// Package exporter runs the scrape on a schedule and serves the last result.
//
// Scraping is scheduled rather than done per Prometheus request on purpose:
// each reading wakes the car's T-Box over the mobile network and drains the
// traction battery (roughly 0.1 kWh/h at a 5-minute interval on a 60 kWh pack,
// per the Home Assistant integration). Prometheus can scrape /metrics as often
// as it likes; only the schedule reaches the car.
package exporter

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"sync"
	"time"

	"git.tinetunnel.com/thistine/byd-exporter/internal/byd"
	"git.tinetunnel.com/thistine/byd-exporter/internal/jsonv"
	"git.tinetunnel.com/thistine/byd-exporter/internal/metrics"
)

// MetricPrefix is prepended to every field name from the realtime payload.
const MetricPrefix = "byd_"

// Exporter holds the last scrape so /metrics can serve it without touching the car.
type Exporter struct {
	client *byd.Client
	log    *log.Logger

	mu     sync.RWMutex
	latest string
}

func New(client *byd.Client, logger *log.Logger) *Exporter {
	if logger == nil {
		logger = log.Default()
	}
	return &Exporter{client: client, log: logger}
}

// Scrape reads every vehicle and replaces the served metrics. It always
// publishes something — on failure, byd_scrape_success 0 — so that a broken
// scrape is visible in Prometheus rather than silently serving stale data.
func (e *Exporter) Scrape(ctx context.Context) error {
	start := time.Now()
	set := metrics.New()

	err := e.collect(ctx, set)
	if err != nil {
		e.log.Printf("scrape failed: %v", err)
	}

	success := 0.0
	if err == nil {
		success = 1
	}
	set.Add("byd_scrape_success", nil, success)
	set.Add("byd_scrape_duration_seconds", nil, time.Since(start).Seconds())
	set.Add("byd_scrape_timestamp_seconds", nil, float64(start.Unix()))

	e.mu.Lock()
	e.latest = set.String()
	e.mu.Unlock()
	return err
}

// collect fills set with one reading per vehicle. A single unreachable car is
// reported as byd_vehicle_up 0 and does not stop the others.
func (e *Exporter) collect(ctx context.Context, set *metrics.Set) error {
	if err := e.client.EnsureSession(ctx); err != nil {
		return fmt.Errorf("login: %w", err)
	}

	vehicles, err := e.client.Vehicles(ctx)
	if err != nil {
		return fmt.Errorf("vehicle list: %w", err)
	}
	set.Add("byd_vehicles", nil, float64(len(vehicles)))

	var firstErr error
	for _, v := range vehicles {
		if v.VIN == "" {
			continue
		}
		labels := metrics.Labels{"vin": v.VIN, "name": v.Name()}
		set.Add("byd_vehicle_info", metrics.Labels{
			"vin":   v.VIN,
			"name":  v.Name(),
			"model": v.ModelName,
			"brand": v.BrandName,
			"plate": v.AutoPlate,
		}, 1)

		energyType := jsonv.Str(v.EnergyType)
		if energyType == "" {
			energyType = "0" // EV
		}

		data, err := e.client.Realtime(ctx, v.VIN, energyType)
		if err != nil {
			e.log.Printf("realtime %s: %v", v.VIN, err)
			set.Add("byd_vehicle_up", labels, 0)
			if firstErr == nil {
				firstErr = err
			}
			continue
		}
		set.Add("byd_vehicle_up", labels, 1)
		set.AddPayload(MetricPrefix, labels, data)
	}
	return firstErr
}

// Metrics returns the last rendered exposition.
func (e *Exporter) Metrics() string {
	e.mu.RLock()
	defer e.mu.RUnlock()
	return e.latest
}

func (e *Exporter) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "text/plain; version=0.0.4; charset=utf-8")
	fmt.Fprint(w, e.Metrics())
}