// Package allocator coordinates provider allocation with durable control-plane
// state. It does not expose an endpoint until both boundaries succeed.
package allocator

import (
	"context"
	"time"

	"github.com/cosmic-clash/cosmic-clash/server/agones"
	"github.com/cosmic-clash/cosmic-clash/server/domain"
)

type Provider interface {
	Allocate(context.Context, domain.AllocationRequest, map[string]string, time.Time) (agones.AllocatedServer, error)
}

type ProviderRecoverer interface {
	RecoverAllocation(context.Context, domain.AllocationRequest, time.Time) (agones.AllocatedServer, bool, error)
}

type Durable interface {
	RecordProviderAllocation(context.Context, domain.Allocation, time.Time) (domain.Allocation, error)
}

type RosterPublisher interface {
	PublishRoster(context.Context, domain.Assignment, []domain.SignedJoinAuthorisation, func([]byte, []byte) bool) error
}

type AllocationBudget interface {
	Allow(region string, now time.Time) error
}

type SharedAllocationQuota interface {
	Consume(context.Context, string, time.Time) error
}

type AllocationMetrics interface {
	ObserveAttempt(string)
	ObserveSuccess(string)
	ObserveFailure(string)
	ObserveDenied(string)
}

type Service struct {
	Provider Provider
	Durable  Durable
	Roster   RosterPublisher
	Budget   AllocationBudget
	Quota    SharedAllocationQuota
	Metrics  AllocationMetrics
	Now      func() time.Time
}

// AllocateAcceptedProposal is the hand-off from proposal consensus to server
// allocation. Keeping this check beside the provider call prevents a caller
// from allocating capacity for an OPEN/DECLINED proposal or for a request
// whose playlist does not match the proposal that produced it.
func (s Service) AllocateAcceptedProposal(ctx context.Context, proposal domain.Proposal, request domain.AllocationRequest, playlist domain.Playlist, labels map[string]string) (agones.AllocatedServer, error) {
	if proposal.State != domain.Accepted || proposal.Playlist != playlist || len(proposal.Participants) == 0 || (request.Playlist != "" && request.Playlist != playlist) || (proposal.Region != "" && request.Region != proposal.Region) || (proposal.Protocol > 0 && request.Protocol != proposal.Protocol) || request.ArenaPath != proposal.ArenaPath {
		return agones.AllocatedServer{}, domain.ErrAllocationInput
	}
	if proposal.Playlist == domain.Ranked && len(proposal.Participants) != 6 {
		return agones.AllocatedServer{}, domain.ErrAllocationInput
	}
	if proposal.Playlist == domain.Casual && (len(proposal.Participants) < 2 || len(proposal.Participants) > 6) {
		return agones.AllocatedServer{}, domain.ErrAllocationInput
	}
	seen := make(map[string]struct{}, len(proposal.Participants))
	for _, participant := range proposal.Participants {
		if participant.PlayerID == "" || participant.Response != domain.AcceptedResponse {
			return agones.AllocatedServer{}, domain.ErrAllocationInput
		}
		if _, exists := seen[participant.PlayerID]; exists {
			return agones.AllocatedServer{}, domain.ErrAllocationInput
		}
		seen[participant.PlayerID] = struct{}{}
	}
	if request.MatchID == "" {
		return agones.AllocatedServer{}, domain.ErrAllocationInput
	}
	return s.Allocate(ctx, request, labels)
}

func (s Service) PublishRoster(ctx context.Context, assignment domain.Assignment, roster []domain.SignedJoinAuthorisation, verify func([]byte, []byte) bool) error {
	if s.Roster == nil {
		return errNotConfigured
	}
	if assignment.Allocation.State != domain.ServerAllocated || assignment.Endpoint == "" {
		return domain.ErrManifestRejected
	}
	return s.Roster.PublishRoster(ctx, assignment, roster, verify)
}

func (s Service) Allocate(ctx context.Context, request domain.AllocationRequest, labels map[string]string) (agones.AllocatedServer, error) {
	if s.Provider == nil || s.Durable == nil || s.Now == nil {
		return agones.AllocatedServer{}, errNotConfigured
	}
	now := s.Now()
	if s.Metrics != nil {
		s.Metrics.ObserveAttempt(request.Region)
	}
	if s.Budget != nil {
		if err := s.Budget.Allow(request.Region, now); err != nil {
			if s.Metrics != nil {
				s.Metrics.ObserveDenied(request.Region)
			}
			return agones.AllocatedServer{}, err
		}
	}
	if s.Quota != nil {
		if err := s.Quota.Consume(ctx, request.Region, now); err != nil {
			if s.Metrics != nil {
				s.Metrics.ObserveDenied(request.Region)
			}
			return agones.AllocatedServer{}, err
		}
	}
	result, err := s.Provider.Allocate(ctx, request, labels, now)
	if err != nil {
		if s.Metrics != nil {
			s.Metrics.ObserveFailure(request.Region)
		}
		return agones.AllocatedServer{}, err
	}
	if err := validateProviderAllocation(request, result); err != nil {
		if s.Metrics != nil {
			s.Metrics.ObserveFailure(request.Region)
		}
		return agones.AllocatedServer{}, err
	}
	// The client-facing endpoint arrives on the provider result, not on the
	// allocation. Carry it onto the record so publishing the assignment roster
	// -- and recovering after a crash between allocating and publishing -- has
	// an endpoint to work from.
	result.Allocation.Endpoint = result.Endpoint
	recorded, err := s.Durable.RecordProviderAllocation(ctx, result.Allocation, now)
	if err != nil {
		if s.Metrics != nil {
			s.Metrics.ObserveFailure(request.Region)
		}
		return agones.AllocatedServer{}, err
	}
	result.Allocation = recorded
	if s.Metrics != nil {
		s.Metrics.ObserveSuccess(request.Region)
	}
	return result, nil
}

func (s Service) RecordProviderAllocation(ctx context.Context, result agones.AllocatedServer, now time.Time) (domain.Allocation, error) {
	if s.Durable == nil || result.Allocation.State != domain.ServerAllocated || result.Endpoint == "" {
		return domain.Allocation{}, domain.ErrAllocationInput
	}
	// Quota is consumed by Allocate before a fresh provider request. This
	// method only reconciles an already-issued provider result after an
	// ambiguous write, so consuming here would charge one allocation twice.
	result.Allocation.Endpoint = result.Endpoint
	allocation, err := s.Durable.RecordProviderAllocation(ctx, result.Allocation, now)
	if s.Metrics != nil {
		if err != nil {
			s.Metrics.ObserveFailure(result.Allocation.Region)
		} else {
			s.Metrics.ObserveSuccess(result.Allocation.Region)
		}
	}
	return allocation, err
}

var errNotConfigured = &configurationError{}

type configurationError struct{}

func (*configurationError) Error() string { return "allocator service is not configured" }