# AWS VPC Module Template
# Production-ready VPC with public and private subnets

variable "vpc_cidr" {
  description = "CIDR block for VPC"
  type        = string
  default     = "10.0.0.0/16"
}

variable "availability_zones" {
  description = "Availability zones"
  type        = list(string)
  default     = ["us-east-1a", "us-east-1b", "us-east-1c"]
}

variable "enable_nat_gateway" {
  description = "Enable NAT Gateway for private subnets"
  type        = bool
  default     = true
}

locals {
  public_subnets  = [for i, az in var.availability_zones : cidrsubnet(var.vpc_cidr, 8, i)]
  private_subnets = [for i, az in var.availability_zones : cidrsubnet(var.vpc_cidr, 8, i + 10)]
}

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

  tags = {
    Name = "${var.project_name}-vpc"
  }
}

# Internet Gateway
resource "aws_internet_gateway" "main" {
  vpc_id = aws_vpc.main.id

  tags = {
    Name = "${var.project_name}-igw"
  }
}

# Public Subnets
resource "aws_subnet" "public" {
  count                   = length(var.availability_zones)
  vpc_id                  = aws_vpc.main.id
  cidr_block              = local.public_subnets[count.index]
  availability_zone       = var.availability_zones[count.index]
  map_public_ip_on_launch = true

  tags = {
    Name                        = "${var.project_name}-public-${var.availability_zones[count.index]}"
    "kubernetes.io/role/elb"    = "1"
  }
}

# Private Subnets
resource "aws_subnet" "private" {
  count             = length(var.availability_zones)
  vpc_id            = aws_vpc.main.id
  cidr_block        = local.private_subnets[count.index]
  availability_zone = var.availability_zones[count.index]

  tags = {
    Name                              = "${var.project_name}-private-${var.availability_zones[count.index]}"
    "kubernetes.io/role/internal-elb" = "1"
  }
}

# Elastic IP for NAT Gateway
resource "aws_eip" "nat" {
  count  = var.enable_nat_gateway ? 1 : 0
  domain = "vpc"

  tags = {
    Name = "${var.project_name}-nat-eip"
  }
}

# NAT Gateway
resource "aws_nat_gateway" "main" {
  count         = var.enable_nat_gateway ? 1 : 0
  allocation_id = aws_eip.nat[0].id
  subnet_id     = aws_subnet.public[0].id

  tags = {
    Name = "${var.project_name}-nat"
  }

  depends_on = [aws_internet_gateway.main]
}

# Public Route Table
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 = {
    Name = "${var.project_name}-public-rt"
  }
}

# Private Route Table
resource "aws_route_table" "private" {
  vpc_id = aws_vpc.main.id

  dynamic "route" {
    for_each = var.enable_nat_gateway ? [1] : []
    content {
      cidr_block     = "0.0.0.0/0"
      nat_gateway_id = aws_nat_gateway.main[0].id
    }
  }

  tags = {
    Name = "${var.project_name}-private-rt"
  }
}

# Route Table Associations
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_association" "private" {
  count          = length(var.availability_zones)
  subnet_id      = aws_subnet.private[count.index].id
  route_table_id = aws_route_table.private.id
}

# Outputs
output "vpc_id" {
  value = aws_vpc.main.id
}

output "public_subnet_ids" {
  value = aws_subnet.public[*].id
}

output "private_subnet_ids" {
  value = aws_subnet.private[*].id
}