Find the longest period of time when there are no ongoing meetings

Week.scala

import math.max

/*
    James is a businessman. He is on a tight schedule this week. The week starts
    on Monday at 00:00 and ends on Sunday at 24:00. His schedule consists of M
    meetings he needs to take part in. Each of them will take place in a period of
    time, beginning and ending on the same day (there are no two ongoing meetings
    at the same time). James is very tired, thus he needs to find the longest
    possible time slot to sleep. In other words, he wants to find the longest
    period of time when there are no ongoing meetings. The sleeping break can
    begin and end on different days and should begin and end in the same week.
    You are given a string containing M lines. Each line is a substring
    representing one meeting in the schedule, in the format "Ddd hh:mm-hh:mm".
    "Ddd" is a three-letter abbreviation for the day of the week when the meeting
    takes place: "Mon" (Monday), "Tue", "Wed", "Thu", "Fri", "Sat", "Sun".
     "hh:mm-hh:mm" means the beginning time and the ending time of the meeting
    (from 00:00 to 24:00 inclusive).
    The given times represent exact moments of time. So, there are exactly five
    minutes between 13:40 and 13:45.
    For example, given a string:
       "Sun 10:00-20:00
        Fri 05:00-10:00
        Fri 16:30-23:50
        Sat 10:00-24:00
        Sun 01:00-04:00
        Sat 02:00-06:00
        Tue 03:30-18:15
        Tue 19:00-20:00
        Wed 04:25-15:14
        Wed 15:14-22:40
        Thu 00:00-23:59
        Mon 05:00-13:00
        Mon 15:00-21:00"
    The longest time slot when James can sleep is 505 minutes, since James can
    sleep from Tuesday 20:00 to Wednesday 04:25, which gives 8 hours and 25
    minutes = 505 minutes.
    Also, for a string:
       "Mon 01:00-23:00
        Tue 01:00-23:00
        Wed 01:00-23:00
        Thu 01:00-23:00
        Fri 01:00-23:00
        Sat 01:00-23:00
        Sun 01:00-21:00"
    James should sleep on Sunday from 21:00 to 24:00 (180 minutes).
    Write a function:
        object Solution { def solution(s: String): Int }

    that, given a string S representing the schedule, returns the length of the
    longest time slot when James can sleep (in minutes).
    Assume that:
    ● M is an integer within the range [1..100];
    ● Each line of the input string is in the format "Ddd hh:mm-hh:mm" and
          lines are separated with newline characters;
    ● There cannot be two ongoing meetings at any time;
    ● Each meeting lasts at least 1 minute.
    In your solution, focus on correctness. The performance of your solution will
    not be the focus of the assessment.
 */

object Week {
  def largestGapInMinutes(s: String): Int = {
    val startFakeMeeting = new Meeting("Mon 00:00-00:00")
    val finalGap = new Meeting("Sun 24:00-24:00")
    val sortedMeetings = startFakeMeeting +: s.linesIterator.map(new Meeting(_)).toSeq.sortBy { meeting =>
      (meeting.dow, meeting.start)
    } :+ finalGap
    (1 until sortedMeetings.size).foldLeft(0) { case (largestGapInMinutes, i) =>
      val previousMeeting = sortedMeetings(i - 1)
      val meeting = sortedMeetings(i)
      val gap = meeting.gapInMinutes(previousMeeting)
      max(largestGapInMinutes, gap)
    }
  }
}

import Meeting._

import java.time.DayOfWeek
import java.util.Date

import java.util.concurrent.TimeUnit
import TimeUnit.{MINUTES => Minutes}
import TimeUnit.{DAYS => Days}
import TimeUnit.{MILLISECONDS => Milliseconds}

class Meeting(slot: String) {
  private val (startStr, endRaw) = slot.splitAt(DashI)
  private val (dowShort, startTimeStrRaw) = startStr.splitAt(DowI)
  private val startTimeStr = startTimeStrRaw.tail
  private val endStr = endRaw.tail
  val dow: DayOfWeek = DowFromShort(dowShort)
  val start: Date = TimeFormat.parse(startTimeStr)
  val end: Date = TimeFormat.parse(endStr)

  def gapInMinutes(previous: Meeting): Int = {
    def diffInMinutes(f: Meeting => Long, previousF: Meeting => Long, timeUnit: TimeUnit) =
      Minutes.convert(f(this) - previousF(previous), timeUnit).toInt

    val dayDiffF: Meeting => Long = _.dow.getValue
    val dayDiffInMinutes = diffInMinutes(dayDiffF, dayDiffF, Days)
    val timeDiffInMinutes = diffInMinutes(_.start.getTime, _.end.getTime, Milliseconds)
    dayDiffInMinutes + timeDiffInMinutes
  }

  override def toString: String = slot
}

import java.text.SimpleDateFormat

object Meeting {
  private val DashI = 9
  private val DowI = 3
  private val TimeFormat = new SimpleDateFormat("HH:mm")
  private val DowFromShort = DayOfWeek.values.map { dow =>
    val allCapsShort = dow.name.take(3)
    allCapsShort.head + allCapsShort.drop(1).toLowerCase -> dow
  }.toMap
}

WeekSpec.scala

import org.scalatest.flatspec.AnyFlatSpec

class WeekSpec extends AnyFlatSpec {
  "nominal sched" should "work" in {
    val meetings = """Sun 10:00-20:00
                     |Fri 05:00-10:00
                     |Fri 16:30-23:50
                     |Sat 10:00-24:00
                     |Sun 01:00-04:00
                     |Sat 02:00-06:00
                     |Tue 03:30-18:15
                     |Tue 19:00-20:00
                     |Wed 04:25-15:14
                     |Wed 15:14-22:40
                     |Thu 00:00-23:59
                     |Mon 05:00-13:00
                     |Mon 15:00-21:00""".stripMargin
    assert(Week.largestGapInMinutes(meetings) === 505)
  }
  "last gap (it is the largest)" should "be chosen" in {
    val meetings = """Mon 01:00-23:00
                     |Tue 01:00-23:00
                     |Wed 01:00-23:00
                     |Thu 01:00-23:00
                     |Fri 01:00-23:00
                     |Sat 01:00-23:00
                     |Sun 01:00-21:00""".stripMargin
    assert(Week.largestGapInMinutes(meetings) === 180)
  }
  "initial gap (it is the largest)" should "be chosen" in {
    val meetings = """Tue 01:00-23:00
                     |Wed 01:00-23:00
                     |Thu 01:00-23:00
                     |Fri 01:00-23:00
                     |Sat 01:00-23:00
                     |Sun 01:00-21:00""".stripMargin
    assert(Week.largestGapInMinutes(meetings) === 1500)
  }
}