// Package order models an order as an actor grain (same framework as the cart
// and checkout grains). Mutations are the proto messages in proto/order; the
// grain's event log is the source of truth and the OrderGrain below is the
// projection rebuilt by replaying them. The order state machine (transitions
// map + canTransition) is the guardrail enforced inside the mutation handlers.
package order

import (
	"encoding/json"
	"sync"
	"time"

	"git.k6n.net/mats/platform/money"
)

// Status is the order lifecycle state.
type Status string

const (
	StatusNew                Status = ""                    // not yet placed
	StatusPending            Status = "pending"             // placed, awaiting payment
	StatusAuthorized         Status = "authorized"          // payment authorized
	StatusCaptured           Status = "captured"            // payment captured (paid)
	StatusPartiallyFulfilled Status = "partially_fulfilled" // some lines shipped
	StatusFulfilled          Status = "fulfilled"           // all lines shipped
	StatusCompleted          Status = "completed"           // closed out
	StatusCancelled          Status = "cancelled"           // terminal
	StatusRefunded           Status = "refunded"            // terminal
)

// transitions is the legal status graph. A target absent from a source's list
// is rejected by the handler that would have caused it. Returns/refunds that do
// not move status are validated separately in their handlers.
var transitions = map[Status][]Status{
	StatusNew:                {StatusPending},
	StatusPending:            {StatusAuthorized, StatusCancelled},
	StatusAuthorized:         {StatusCaptured, StatusCancelled},
	StatusCaptured:           {StatusPartiallyFulfilled, StatusFulfilled, StatusRefunded},
	StatusPartiallyFulfilled: {StatusPartiallyFulfilled, StatusFulfilled, StatusRefunded},
	StatusFulfilled:          {StatusCompleted, StatusRefunded},
	StatusCompleted:          {StatusRefunded},
	StatusCancelled:          {},
	StatusRefunded:           {},
}

// canTransition reports whether from -> to is a legal status change.
func canTransition(from, to Status) bool {
	for _, s := range transitions[from] {
		if s == to {
			return true
		}
	}
	return false
}

// Line is an ordered line item (projected from PlaceOrder).
type Line struct {
	Reference   string `json:"reference"`
	Sku         string `json:"sku"`
	Name        string `json:"name"`
	Quantity    int    `json:"quantity"`
	UnitPrice   money.Cents `json:"unitPrice"`
	TaxRate     int         `json:"taxRate"`
	TotalAmount money.Cents `json:"totalAmount"`
	TotalTax    money.Cents `json:"totalTax"`
	// Location is the inventory location / store id to commit against (empty =
	// order country). Carried through to the order.created event for commit.
	Location string `json:"location,omitempty"`
	// Fulfilled tracks how many units of this line have shipped.
	Fulfilled int `json:"fulfilled"`
}

// Payment records one authorization/capture against a provider.
type Payment struct {
	Provider     string      `json:"provider"`
	Authorized   money.Cents `json:"authorized"`
	Captured     money.Cents `json:"captured"`
	Refunded     money.Cents `json:"refunded"`
	AuthRef      string      `json:"authRef,omitempty"`
	CaptureRef   string `json:"captureRef,omitempty"`
	AuthorizedAt string `json:"authorizedAt,omitempty"`
	CapturedAt   string `json:"capturedAt,omitempty"`
}

// Fulfillment records a shipment of some lines.
type Fulfillment struct {
	ID             string             `json:"id"`
	Carrier        string             `json:"carrier,omitempty"`
	TrackingNumber string             `json:"trackingNumber,omitempty"`
	TrackingURI    string             `json:"trackingUri,omitempty"`
	Lines          []FulfillmentEntry `json:"lines,omitempty"`
	CreatedAt      string             `json:"createdAt,omitempty"`
}

// FulfillmentEntry is one shipped line within a fulfillment.
type FulfillmentEntry struct {
	Reference string `json:"reference"`
	Quantity  int    `json:"quantity"`
}

// Return records an RMA request.
type Return struct {
	ID          string             `json:"id"`
	Reason      string             `json:"reason,omitempty"`
	Lines       []FulfillmentEntry `json:"lines,omitempty"`
	RequestedAt string             `json:"requestedAt,omitempty"`
}

// Exchange records an exchange request.
type Exchange struct {
	ID          string             `json:"id"`
	ReturnID    string             `json:"returnId"`
	Reason      string             `json:"reason,omitempty"`
	ReturnLines []FulfillmentEntry `json:"returnLines,omitempty"`
	NewLines    []Line             `json:"newLines,omitempty"`
	RequestedAt string             `json:"requestedAt,omitempty"`
}

// Refund records a refund issued against the order.
type Refund struct {
	Provider  string      `json:"provider"`
	Amount    money.Cents `json:"amount"`
	Reference string      `json:"reference,omitempty"`
	ReturnID  string `json:"returnId,omitempty"`
	IssuedAt  string `json:"issuedAt,omitempty"`
}

// OrderGrain is the projected current state of an order. It implements
// actor.Grain[OrderGrain].
type OrderGrain struct {
	mu         sync.RWMutex
	lastAccess time.Time
	lastChange time.Time

	Id             uint64 `json:"id"`
	OrderReference string `json:"orderReference,omitempty"`
	CartId         string `json:"cartId,omitempty"`
	Status         Status `json:"status"`
	Currency       string `json:"currency,omitempty"`
	Locale         string `json:"locale,omitempty"`
	Country        string `json:"country,omitempty"`

	TotalAmount money.Cents `json:"totalAmount"`
	TotalTax    money.Cents `json:"totalTax"`
	Lines       []Line      `json:"lines,omitempty"`

	CustomerEmail   string          `json:"customerEmail,omitempty"`
	CustomerName    string          `json:"customerName,omitempty"`
	BillingAddress  json.RawMessage `json:"billingAddress,omitempty"`
	ShippingAddress json.RawMessage `json:"shippingAddress,omitempty"`

	Payments     []*Payment    `json:"payments,omitempty"`
	Fulfillments []Fulfillment `json:"fulfillments,omitempty"`
	Returns      []Return      `json:"returns,omitempty"`
	Exchanges    []Exchange    `json:"exchanges,omitempty"`
	Refunds      []Refund      `json:"refunds,omitempty"`


	CapturedAmount money.Cents `json:"capturedAmount"`
	RefundedAmount money.Cents `json:"refundedAmount"`

	PlacedAt  string `json:"placedAt,omitempty"`
	UpdatedAt string `json:"updatedAt,omitempty"`
}

// NewOrderGrain returns an empty (not-yet-placed) order grain for id.
func NewOrderGrain(id uint64, ts time.Time) *OrderGrain {
	return &OrderGrain{
		Id:         id,
		Status:     StatusNew,
		lastAccess: ts,
		lastChange: ts,
	}
}

// --- actor.Grain[OrderGrain] ---

func (o *OrderGrain) GetId() uint64 { return o.Id }

func (o *OrderGrain) GetLastAccess() time.Time { return o.lastAccess }

func (o *OrderGrain) GetLastChange() time.Time { return o.lastChange }

func (o *OrderGrain) GetCurrentState() (*OrderGrain, error) {
	o.lastAccess = time.Now()
	return o, nil
}

func (o *OrderGrain) GetState() ([]byte, error) { return json.Marshal(o) }

// touch records a successful mutation, advancing UpdatedAt and lastChange.
func (o *OrderGrain) touch(at string) {
	now := time.Now()
	o.lastChange = now
	if at != "" {
		o.UpdatedAt = at
	}
}

// findLine returns the line with the given reference, or nil.
func (o *OrderGrain) findLine(ref string) *Line {
	for i := range o.Lines {
		if o.Lines[i].Reference == ref {
			return &o.Lines[i]
		}
	}
	return nil
}

// allLinesFulfilled reports whether every line's full quantity has shipped.
func (o *OrderGrain) allLinesFulfilled() bool {
	if len(o.Lines) == 0 {
		return false
	}
	for _, l := range o.Lines {
		if l.Fulfilled < l.Quantity {
			return false
		}
	}
	return true
}

// msToString renders a caller-supplied unix-millis timestamp as RFC3339, or ""
// when zero (so replay stays deterministic — the value comes from the event).
func msToString(ms int64) string {
	if ms == 0 {
		return ""
	}
	return time.UnixMilli(ms).UTC().Format(time.RFC3339)
}