package main

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"time"

	"git.k6n.net/mats/go-cart-actor/pkg/flow"
	"git.k6n.net/mats/go-cart-actor/pkg/order"
	messages "git.k6n.net/mats/go-cart-actor/proto/order"
)

// fromCheckoutReq is the payload the checkout service sends to create an order
// from a settled (paid) checkout. All payment processing has already happened
// via Klarna/Adyen on the checkout grain; the order service records the result
// in its event-sourced grain.
type fromCheckoutReq struct {
	CheckoutId     string    `json:"checkoutId"`
	IdempotencyKey string    `json:"idempotencyKey"`
	Flow           string    `json:"flow,omitempty"`

	CartId        string    `json:"cartId"`
	Currency      string    `json:"currency"`
	Locale        string    `json:"locale,omitempty"`
	Country       string    `json:"country"`
	CustomerEmail string    `json:"customerEmail,omitempty"`
	CustomerName  string    `json:"customerName,omitempty"`
	Lines         []lineReq `json:"lines"`

	// Payment carries the externally-settled payment result. The provider has
	// already authorized and captured; the order grain records these facts.
	Payment struct {
		Provider  string `json:"provider"`  // "klarna" or "adyen"
		Reference string `json:"reference"` // processor reference (PSP reference)
		Amount    int64  `json:"amount"`    // minor units
	} `json:"payment"`
}

// handleFromCheckout creates an event-sourced order from a settled checkout.
// It runs the place-and-pay flow with a passthrough provider that records the
// already-completed authorization and capture, bypassing any external payment
// call. The response carries the order grain, flow result, and order ID.
//
// Idempotent: a retry with the same idempotencyKey returns the existing order
// (409 Conflict) rather than creating a duplicate.
func (s *server) handleFromCheckout(w http.ResponseWriter, r *http.Request) {
	var req fromCheckoutReq
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeErr(w, http.StatusBadRequest, fmt.Errorf("bad body: %w", err))
		return
	}
	if len(req.Lines) == 0 {
		writeErr(w, http.StatusBadRequest, fmt.Errorf("from-checkout: at least one line required"))
		return
	}

	ordID, flowRes, grain, exists, runErr, err := s.createOrderFromCheckoutInternal(r.Context(), &req)
	if err != nil {
		writeErr(w, http.StatusInternalServerError, err)
		return
	}

	if exists {
		writeJSON(w, http.StatusConflict, map[string]any{
			"orderId":  order.OrderId(ordID).String(),
			"order":    grain,
			"existing": true,
		})
		return
	}

	status := http.StatusCreated
	if runErr != nil {
		status = http.StatusPaymentRequired
	}

	writeJSON(w, status, map[string]any{
		"orderId": order.OrderId(ordID).String(),
		"flow":    flowRes,
		"order":   grain,
	})
}

// createOrderFromCheckoutInternal runs the core idempotent checkout-to-order logic.
// It returns (orderID, flowResult, grain, exists, runErr, err).
// - exists is true if the order already existed (idempotency hit).
// - runErr is the flow run error (payment flow failed, e.g. compensating was run).
// - err is a structural/storage error.
func (s *server) createOrderFromCheckoutInternal(ctx context.Context, req *fromCheckoutReq) (uint64, *flow.Result, *order.OrderGrain, bool, error, error) {
	if req.IdempotencyKey != "" {
		unlock := s.idem.Lock(req.IdempotencyKey)
		defer unlock()
		if existingID, ok := s.idem.Get(req.IdempotencyKey); ok {
			g, err := s.applier.Get(ctx, existingID)
			if err != nil {
				return 0, nil, nil, false, nil, fmt.Errorf("idempotent lookup: %w", err)
			}
			return existingID, nil, g, true, nil, nil
		}
	}

	id, err := order.NewOrderId()
	if err != nil {
		return 0, nil, nil, false, nil, fmt.Errorf("new order id: %w", err)
	}
	ordID := uint64(id)

	po := buildFromCheckoutPlaceOrder(id, req)
	provider := order.NewPassthroughProvider(req.Payment.Provider, req.Payment.Reference, req.Payment.Amount)

	flowName := req.Flow
	if flowName == "" {
		flowName = s.defaultFlow
	}
	def, ok := s.flows.get(flowName)
	if !ok {
		return 0, nil, nil, false, nil, fmt.Errorf("unknown flow %q", flowName)
	}

	freg := flow.NewRegistry()
	flow.RegisterBuiltinHooks(freg)
	order.RegisterFlowActions(freg, s.applier, provider)
	order.RegisterEmitHook(freg, nil)

	engine := flow.NewEngine(freg, s.logger)
	st := flow.NewState(ordID, s.logger)
	st.Vars[order.PlaceOrderVar] = po

	res, runErr := engine.Run(ctx, def, st)
	grain, getErr := s.applier.Get(ctx, ordID)
	if getErr != nil {
		return 0, nil, nil, false, nil, fmt.Errorf("get order grain: %w", getErr)
	}

	if runErr != nil {
		s.logger.Warn("from-checkout flow failed", "orderId", id.String(), "err", runErr)
	}

	if req.IdempotencyKey != "" && runErr == nil {
		if err := s.idem.Put(req.IdempotencyKey, ordID); err != nil {
			s.logger.Error("idempotency record failed", "key", req.IdempotencyKey, "orderId", id.String(), "err", err)
		}
	}

	return ordID, res, grain, false, runErr, nil
}

// buildFromCheckoutPlaceOrder converts a from-checkout request into a PlaceOrder
// proto message, computing per-line and order totals from the lineReq entries.
func buildFromCheckoutPlaceOrder(id order.OrderId, req *fromCheckoutReq) *messages.PlaceOrder {
	orderRef := "ord-" + id.String()
	po := &messages.PlaceOrder{
		OrderReference: orderRef,
		CartId:         req.CartId,
		Currency:       req.Currency,
		Locale:         req.Locale,
		Country:        req.Country,
		CustomerEmail:  req.CustomerEmail,
		CustomerName:   req.CustomerName,
		PlacedAtMs:     time.Now().UnixMilli(),
	}
	var total, totalTax int64
	for _, l := range req.Lines {
		lineTotal := l.UnitPrice * int64(l.Quantity)
		lineTax := order.ComputeTax(lineTotal, int(l.TaxRate))
		total += lineTotal
		totalTax += lineTax
		po.Lines = append(po.Lines, &messages.OrderLine{
			Reference:   l.Reference,
			Sku:         l.Sku,
			Name:        l.Name,
			Quantity:    l.Quantity,
			UnitPrice:   l.UnitPrice,
			TaxRate:     l.TaxRate,
			TotalAmount: lineTotal,
			TotalTax:    lineTax,
		})
	}
	po.TotalAmount = total
	po.TotalTax = totalTax
	return po
}