# VPC Module - Multi-AZ Networking
# RFC 0039: ADR-Compliant Foundation Infrastructure
#
# Architecture:
# - 3 AZs for high availability
# - Public subnets for NLB and NAT Gateways
# - Private subnets for EKS nodes and workloads
# - Database subnets for CockroachDB (isolated)
# - NAT Gateway per AZ for HA outbound traffic

locals {
  # Calculate subnet CIDRs
  # /16 VPC -> /20 subnets (4096 IPs each)
  # AZ a: public=10.0.0.0/20, private=10.0.16.0/20, database=10.0.32.0/20
  # AZ b: public=10.0.48.0/20, private=10.0.64.0/20, database=10.0.80.0/20
  # AZ c: public=10.0.96.0/20, private=10.0.112.0/20, database=10.0.128.0/20
  public_subnets   = [for i, az in var.availability_zones : cidrsubnet(var.cidr, 4, i * 3)]
  private_subnets  = [for i, az in var.availability_zones : cidrsubnet(var.cidr, 4, i * 3 + 1)]
  database_subnets = [for i, az in var.availability_zones : cidrsubnet(var.cidr, 4, i * 3 + 2)]
}

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

  tags = merge(var.tags, {
    Name = var.name
  })
}

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

  tags = merge(var.tags, {
    Name = "${var.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 = merge(var.tags, {
    Name                                = "${var.name}-public-${var.availability_zones[count.index]}"
    "kubernetes.io/role/elb"            = "1"
    "kubernetes.io/cluster/${var.name}" = "shared"
  })
}

# 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 = merge(var.tags, {
    Name                                = "${var.name}-private-${var.availability_zones[count.index]}"
    "kubernetes.io/role/internal-elb"   = "1"
    "kubernetes.io/cluster/${var.name}" = "shared"
    "karpenter.sh/discovery"            = "true"
  })
}

# Database Subnets (isolated - no internet access)
resource "aws_subnet" "database" {
  count = length(var.availability_zones)

  vpc_id            = aws_vpc.main.id
  cidr_block        = local.database_subnets[count.index]
  availability_zone = var.availability_zones[count.index]

  tags = merge(var.tags, {
    Name = "${var.name}-database-${var.availability_zones[count.index]}"
  })
}

# Elastic IPs for NAT Gateways
resource "aws_eip" "nat" {
  count = var.enable_nat_gateway ? (var.single_nat_gateway ? 1 : length(var.availability_zones)) : 0

  domain = "vpc"

  tags = merge(var.tags, {
    Name = "${var.name}-nat-${count.index + 1}"
  })

  depends_on = [aws_internet_gateway.main]
}

# NAT Gateways
resource "aws_nat_gateway" "main" {
  count = var.enable_nat_gateway ? (var.single_nat_gateway ? 1 : length(var.availability_zones)) : 0

  allocation_id = aws_eip.nat[count.index].id
  subnet_id     = aws_subnet.public[count.index].id

  tags = merge(var.tags, {
    Name = "${var.name}-nat-${var.availability_zones[count.index]}"
  })

  depends_on = [aws_internet_gateway.main]
}

# Public Route Table
resource "aws_route_table" "public" {
  vpc_id = aws_vpc.main.id

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

resource "aws_route" "public_internet" {
  route_table_id         = aws_route_table.public.id
  destination_cidr_block = "0.0.0.0/0"
  gateway_id             = aws_internet_gateway.main.id
}

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
}

# Private Route Tables (one per AZ for HA)
resource "aws_route_table" "private" {
  count = length(var.availability_zones)

  vpc_id = aws_vpc.main.id

  tags = merge(var.tags, {
    Name = "${var.name}-private-${var.availability_zones[count.index]}"
  })
}

resource "aws_route" "private_nat" {
  count = var.enable_nat_gateway ? length(var.availability_zones) : 0

  route_table_id         = aws_route_table.private[count.index].id
  destination_cidr_block = "0.0.0.0/0"
  nat_gateway_id         = var.single_nat_gateway ? aws_nat_gateway.main[0].id : aws_nat_gateway.main[count.index].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[count.index].id
}

# Database Route Table (no internet access)
resource "aws_route_table" "database" {
  vpc_id = aws_vpc.main.id

  tags = merge(var.tags, {
    Name = "${var.name}-database"
  })
}

resource "aws_route_table_association" "database" {
  count = length(var.availability_zones)

  subnet_id      = aws_subnet.database[count.index].id
  route_table_id = aws_route_table.database.id
}

# VPC Flow Logs for security auditing
resource "aws_flow_log" "main" {
  count = var.enable_flow_logs ? 1 : 0

  vpc_id                   = aws_vpc.main.id
  traffic_type             = "ALL"
  log_destination_type     = "cloud-watch-logs"
  log_destination          = aws_cloudwatch_log_group.flow_logs[0].arn
  iam_role_arn             = aws_iam_role.flow_logs[0].arn
  max_aggregation_interval = 60

  tags = merge(var.tags, {
    Name = "${var.name}-flow-logs"
  })
}

resource "aws_cloudwatch_log_group" "flow_logs" {
  count = var.enable_flow_logs ? 1 : 0

  name              = "/aws/vpc/${var.name}/flow-logs"
  retention_in_days = 30

  tags = var.tags
}

resource "aws_iam_role" "flow_logs" {
  count = var.enable_flow_logs ? 1 : 0

  name = "${var.name}-flow-logs"

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

  tags = var.tags
}

resource "aws_iam_role_policy" "flow_logs" {
  count = var.enable_flow_logs ? 1 : 0

  name = "${var.name}-flow-logs"
  role = aws_iam_role.flow_logs[0].id

  policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Effect = "Allow"
        Action = [
          "logs:CreateLogGroup",
          "logs:CreateLogStream",
          "logs:PutLogEvents",
          "logs:DescribeLogGroups",
          "logs:DescribeLogStreams"
        ]
        Resource = "*"
      }
    ]
  })
}

# VPC Endpoints for AWS services (cost optimization - no NAT charges)
resource "aws_vpc_endpoint" "s3" {
  vpc_id            = aws_vpc.main.id
  service_name      = "com.amazonaws.${data.aws_region.current.name}.s3"
  vpc_endpoint_type = "Gateway"

  route_table_ids = concat(
    [aws_route_table.public.id],
    aws_route_table.private[*].id,
    [aws_route_table.database.id]
  )

  tags = merge(var.tags, {
    Name = "${var.name}-s3-endpoint"
  })
}

resource "aws_vpc_endpoint" "ecr_api" {
  vpc_id              = aws_vpc.main.id
  service_name        = "com.amazonaws.${data.aws_region.current.name}.ecr.api"
  vpc_endpoint_type   = "Interface"
  subnet_ids          = aws_subnet.private[*].id
  security_group_ids  = [aws_security_group.vpc_endpoints.id]
  private_dns_enabled = true

  tags = merge(var.tags, {
    Name = "${var.name}-ecr-api-endpoint"
  })
}

resource "aws_vpc_endpoint" "ecr_dkr" {
  vpc_id              = aws_vpc.main.id
  service_name        = "com.amazonaws.${data.aws_region.current.name}.ecr.dkr"
  vpc_endpoint_type   = "Interface"
  subnet_ids          = aws_subnet.private[*].id
  security_group_ids  = [aws_security_group.vpc_endpoints.id]
  private_dns_enabled = true

  tags = merge(var.tags, {
    Name = "${var.name}-ecr-dkr-endpoint"
  })
}

resource "aws_vpc_endpoint" "sts" {
  vpc_id              = aws_vpc.main.id
  service_name        = "com.amazonaws.${data.aws_region.current.name}.sts"
  vpc_endpoint_type   = "Interface"
  subnet_ids          = aws_subnet.private[*].id
  security_group_ids  = [aws_security_group.vpc_endpoints.id]
  private_dns_enabled = true

  tags = merge(var.tags, {
    Name = "${var.name}-sts-endpoint"
  })
}

resource "aws_vpc_endpoint" "ec2" {
  vpc_id              = aws_vpc.main.id
  service_name        = "com.amazonaws.${data.aws_region.current.name}.ec2"
  vpc_endpoint_type   = "Interface"
  subnet_ids          = aws_subnet.private[*].id
  security_group_ids  = [aws_security_group.vpc_endpoints.id]
  private_dns_enabled = true

  tags = merge(var.tags, {
    Name = "${var.name}-ec2-endpoint"
  })
}

# Security Group for VPC Endpoints
resource "aws_security_group" "vpc_endpoints" {
  name        = "${var.name}-vpc-endpoints"
  description = "Security group for VPC endpoints"
  vpc_id      = aws_vpc.main.id

  ingress {
    description = "HTTPS from VPC"
    from_port   = 443
    to_port     = 443
    protocol    = "tcp"
    cidr_blocks = [var.cidr]
  }

  egress {
    description = "All outbound"
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }

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

data "aws_region" "current" {}