package extraction

import (
	"context"
	"errors"
	"fmt"
	"time"

	domain "proxy-pool/internal/domain/extraction"
)

var (
	ErrInvalidRequest       = errors.New("invalid extraction request")
	ErrCountExceeded        = errors.New("extraction count exceeds policy")
	ErrInvalidFulfillment   = errors.New("invalid extraction fulfillment")
	ErrInvalidServicePolicy = errors.New("invalid extraction service policy")
	ErrAdmissionRejected    = errors.New("extraction admission rejected")
	ErrUnavailable          = errors.New("extraction service unavailable")
)

type Policy struct {
	MaxCountPerRequest int
	DefaultFulfillment domain.Fulfillment
	MinRemainingTTL    time.Duration
	MaxHealthCheckAge  time.Duration
	ReserveForGateway  int
	IdempotencyTTL     time.Duration
}

type Filters struct {
	Protocols []string
	Regions   []string
	Carriers  []string
	Upstreams []string
}

type Request struct {
	RequestID      string
	ClientID       string
	SourceIP       string
	IdempotencyKey string
	Count          int
	Fulfillment    domain.Fulfillment
	Filters        Filters
}

type ExtractedProxy struct {
	ID                  string
	Protocol            string
	Host                string
	Port                uint16
	Username            string
	Password            string
	URL                 string
	Region              string
	Carrier             string
	Upstream            string
	ExpiresAt           time.Time
	RemainingTTLSeconds int64
	ExtractedAt         time.Time
}

type Response struct {
	RequestID string
	Requested int
	Returned  int
	Proxies   []ExtractedProxy
}

type Service struct {
	store     domain.Store
	policy    Policy
	admission Admission
	now       func() time.Time
}

type Admission interface {
	Admit(context.Context, string) error
}

func NewService(store domain.Store, policy Policy, admission Admission, now func() time.Time) (*Service, error) {
	if admission == nil {
		return nil, fmt.Errorf("%w: admission is required", ErrInvalidServicePolicy)
	}
	if store == nil {
		return nil, fmt.Errorf("%w: store is required", ErrInvalidServicePolicy)
	}
	if policy.MaxCountPerRequest <= 0 || policy.MinRemainingTTL < 0 ||
		policy.MaxHealthCheckAge < 0 || policy.ReserveForGateway < 0 || policy.IdempotencyTTL < 0 {
		return nil, ErrInvalidServicePolicy
	}
	if policy.DefaultFulfillment != domain.Partial && policy.DefaultFulfillment != domain.AllOrNothing {
		return nil, ErrInvalidServicePolicy
	}
	if now == nil {
		now = time.Now
	}
	return &Service{store: store, policy: policy, admission: admission, now: now}, nil
}

func (s *Service) Extract(ctx context.Context, request Request) (Response, error) {
	response := Response{RequestID: request.RequestID, Requested: request.Count}
	if request.RequestID == "" || (request.ClientID == "" && request.SourceIP == "") || request.Count <= 0 {
		return response, ErrInvalidRequest
	}
	if request.Count > s.policy.MaxCountPerRequest {
		return response, ErrCountExceeded
	}
	fulfillment := request.Fulfillment
	if fulfillment == "" {
		fulfillment = s.policy.DefaultFulfillment
	}
	if fulfillment != domain.Partial && fulfillment != domain.AllOrNothing {
		return response, ErrInvalidFulfillment
	}
	if err := s.admission.Admit(ctx, admissionKey(request)); err != nil {
		return response, errors.Join(ErrAdmissionRejected, err)
	}

	now := s.now().UTC()
	clientID := request.ClientID
	if clientID == "" {
		clientID = request.SourceIP
	}
	result, err := s.store.Extract(ctx, domain.Command{
		RequestID:         request.RequestID,
		ClientID:          clientID,
		SourceIP:          request.SourceIP,
		IdempotencyKey:    request.IdempotencyKey,
		IdempotencyTTL:    s.policy.IdempotencyTTL,
		Requested:         request.Count,
		Fulfillment:       fulfillment,
		Now:               now,
		MinRemainingTTL:   s.policy.MinRemainingTTL,
		MaxHealthCheckAge: s.policy.MaxHealthCheckAge,
		ReserveForGateway: s.policy.ReserveForGateway,
		Protocols:         append([]string(nil), request.Filters.Protocols...),
		Regions:           append([]string(nil), request.Filters.Regions...),
		Carriers:          append([]string(nil), request.Filters.Carriers...),
		Upstreams:         append([]string(nil), request.Filters.Upstreams...),
	})
	if err != nil {
		return response, err
	}

	response.Proxies = make([]ExtractedProxy, 0, len(result.Items))
	extractedAt := result.ExtractedAt
	if extractedAt.IsZero() {
		extractedAt = now
	}
	for _, candidate := range result.Items {
		remaining := int64(0)
		if !candidate.ExpiresAt.IsZero() && candidate.ExpiresAt.After(extractedAt) {
			remaining = int64(candidate.ExpiresAt.Sub(extractedAt) / time.Second)
		}
		response.Proxies = append(response.Proxies, ExtractedProxy{
			ID:                  candidate.ID,
			Protocol:            candidate.Protocol,
			Host:                candidate.Host,
			Port:                candidate.Port,
			Username:            candidate.Username,
			Password:            candidate.Password,
			URL:                 candidate.URL,
			Region:              candidate.Region,
			Carrier:             candidate.Carrier,
			Upstream:            candidate.Upstream,
			ExpiresAt:           candidate.ExpiresAt,
			RemainingTTLSeconds: remaining,
			ExtractedAt:         extractedAt,
		})
	}
	response.Returned = len(response.Proxies)
	return response, nil
}

func admissionKey(request Request) string {
	if request.ClientID != "" {
		return "client:" + request.ClientID
	}
	return "source:" + request.SourceIP
}