package main

import (
	"bufio"
	"fmt"
	"io"
	"log"
	"math"
	"os"
	"strings"
)

type Seat string

func half(chain string, size int, lower rune, upper rune) int {
	rowPart := chain[0:int(math.Log2(float64(size)))]
	half := size / 2
	row := 0
	for _, c := range rowPart {
		switch c {
		case lower:
		case upper:
			row += half
		default:
			panic("wrong letter")
		}
		half /= 2
	}
	return row
}

func (s Seat) Row() int {
	return half(string(s[0:7]), 128, 'F', 'B')
}

func (s Seat) Col() int {
	return half(string(s[7:10]), 8, 'L', 'R')
}

func (s Seat) ID() int {
	return (s.Row() * 8) + s.Col()
}

func (s Seat) String() string {
	return fmt.Sprintf("row %d, col %d, ID %d", s.Row(), s.Col(), s.ID())
}

func main() {
	// I'm lazy and need this done quick
	seats := map[int]Seat{}
	f, err := os.Open("input")
	if err != nil {
		panic(err)
	}
	r := bufio.NewReader(f)
	for {
		line, err := r.ReadString('\n')
		if err == io.EOF {
			break
		}
		if err != nil {
			panic(err)
		}
		line = strings.TrimSpace(line)
		seat := Seat(line)
		seatID := seat.ID()
		seats[seatID] = seat
	}
	// skip row 0 and row 127
	for seatID := 8; seatID < (128-1)*8; seatID++ {
		// has ID + 1 and ID - 1?
		if _, exists := seats[seatID]; !exists {
			if _, hasSeatIDPlus1 := seats[seatID+1]; hasSeatIDPlus1 {
				if _, hasSeatIDMinus1 := seats[seatID-1]; hasSeatIDMinus1 {
					log.Printf("Matching seat ID: %d", seatID)
				}
			}
		}
	}
}