# ─── VPC ──────────────────────────────────────────────────────────────

resource "aws_vpc" "main" {
  cidr_block           = var.vpc_cidr
  enable_dns_hostnames = true
  enable_dns_support   = true

  tags = merge(var.tags, { Name = "${var.prefix}-vpc" })
}

resource "aws_internet_gateway" "main" {
  vpc_id = aws_vpc.main.id
  tags   = merge(var.tags, { Name = "${var.prefix}-igw" })
}

# Public subnets (one per AZ) — for NAT gateways and load balancers
resource "aws_subnet" "public" {
  count             = length(var.availability_zones)
  vpc_id            = aws_vpc.main.id
  cidr_block        = cidrsubnet(var.vpc_cidr, 4, count.index)
  availability_zone = var.availability_zones[count.index]

  map_public_ip_on_launch = true

  tags = merge(var.tags, {
    Name                                        = "${var.prefix}-public-${count.index + 1}"
    "kubernetes.io/cluster/${var.prefix}-eks"   = "shared"
    "kubernetes.io/role/elb"                    = "1"
  })
}

# Private subnets (one per AZ) — for EKS nodes
resource "aws_subnet" "private" {
  count             = length(var.availability_zones)
  vpc_id            = aws_vpc.main.id
  cidr_block        = cidrsubnet(var.vpc_cidr, 4, count.index + length(var.availability_zones))
  availability_zone = var.availability_zones[count.index]

  tags = merge(var.tags, {
    Name                                        = "${var.prefix}-private-${count.index + 1}"
    "kubernetes.io/cluster/${var.prefix}-eks"   = "shared"
    "kubernetes.io/role/internal-elb"           = "1"
  })
}

# NAT Gateway (single, in first public subnet — use one per AZ for prod HA)
resource "aws_eip" "nat" {
  domain = "vpc"
  tags   = merge(var.tags, { Name = "${var.prefix}-nat-eip" })
}

resource "aws_nat_gateway" "main" {
  allocation_id = aws_eip.nat.id
  subnet_id     = aws_subnet.public[0].id
  tags          = merge(var.tags, { Name = "${var.prefix}-nat" })

  depends_on = [aws_internet_gateway.main]
}

resource "aws_route_table" "public" {
  vpc_id = aws_vpc.main.id

  route {
    cidr_block = "0.0.0.0/0"
    gateway_id = aws_internet_gateway.main.id
  }

  tags = merge(var.tags, { Name = "${var.prefix}-public-rt" })
}

resource "aws_route_table_association" "public" {
  count          = length(var.availability_zones)
  subnet_id      = aws_subnet.public[count.index].id
  route_table_id = aws_route_table.public.id
}

resource "aws_route_table" "private" {
  vpc_id = aws_vpc.main.id

  route {
    cidr_block     = "0.0.0.0/0"
    nat_gateway_id = aws_nat_gateway.main.id
  }

  tags = merge(var.tags, { Name = "${var.prefix}-private-rt" })
}

resource "aws_route_table_association" "private" {
  count          = length(var.availability_zones)
  subnet_id      = aws_subnet.private[count.index].id
  route_table_id = aws_route_table.private.id
}

# ─── EKS Cluster ──────────────────────────────────────────────────────

resource "aws_iam_role" "eks_cluster" {
  name_prefix = "${var.prefix}-eks-cluster-"

  assume_role_policy = jsonencode({
    Version = "2012-10-17"
    Statement = [{
      Action    = "sts:AssumeRole"
      Effect    = "Allow"
      Principal = { Service = "eks.amazonaws.com" }
    }]
  })

  tags = var.tags
}

resource "aws_iam_role_policy_attachment" "eks_cluster_policy" {
  policy_arn = "arn:aws:iam::aws:policy/AmazonEKSClusterPolicy"
  role       = aws_iam_role.eks_cluster.name
}

resource "aws_eks_cluster" "main" {
  name     = "${var.prefix}-eks"
  role_arn = aws_iam_role.eks_cluster.arn
  version  = var.kubernetes_version

  vpc_config {
    subnet_ids              = concat(aws_subnet.private[*].id, aws_subnet.public[*].id)
    endpoint_private_access = true
    endpoint_public_access  = true
  }

  # Enable OIDC issuer for IRSA (IAM Roles for Service Accounts)
  access_config {
    authentication_mode = "API_AND_CONFIG_MAP"
  }

  tags = var.tags

  depends_on = [aws_iam_role_policy_attachment.eks_cluster_policy]
}

# OIDC provider — required for IRSA (IAM Roles for Service Accounts)
data "tls_certificate" "eks" {
  url = aws_eks_cluster.main.identity[0].oidc[0].issuer
}

resource "aws_iam_openid_connect_provider" "eks" {
  client_id_list  = ["sts.amazonaws.com"]
  thumbprint_list = [data.tls_certificate.eks.certificates[0].sha1_fingerprint]
  url             = aws_eks_cluster.main.identity[0].oidc[0].issuer

  tags = var.tags
}

# EKS Node Group

resource "aws_iam_role" "eks_nodes" {
  name_prefix = "${var.prefix}-eks-nodes-"

  assume_role_policy = jsonencode({
    Version = "2012-10-17"
    Statement = [{
      Action    = "sts:AssumeRole"
      Effect    = "Allow"
      Principal = { Service = "ec2.amazonaws.com" }
    }]
  })

  tags = var.tags
}

resource "aws_iam_role_policy_attachment" "eks_worker_node_policy" {
  policy_arn = "arn:aws:iam::aws:policy/AmazonEKSWorkerNodePolicy"
  role       = aws_iam_role.eks_nodes.name
}

resource "aws_iam_role_policy_attachment" "eks_cni_policy" {
  policy_arn = "arn:aws:iam::aws:policy/AmazonEKS_CNI_Policy"
  role       = aws_iam_role.eks_nodes.name
}

resource "aws_iam_role_policy_attachment" "eks_ecr_readonly" {
  policy_arn = "arn:aws:iam::aws:policy/AmazonEC2ContainerRegistryReadOnly"
  role       = aws_iam_role.eks_nodes.name
}

resource "aws_eks_node_group" "main" {
  cluster_name    = aws_eks_cluster.main.name
  node_group_name = "${var.prefix}-nodes"
  node_role_arn   = aws_iam_role.eks_nodes.arn
  subnet_ids      = aws_subnet.private[*].id

  instance_types = [var.node_instance_type]

  scaling_config {
    desired_size = var.node_count
    max_size     = var.node_max_count
    min_size     = var.node_min_count
  }

  update_config {
    max_unavailable = 1
  }

  tags = var.tags

  depends_on = [
    aws_iam_role_policy_attachment.eks_worker_node_policy,
    aws_iam_role_policy_attachment.eks_cni_policy,
    aws_iam_role_policy_attachment.eks_ecr_readonly,
  ]
}