// Package stripe adapts Stripe Checkout to provider.Provider: Create → hosted
// Checkout Session (redirect), VerifyCallback → webhook signature verify, Query →
// session lookup. The *client.API + webhook secret are injected at assembly (default
// backend in prod; httptest backend in tests) so nothing hits the real network in CI.
package stripe

import (
	"context"
	"encoding/json"
	"fmt"
	"strings"
	"time"

	gostripe "github.com/stripe/stripe-go/v79"
	"github.com/stripe/stripe-go/v79/client"
	"github.com/stripe/stripe-go/v79/webhook"

	"github.com/wangjia/pay/internal/provider"
)

// USD 是 Stripe 最小单位(cent)= money 包的 USD minor(均为 1e-2),两边天然对齐,
// Create/Query/VerifyCallback 全程直传 int64 分,不经 money.Parse/Format。
//
// 零小数币种注意(如 JPY/KRW):Stripe 对这类币种的"最小单位"就是整数主单位本身(无 cent
// 概念),若未来扩展这类币种,不能再假设 AmountMinor 与 Stripe 金额 1:1——当前仅支持
// USD,不涉及该分支,留此注释供后续扩展参考。
const supportedCurrency = "USD"

type Provider struct {
	sc            *client.API
	webhookSecret string
}

// New 装配期注入已配置好 backend(生产走默认;测试注入指向 httptest 的 backend)的
// *client.API,以及来自 env(CredentialEnvPrefix)的 webhook 签名密钥。
func New(sc *client.API, webhookSecret string) *Provider {
	return &Provider{sc: sc, webhookSecret: webhookSecret}
}

func (p *Provider) Method() string { return "stripe" }

func (p *Provider) Capabilities() provider.Capabilities {
	return provider.Capabilities{
		RenderTypes:      []provider.RenderType{provider.RenderRedirect},
		SupportsRefund:   false, // P4
		SettleCurrencies: []string{supportedCurrency},
		Regions:          []string{"global"},
	}
}

func (p *Provider) Create(_ context.Context, req provider.CreateRequest) (*provider.Session, error) {
	if req.Currency != supportedCurrency {
		return nil, fmt.Errorf("stripe: 仅支持 %s, got %s", supportedCurrency, req.Currency)
	}
	params := &gostripe.CheckoutSessionParams{
		Mode:              gostripe.String(string(gostripe.CheckoutSessionModePayment)),
		SuccessURL:        gostripe.String(req.ReturnURL),
		ClientReferenceID: gostripe.String(req.OutTradeNo),
		LineItems: []*gostripe.CheckoutSessionLineItemParams{{
			Quantity: gostripe.Int64(1),
			PriceData: &gostripe.CheckoutSessionLineItemPriceDataParams{
				Currency:   gostripe.String(strings.ToLower(supportedCurrency)),
				UnitAmount: gostripe.Int64(req.AmountMinor), // cent = USD minor,直传
				ProductData: &gostripe.CheckoutSessionLineItemPriceDataProductDataParams{
					Name: gostripe.String(req.Subject),
				},
			},
		}},
	}
	sess, err := p.sc.CheckoutSessions.New(params)
	if err != nil {
		return nil, fmt.Errorf("stripe: 创建 Checkout Session 失败: %w", err)
	}
	return &provider.Session{
		ProviderRef: sess.ID,
		RenderType:  provider.RenderRedirect,
		Payload:     map[string]any{"url": sess.URL},
	}, nil
}

func (p *Provider) VerifyCallback(_ context.Context, in provider.CallbackInput) (*provider.PaidEvent, error) {
	sig := in.Headers["Stripe-Signature"]
	// stripe-go 默认 ConstructEvent 会额外校验 event.api_version == SDK 编译期常量
	// stripe.APIVersion,但 webhook 端点的 API 版本是在 Stripe Dashboard 独立配置的,
	// 与所拉取的 SDK 版本不必一致——我们又不依赖 SDK 按版本反序列化(下面对
	// event.Data.Raw 自己 json.Unmarshal 成 CheckoutSession,不吃 SDK 的类型化解码),
	// 所以显式 IgnoreAPIVersionMismatch:true,避免把"版本不同"误判成"验签失败"。
	// 时间容差不受影响:Tolerance 留零值,constructEvent 内部仍回退到 DefaultTolerance
	// (5 分钟),签名 HMAC 校验本身完全不受此 flag 影响。
	event, err := webhook.ConstructEventWithOptions(in.Raw, sig, p.webhookSecret,
		webhook.ConstructEventOptions{IgnoreAPIVersionMismatch: true})
	if err != nil {
		return nil, fmt.Errorf("stripe: webhook 验签失败: %w", err)
	}
	if event.Type != "checkout.session.completed" {
		// 其它事件此阶段不处理:归一化 pending(管线 Settle 视为 ignored)。
		return &provider.PaidEvent{Status: provider.PaidPending, Raw: string(in.Raw)}, nil
	}
	var sess gostripe.CheckoutSession
	if err := json.Unmarshal(event.Data.Raw, &sess); err != nil {
		return nil, fmt.Errorf("stripe: 解析 session 失败: %w", err)
	}
	ev := sessionToEvent(&sess, in.Raw)
	if event.Created > 0 {
		paidAt := unixToTime(event.Created)
		ev.PaidAt = &paidAt
	}
	return ev, nil
}

func (p *Provider) Query(_ context.Context, req provider.QueryRequest) (*provider.PaidEvent, error) {
	sess, err := p.sc.CheckoutSessions.Get(req.ProviderRef, nil)
	if err != nil {
		return nil, fmt.Errorf("stripe: 查询 session 失败: %w", err)
	}
	ev := sessionToEvent(sess, nil)
	ev.ProviderRef = req.ProviderRef
	return ev, nil
}

func unixToTime(sec int64) time.Time { return time.Unix(sec, 0).UTC() }

func sessionToEvent(sess *gostripe.CheckoutSession, raw []byte) *provider.PaidEvent {
	status := provider.PaidPending
	switch sess.PaymentStatus {
	case gostripe.CheckoutSessionPaymentStatusPaid, gostripe.CheckoutSessionPaymentStatusNoPaymentRequired:
		status = provider.PaidSucceeded
	case gostripe.CheckoutSessionPaymentStatusUnpaid:
		status = provider.PaidPending
	}
	return &provider.PaidEvent{
		ProviderRef:     sess.ID,
		Status:          status,
		PaidAmountMinor: sess.AmountTotal, // cent
		PaidCurrency:    strings.ToUpper(string(sess.Currency)),
		Raw:             string(raw),
	}
}