From b91819c4cf903e76bd2051f66766e8c13c4d225d Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Fri, 4 Dec 2020 19:54:14 -0800
Subject: [PATCH] Reimplement day 4 using validators.

---
 day4.cr      |  9 +++---
 passports.cr | 83 ++++++++++++++++++++++++++++++++++++++++------------
 2 files changed, 70 insertions(+), 22 deletions(-)

diff --git a/day4.cr b/day4.cr
index b00a064..626920e 100644
--- a/day4.cr
+++ b/day4.cr
@@ -15,12 +15,13 @@ end
 def part2
   input = INPUT.clone
   passports = parse_passports(input)
-  total = passports.count do |passport|
-    DEFAULT_VALIDATORS.all? do |k, v|
-      passport[k]?.try { |s| v.call(s) }
+  valid_passports = [] of Passport
+  passports.each do |p|
+    if vp = Passport.from_hash?(p)
+      valid_passports << vp 
     end
   end
-  puts total
+  puts valid_passports.size
 end
 
 part1
diff --git a/passports.cr b/passports.cr
index 4ead063..ffeab74 100644
--- a/passports.cr
+++ b/passports.cr
@@ -13,27 +13,74 @@ def parse_passports(lines)
   end
 end
 
-def validate_range(range)
-  ->(s : String) { s.to_i32?.try { |i| range.includes? i } }
+class Validator(T, R)
+  def initialize(@proc : Proc(T, R?))
+  end
+
+  def >>(other)
+    Validator.new(->(i : T) { @proc.call(i).try { |j| other.@proc.call(j) } })
+  end
+
+  def then(&block : R -> S?) forall S
+    Validator(T, S).new(->(i : T) { @proc.call(i).try { |j| block.call(j) } })
+  end
+
+  def run(input)
+    @proc.call(input)
+  end
 end
 
-def validate_regex(regex)
-  ->(s : String) { s.matches?(regex) }
+class Hash(K,V)
+  def validate(k, vl)
+    self[k]?.try { |v| vl.run(v) }
+  end
 end
 
-def validate_unit_range(unit_ranges)
-  ->(s : String) {
-    return false unless s.match(/^(\d+)([a-zA-Z]+)$/)
-    unit_ranges[$~[2]]?.try { |rng| validate_range(rng).call($~[1]) }
-  }
+def range(range) : Validator(Int32, Int32)
+  Validator.new ->(i : Int32) { (range.includes? i) ? i : nil }
 end
 
-DEFAULT_VALIDATORS = {
-  "byr" => validate_range(1920..2002),
-  "iyr" => validate_range(2010..2020),
-  "eyr" => validate_range(2020..2030),
-  "hgt" => validate_unit_range({"cm" => (150..193), "in" => (59..76)}),
-  "hcl" => validate_regex(/^#[0-9a-f]{6}$/),
-  "ecl" => ->(s : String) { "amb blu brn gry grn hzl oth".split(" ").includes? s },
-  "pid" => ->(s : String) { s =~ /^[0-9]{9}$/ },
-}
+def int : Validator(String, Int32)
+  Validator.new ->(s : String) { s.to_i32? }
+end
+
+def regex(regex) : Validator(String, Regex::MatchData)
+  Validator(String, Regex::MatchData).new ->(s : String) { s.match(regex) }
+end
+
+def oneof(strs : Array(A)) : Validator(A, A) forall A
+  Validator(String, String).new ->(s : String) { (strs.includes? s) ? s : nil }
+end
+
+def length(len) : Validator(String, String)
+  Validator(String, String).new ->(s : String) { (s.size == len) ? s : nil }
+end
+
+def year(rng) : Validator(String, Int32)
+  length(4) >> int >> range(rng)
+end
+
+def unit_range(map) : Validator(String, {String, Int32})
+  regex(/(\d+)([a-zA-Z]+)/).then do |md|
+    map[md[2]]?.try { |r| (int >> range(r)).run(md[1]).try { |i| {md[2], i} } }
+  end
+end
+
+class Passport
+  def initialize(
+    @byr : Int32, @iyr : Int32,
+    @eyr : Int32, @hgt : {String, Int32},
+    @hcl : String, @ecl : String, @pid : Int32)
+  end
+
+  def self.from_hash?(hash)
+    return nil unless byr = hash.validate("byr", year(1920..2002))
+    return nil unless iyr = hash.validate("iyr", year(2010..2020))
+    return nil unless eyr = hash.validate("eyr", year(2020..2030))
+    return nil unless hgt = hash.validate("hgt", unit_range({"cm" => (150..193), "in" => (59..76)}))
+    return nil unless hcl = hash.validate("hcl", regex(/^#([0-9a-f]{6})$/).then { |d| d[1] })
+    return nil unless ecl = hash.validate("ecl", oneof(["amb", "blu", "brn", "gry", "grn", "hzl", "oth"]))
+    return nil unless pid = hash.validate("pid", length(9) >> int)
+    Passport.new(byr, iyr, eyr, hgt, hcl, ecl, pid)
+  end
+end