package usage

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"time"

	"github.com/redis/go-redis/v9"
	"github.com/wangjia/pangolin/server/internal/apierr"
)

// nowFunc is overridable in tests to pin "today".
var nowFunc = time.Now

// utcToday returns the current UTC calendar date (time truncated).
func utcToday() time.Time {
	n := nowFunc().UTC()
	return time.Date(n.Year(), n.Month(), n.Day(), 0, 0, 0, 0, time.UTC)
}

// Service serves usage queries, the /v1/me usage summary, the ads-unlock flow,
// and the free-plan connect quota check.
type Service struct {
	store      *Store
	rdb        *redis.Client
	verifier   AdVerifier
	adNonceTTL time.Duration
}

// NewService builds a Service.  rdb may be nil (ad-token replay protection is
// then disabled — not recommended in production).  verifier may be nil if the
// ads-unlock endpoint is not mounted.  adNonceTTL <= 0 defaults to 1h.
func NewService(store *Store, rdb *redis.Client, verifier AdVerifier, adNonceTTL time.Duration) *Service {
	if adNonceTTL <= 0 {
		adNonceTTL = time.Hour
	}
	return &Service{store: store, rdb: rdb, verifier: verifier, adNonceTTL: adNonceTTL}
}

// UsagePoint is one day of the usage curve.
type UsagePoint struct {
	Date        string `json:"date"` // YYYY-MM-DD (UTC)
	BytesUp     uint64 `json:"bytes_up"`
	BytesDown   uint64 `json:"bytes_down"`
	MinutesUsed int    `json:"minutes_used"`
}

// UsageCurve returns the last `days` usage points for userID bucketed in the
// CLIENT's timezone (offsetMin = client UTC offset in minutes, e.g. 480 for
// UTC+8), missing days zero-filled, oldest first. days clamped to [1,90].
//
// It reads UTC hourly buckets (usage_hourly) and re-aggregates by local calendar
// day, so "today" matches the user's local date regardless of server timezone
// (fixes "29号却显示28号数据"). offsetMin out of ±14h falls back to 0 (UTC).
// deviceUUID == "" → account-level curve; non-empty → that device's curve only.
func (svc *Service) UsageCurve(ctx context.Context, userID int64, days, offsetMin int, deviceUUID string) ([]UsagePoint, *apierr.Error) {
	if days < 1 {
		days = 7
	}
	if days > 90 {
		days = 90
	}
	if offsetMin < -14*60 || offsetMin > 14*60 {
		offsetMin = 0
	}
	loc := time.FixedZone("client", offsetMin*60)

	now := nowFunc().UTC()
	ln := now.In(loc)
	localToday := time.Date(ln.Year(), ln.Month(), ln.Day(), 0, 0, 0, 0, loc)
	fromLocal := localToday.AddDate(0, 0, -(days - 1))

	fromHour := fromLocal.UTC().Unix() / 3600
	toHour := now.Unix() / 3600

	var rows []HourBucket
	var err error
	if deviceUUID == "" {
		rows, err = svc.store.HourlyRange(ctx, userID, fromHour, toHour)
	} else {
		rows, err = svc.store.DeviceHourlyRange(ctx, userID, deviceUUID, fromHour, toHour)
	}
	if err != nil {
		return nil, apierr.ErrInternal
	}
	type agg struct {
		up, down uint64
		min      int
	}
	byDay := make(map[string]*agg)
	for _, b := range rows {
		key := time.Unix(b.Hour*3600, 0).In(loc).Format(dateLayout)
		a := byDay[key]
		if a == nil {
			a = &agg{}
			byDay[key] = a
		}
		a.up += b.BytesUp
		a.down += b.BytesDown
		a.min += b.MinutesUsed
	}

	points := make([]UsagePoint, 0, days)
	for i := 0; i < days; i++ {
		d := fromLocal.AddDate(0, 0, i).Format(dateLayout)
		if a, ok := byDay[d]; ok {
			points = append(points, UsagePoint{Date: d, BytesUp: a.up, BytesDown: a.down, MinutesUsed: a.min})
		} else {
			points = append(points, UsagePoint{Date: d})
		}
	}
	return points, nil
}

// DeviceUsagePoint is one device's aggregated usage over the requested window,
// used by the stats page's per-device ("下分设备") breakdown.
type DeviceUsagePoint struct {
	UUID        string `json:"uuid"`
	Name        string `json:"name"`
	Platform    string `json:"platform"` // ios | android | windows | macos
	BytesUp     uint64 `json:"bytes_up"`
	BytesDown   uint64 `json:"bytes_down"`
	MinutesUsed int    `json:"minutes_used"`
}

// DeviceUsage returns per-device usage totals for userID over the last `days`
// (UTC), busiest device first.  days is clamped to [1, 90].  Devices with no
// usage in the window are omitted (the response is never nil — empty slice).
func (svc *Service) DeviceUsage(ctx context.Context, userID int64, days int) ([]DeviceUsagePoint, *apierr.Error) {
	if days < 1 {
		days = 7
	}
	if days > 90 {
		days = 90
	}

	today := utcToday()
	from := today.AddDate(0, 0, -(days - 1))

	rows, err := svc.store.DeviceUsageRange(ctx, userID, from, today)
	if err != nil {
		return nil, apierr.ErrInternal
	}
	points := make([]DeviceUsagePoint, 0, len(rows))
	for _, r := range rows {
		points = append(points, DeviceUsagePoint{
			UUID:        r.UUID,
			Name:        r.Name,
			Platform:    r.Platform,
			BytesUp:     r.BytesUp,
			BytesDown:   r.BytesDown,
			MinutesUsed: r.MinutesUsed,
		})
	}
	return points, nil
}

// TodaySummary is the /v1/me today_usage block.
type TodaySummary struct {
	MinutesUsed      int  `json:"minutes_used"`
	MinutesRemaining *int `json:"minutes_remaining"` // nil = unlimited (pro/team)
	AdUnlocked       bool `json:"ad_unlocked"`
}

// TodaySummary returns the current user's usage summary for today (UTC),
// reflecting plan limits and ad-unlock state.
func (svc *Service) TodaySummary(ctx context.Context, userID int64) (*TodaySummary, *apierr.Error) {
	plan, err := svc.store.EffectivePlan(ctx, userID)
	if err != nil {
		return nil, apierr.ErrInternal
	}
	day, err := svc.store.GetDay(ctx, userID, utcToday())
	if err != nil {
		return nil, apierr.ErrInternal
	}

	used := 0
	adUnlocked := false
	if day != nil {
		used = day.MinutesUsed
		adUnlocked = day.AdUnlockedAt.Valid
	}

	out := &TodaySummary{MinutesUsed: used, AdUnlocked: adUnlocked}
	if plan.DailyMinutes.Valid {
		remaining := int(plan.DailyMinutes.Int64) - used
		if remaining < 0 {
			remaining = 0
		}
		out.MinutesRemaining = &remaining
	}
	return out, nil
}

// UnlockAd verifies a rewarded-ad receipt and records the day's ad-unlock.
//
// Flow: validate inputs → verify the receipt with the ad network → consume the
// ad_token as a one-time nonce (replay-protected) → set ad_unlocked_at.  A
// second unlock on a day already unlocked is idempotent (alreadyUnlocked=true).
func (svc *Service) UnlockAd(ctx context.Context, userID int64, deviceID, adToken string) (alreadyUnlocked bool, apiErr *apierr.Error) {
	if deviceID == "" || adToken == "" {
		return false, apierr.ErrBadRequest
	}
	if svc.verifier == nil {
		return false, apierr.ErrInternal
	}

	// 1. Authenticate the receipt with the ad network.
	if err := svc.verifier.Verify(ctx, AdVerifyRequest{
		UserID:   userID,
		DeviceID: deviceID,
		AdToken:  adToken,
	}); err != nil {
		return false, apierr.ErrAdVerifyFailed
	}

	// 2. One-time nonce: a genuine receipt may only be redeemed once.
	if dup, err := svc.consumeAdNonce(ctx, adToken); err != nil {
		return false, apierr.ErrInternal
	} else if dup {
		return false, apierr.ErrAdReplay
	}

	// 3. Record the unlock (idempotent per UTC day).
	already, err := svc.store.MarkAdUnlocked(ctx, userID, utcToday())
	if err != nil {
		return false, apierr.ErrInternal
	}
	return already, nil
}

// consumeAdNonce atomically records the ad_token so it cannot be reused.
// Returns dup=true if the token was already consumed.  No-ops (dup=false) when
// Redis is not configured.
func (svc *Service) consumeAdNonce(ctx context.Context, adToken string) (bool, error) {
	if svc.rdb == nil {
		return false, nil
	}
	sum := sha256.Sum256([]byte(adToken))
	key := "ads:nonce:" + hex.EncodeToString(sum[:])
	set, err := svc.rdb.SetNX(ctx, key, "1", svc.adNonceTTL).Result()
	if err != nil {
		return false, err
	}
	return !set, nil
}