package ec2

import (
	"encoding/xml"
	"fmt"
	"strings"

	"github.com/VictoriaMetrics/VictoriaMetrics/lib/promscrape/discoveryutils"
)

// getInstancesLabels returns labels for ec2 instances obtained from the given cfg
func getInstancesLabels(cfg *apiConfig) ([]map[string]string, error) {
	rs, err := getReservations(cfg)
	if err != nil {
		return nil, err
	}
	var ms []map[string]string
	for _, r := range rs {
		for _, inst := range r.InstanceSet.Items {
			ms = inst.appendTargetLabels(ms, r.OwnerID, cfg.port)
		}
	}
	return ms, nil
}

func getReservations(cfg *apiConfig) ([]Reservation, error) {
	// See https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DescribeInstances.html
	action := "DescribeInstances"
	var rs []Reservation
	pageToken := ""
	for {
		data, err := getAPIResponse(cfg, action, pageToken)
		if err != nil {
			return nil, fmt.Errorf("cannot obtain instances: %w", err)
		}
		ir, err := parseInstancesResponse(data)
		if err != nil {
			return nil, fmt.Errorf("cannot parse instance list: %w", err)
		}
		rs = append(rs, ir.ReservationSet.Items...)
		if len(ir.NextPageToken) == 0 {
			return rs, nil
		}
		pageToken = ir.NextPageToken
	}
}

// InstancesResponse represents response to https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DescribeInstances.html
type InstancesResponse struct {
	ReservationSet ReservationSet `xml:"reservationSet"`
	NextPageToken  string         `xml:"nextToken"`
}

// ReservationSet represetns ReservationSet from https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DescribeInstances.html
type ReservationSet struct {
	Items []Reservation `xml:"item"`
}

// Reservation represents Reservation from https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_Reservation.html
type Reservation struct {
	OwnerID     string      `xml:"ownerId"`
	InstanceSet InstanceSet `xml:"instancesSet"`
}

// InstanceSet represents InstanceSet from https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_Reservation.html
type InstanceSet struct {
	Items []Instance `xml:"item"`
}

// Instance represents Instance from https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_Instance.html
type Instance struct {
	PrivateIPAddress    string              `xml:"privateIpAddress"`
	Architecture        string              `xml:"architecture"`
	Placement           Placement           `xml:"placement"`
	ImageID             string              `xml:"imageId"`
	ID                  string              `xml:"instanceId"`
	Lifecycle           string              `xml:"instanceLifecycle"`
	State               InstanceState       `xml:"instanceState"`
	Type                string              `xml:"instanceType"`
	Platform            string              `xml:"platform"`
	SubnetID            string              `xml:"subnetId"`
	PrivateDNSName      string              `xml:"privateDnsName"`
	PublicDNSName       string              `xml:"dnsName"`
	PublicIPAddress     string              `xml:"ipAddress"`
	VPCID               string              `xml:"vpcId"`
	NetworkInterfaceSet NetworkInterfaceSet `xml:"networkInterfaceSet"`
	TagSet              TagSet              `xml:"tagSet"`
}

// Placement represents Placement from https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_Placement.html
type Placement struct {
	AvailabilityZone string `xml:"availabilityZone"`
}

// InstanceState represents InstanceState from https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_InstanceState.html
type InstanceState struct {
	Name string `xml:"name"`
}

// NetworkInterfaceSet represents NetworkInterfaceSet from https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_Instance.html
type NetworkInterfaceSet struct {
	Items []NetworkInterface `xml:"item"`
}

// NetworkInterface represents NetworkInterface from https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_InstanceNetworkInterface.html
type NetworkInterface struct {
	SubnetID string `xml:"subnetId"`
}

// TagSet represents TagSet from https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_Instance.html
type TagSet struct {
	Items []Tag `xml:"item"`
}

// Tag represents Tag from https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_Tag.html
type Tag struct {
	Key   string `xml:"key"`
	Value string `xml:"value"`
}

func parseInstancesResponse(data []byte) (*InstancesResponse, error) {
	var v InstancesResponse
	if err := xml.Unmarshal(data, &v); err != nil {
		return nil, fmt.Errorf("cannot unmarshal InstancesResponse from %q: %w", data, err)
	}
	return &v, nil
}

func (inst *Instance) appendTargetLabels(ms []map[string]string, ownerID string, port int) []map[string]string {
	if len(inst.PrivateIPAddress) == 0 {
		// Cannot scrape instance without private IP address
		return ms
	}
	addr := discoveryutils.JoinHostPort(inst.PrivateIPAddress, port)
	m := map[string]string{
		"__address__":                   addr,
		"__meta_ec2_architecture":       inst.Architecture,
		"__meta_ec2_ami":                inst.ImageID,
		"__meta_ec2_availability_zone":  inst.Placement.AvailabilityZone,
		"__meta_ec2_instance_id":        inst.ID,
		"__meta_ec2_instance_lifecycle": inst.Lifecycle,
		"__meta_ec2_instance_state":     inst.State.Name,
		"__meta_ec2_instance_type":      inst.Type,
		"__meta_ec2_owner_id":           ownerID,
		"__meta_ec2_platform":           inst.Platform,
		"__meta_ec2_primary_subnet_id":  inst.SubnetID,
		"__meta_ec2_private_dns_name":   inst.PrivateDNSName,
		"__meta_ec2_private_ip":         inst.PrivateIPAddress,
		"__meta_ec2_public_dns_name":    inst.PublicDNSName,
		"__meta_ec2_public_ip":          inst.PublicIPAddress,
		"__meta_ec2_vpc_id":             inst.VPCID,
	}
	if len(inst.VPCID) > 0 {
		// Deduplicate VPC Subnet IDs maintaining the order of the network interfaces returned by EC2.
		subnets := make([]string, 0, len(inst.NetworkInterfaceSet.Items))
		seenSubnets := make(map[string]bool, len(inst.NetworkInterfaceSet.Items))
		for _, ni := range inst.NetworkInterfaceSet.Items {
			if len(ni.SubnetID) == 0 {
				continue
			}
			if !seenSubnets[ni.SubnetID] {
				seenSubnets[ni.SubnetID] = true
				subnets = append(subnets, ni.SubnetID)
			}
		}
		// We surround the separated list with the separator as well. This way regular expressions
		// in relabeling rules don't have to consider tag positions.
		m["__meta_ec2_subnet_id"] = "," + strings.Join(subnets, ",") + ","
	}
	for _, t := range inst.TagSet.Items {
		if len(t.Key) == 0 || len(t.Value) == 0 {
			continue
		}
		name := discoveryutils.SanitizeLabelName(t.Key)
		m["__meta_ec2_tag_"+name] = t.Value
	}
	ms = append(ms, m)
	return ms
}