#!/bin/bash
rulesdir=~/.golly/Rules
rulename=AoC2018Day18
title='Advent of Code 2018 - Day 18: Settlers of The North Pole'

mkdir -p "$rulesdir"
cat <<EOF >"$rulesdir/$rulename.rule"
@RULE $rulename

--- $title ---

On the outskirts of the North Pole base construction project, many
Elves are collecting lumber.

The lumber collection area is 50 acres by 50 acres; each acre can be
either open ground (.), trees (|), or a lumberyard (#). You take a
scan of the area (your puzzle input).

Strange magic is at work here: each minute, the landscape looks
entirely different. In exactly one minute, an open acre can fill with
trees, a wooded acre can be converted to a lumberyard, or a lumberyard
can be cleared to open ground (the lumber having been sent to other
projects).

The change to each acre is based entirely on the contents of that acre
as well as the number of open, wooded, or lumberyard acres adjacent to
it at the start of each minute. Here, "adjacent" means any of the eight
acres surrounding that acre. (Acres on the edges of the lumber
collection area might have fewer than eight adjacent acres; the missing
acres aren't counted.)

In particular:

    - An open acre will become filled with trees if three or more
      adjacent acres contained trees. Otherwise, nothing happens.

    - An acre filled with trees will become a lumberyard if three or
      more adjacent acres were lumberyards. Otherwise, nothing happens.

    - An acre containing a lumberyard will remain a lumberyard if it
      was adjacent to at least one other lumberyard and at least one
      acre containing trees. Otherwise, it becomes open.

These changes happen across all acres simultaneously, each of them using
the state of all acres at the beginning of the minute and changing to
their new form by the end of that same minute. Changes that happen
during the minute don't affect each other.

@TABLE

n_states:3
neighborhood:Moore
symmetries:permute

# 0 : open
# 1 : trees
# 2 : lumberyard

# don't cares
# (multiple vars defined with the same value allows input states
# described by those vars not to need to match each other)

var a={0,1,2}
var b={a}
var c={a}
var d={a}
var e={a}
var f={a}
var g={a}
var h={a}

# not trees

var i={0,2}
var j={i}
var k={i}
var l={i}
var m={i}
var n={i}
var o={i}
var p={i}

# not lumberyard

var q={0,1}
var r={q}
var s={q}
var t={q}
var u={q}
var v={q}
var w={q}
var x={q}

# Open with three or more treed neighbors: becomes trees

0,a,b,c,d,e,1,1,1,1

# Trees with three or more lumberyard neigbors: becomes lumberyard

1,a,b,c,d,e,2,2,2,2

# Lumberyard with no treed *and* lumberyard neighbor: becomes open

2,i,j,k,l,m,n,o,2,0  # No trees, one lumberyard
2,q,r,s,t,u,v,w,x,0  # No lumberyards

@COLORS

0  51  51 51 dark grey
1   0 102  0 dark green
2 102 51   0 dark brown

EOF

input=${1:-input.txt}
rle=${input%.txt}.rle
rle=/tmp/${rle%%*/}

set -- $(wc -lL <"$input")
sed -f- "$input" <<EOF >"$rle"
1i\
# $title\n\
\n\
x = $2, y = $1, rule = $rulename:P$2,$1\n
s/|/A/g
s/#/B/g
s/$/$/
EOF

golly "$rle" >/dev/null 2>&1

sed "$rle" -Ee '
1,3d
s/[^0-9AB.]*//g
y/.AB/otl/
s/([0-9]*)([otl])/\1\2\n/g
' |

sed -Ee '
s/^([^0-9])/1\1/
s/([0-9]+)([otl])/\2 += \1/
$a t * l
' |

bc