module advent_of_code.tasks.day_5.Star2

open System
open System.IO

let stream = new StreamReader("tasks/day-5/input.txt")

let rec buildFresh() =
    let line = stream.ReadLine()
    if line.Length = 0 then
        List.empty
    else
        let splitLine = line.Split("-")
        let low, high = splitLine[0] |> int64, splitLine[1] |> int64
        List.append [ (low, high) ] (buildFresh())

let isFresh (fruit: int64) (range: int64 * int64) =
    let low, high = range.Deconstruct()
    if (fruit >= low && fruit <= high) then 1 else 0

let matchRange (a: int64 * int64) (b: int64 * int64) =
    let aMin, aMax = a.Deconstruct()
    let bMin, bMax = b.Deconstruct()
    (aMin <= bMin && bMin <= aMax) || (bMin <= aMin && aMin <= bMax) ||
    (aMin <= bMin && aMax >= bMax) || (bMin <= aMin && bMax >= aMax)

let combineRange (a: int64 * int64) (b: int64 * int64) =
    let aMin, aMax = a.Deconstruct()
    let bMin, bMax = b.Deconstruct()
    (min aMin bMin, max aMax bMax)

let rec trimFresh (trimmedFreshList: (int64 * int64) list) (fullFreshList: (int64 * int64) list) =
    let currentRange, tail = fullFreshList.Head, fullFreshList.Tail
    let overlaps = trimmedFreshList |> List.map (matchRange currentRange)
    let firstOverlap = List.tryFindIndex ((=) true) overlaps
    let newTrimmedList =
        match firstOverlap with
        | None -> List.append trimmedFreshList [currentRange]
        | Some 0 -> List.append [combineRange currentRange trimmedFreshList[0]] trimmedFreshList[1 ..]
        | Some index -> List.append (List.append trimmedFreshList[.. index - 1] [combineRange currentRange trimmedFreshList[index]]) trimmedFreshList[index + 1 ..]
    if tail.IsEmpty then newTrimmedList else trimFresh newTrimmedList tail

let rec trimLoop (fullFreshList: (int64 * int64) list) =
    let trimmedList = trimFresh List.empty fullFreshList
    if trimmedList.Length = fullFreshList.Length then trimmedList else trimLoop trimmedList

let rec addRanges (ranges: (int64 * int64) list) =
    let range, tail = ranges.Head, ranges.Tail
    let low, high = range.Deconstruct()
    ((high - low) + (1 |> int64)) + (if tail.IsEmpty then 0 |> int64 else (addRanges tail))

let main =
    let freshSet = List.sort (buildFresh())
    let trimmed = trimLoop freshSet
    addRanges trimmed