// Package awsmembership is the AWS adapter of the console's membership
// read (region HA spec 2 §5 step 5, §25; H16, H28): read-only Auto Scaling
// and EC2 describe calls, made in the AWS region the roster names for the
// attempt's placement. The console role needs
// autoscaling:DescribeAutoScalingInstances and ec2:DescribeInstances,
// conditioned on aws:RequestedRegion being one of the deployment's AWS
// regions. No box role has either.
package awsmembership

import (
	"context"
	"errors"

	"github.com/aws/aws-sdk-go-v2/aws"
	awsmiddleware "github.com/aws/aws-sdk-go-v2/aws/middleware"
	awshttp "github.com/aws/aws-sdk-go-v2/aws/transport/http"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/service/autoscaling"
	"github.com/aws/aws-sdk-go-v2/service/ec2"
	ec2types "github.com/aws/aws-sdk-go-v2/service/ec2/types"
	"github.com/aws/smithy-go/middleware"

	"github.com/carlosframework/platform/internal/hostactors"
)

// Reader is hostactors.MembershipReader over the console's own credentials.
type Reader struct{ cfg aws.Config }

// New loads the console's AWS configuration (its instance role).
func New(ctx context.Context) (*Reader, error) {
	cfg, err := config.LoadDefaultConfig(ctx)
	if err != nil {
		return nil, err
	}
	return &Reader{cfg: cfg}, nil
}

// Member describes instance's Auto Scaling membership, then its EC2 state
// and owner: two calls, two request ids. A call that fails ends the read;
// the ids of the calls made come back with the error, the failed call's
// from the cloud's error response (failedID).
func (r *Reader) Member(ctx context.Context, awsRegion, instance string) (hostactors.Membership, error) {
	asg := autoscaling.NewFromConfig(r.cfg, func(o *autoscaling.Options) { o.Region = awsRegion })
	ao, err := asg.DescribeAutoScalingInstances(ctx, &autoscaling.DescribeAutoScalingInstancesInput{InstanceIds: []string{instance}})
	if err != nil {
		return hostactors.Membership{RequestIDs: []string{failedID(err)}}, err
	}
	ec := ec2.NewFromConfig(r.cfg, func(o *ec2.Options) { o.Region = awsRegion })
	eo, err := ec.DescribeInstances(ctx, &ec2.DescribeInstancesInput{Filters: []ec2types.Filter{{Name: aws.String("instance-id"), Values: []string{instance}}}})
	if err != nil {
		return hostactors.Membership{RequestIDs: []string{requestID(ao.ResultMetadata), failedID(err)}}, err
	}
	return membershipFrom(instance, ao, eo), nil
}

// failedID is the request id of a call that failed: the one the cloud gave
// in its error response, or hostactors.NoRequestID when the call failed
// before the cloud answered (no connection, a cancelled context).
func failedID(err error) string {
	var re *awshttp.ResponseError
	if errors.As(err, &re) && re.ServiceRequestID() != "" {
		return re.ServiceRequestID()
	}
	return hostactors.NoRequestID
}

// membershipFrom reads the two replies. Anything but exactly the one
// instance asked about, in exactly one group, is no membership.
func membershipFrom(instance string, ao *autoscaling.DescribeAutoScalingInstancesOutput, eo *ec2.DescribeInstancesOutput) hostactors.Membership {
	m := hostactors.Membership{RequestIDs: []string{requestID(ao.ResultMetadata), requestID(eo.ResultMetadata)}}
	if len(ao.AutoScalingInstances) == 1 && aws.ToString(ao.AutoScalingInstances[0].InstanceId) == instance {
		d := ao.AutoScalingInstances[0]
		m.GroupName = aws.ToString(d.AutoScalingGroupName)
		m.LifecycleState = aws.ToString(d.LifecycleState)
		m.AvailabilityZoneRegion = zoneRegion(aws.ToString(d.AvailabilityZone))
	}
	if len(eo.Reservations) == 1 && len(eo.Reservations[0].Instances) == 1 && aws.ToString(eo.Reservations[0].Instances[0].InstanceId) == instance {
		res := eo.Reservations[0]
		m.Owner = aws.ToString(res.OwnerId)
		if st := res.Instances[0].State; st != nil {
			m.InstanceState = string(st.Name)
		}
	}
	return m
}

// zoneRegion is the region of an availability zone name ("eu-west-1a" is
// in "eu-west-1"): the name less one trailing letter after a digit. Any
// other shape (a Local Zone, a zone id) answers "", which matches no
// region.
func zoneRegion(az string) string {
	n := len(az)
	if n < 3 || az[n-1] < 'a' || az[n-1] > 'z' || az[n-2] < '0' || az[n-2] > '9' {
		return ""
	}
	return az[:n-1]
}

func requestID(md middleware.Metadata) string {
	id, _ := awsmiddleware.GetRequestIDMetadata(md)
	return id
}

var _ hostactors.MembershipReader = (*Reader)(nil)