export const groupByQuadrants = (items) => (
  items.reduce((quadrants, item) => ({
    ...quadrants,
    [item.quadrant]: addItemToQuadrant(quadrants[item.quadrant], item),
  }), {})
);

export const groupByRing = (items) => (
  items.reduce((rings, item) => ({
    ...rings,
    [item.ring]: addItemToList(rings[item.ring], item),
  }), {})
);

export const groupByFirstLetter = (items) => {
  const index = items.reduce((letterIndex, item) => ({
    ...letterIndex,
    [getFirstLetter(item)]: addItemToList(letterIndex[getFirstLetter(item)], item),
  }), {});

  return Object.keys(index).sort().map((letter) => ({
    letter,
    items: index[letter],
  }));
}

const addItemToQuadrant = (quadrant = {}, item) => ({
  ...quadrant,
  [item.ring]: addItemToRing(quadrant[item.ring], item),
});

const addItemToList = (list = [], item) => ([
  ...list,
  item,
]);

const addItemToRing = (ring = [], item) => ([
  ...ring,
  item,
]);

export const getFirstLetter = (item) => item.title.substr(0,1).toUpperCase();