package service

import (
	"context"
	"fmt"
	"log"
	"math"
	"net/http"
	"os/exec"
	"strings"
	"time"

	"scm.bstein.dev/bstein/hecate/internal/cluster"
	"scm.bstein.dev/bstein/hecate/internal/config"
	"scm.bstein.dev/bstein/hecate/internal/metrics"
	"scm.bstein.dev/bstein/hecate/internal/ups"
)

type Target struct {
	Name     string
	Target   string
	Provider ups.Provider
}

type Daemon struct {
	cfg      config.Config
	orch     *cluster.Orchestrator
	targets  []Target
	log      *log.Logger
	exporter *metrics.Exporter
}

func NewDaemon(cfg config.Config, orch *cluster.Orchestrator, targets []Target, logger *log.Logger) *Daemon {
	return &Daemon{
		cfg:      cfg,
		orch:     orch,
		targets:  targets,
		log:      logger,
		exporter: metrics.New(),
	}
}

func (d *Daemon) Run(ctx context.Context) error {
	if !d.cfg.UPS.Enabled {
		return fmt.Errorf("ups monitoring is disabled in config")
	}
	if len(d.targets) == 0 {
		return fmt.Errorf("no UPS targets configured")
	}

	poll := time.Duration(d.cfg.UPS.PollSeconds) * time.Second
	if poll <= 0 {
		poll = 5 * time.Second
	}
	telemetryTimeout := time.Duration(d.cfg.UPS.TelemetryTimeoutSeconds) * time.Second
	if telemetryTimeout <= 0 {
		telemetryTimeout = 90 * time.Second
	}
	debounce := d.cfg.UPS.DebounceCount
	if debounce <= 0 {
		debounce = 3
	}

	if d.cfg.Metrics.Enabled {
		if err := d.startMetricsServer(); err != nil {
			return err
		}
	}

	t := time.NewTicker(poll)
	defer t.Stop()

	lastGood := map[string]time.Time{}
	lastOnBattery := map[string]bool{}
	breachCount := map[string]int{}
	for _, t := range d.targets {
		lastGood[t.Name] = time.Now()
	}

	d.log.Printf("hecate daemon started: poll=%s debounce=%d telemetry_timeout=%s targets=%s",
		poll, debounce, telemetryTimeout, d.targetList())

	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-t.C:
			budget := d.orch.EstimatedShutdownSeconds()
			threshold := int(math.Ceil(float64(budget) * d.cfg.UPS.RuntimeSafetyFactor))

			d.exporter.UpdateBudget(budget)

			for _, target := range d.targets {
				sample, err := target.Provider.Read(ctx)
				if err != nil {
					d.log.Printf("warning: ups read failed target=%s (%s): %v", target.Name, target.Target, err)
					d.exporter.UpdateSample(metrics.Sample{
						Name:         target.Name,
						Target:       target.Target,
						ThresholdSec: threshold,
						BreachCount:  breachCount[target.Name],
						LastError:    err.Error(),
						UpdatedAt:    time.Now().UTC(),
					})
					if lastOnBattery[target.Name] && time.Since(lastGood[target.Name]) > telemetryTimeout {
						d.log.Printf("ups telemetry timeout while on battery (target=%s), triggering shutdown", target.Name)
						reason := fmt.Sprintf("ups-telemetry-timeout target=%s", target.Name)
						return d.triggerShutdown(ctx, reason)
					}
					continue
				}

				lastGood[target.Name] = time.Now()
				lastOnBattery[target.Name] = sample.OnBattery

				trigger := sample.LowBattery || (sample.OnBattery && sample.RuntimeSeconds > 0 && sample.RuntimeSeconds <= threshold)
				if trigger {
					breachCount[target.Name]++
				} else {
					breachCount[target.Name] = 0
				}

				d.log.Printf("ups target=%s status=%s on_battery=%t runtime_s=%d threshold_s=%d budget_s=%d trigger=%t breach=%d",
					target.Name, sample.RawStatus, sample.OnBattery, sample.RuntimeSeconds, threshold, budget, trigger, breachCount[target.Name])

				d.exporter.UpdateSample(metrics.Sample{
					Name:          target.Name,
					Target:        target.Target,
					OnBattery:     sample.OnBattery,
					LowBattery:    sample.LowBattery,
					RuntimeSecond: sample.RuntimeSeconds,
					BatteryCharge: sample.BatteryCharge,
					LoadPercent:   sample.LoadPercent,
					PowerNominalW: sample.NominalPowerW,
					ThresholdSec:  threshold,
					Trigger:       trigger,
					BreachCount:   breachCount[target.Name],
					Status:        sample.RawStatus,
					UpdatedAt:     time.Now().UTC(),
				})

				if breachCount[target.Name] >= debounce {
					reason := fmt.Sprintf("ups-threshold target=%s runtime=%ds threshold=%ds status=%s", target.Name, sample.RuntimeSeconds, threshold, sample.RawStatus)
					return d.triggerShutdown(ctx, reason)
				}
			}
		}
	}
}

func (d *Daemon) triggerShutdown(ctx context.Context, reason string) error {
	d.log.Printf("triggering shutdown: %s", reason)
	d.exporter.MarkShutdown(reason)
	if d.cfg.Coordination.ForwardShutdownHost != "" {
		if err := d.forwardShutdown(ctx, reason); err == nil {
			d.log.Printf("shutdown trigger forwarded to %s", d.cfg.Coordination.ForwardShutdownHost)
			return nil
		} else if !d.cfg.Coordination.FallbackLocalShutdown {
			return fmt.Errorf("forward shutdown failed and local fallback disabled: %w", err)
		} else {
			d.log.Printf("warning: forward shutdown failed; falling back to local shutdown: %v", err)
		}
	}
	return d.orch.Shutdown(ctx, cluster.ShutdownOptions{Reason: reason})
}

func (d *Daemon) forwardShutdown(ctx context.Context, reason string) error {
	userHost := d.cfg.Coordination.ForwardShutdownHost
	if d.cfg.Coordination.ForwardShutdownUser != "" {
		userHost = d.cfg.Coordination.ForwardShutdownUser + "@" + userHost
	}
	timeout := time.Duration(d.cfg.Coordination.CommandTimeoutSeconds) * time.Second
	if timeout <= 0 {
		timeout = 25 * time.Second
	}
	runCtx, cancel := context.WithTimeout(ctx, timeout)
	defer cancel()

	remoteCmd := fmt.Sprintf(
		"sudo /usr/local/bin/hecate shutdown --config %q --execute --reason %q",
		d.cfg.Coordination.ForwardShutdownConfig,
		reason,
	)
	cmd := exec.CommandContext(runCtx, "ssh", "-o", "BatchMode=yes", "-o", "ConnectTimeout=8", userHost, remoteCmd)
	out, err := cmd.CombinedOutput()
	if err != nil {
		trimmed := strings.TrimSpace(string(out))
		if trimmed == "" {
			return fmt.Errorf("forward shutdown via ssh failed: %w", err)
		}
		return fmt.Errorf("forward shutdown via ssh failed: %w: %s", err, trimmed)
	}
	return nil
}

func (d *Daemon) targetList() string {
	names := make([]string, 0, len(d.targets))
	for _, t := range d.targets {
		names = append(names, t.Name+"="+t.Target)
	}
	return strings.Join(names, ",")
}

func (d *Daemon) startMetricsServer() error {
	if d.cfg.Metrics.BindAddr == "" {
		return fmt.Errorf("metrics.bind_addr must not be empty when metrics are enabled")
	}
	handler := d.exporter.Handler(d.cfg.Metrics.Path)
	srv := &http.Server{
		Addr:              d.cfg.Metrics.BindAddr,
		Handler:           handler,
		ReadHeaderTimeout: 5 * time.Second,
	}
	go func() {
		d.log.Printf("metrics server listening on %s%s", d.cfg.Metrics.BindAddr, d.cfg.Metrics.Path)
		if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
			d.log.Printf("warning: metrics server failed: %v", err)
		}
	}()
	return nil
}