// Package gateway is the channel-neutral payment pipeline: it turns a client
// {sku, method} into an authoritative Order + a payment Session (render_type +
// payload), and settles callbacks/queries into paid + a business webhook. It
// depends only on provider.Registry, store.OrderStore (P1), accounts.Registry
// (P1) — never on a concrete channel.
package gateway

import (
	"context"
	"errors"
	"time"

	"github.com/wangjia/pay/internal/accounts"
	"github.com/wangjia/pay/internal/model"
	"github.com/wangjia/pay/internal/provider"
	"github.com/wangjia/pay/internal/store"
	"github.com/wangjia/pay/internal/util"
)

var (
	ErrProductNotFound = errors.New("gateway: product not found")
	ErrNoAccount       = errors.New("gateway: no enabled account for method/region")
	ErrOrderNotPending = errors.New("gateway: order not pending")
)

// ProductResolver maps a client-facing SKU to the authoritative amount/currency.
// Amount authority lives in pay (设计 §3.1); the client never sends raw amounts.
type ProductResolver interface {
	Resolve(sku string) (amountMinor int64, currency, subject, bizCode string, err error)
}

// WebhookEnqueuer receives a domain payload to deliver to the business system.
type WebhookEnqueuer interface {
	Enqueue(outTradeNo, bizSystem, eventType string, data map[string]any) error
}

type Gateway struct {
	orders    *store.OrderStore
	providers *provider.Registry
	accounts  *accounts.Registry
	products  ProductResolver
	webhook   WebhookEnqueuer
	region    string
}

func New(orders *store.OrderStore, providers *provider.Registry, accts *accounts.Registry,
	products ProductResolver, webhook WebhookEnqueuer, region string) *Gateway {
	return &Gateway{orders: orders, providers: providers, accounts: accts,
		products: products, webhook: webhook, region: region}
}

type CreateOrderInput struct {
	SKU       string
	Method    string
	BizSystem string
	BizRef    string
	ReturnURL string
}

type SessionView struct {
	RenderType string         `json:"render_type"`
	Payload    map[string]any `json:"payload"`
	ExpiresAt  *time.Time     `json:"expires_at,omitempty"`
}

type OrderResult struct {
	OrderNo string      `json:"order_no"`
	Session SessionView `json:"session"`
}

// CreateOrder resolves the product (authoritative amount), picks a provider +
// account, persists a pending Order + Attempt (P1 OrderStore), and returns the
// payment session {render_type, payload}. 加渠道不改 client(设计 §4.2)。
func (g *Gateway) CreateOrder(ctx context.Context, in CreateOrderInput) (*OrderResult, error) {
	amountMinor, currency, subject, _, err := g.products.Resolve(in.SKU)
	if err != nil {
		return nil, err // ErrProductNotFound
	}
	prov, err := g.providers.Get(in.Method)
	if err != nil {
		return nil, err // ErrUnknownMethod
	}
	accts := g.accounts.EnabledFor(in.Method, g.region)
	if len(accts) == 0 {
		return nil, ErrNoAccount
	}
	acct := accts[0] // 路由策略(round_robin/weighted/…)在 P5;P2 取首个 enabled。

	outNo := util.NewOutTradeNo("pay")
	if err := g.orders.CreateOrder(&model.OrderV2{
		OutTradeNo: outNo, BizSystem: in.BizSystem, BizRef: in.BizRef,
		Subject: subject, AmountMinor: amountMinor, Currency: currency,
		Status: model.OrderPendingV2,
	}); err != nil {
		return nil, err
	}

	sess, err := prov.Create(ctx, provider.CreateRequest{
		OutTradeNo: outNo, Subject: subject, AmountMinor: amountMinor,
		Currency: currency, Account: acct, ReturnURL: in.ReturnURL,
	})
	if err != nil {
		return nil, err
	}
	if err := g.orders.CreateAttempt(&model.Attempt{
		OutTradeNo: outNo, Channel: in.Method, AccountID: acct.AccountID,
		Provider: prov.Method(), ProviderRef: sess.ProviderRef,
		RenderType: string(sess.RenderType), AmountMinor: amountMinor, Currency: currency,
		Status: model.AttemptPending, ExpiresAt: sess.ExpiresAt,
	}); err != nil {
		return nil, err
	}

	return &OrderResult{OrderNo: outNo, Session: SessionView{
		RenderType: string(sess.RenderType), Payload: sess.Payload, ExpiresAt: sess.ExpiresAt,
	}}, nil
}

type OrderStatusView struct {
	OrderNo     string     `json:"order_no"`
	Status      string     `json:"status"`
	Subject     string     `json:"subject"`
	AmountMinor int64      `json:"amount_minor"`
	Currency    string     `json:"currency"`
	PaidAt      *time.Time `json:"paid_at,omitempty"`
}

func (g *Gateway) GetOrder(outTradeNo string) (*OrderStatusView, error) {
	o, err := g.orders.GetOrder(outTradeNo)
	if err != nil {
		return nil, err // ErrOrderNotFound
	}
	return &OrderStatusView{
		OrderNo: o.OutTradeNo, Status: string(o.Status), Subject: o.Subject,
		AmountMinor: o.AmountMinor, Currency: o.Currency, PaidAt: o.PaidAt,
	}, nil
}

// RetryOrder spawns a fresh attempt (possibly a different method) on a still-pending
// order; old pending attempts are expired. attempt 超时 ≠ order 关闭(设计 §3.2)。
func (g *Gateway) RetryOrder(ctx context.Context, outTradeNo, method string) (*OrderResult, error) {
	o, err := g.orders.GetOrder(outTradeNo)
	if err != nil {
		return nil, err
	}
	if o.Status != model.OrderPendingV2 {
		return nil, ErrOrderNotPending
	}
	prov, err := g.providers.Get(method)
	if err != nil {
		return nil, err
	}
	accts := g.accounts.EnabledFor(method, g.region)
	if len(accts) == 0 {
		return nil, ErrNoAccount
	}
	acct := accts[0]

	if _, err := g.orders.ExpirePendingAttempts(outTradeNo); err != nil {
		return nil, err
	}
	sess, err := prov.Create(ctx, provider.CreateRequest{
		OutTradeNo: outTradeNo, Subject: o.Subject, AmountMinor: o.AmountMinor,
		Currency: o.Currency, Account: acct,
	})
	if err != nil {
		return nil, err
	}
	if err := g.orders.CreateAttempt(&model.Attempt{
		OutTradeNo: outTradeNo, Channel: method, AccountID: acct.AccountID,
		Provider: prov.Method(), ProviderRef: sess.ProviderRef,
		RenderType: string(sess.RenderType), AmountMinor: o.AmountMinor, Currency: o.Currency,
		Status: model.AttemptPending, ExpiresAt: sess.ExpiresAt,
	}); err != nil {
		return nil, err
	}
	return &OrderResult{OrderNo: outTradeNo, Session: SessionView{
		RenderType: string(sess.RenderType), Payload: sess.Payload, ExpiresAt: sess.ExpiresAt,
	}}, nil
}

func (g *Gateway) CancelOrder(outTradeNo string) (bool, error) {
	return g.orders.CancelOrder(outTradeNo)
}