Expressions, functions and meta-arguments

# Create 3 EC2 instances
resource "aws_instance" "web" {
  count         = 3                       # integer number
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t3.micro"

  tags = {
    Name = "web-${count.index}"          # count.index: 0, 1, 2
  }
}

# Address of each instance:
# aws_instance.web[0]
# aws_instance.web[1]
# aws_instance.web[2]

# Access in outputs or references:
output "web_ids" {
  value = aws_instance.web[*].id         # splat: list of all the IDs
}

# Use a variable for the count:
variable "instance_count" { default = 3 }

resource "aws_instance" "app" {
  count = var.instance_count
  # ...
}

# Conditional creation (count = 0 = don't create, count = 1 = create):
resource "aws_eip" "nat" {
  count  = var.create_nat_gateway ? 1 : 0
  domain = "vpc"
}

# for_each with a SET of strings
resource "aws_iam_user" "team" {
  for_each = toset(["alice", "bob", "carol"])   # converts list to set
  name     = each.key                           # each.key == the set element
}

# Address of each instance:
# aws_iam_user.team["alice"]
# aws_iam_user.team["bob"]
# aws_iam_user.team["carol"]

# for_each with a MAP (key → object)
variable "buckets" {
  default = {
    logs    = { region = "us-east-1", versioning = true }
    backups = { region = "us-west-2", versioning = false }
  }
}

resource "aws_s3_bucket" "storage" {
  for_each = var.buckets
  bucket   = "company-${each.key}"             # each.key = "logs" or "backups"
}

resource "aws_s3_bucket_versioning" "storage" {
  for_each = var.buckets
  bucket   = aws_s3_bucket.storage[each.key].id  # reference with the same key

  versioning_configuration {
    status = each.value.versioning ? "Enabled" : "Suspended"
  }
}

# Splat does not work with for_each — use a for expression instead:
output "bucket_ids" {
  value = { for k, v in aws_s3_bucket.storage : k => v.id }
}

# for expression — generates lists or maps
# [for <item> in <collection> : <expression>]
# {for <key>, <val> in <map> : <new_key> => <new_val>}

variable "users" {
  default = [
    { name = "alice", admin = true },
    { name = "bob",   admin = false },
  ]
}

# List of names
locals {
  names = [for u in var.users : u.name]
  # result: ["alice", "bob"]

  # Only the admins (with if condition)
  admin_names = [for u in var.users : u.name if u.admin]
  # result: ["alice"]

  # Map name → admin
  user_map = {for u in var.users : u.name => u.admin}
  # result: {alice = true, bob = false}
}

# Conditional expression (ternary)
# condition ? value_if_true : value_if_false
resource "aws_instance" "web" {
  instance_type = var.environment == "prod" ? "t3.large" : "t3.micro"
}