backend/src/modules/investments/income/income-period.ts

import { BadRequestException } from '@nestjs/common';

import { ISO_DATE_LENGTH, ISO_DATE_START, MILLISECONDS_PER_DAY } from '../../../common/time';
import {
  DateOnlyRange,
  dateParts,
  moscowDate,
  utcDate,
} from '../investment-calendar';

const MONDAY_WEEKDAY_INDEX = 1;
const INCLUSIVE_DAY_OFFSET = 1;
const NEXT_DAY_OFFSET = 1;
const PREVIOUS_MONTH_LAST_DAY = 0;
const PREVIOUS_DAY_OFFSET = -1;
const PREVIOUS_YEAR_OFFSET = 1;
const DATE_COMPONENT_DIGITS = 2;

const DAILY_BUCKET_MAX_DAYS = 45;
const WEEKLY_BUCKET_MAX_DAYS = 180;
const DAYS_PER_WEEK = 7;
const ISO_MONTH_LENGTH = 7;
const ISO_YEAR_LENGTH = 4;

export type IncomeBucketGranularity = 'day' | 'month' | 'week';

export function planIncomePeriod(
  from: string | undefined,
  to: string | undefined,
  openedDate?: Date,
): {
  granularity: IncomeBucketGranularity;
  previous: DateOnlyRange;
  selected: DateOnlyRange;
  yearAgo: DateOnlyRange | null;
} {
  if (Boolean(from) !== Boolean(to)) throw invalidPeriod();
  const today = moscowDate(new Date());
  const selected =
    from && to ? { from, to } : { from: firstOfMonth(today), to: today };
  assertRange(selected, today);
  const previous = isFullMonth(selected) ?
      previousMonth(selected.from) :
      shiftDays(selected, -rangeDays(selected));
  const candidate = yearAgo(selected);
  const yearAgoRange =
    candidate && (!openedDate || candidate.from >= moscowDate(openedDate)) ?
      candidate :
      null;
  return {
    selected,
    previous,
    yearAgo: yearAgoRange,
    granularity:
      rangeDays(selected) <= DAILY_BUCKET_MAX_DAYS ?
        'day' :
        rangeDays(selected) <= WEEKLY_BUCKET_MAX_DAYS ?
          'week' :
          'month',
  };
}

export function rangeBuckets(
  range: DateOnlyRange,
  granularity: IncomeBucketGranularity,
): DateOnlyRange[] {
  if (granularity === 'day') {
    return dates(range).map((date) => ({ from: date, to: date }));
  }
  const buckets: DateOnlyRange[] = [];
  let cursor =
    granularity === 'week' ?
        addDays(
          range.from,
          -(
            (utcDate(range.from).getUTCDay() + DAYS_PER_WEEK - MONDAY_WEEKDAY_INDEX) %
            DAYS_PER_WEEK
          ),
        ) :
      `${range.from.slice(ISO_DATE_START, ISO_MONTH_LENGTH)}-01`;
  while (cursor <= range.to) {
    const end =
      granularity === 'week' ?
          addDays(cursor, DAYS_PER_WEEK - INCLUSIVE_DAY_OFFSET) :
          endOfMonth(cursor);
    buckets.push({
      from: cursor < range.from ? range.from : cursor,
      to: end > range.to ? range.to : end,
    });
    cursor = addDays(end, NEXT_DAY_OFFSET);
  }
  return buckets;
}

export function rangeDays(range: DateOnlyRange): number {
  return (
    Math.round(
      (utcDate(range.to).valueOf() - utcDate(range.from).valueOf()) /
      MILLISECONDS_PER_DAY,
    ) + INCLUSIVE_DAY_OFFSET
  );
}

function assertRange(range: DateOnlyRange, today: string): void {
  try {
    dateParts(range.from);
    dateParts(range.to);
  } catch {
    throw invalidPeriod();
  }
  if (range.from > range.to || range.to > today) throw invalidPeriod();
}

function addDays(value: string, days: number): string {
  const date = utcDate(value);
  date.setUTCDate(date.getUTCDate() + days);
  return date.toISOString().slice(ISO_DATE_START, ISO_DATE_LENGTH);
}

function dates(range: DateOnlyRange): string[] {
  const result: string[] = [];
  for (let date = range.from; date <= range.to; date = addDays(date, NEXT_DAY_OFFSET)) {
    result.push(date);
  }
  return result;
}

function firstOfMonth(value: string): string {
  return `${value.slice(ISO_DATE_START, ISO_MONTH_LENGTH)}-01`;
}

function endOfMonth(value: string): string {
  const [year, month] = dateParts(firstOfMonth(value));
  return new Date(Date.UTC(year, month, PREVIOUS_MONTH_LAST_DAY)).toISOString().slice(ISO_DATE_START, ISO_DATE_LENGTH);
}

function isFullMonth(range: DateOnlyRange): boolean {
  return (
    range.from === firstOfMonth(range.from) && range.to === endOfMonth(range.to)
  );
}

function previousMonth(from: string): DateOnlyRange {
  const last = addDays(firstOfMonth(from), PREVIOUS_DAY_OFFSET);
  return { from: firstOfMonth(last), to: last };
}

function shiftDays(range: DateOnlyRange, days: number): DateOnlyRange {
  return { from: addDays(range.from, days), to: addDays(range.to, days) };
}

function yearAgo(range: DateOnlyRange): DateOnlyRange | null {
  const shift = (value: string) => {
    const [year, month, day] = dateParts(value);
    const result = `${String(year - PREVIOUS_YEAR_OFFSET).padStart(ISO_YEAR_LENGTH, '0')}-${String(month).padStart(DATE_COMPONENT_DIGITS, '0')}-${String(day).padStart(DATE_COMPONENT_DIGITS, '0')}`;
    return utcDate(result).toISOString().slice(ISO_DATE_START, ISO_DATE_LENGTH) === result ?
      result :
      null;
  };
  const from = shift(range.from);
  const to = shift(range.to);
  return from && to ? { from, to } : null;
}

function invalidPeriod(): BadRequestException {
  return new BadRequestException({ code: 'INVALID_INCOME_PERIOD' });
}