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provider "aws" {
  region = "ap-northeast-2"
}

# --------------------------------------------------
# S3 bucket
# --------------------------------------------------
resource "aws_s3_bucket" "app_bucket" {
  # bucket name must be unique
  bucket = "my-sts-demo-bucket-1234567890"
}

resource "aws_s3_bucket_public_access_block" "app_bucket" {
  bucket = aws_s3_bucket.app_bucket.id

  block_public_acls       = true
  block_public_policy     = true
  ignore_public_acls      = true
  restrict_public_buckets = true
}

# --------------------------------------------------
# IAM role for EC2
# EC2 can assume this role
# --------------------------------------------------
data "aws_iam_policy_document" "ec2_assume_role" {
  statement {
    effect = "Allow"

    actions = ["sts:AssumeRole"]

    principals {
      type        = "Service"
      identifiers = ["ec2.amazonaws.com"]
    }
  }
}

resource "aws_iam_role" "ec2_s3_role" {
  name               = "ec2-s3-access-role"
  # Trust Policy
  assume_role_policy = data.aws_iam_policy_document.ec2_assume_role.json
}

# --------------------------------------------------
# Policy: allow EC2 role to read objects from S3
# --------------------------------------------------
data "aws_iam_policy_document" "s3_read_policy" {
  statement {
    effect = "Allow"

    actions = [
      "s3:ListBucket"
    ]

    resources = [
      aws_s3_bucket.app_bucket.arn
    ]
  }

  statement {
    effect = "Allow"

    actions = [
      "s3:GetObject"
    ]

    resources = [
      "${aws_s3_bucket.app_bucket.arn}/*"
    ]
  }
}

resource "aws_iam_policy" "s3_read_policy" {
  name   = "ec2-s3-read-policy"
  policy = data.aws_iam_policy_document.s3_read_policy.json
}

resource "aws_iam_role_policy_attachment" "attach_s3_read" {
  role       = aws_iam_role.ec2_s3_role.name
  policy_arn = aws_iam_policy.s3_read_policy.arn
}

# --------------------------------------------------
# Instance profile for EC2
# --------------------------------------------------
resource "aws_iam_instance_profile" "ec2_profile" {
  name = "ec2-s3-instance-profile"
  role = aws_iam_role.ec2_s3_role.name
}

# --------------------------------------------------
# Networking (simple example)
# Replace with your existing VPC/subnet/security group if needed
# --------------------------------------------------
data "aws_vpc" "default" {
  default = true
}

data "aws_subnets" "default" {
  filter {
    name   = "vpc-id"
    values = [data.aws_vpc.default.id]
  }
}

resource "aws_security_group" "ec2_sg" {
  name        = "ec2-s3-demo-sg"
  description = "Security group for EC2 S3 demo"
  vpc_id      = data.aws_vpc.default.id

  ingress {
    description = "SSH"
    from_port   = 22
    to_port     = 22
    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"]
  }
}

# --------------------------------------------------
# EC2 instance
# Replace ami with one valid in your region
# --------------------------------------------------
resource "aws_instance" "app" {
  ami                    = var.ami
  instance_type          = "t3.micro"
  subnet_id              = data.aws_subnets.default.ids[0]
  vpc_security_group_ids = [aws_security_group.ec2_sg.id]
  iam_instance_profile   = aws_iam_instance_profile.ec2_profile.name

  tags = {
    Name = "sts-demo-ec2"
  }
}