terraform {
  required_version = ">= 1.9, < 2.0"
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "6.70.0"
    }
  }
}

provider "aws" {
  region = var.region
}

variable "region" {
  type    = string
  default = "us-east-1"
}

variable "ami_id" {
  description = "An Amazon Linux 2023 x86_64 AMI available in the selected region."
  type        = string
  validation {
    condition     = can(regex("^ami-[0-9a-f]+$", var.ami_id))
    error_message = "Provide an AMI ID for the selected region."
  }
}

data "aws_availability_zones" "available" {
  state = "available"
}

resource "aws_vpc" "lab" {
  cidr_block           = "10.10.0.0/16"
  enable_dns_support   = true
  enable_dns_hostnames = true
  tags                 = { Name = "asg-lab" }
}

resource "aws_subnet" "public" {
  count                   = 2
  vpc_id                  = aws_vpc.lab.id
  cidr_block              = cidrsubnet(aws_vpc.lab.cidr_block, 8, count.index + 1)
  availability_zone       = data.aws_availability_zones.available.names[count.index]
  map_public_ip_on_launch = true
}

resource "aws_internet_gateway" "lab" {
  vpc_id = aws_vpc.lab.id
}

resource "aws_route_table" "public" {
  vpc_id = aws_vpc.lab.id
  route {
    cidr_block = "0.0.0.0/0"
    gateway_id = aws_internet_gateway.lab.id
  }
}

resource "aws_route_table_association" "public" {
  count          = 2
  subnet_id      = aws_subnet.public[count.index].id
  route_table_id = aws_route_table.public.id
}

resource "aws_security_group" "alb" {
  name_prefix = "asg-lab-alb-"
  vpc_id      = aws_vpc.lab.id
  ingress {
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }
  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

resource "aws_security_group" "web" {
  name_prefix = "asg-lab-web-"
  vpc_id      = aws_vpc.lab.id
  ingress {
    from_port       = 80
    to_port         = 80
    protocol        = "tcp"
    security_groups = [aws_security_group.alb.id]
  }
  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

resource "aws_lb" "web" {
  name               = "asg-lab-web"
  load_balancer_type = "application"
  internal           = false
  security_groups    = [aws_security_group.alb.id]
  subnets            = aws_subnet.public[*].id
}

resource "aws_lb_target_group" "web" {
  name     = "asg-lab-web"
  port     = 80
  protocol = "HTTP"
  vpc_id   = aws_vpc.lab.id
  health_check {
    path    = "/"
    matcher = "200"
  }
}

resource "aws_lb_listener" "http" {
  load_balancer_arn = aws_lb.web.arn
  port              = 80
  protocol          = "HTTP"
  default_action {
    type             = "forward"
    target_group_arn = aws_lb_target_group.web.arn
  }
}

resource "aws_launch_template" "web" {
  name_prefix            = "asg-lab-web-"
  image_id               = var.ami_id
  instance_type          = "t3.micro"
  vpc_security_group_ids = [aws_security_group.web.id]
  metadata_options {
    http_endpoint = "enabled"
    http_tokens   = "required"
  }
  user_data = base64encode(<<-USERDATA
    #!/bin/bash
    set -euo pipefail
    dnf install -y httpd
    printf 'ASG lab: %s\n' "$(hostname)" > /var/www/html/index.html
    systemctl enable --now httpd
  USERDATA
  )
}

resource "aws_autoscaling_group" "web" {
  name                      = "asg-lab-web"
  min_size                  = 2
  desired_capacity          = 2
  max_size                  = 4
  health_check_type         = "ELB"
  health_check_grace_period = 300
  default_instance_warmup   = 120
  vpc_zone_identifier       = aws_subnet.public[*].id
  target_group_arns         = [aws_lb_target_group.web.arn]

  launch_template {
    id      = aws_launch_template.web.id
    version = tostring(aws_launch_template.web.latest_version)
  }

  instance_refresh {
    strategy = "Rolling"
    preferences {
      min_healthy_percentage = 100
      max_healthy_percentage = 200
    }
  }

  lifecycle {
    ignore_changes = [desired_capacity]
  }
  tag {
    key                 = "Name"
    value               = "asg-lab-web"
    propagate_at_launch = true
  }
  depends_on = [aws_route_table_association.public, aws_lb_listener.http]
}

resource "aws_autoscaling_policy" "cpu" {
  name                   = "asg-lab-cpu"
  policy_type            = "TargetTrackingScaling"
  autoscaling_group_name = aws_autoscaling_group.web.name
  target_tracking_configuration {
    predefined_metric_specification {
      predefined_metric_type = "ASGAverageCPUUtilization"
    }
    target_value = 50
  }
}

output "lab_url" {
  value = "http://${aws_lb.web.dns_name}"
}