package orchestrate

import (
	"context"
	"fmt"
	"log/slog"
	"time"

	"github.com/redis/go-redis/v9"

	"github.com/wangjia/pangolin/server/internal/alert"
)

// ─────────────────────────────────────────────────────────────────────────────
// PoolReader — pool capacity interface
// ─────────────────────────────────────────────────────────────────────────────

// PoolStat holds capacity metrics for a single tier+region pool.
type PoolStat struct {
	Tier    string
	Region  string
	UpCount int // number of nodes currently in "up" status
	Target  int // configured target node count for this pool
}

// PoolReader provides pool capacity information for the capacity monitor and
// circuit breaker. The real implementation (wired by task 15H) queries the
// lifecycle service.
type PoolReader interface {
	// AllPools returns all known pools with their current UpCount and Target.
	AllPools(ctx context.Context) ([]PoolStat, error)

	// PoolCapacity returns (upCount, target) for the named pool.
	// Returns (0, 0, nil) when the pool is not found.
	PoolCapacity(ctx context.Context, tier, region string) (int, int, error)
}

// ─────────────────────────────────────────────────────────────────────────────
// Redis key constants
// ─────────────────────────────────────────────────────────────────────────────

const (
	// capAlertPoolPrefix is the dedup key prefix for pool-watermark alerts.
	// Full key: sched:cap:pool:{tier}:{region}   TTL = AlertSuppressMin
	capAlertPoolPrefix = "sched:cap:pool:"

	// capAlertProbePrefix is the dedup key prefix for probe-lost-contact alerts.
	// Full key: sched:cap:probe:{probeId}   TTL = AlertSuppressMin
	capAlertProbePrefix = "sched:cap:probe:"

	// probeHBKeyPrefix is the heartbeat key prefix written by the probe package.
	// Full key: probe:hb:{probeId}   TTL = 15 min (from probe.heartbeatTTL)
	probeHBKeyPrefix = "probe:hb:"
)

// ─────────────────────────────────────────────────────────────────────────────
// CapacityMonitor
// ─────────────────────────────────────────────────────────────────────────────

// CapacityMonitorConfig holds all dependencies for CapacityMonitor.
type CapacityMonitorConfig struct {
	RDB      *redis.Client
	Pools    PoolReader
	Notifier Notifier
	Gray     *Grayscale        // grayscale weight-ramp driver
	LC       LifecycleService  // for WriteAuditLog; may be nil
	CfgMgr   *ConfigManager
	Clock    Clock
}

// CapacityMonitor checks pool watermarks and probe heartbeats, and drives
// the grayscale weight ramp. It is called by the CapacityLoop (task 15H)
// approximately every 1–2 minutes.
//
// Each RunOnce call:
//  1. Checks pool fill-rates; emits a throttled alert per pool below threshold.
//  2. Checks probe heartbeats for every configured probe ID; emits a throttled
//     「探针失联」alert for each probe whose heartbeat key is absent.
//  3. Calls Grayscale.Advance to advance any in-progress weight ramps.
type CapacityMonitor struct {
	rdb      *redis.Client
	pools    PoolReader
	notifier Notifier
	gray     *Grayscale
	lc       LifecycleService
	cfgMgr   *ConfigManager
	clock    Clock
}

// NewCapacityMonitor constructs a CapacityMonitor from the given config.
// If Clock is nil, RealClock is used.
func NewCapacityMonitor(cfg CapacityMonitorConfig) *CapacityMonitor {
	if cfg.Clock == nil {
		cfg.Clock = RealClock{}
	}
	return &CapacityMonitor{
		rdb:      cfg.RDB,
		pools:    cfg.Pools,
		notifier: cfg.Notifier,
		gray:     cfg.Gray,
		lc:       cfg.LC,
		cfgMgr:   cfg.CfgMgr,
		clock:    cfg.Clock,
	}
}

// RunOnce executes one full capacity-monitoring cycle. Errors from individual
// steps are logged but do not abort subsequent steps.
func (m *CapacityMonitor) RunOnce(ctx context.Context) error {
	cfg := m.cfgMgr.Current()

	// Step 1: pool watermark checks.
	if err := m.checkWatermarks(ctx, cfg); err != nil {
		slog.Error("capacity: watermark check error", "error", err)
	}

	// Step 2: probe heartbeat checks.
	if err := m.checkProbeHeartbeats(ctx, cfg); err != nil {
		slog.Error("capacity: probe heartbeat check error", "error", err)
	}

	// Step 3: advance grayscale weight ramps (Grayscale.Advance is 15E's
	// warm-up entry point; CapacityLoop drives it per the spec).
	if m.gray != nil {
		if err := m.gray.Advance(ctx); err != nil {
			slog.Error("capacity: grayscale advance error", "error", err)
		}
	}

	return nil
}

// checkWatermarks iterates all known pools. For each pool whose fill-rate
// (upCount/target) is below WatermarkThreshold, an alert is emitted — but
// at most once per AlertSuppressMin to suppress repeated notifications.
func (m *CapacityMonitor) checkWatermarks(ctx context.Context, cfg *SchedConfig) error {
	stats, err := m.pools.AllPools(ctx)
	if err != nil {
		return fmt.Errorf("capacity: list pools: %w", err)
	}

	threshold := cfg.Capacity.WatermarkThreshold
	suppressTTL := time.Duration(cfg.Capacity.AlertSuppressMin) * time.Minute

	for _, stat := range stats {
		if stat.Target <= 0 {
			continue // skip misconfigured pools with no target
		}
		fillRate := float64(stat.UpCount) / float64(stat.Target)
		if fillRate >= threshold {
			continue // pool is healthy
		}

		// Throttle: at most one alert per pool per AlertSuppressMin.
		dedupKey := capAlertPoolPrefix + stat.Tier + ":" + stat.Region
		set, setErr := m.rdb.SetNX(ctx, dedupKey, "1", suppressTTL).Result()
		if setErr != nil {
			slog.Error("capacity: watermark dedup key error",
				"key", dedupKey, "error", setErr)
			continue
		}
		if !set {
			continue // alert already sent within suppression window
		}

		poolID := "pool:" + stat.Tier + ":" + stat.Region
		reason := fmt.Sprintf(
			"capacity watermark below %.0f%%: %d/%d up (fill_rate=%.1f%%)",
			threshold*100, stat.UpCount, stat.Target, fillRate*100,
		)

		slog.Warn("capacity: pool below watermark",
			"tier", stat.Tier,
			"region", stat.Region,
			"up", stat.UpCount,
			"target", stat.Target,
			"fill_rate_pct", fmt.Sprintf("%.1f", fillRate*100),
		)

		if m.notifier != nil {
			event := alert.NewEvent(alert.EventTypeWatermarkLow, "", map[string]string{"reason": reason})
			event.Pool = poolID
			if notifyErr := m.notifier.Notify(ctx, event); notifyErr != nil {
				slog.Error("capacity: notify watermark alert",
					"pool", poolID, "error", notifyErr)
			}
		}
	}
	return nil
}

// checkProbeHeartbeats verifies that every configured probe agent has a live
// heartbeat key in Redis. A missing key means the probe has not reported
// within the 15-minute heartbeat TTL (probe package constant heartbeatTTL).
//
// Semantics: absence of the key is "no recent data", NOT "node blocked". It
// must NOT feed into any determination logic — only ops alerting.
func (m *CapacityMonitor) checkProbeHeartbeats(ctx context.Context, cfg *SchedConfig) error {
	probeIDs := cfg.Capacity.ExpectedProbeIDs
	if len(probeIDs) == 0 {
		return nil // no probes configured; nothing to check
	}

	suppressTTL := time.Duration(cfg.Capacity.AlertSuppressMin) * time.Minute

	for _, pid := range probeIDs {
		hbKey := probeHBKeyPrefix + pid
		exists, err := m.rdb.Exists(ctx, hbKey).Result()
		if err != nil {
			slog.Error("capacity: probe heartbeat check error",
				"probe_id", pid, "error", err)
			continue
		}
		if exists > 0 {
			continue // heartbeat key present — probe is alive
		}

		// Heartbeat key absent: throttled 「探针失联」alert.
		dedupKey := capAlertProbePrefix + pid
		set, setErr := m.rdb.SetNX(ctx, dedupKey, "1", suppressTTL).Result()
		if setErr != nil {
			slog.Error("capacity: probe alert dedup key error",
				"probe_id", pid, "error", setErr)
			continue
		}
		if !set {
			continue // alert already sent within suppression window
		}

		probeNodeID := "probe:" + pid
		reason := "探针失联: no heartbeat received in last 15 min (no data, not a block signal)"

		slog.Warn("capacity: probe lost contact",
			"probe_id", pid,
			"hb_key", hbKey,
		)

		if m.notifier != nil {
			event := alert.NewEvent(alert.EventTypeProbeAgentLost, probeNodeID, map[string]string{"reason": reason})
			if notifyErr := m.notifier.Notify(ctx, event); notifyErr != nil {
				slog.Error("capacity: notify probe lost contact",
					"probe_id", pid, "error", notifyErr)
			}
		}
	}
	return nil
}