<T>[]) => {
  const alphabetEntrySet: [string, IData<T>[]][] = getAlphabetEntrySet(data);

  return alphabetEntrySet
    .map(formatEntry)
    .sort(sortSectionsAlphabetically)
    .map((section: ISectionData, index: number) => ({...section, index}));
};

const getAlphabetEntrySet = (data: IData[]) => {
  const alphabetSet: IAlphabetSet = {};

  data.forEach(item => {
    const letter = getItemFirstLetter(item.value);

    if (!letter) {
      return;
    }

    if (!alphabetSet[letter]) {
      alphabetSet[letter] = [];
    }

    alphabetSet[letter].push(item);
  });

  return Object.entries(alphabetSet);
};

const getItemFirstLetter = (value: string) => {
  const firstChar: string = value.substring(0, 1);
  const isValidLetter: boolean = validLetters[firstChar.toLowerCase()];

  if (isValidLetter) {
    return firstChar.toUpperCase();
  }

  return '#';
};

const formatEntry = (entry: [string, any[]]) => {
  const [title, unsortedData] = entry;

  const data = unsortedData.sort((a, b) =>
    alphabeticComparison(a.value, b.value),
  );

  return {title, data} as IEntry;
};

const sortSectionsAlphabetically = (a: IEntry, b: IEntry) => {
  const {title: charA} = a;
  const {title: charB} = b;

  const isBHash = charA !== '#' && charB === '#';
  if (isBHash) {
    return -1;
  }

  const isAHash = charA === '#' && charB !== '#';
  if (isAHash) {
    return 1;
  }

  return alphabeticComparison(charA, charB);
};

const alphabeticComparison = (a: string, b: string) => {
  const aCap = a.toUpperCase();
  const bCap = b.toUpperCase();

  if (aCap < bCap) {
    return -1;
  }

  if (aCap > bCap) {
    return 1;
  }

  return 0;
};

export default getSectionData;