package processor

import (
	"context"
	"math"
	"sort"
	"time"

	"github.com/google/uuid"

	"apskel-pos-be/internal/constants"
	"apskel-pos-be/internal/entities"
	"apskel-pos-be/internal/models"
)

// The kinds of reward component (D6).
const (
	// The game's own reward, paid by the global budget.
	gameRewardKindBase = "BASE"
	// What one event adds, paid by the event's budget.
	gameRewardKindEvent = "EVENT"
)

// The event limits (PRD §35), by the name the breakdown and the response give them.
const (
	gameLimitEvent          = "EVENT_LIMIT"
	gameLimitEventUserDaily = "EVENT_USER_DAILY"
)

// eventLifetimeDay is the day of an event's counter over its whole run (§5.8).
var eventLifetimeDay = time.Date(1, 1, 1, 0, 0, 0, 0, time.UTC)

// eventUserScope is the counter of one customer in one event: a name derived from
// both, since a counter has one scope id (§5.8).
func eventUserScope(eventID, customerID uuid.UUID) uuid.UUID {
	return uuid.NewSHA1(eventID, customerID[:])
}

// eventExtra is what an event adds to a base reward: base × (multiplier − 1), rounded
// down to whole EnakCoin, plus the bonus. Each event works on the base, so events do
// not multiply each other (PRD §16, "controlled stacking").
func eventExtra(base int64, e *entities.GameEvent) int64 {
	var extra int64
	if e.Multiplier != nil {
		hundredths := int64(math.Round(*e.Multiplier * 100))
		extra = base * (hundredths - 100) / 100
	}
	if e.Bonus != nil {
		extra += *e.Bonus
	}
	return extra
}

// rewardComponents prices a believed base reward into its parts: the base, capped by
// max_reward, then what each active event adds, highest priority first. The cap holds
// for the total: what passes it is cut from the lowest priority event first. An event
// adds nothing to a play that earned nothing.
func rewardComponents(base, maxReward int64, events []entities.GameEvent) ([]gameRewardComponent, bool) {
	capped := false
	if maxReward > 0 && base > maxReward {
		base, capped = maxReward, true
	}
	if base <= 0 {
		return nil, capped
	}
	parts := []gameRewardComponent{{Kind: gameRewardKindBase, Earned: base, Amount: base}}
	total := base
	for i := range events {
		e := &events[i]
		extra := eventExtra(base, e)
		if extra <= 0 {
			continue
		}
		id := e.ID
		parts = append(parts, gameRewardComponent{
			Kind: gameRewardKindEvent, BudgetID: e.BudgetID, EventID: &id, Multiplier: e.Multiplier, Bonus: e.Bonus,
			Earned: extra, Amount: extra,
		})
		total += extra
	}
	if maxReward > 0 && total > maxReward {
		capped = true
		trimFromEnd(parts, total-maxReward, nil)
	}
	return parts, capped
}

// trimFromEnd takes cut off the parts, lowest priority event first and the base last.
// release, when given, is told what came off each part.
func trimFromEnd(parts []gameRewardComponent, cut int64, release func(*gameRewardComponent, int64) error) error {
	for i := len(parts) - 1; i >= 0 && cut > 0; i-- {
		d := parts[i].Amount
		if d > cut {
			d = cut
		}
		parts[i].Amount -= d
		cut -= d
		if release != nil && d > 0 {
			if err := release(&parts[i], d); err != nil {
				return err
			}
		}
	}
	return nil
}

// guardReward runs the parts of a reward through every limit (§9, PRD §35): first
// each event's own limits on what it adds, then the daily limits on the total, which
// cut events before the base. It returns the limits that cut.
//
// Counters are taken in one order for every completion (events by id, then user,
// game, organization), so no two completions wait on each other the other way round.
func (p *GameSessionProcessor) guardReward(ctx context.Context, session *entities.GameSession, game *entities.Game, events []entities.GameEvent,
	settings *models.OrganizationLoyaltySettings, now time.Time, parts []gameRewardComponent) ([]gameGuardCut, error) {
	byID := map[uuid.UUID]*entities.GameEvent{}
	for i := range events {
		byID[events[i].ID] = &events[i]
	}
	day := walletDay(now)
	order := make([]int, 0, len(parts))
	for i := range parts {
		if parts[i].Kind == gameRewardKindEvent {
			order = append(order, i)
		}
	}
	sort.Slice(order, func(a, b int) bool { return parts[order[a]].EventID.String() < parts[order[b]].EventID.String() })

	var cuts []gameGuardCut
	for _, i := range order {
		part := &parts[i]
		e := byID[*part.EventID]
		asked := part.Amount
		lifetime, err := p.counters.Consume(ctx, session.OrganizationID, constants.GameRewardScopeEvent, e.ID, eventLifetimeDay, asked, optionalLimit(e.RewardLimit))
		if err != nil {
			return nil, err
		}
		if lifetime < asked {
			cuts = append(cuts, gameGuardCut{Limit: gameLimitEvent, EventID: part.EventID, Value: optionalLimit(e.RewardLimit), Asked: asked, Allowed: lifetime})
			part.LimitedBy = append(part.LimitedBy, gameLimitEvent)
		}
		perUser, err := p.counters.Consume(ctx, session.OrganizationID, constants.GameRewardScopeEvent, eventUserScope(e.ID, session.CustomerID), day, lifetime, optionalLimit(e.UserDailyLimit))
		if err != nil {
			return nil, err
		}
		if perUser < lifetime {
			cuts = append(cuts, gameGuardCut{Limit: gameLimitEventUserDaily, EventID: part.EventID, Value: optionalLimit(e.UserDailyLimit), Asked: lifetime, Allowed: perUser})
			part.LimitedBy = append(part.LimitedBy, gameLimitEventUserDaily)
			if err := p.counters.Release(ctx, session.OrganizationID, constants.GameRewardScopeEvent, e.ID, eventLifetimeDay, lifetime-perUser); err != nil {
				return nil, err
			}
		}
		part.Amount = perUser
	}

	total := sumComponents(parts)
	if total == 0 {
		return cuts, nil
	}
	allowed, daily, err := p.applyGuard(ctx, session, game, settings, now, total)
	if err != nil {
		return nil, err
	}
	cuts = append(cuts, daily...)
	// The event counters took what the daily limits then cut: give it back.
	err = trimFromEnd(parts, total-allowed, func(part *gameRewardComponent, d int64) error {
		if part.Kind != gameRewardKindEvent {
			return nil
		}
		if err := p.counters.Release(ctx, session.OrganizationID, constants.GameRewardScopeEvent, *part.EventID, eventLifetimeDay, d); err != nil {
			return err
		}
		return p.counters.Release(ctx, session.OrganizationID, constants.GameRewardScopeEvent, eventUserScope(*part.EventID, session.CustomerID), day, d)
	})
	return cuts, err
}

func optionalLimit(limit *int64) int64 {
	if limit == nil {
		return 0
	}
	return *limit
}

func sumComponents(parts []gameRewardComponent) int64 {
	var total int64
	for _, part := range parts {
		total += part.Amount
	}
	return total
}

// rewardParts sums a stored breakdown's components into what the customer sees.
func rewardParts(b gameRewardBreakdown) models.GameSessionRewardParts {
	var out models.GameSessionRewardParts
	for _, c := range b.Components {
		if c.Kind == gameRewardKindEvent {
			out.Event += c.Amount
		} else {
			out.Base += c.Amount
		}
	}
	return out
}

// paymentsByBudget merges the components paid by the same budget, in order, since a
// budget pays one ledger row per session (D6).
func paymentsByBudget(parts []gameRewardComponent) []gameRewardComponent {
	var out []gameRewardComponent
	index := map[uuid.UUID]int{}
	for _, part := range parts {
		if part.Amount <= 0 {
			continue
		}
		if i, ok := index[part.BudgetID]; ok {
			out[i].Amount += part.Amount
			continue
		}
		index[part.BudgetID] = len(out)
		out = append(out, gameRewardComponent{BudgetID: part.BudgetID, Kind: part.Kind, Amount: part.Amount})
	}
	return out
}