// Package buildinfo exposes stamped build metadata and the shared ops /healthz JSON.
package buildinfo

import (
	"encoding/json"
	"net/http"
	"time"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
)

// Populated at link time via -ldflags -X.
var (
	Date   = "unknown"
	Commit = "dev"
	Branch = "unknown"
)

// Hardcoded service identity for autodiscovery / status dashboard.
const (
	Name        = "l-ai-agent-kaya"
	Description = "Tasks board agent Kaya: @kaya mention replies via core RunAgent"
)

// Tags is the controlled vocabulary for this service (see l-ai-docs services/healthz.md).
var Tags = []string{"agent", "tasks", "llm"}

var startedAt = time.Now()

func init() {
	promauto.NewGaugeVec(
		prometheus.GaugeOpts{
			Name: "build_info",
			Help: "Build metadata for this process (always 1).",
		},
		[]string{"name", "commit", "branch", "date"},
	).With(prometheus.Labels{
		"name":   Name,
		"commit": Commit,
		"branch": Branch,
		"date":   Date,
	}).Set(1)
}

// Build is the nested build object in /healthz.
type Build struct {
	Date   string `json:"date"`
	Commit string `json:"commit"`
	Branch string `json:"branch"`
}

// Response is the shared /healthz JSON contract.
type Response struct {
	Status        string   `json:"status"`
	Name          string   `json:"name"`
	Description   string   `json:"description"`
	Tags          []string `json:"tags"`
	UptimeSeconds int64    `json:"uptime_seconds"`
	Build         Build    `json:"build"`
}

// Snapshot returns the current health payload with status "ok".
func Snapshot() Response {
	tags := make([]string, len(Tags))
	copy(tags, Tags)
	return Response{
		Status:        "ok",
		Name:          Name,
		Description:   Description,
		Tags:          tags,
		UptimeSeconds: int64(time.Since(startedAt).Seconds()),
		Build: Build{
			Date:   Date,
			Commit: Commit,
			Branch: Branch,
		},
	}
}

// Handler serves GET/HEAD /healthz as application/json (always 200 while process is up).
func Handler() http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet && r.Method != http.MethodHead {
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
			return
		}
		writeJSON(w, http.StatusOK, Snapshot())
	})
}

func writeJSON(w http.ResponseWriter, code int, body Response) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(code)
	_ = json.NewEncoder(w).Encode(body)
}