Liberally use try, document idea

No one's going to stop me, not even common sense

2024/bonus/README.md

@@ -0,0 +1,49 @@
+# Bonus Challenge
+
+This part of the repo holds the bonus challenge for 2024: implement as much as possible in pure
+Terraform.
+
+## Usage
+
+The infrastructure definitions expect the input files to be located at `../inputs/[\d]{2}.txt`.
+After storing the input files there, the code should be runnable as follows:
+
+```console
+$ terraform init
+< a lot of modules being installed >
+$ terraform plan
+
+Changes to Outputs:
+  + day01_1 = 42
+  + day01_2 = 12
+  + day02_1 = …
+
+You can apply this plan to save these new output values to the Terraform state, without changing any real infrastructure.
+```
+
+Note that Terraform may freeze for tens of seconds while it's running the computations. This is
+normal, and all Terraform code ought to think a little before doing anything. It would save people
+some bad rollbacks.
+
+## Development
+
+I use [Terraform tests](https://developer.hashicorp.com/terraform/language/tests) to automatically
+run my terraform code on the sample inputs. It's almost a normal development workflow.
+
+The only rule is that the code should be all terraform, no cheating by shelling out to external
+programs. Using providers is allowed, as long as the providers don't actually interact with external
+systems and are reasonably self-contained. I will try to limit my use of those regardless.
+
+## Why
+
+DevOps will continue until morale improves. But really, a friend remarked that my Python solutions
+were strangely normal for me, so I opted to use a language that I do use professionally.
+
+Terraform is a unique beast. It can do a lot, but it is also very limited, and intentionally so.
+There's a standard library of functions you might want to use, but all of them work in strange ways
+and there isn't that much to begin with. You can never mutate any variables, you can only declare
+new ones. You don't have recursion and your only source of loops are list- and map comprehensions,
+or multiple instantiations or a module.
+
+These make for a very constrained programming environment, and constrained programming is fun. It
+makes you think outside the box.

2024/bonus/day01/main.tf

@@ -5,18 +5,18 @@ variable "input" {
 locals {
   cleaned_input = replace(var.input, "/ +/", " ")
   lines         = split("\n", trim(local.cleaned_input, "\n"))
-  lines_split = [for line in local.lines: split(" ", line)]
-  left = [for line in local.lines_split: parseint(line[0], 10)]
-  right = [for line in local.lines_split: parseint(line[1], 10)]
+  lines_split   = [for line in local.lines : split(" ", line)]
+  left          = [for line in local.lines_split : parseint(line[0], 10)]
+  right         = [for line in local.lines_split : parseint(line[1], 10)]
 
   left_sorted  = sort(local.left)
   right_sorted = sort(local.right)
 
-  diffs = [for i in range(length(local.left_sorted)): abs(local.left_sorted[i] - local.right_sorted[i])]
+  diffs = [for i in range(length(local.left_sorted)) : abs(local.left_sorted[i] - local.right_sorted[i])]
 
-  counts = {for num in local.right: num => num...}
+  counts = { for num in local.right : num => num... }
 
-  matching = [for left in local.left: left * length(lookup(local.counts, left, []))]
+  matching = [for left in local.left : left * try(length(local.counts[left]), 0)]
 }
 
 output "part1" {

2024/bonus/day02/is_savable/main.tf

@@ -8,7 +8,7 @@ module "is_valid" {
 
   report = concat(
     count.index > 0 ? slice(var.report, 0, count.index) : [],
-    count.index < length(var.report) - 1 ? slice(var.report, count.index + 1, length(var.report)) : []
+    try(slice(var.report, count.index + 1, length(var.report)), [])
   )
 }
 

2024/bonus/day03/main.tf

@@ -4,8 +4,21 @@ variable "input" {
 
 locals {
   muls = regexall("mul\\((\\d+),(\\d+)\\)", var.input)
+  ops  = regexall("(don't\\(\\)|do\\(\\)|mul\\((\\d+),(\\d+)\\))", var.input)
+}
+
+module "should_execute" {
+  count  = length(local.ops)
+  source = "./should_execute"
+
+  index = count.index
+  ops   = local.ops
 }
 
 output "part1" {
   value = sum([for mul in local.muls : parseint(mul[1], 10) * parseint(mul[0], 10)])
 }
+
+output "part2" {
+  value = sum(module.should_execute[*].value)
+}

2024/bonus/day03/should_execute/main.tf

@@ -0,0 +1,19 @@
+variable "ops" {
+  type = list(list(string))
+}
+
+variable "index" {
+  type = number
+}
+
+locals {
+  is_mul   = startswith(var.ops[var.index][0], "mul")
+  subslice = reverse(slice(var.ops[*][0], 0, var.index))
+
+  do_pos   = try(index(local.subslice, "do()"), var.index)
+  dont_pos = try(index(local.subslice, "don't()"), var.index + 1)
+}
+
+output "value" {
+  value = (local.is_mul && local.do_pos < local.dont_pos) ? (parseint(var.ops[var.index][1], 10) * parseint(var.ops[var.index][2], 10)) : 0
+}

2024/bonus/main.tf

@@ -36,3 +36,7 @@ module "day03" {
 output "day03_1" {
   value = module.day03.part1
 }
+
+output "day03_2" {
+  value = module.day03.part2
+}

2024/bonus/tests.tftest.hcl

@@ -57,3 +57,20 @@ run "day3_1" {
     error_message = "Part1 output is wrong"
   }
 }
+
+run "day3_2" {
+  command = plan
+
+  module {
+    source = "./day03"
+  }
+
+  variables {
+    input = "xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))"
+  }
+
+  assert {
+    condition     = output.part2 == 48
+    error_message = "Part2 output is wrong"
+  }
+}