package adminapi

import (
	"net"
	"net/http"
	"os"
	"sort"
	"strings"
)

// Prometheus service discovery: the machines of the cluster as scrape targets
// for their node exporters, which say what llmgw does not — network and disk
// traffic, filesystems, every CPU's time. Served by the control plane, which
// knows the fleet, so a node added is a node scraped with nothing edited; and
// labelled with the node's id in llmgw, so its charts can be put beside the
// cluster's own.

// NodeExporterPort is where prometheus-node-exporter listens.
const NodeExporterPort = "9100"

// SDGroup is one target group of Prometheus' HTTP service discovery.
type SDGroup struct {
	Targets []string          `json:"targets"`
	Labels  map[string]string `json:"labels"`
}

// NodeExporterTargets is every machine of the cluster: the nodes, this
// control plane, as the request reached it, and the store's members.
func (a *API) NodeExporterTargets(r *http.Request) []SDGroup {
	return a.nodeExporterTargetsWith(r, a.Nodes())
}

func (a *API) nodeExporterTargetsWith(r *http.Request, nodes []NodeView) []SDGroup {
	seen := map[string]bool{}
	var out []SDGroup
	add := func(host, node, role string) {
		if host == "" || seen[host] {
			return
		}
		seen[host] = true
		out = append(out, SDGroup{Targets: []string{net.JoinHostPort(host, NodeExporterPort)},
			Labels: map[string]string{"node": node, "role": role}})
	}
	if host, _, err := net.SplitHostPort(r.Host); err == nil {
		name, _ := os.Hostname()
		add(host, name, "control-plane")
	}
	// Every control plane, not this one only, before the store's members:
	// Prometheus asks each of them, and a machine that one called a control
	// plane and another a store member was two targets, its every series
	// counted twice.
	if a.controlPlanes != nil {
		for _, cp := range a.controlPlanes().Members {
			host := cp.Address
			if h, _, err := net.SplitHostPort(host); err == nil {
				host = h
			}
			add(strings.TrimSpace(host), cp.Name, "control-plane")
		}
	}
	for _, n := range nodes {
		host := n.MgmtAddr
		if h, _, err := net.SplitHostPort(host); err == nil {
			host = h
		}
		add(host, n.ID, "node")
	}
	if a.storeStatus != nil {
		if members, err := a.storeStatus(); err == nil {
			for _, m := range members {
				host := m.Host
				if h, _, err := net.SplitHostPort(host); err == nil {
					host = h
				}
				add(strings.TrimSpace(host), m.Name, "store")
			}
		}
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Labels["node"] < out[j].Labels["node"] })
	return out
}

// PromSD serves the targets as Prometheus' http_sd_configs reads them.
func (a *API) PromSD(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, a.NodeExporterTargets(r))
}