package controllers

import (
	"encoding/json"
	"strconv"
	"strings"
	"time"

	"doormile/constants"
	"doormile/db"
	"doormile/internal/assignment"
	"doormile/internal/cxstage"
	"doormile/middlewares"
	"doormile/models"
	"doormile/utils"

	"github.com/gofiber/fiber/v2"
	"gorm.io/gorm"
)

// Bookings — §9 of the contract.
//
// A customer books a PICKUP: one visit, 1..N destinations, and no tracking
// number anywhere in this file. Tracking numbers are minted per destination
// when the miler completes the pickup, because until the parcels are in
// someone's hands there is no shipment to track — only an intention to collect
// one.

const (
	cxDefaultPageSize = 20
	cxMaxPageSize     = 50

	// cxAbsoluteMaxDestinations is a hard ceiling checked BEFORE any database
	// work, independent of the configured per-city cap.
	//
	// The configured cap (customerbookinglimits.maxdestinations) is the real
	// policy and stays authoritative — but reading it costs two queries, and
	// the district lookup above it builds a `WHERE districtcode IN (...)` from
	// however many entries the caller sent. Without a ceiling, a request
	// carrying ten thousand destinations does all of that work before anything
	// says no.
	//
	// Set well above any plausible policy so it never masks the real cap: this
	// is a sanity guard on unbounded input, not a product limit.
	cxAbsoluteMaxDestinations = 25
)

type cxDetailsInput struct {
	Street         *string `json:"street"`
	Building       *string `json:"building"`
	Landmark       *string `json:"landmark"`
	RecipientName  *string `json:"recipientName"`
	RecipientPhone *string `json:"recipientPhone"`
	Instructions   *string `json:"instructions"`
	Pin            *struct {
		Lat float64 `json:"lat"`
		Lng float64 `json:"lng"`
	} `json:"pin"`
	// CodAmount is money the customer wants collected at this door on their
	// behalf. Doormile is the carrier, not the seller.
	CodAmount *float64 `json:"codAmount"`
}

type cxCreateBookingRequest struct {
	Pickup struct {
		Title string  `json:"title"`
		Sub   string  `json:"sub"`
		Lat   float64 `json:"lat"`
		Lng   float64 `json:"lng"`
	} `json:"pickup"`
	SlotID       string `json:"slotId"`
	Destinations []struct {
		StateCode    string          `json:"stateCode"`
		DistrictCode string          `json:"districtCode"`
		PackageCount int             `json:"packageCount"`
		Details      *cxDetailsInput `json:"details"`
	} `json:"destinations"`
	// Estimate is what the customer was shown on Review. Recorded for dispute
	// audit — when the settled price is questioned months later, the number on
	// the screen is the fact that matters, not a re-run of today's pricing.
	Estimate *struct {
		Min int `json:"min"`
		Max int `json:"max"`
	} `json:"estimate"`
	// Remarks is the free-text note the customer adds on Review ("Handle with
	// care"). It is top-level in the documented payload
	// (docs/customer-app-api-crisp.md) and lands in PickupBooking.Notes, which
	// the admin Orders table displays and searches. Without the field here
	// BodyParser drops it silently and every customer-app booking reaches the
	// console with an empty note.
	Remarks string `json:"remarks"`
}

// CreateCxBooking creates the pickup.
func CreateCxBooking(c *fiber.Ctx) error {
	customerID := c.Locals("userid").(int)

	var req cxCreateBookingRequest
	if err := c.BodyParser(&req); err != nil {
		return utils.CxBadRequest(c, "We could not read that request")
	}

	// "No destinations at all" and "a destination is missing its state or
	// district" are different problems with different fixes, and the customer
	// is shown this message verbatim. Telling someone who added nothing that
	// "every destination needs a serviceable state and district" describes a
	// problem they do not have and hides the one they do — they need to add a
	// destination, not correct one. The estimate endpoint already says this
	// correctly; these two now agree.
	if len(req.Destinations) == 0 {
		return utils.CxBadRequest(c, "Add at least one destination")
	}
	if strings.TrimSpace(req.SlotID) == "" {
		return utils.CxBadRequest(c, "Pick a pickup slot")
	}
	// Cheapest validation first, before anything reaches the database. A slot id
	// carries its own date, so a stale one is provably stale without a query —
	// and this is the case an app left open across midnight actually hits.
	if CxSlotDateIsPast(req.SlotID) {
		return utils.CxBadRequest(c, "That pickup time has passed — pick a new slot")
	}
	// Unbounded input, bounded before it costs anything. The configured cap
	// below is the real policy; this only stops a caller making the server do
	// three queries and build an arbitrarily long IN clause to be told no.
	if len(req.Destinations) > cxAbsoluteMaxDestinations {
		return utils.CxBadRequest(c, "That is more destinations than one pickup can carry")
	}

	// The pickup point has to be somewhere Doormile actually collects from.
	// CityGateMiddleware sniffs the body for a `pickuppincode`, which this
	// request shape does not have — its pickup is a title/sub/lat/lng from the
	// place search — so it waves every customer booking through. The check is
	// done here, against the pincode resolved from the coordinates.
	pickupPincode := pincodeForPoint(req.Pickup.Lat, req.Pickup.Lng)
	if _, served := middlewares.PincodeInOperatingCity(pickupPincode); !served {
		return utils.CxFail(c, fiber.StatusUnprocessableEntity, utils.CxErrUnserviceable,
			"We are not collecting from that area yet")
	}

	appLocationID := appLocationForPoint(req.Pickup.Lat, req.Pickup.Lng)
	maxPackages, maxDestinations := CxBookingLimits(appLocationID)
	if len(req.Destinations) > maxDestinations {
		return utils.CxBadRequest(c, "Up to "+strconv.Itoa(maxDestinations)+" destinations per pickup")
	}

	// Resolve every district in one query, then validate. Names are copied onto
	// the destination rather than joined at read time — the client renders
	// "Chennai, Tamil Nadu" straight from the booking.
	codes := make([]string, 0, len(req.Destinations))
	for _, d := range req.Destinations {
		codes = append(codes, strings.ToUpper(strings.TrimSpace(d.DistrictCode)))
	}
	var districtRows []models.ServiceableDistrict
	if err := db.DB.Where("districtcode IN ?", codes).Find(&districtRows).Error; err != nil {
		utils.Error("CreateCxBooking: district lookup failed", "error", err)
		return utils.CxInternal(c)
	}
	districts := make(map[string]models.ServiceableDistrict, len(districtRows))
	for _, d := range districtRows {
		districts[d.Districtcode] = d
	}

	stateNames, err := cxStateNames(districtRows)
	if err != nil {
		utils.Error("CreateCxBooking: state lookup failed", "error", err)
		return utils.CxInternal(c)
	}

	totalPackages := 0
	for _, d := range req.Destinations {
		code := strings.ToUpper(strings.TrimSpace(d.DistrictCode))
		district, ok := districts[code]
		if !ok || strings.TrimSpace(d.StateCode) == "" {
			return utils.CxBadRequest(c, "Every destination needs a serviceable state and district")
		}
		if !district.Available {
			// The district was open when the customer picked it and closed
			// before they confirmed. A distinct code, because the app has a
			// specific recovery for it: send them back to change that one
			// destination rather than to a generic retry.
			return utils.CxFail(c, fiber.StatusUnprocessableEntity, utils.CxErrUnserviceable,
				"That district is no longer available")
		}
		packages := d.PackageCount
		if packages < 1 {
			packages = 1
		}
		totalPackages += packages
	}
	if totalPackages > maxPackages {
		return utils.CxBadRequest(c, "Up to "+strconv.Itoa(maxPackages)+" packages per pickup")
	}

	slotFrom, slotTo, slotOK := ResolveCxSlot(req.SlotID)
	if !slotOK {
		return utils.CxBadRequest(c, "Pick a pickup slot")
	}

	// An EXPIRED slot and a FULL slot are different failures and must not share
	// a message. A slot id encodes its own date, so an app left open across
	// midnight — or one that cached the slot list for a session — sends
	// yesterday's window in good faith. Telling that customer the window "just
	// filled up" is untrue and points them at the wrong recovery: they need to
	// re-fetch the slot list, not try again for a place in a queue.
	//
	// 400 rather than 409 for the same reason. The contract maps 400/invalid to
	// "Pick a pickup slot", which is exactly the action required, while 409 is
	// the capacity race below.
	if !slotFrom.After(utils.ISTNow()) {
		return utils.CxBadRequest(c, "That pickup time has passed — pick a new slot")
	}

	if !CxSlotHasCapacity(req.SlotID, req.Pickup.Lat, req.Pickup.Lng) {
		return utils.CxConflict(c, "That pickup window just filled up")
	}

	// Price the pickup as one visit. A failed estimate must never block a
	// booking, so a zero range is stored rather than an error returned — the
	// receipt settles on what the miler weighs regardless.
	estimateDestinations := make([]cxEstimateDestination, 0, len(req.Destinations))
	for _, d := range req.Destinations {
		estimateDestinations = append(estimateDestinations, cxEstimateDestination{
			StateCode:    d.StateCode,
			DistrictCode: d.DistrictCode,
			PackageCount: d.PackageCount,
		})
	}
	quote := quoteCxPickup(req.Pickup.Lat, req.Pickup.Lng, estimateDestinations)
	estimateMin, estimateMax := quote.Min, quote.Max
	if req.Estimate != nil && req.Estimate.Max > 0 {
		// The customer's number wins. They agreed to what was on their screen,
		// and re-pricing at confirm time would quietly change the deal.
		estimateMin, estimateMax = req.Estimate.Min, req.Estimate.Max
	}

	now := utils.DBNow()
	pickupFromDB := cxToDBTime(slotFrom)
	pickupToDB := cxToDBTime(slotTo)

	first := req.Destinations[0]
	firstDistrict := districts[strings.ToUpper(strings.TrimSpace(first.DistrictCode))]

	booking := models.PickupBooking{
		Bookingno:     generateBookingNo(),
		Appcustomerid: customerID,
		Pickupaddress: joinNonEmpty(", ", req.Pickup.Title, req.Pickup.Sub),
		Pickuptitle:   req.Pickup.Title,
		Pickupsub:     req.Pickup.Sub,
		Pickuppincode: pickupPincode,

		Pickuplatitude:  req.Pickup.Lat,
		Pickuplongitude: req.Pickup.Lng,

		// The flat delivery columns mirror destination 0. They are NOT the
		// destination list — that lives in bookingdestinations — but the miler
		// app, the hub console, the routing code and the hyperlocal check all
		// read them, and leaving them empty would make a customer-app booking
		// invisible to every one of those. Destination 0 is the one the rider
		// is told about first, so it is the one that mirrors.
		Deliveryaddress:   cxDestinationAddress(first.Details, firstDistrict),
		Deliverypincode:   firstDistrict.Pincodeprefix,
		Deliverylatitude:  firstDistrict.Centrelatitude,
		Deliverylongitude: firstDistrict.Centrelongitude,
		Deliverycity:      firstDistrict.Districtname,

		Bookingsource:    constants.BookingSourceCustomerApp,
		Pickupsourcetype: constants.PickupSourceCustomer,
		Status:           constants.BookingPendingPickup,

		Preferredpickupfrom: &pickupFromDB,
		Preferredpickupto:   &pickupToDB,

		Slotid:            req.SlotID,
		Customerstage:     constants.CxStageBooked,
		Customerstatus:    constants.CxStatusActive,
		Estimateminrupees: estimateMin,
		Estimatemaxrupees: estimateMax,
		Routekm:           quote.RouteKM,

		Notes: req.Remarks,

		Createdat: now,
		Updatedat: now,
	}

	if pin := cxFirstPin(first.Details); pin != nil {
		booking.Deliverylatitude, booking.Deliverylongitude = pin[0], pin[1]
	}

	tx := db.DB.Begin()
	if err := tx.Create(&booking).Error; err != nil {
		tx.Rollback()
		utils.Error("CreateCxBooking: could not create booking", "customer_id", customerID, "error", err)
		return utils.CxInternal(c)
	}

	for i, d := range req.Destinations {
		code := strings.ToUpper(strings.TrimSpace(d.DistrictCode))
		district := districts[code]
		packages := d.PackageCount
		if packages < 1 {
			packages = 1
		}

		dest := models.BookingDestination{
			Bookingid:    booking.Bookingid,
			Seq:          i,
			Statecode:    district.Statecode,
			Statename:    stateNames[district.Statecode],
			Districtcode: district.Districtcode,
			Districtname: district.Districtname,
			Packagecount: packages,
			Pincode:      district.Pincodeprefix,
			Createdat:    now,
			Updatedat:    now,
		}
		applyCxDetails(&dest, d.Details)

		if err := tx.Create(&dest).Error; err != nil {
			tx.Rollback()
			utils.Error("CreateCxBooking: could not create destination", "booking_id", booking.Bookingid, "error", err)
			return utils.CxInternal(c)
		}

		// One parcel row per package, linked to its destination. The miler
		// weighs and photographs each package at the door, so each needs a row
		// to be weighed into — and each has to know which order it belongs to.
		// Weight is deliberately left at zero: it is never collected from the
		// customer, and a guess here would look like a measurement on the
		// receipt.
		for p := 0; p < packages; p++ {
			parcel := models.BookingParcel{
				Bookingid:            booking.Bookingid,
				Bookingdestinationid: &dest.Bookingdestinationid,
				Itemcategory:         "General",
				Createdat:            now,
				Updatedat:            now,
			}
			if err := tx.Create(&parcel).Error; err != nil {
				tx.Rollback()
				utils.Error("CreateCxBooking: could not create parcel", "booking_id", booking.Bookingid, "error", err)
				return utils.CxInternal(c)
			}
		}
	}

	// The service option is what the REST of the platform reads a booking's
	// value from, and it is not optional just because the customer surface
	// keeps its own estimate columns:
	//
	//   * MilerDeliverConsignment and MilerInwardConsignmentAtHub copy
	//     Estimatedprice onto BookingAssignment.ridercharges when a leg closes,
	//     and GET /miler/earnings sums that column — so with no row here every
	//     customer-app job a rider completes would show ₹0 on their Earnings
	//     screen.
	//   * The admin console's Orders list renders serviceoptions[0].estimatedprice
	//     as the Price column, which would read "N/A" for every customer booking.
	//
	// The midpoint of the band the customer was shown is the honest figure
	// before the miler weighs anything, and it is what lookupDoormilePrice
	// returns everywhere else in this codebase.
	slaDue := cxToDBTime(slotTo.Add(48 * time.Hour))
	estimatedDelivery := cxToDBTime(slotTo.Add(24 * time.Hour))
	srvOption := models.BookingServiceOption{
		Bookingid:           booking.Bookingid,
		Servicetype:         "Normal",
		Estimatedprice:      float64(estimateMin+estimateMax) / 2,
		Estimateddeliveryat: &estimatedDelivery,
		Sladueat:            &slaDue,
		Createdat:           now,
	}
	if err := tx.Create(&srvOption).Error; err != nil {
		tx.Rollback()
		utils.Error("CreateCxBooking: could not create service option", "booking_id", booking.Bookingid, "error", err)
		return utils.CxInternal(c)
	}

	if err := cxstage.Record(tx, cxstage.Event{
		BookingID: booking.Bookingid,
		Stage:     constants.CxStageBooked,
		ActorType: constants.CxActorCustomer,
		ActorID:   &customerID,
		Source:    "POST /customer/bookings",
		At:        now,
	}); err != nil {
		tx.Rollback()
		utils.Error("CreateCxBooking: could not record booked stage", "booking_id", booking.Bookingid, "error", err)
		return utils.CxInternal(c)
	}

	if err := tx.Commit().Error; err != nil {
		utils.Error("CreateCxBooking: commit failed", "customer_id", customerID, "error", err)
		return utils.CxInternal(c)
	}

	// Fire-and-forget, after commit, exactly as the express path does.
	go assignment.AssignCustomerMiler(booking.Bookingid)
	publishCxBookingCreated(&booking, len(req.Destinations))

	return cxRespondWithBooking(c, booking.Bookingid, fiber.StatusCreated)
}

// GetCxBookings backs the Orders tabs, Home's recent list and pull-to-refresh.
func GetCxBookings(c *fiber.Ctx) error {
	customerID := c.Locals("userid").(int)

	limit := cxDefaultPageSize
	if v, err := strconv.Atoi(c.Query("limit")); err == nil && v > 0 {
		limit = v
	}
	if limit > cxMaxPageSize {
		limit = cxMaxPageSize
	}

	// One filter, applied to both the page and the count, so `total` is the size
	// of the tab the customer is actually looking at. Counting every booking
	// they have ever made would put "48" above a Cancelled tab holding two rows.
	status := strings.ToLower(strings.TrimSpace(c.Query("status")))
	scoped := func() *gorm.DB {
		q := db.DB.Model(&models.PickupBooking{}).Where("appcustomerid = ?", customerID)
		switch status {
		case constants.CxStatusActive:
			// Rows written before this surface existed carry no customerstatus.
			// Treating a null as active keeps a live booking visible rather
			// than hiding it from the customer who is waiting on it.
			// Parenthesised explicitly rather than relying on AND binding
			// tighter than OR — the two readings differ by "shows every
			// cancelled booking in the active tab", which is not a thing to
			// leave to operator precedence.
			q = q.Where("(customerstatus = ?) OR ((customerstatus IS NULL OR customerstatus = '') AND status <> ?)",
				constants.CxStatusActive, constants.BookingCancelled)
		case constants.CxStatusCompleted:
			q = q.Where("customerstatus = ?", constants.CxStatusCompleted)
		case constants.CxStatusCancelled:
			q = q.Where("customerstatus = ? OR status = ?", constants.CxStatusCancelled, constants.BookingCancelled)
		}
		return q
	}

	q := scoped()

	// Keyset pagination on the primary key. Offsets drift when a new booking
	// lands mid-scroll, which shows the customer the same row twice.
	if cursor := strings.TrimSpace(c.Query("cursor")); cursor != "" {
		if after, err := strconv.Atoi(cursor); err == nil {
			q = q.Where("bookingid < ?", after)
		}
	}

	var bookings []models.PickupBooking
	if err := q.Order("bookingid DESC").Limit(limit + 1).Find(&bookings).Error; err != nil {
		utils.Error("GetCxBookings: query failed", "customer_id", customerID, "error", err)
		return utils.CxInternal(c)
	}

	var nextCursor *string
	if len(bookings) > limit {
		bookings = bookings[:limit]
		next := strconv.Itoa(bookings[len(bookings)-1].Bookingid)
		nextCursor = &next
	}

	bundle := loadCxBundle(bookings)
	out := make([]fiber.Map, 0, len(bookings))
	for i := range bookings {
		out = append(out, renderCxBooking(&bookings[i], bundle))
	}

	var total int64
	if err := scoped().Count(&total).Error; err != nil {
		utils.Warn("GetCxBookings: count failed, reporting the page size", "customer_id", customerID, "error", err)
		total = int64(len(out))
	}

	return utils.CxList(c, out, int(total), nextCursor)
}

// GetCxBookingDetail is the canonical read — the tracking screen and the
// receipt are both rendered from it, and it is polled while tracking is open.
func GetCxBookingDetail(c *fiber.Ctx) error {
	customerID := c.Locals("userid").(int)
	reference := strings.TrimSpace(c.Params("reference"))

	booking, err := cxLoadBooking(customerID, reference)
	if err != nil {
		return utils.CxNotFound(c, "We could not find that pickup")
	}

	bundle := loadCxBundle([]models.PickupBooking{*booking})
	payload := renderCxBooking(booking, bundle)

	// Polled every few seconds while the tracking screen is open. A 304 turns
	// most of those polls into a header exchange instead of a full render.
	if served := serveIfNotModified(c, payload); served {
		return nil
	}
	c.Set("Cache-Control", "no-cache")
	return utils.CxOK(c, payload)
}

// GetCxOrder returns one order by tracking number, for push deep links.
//
// It answers with the whole booking object rather than a slimmer order shape —
// the client already parses this one, and a second shape for the same data is
// a second parser to keep in step.
func GetCxOrder(c *fiber.Ctx) error {
	customerID := c.Locals("userid").(int)
	trackingID := strings.TrimSpace(c.Params("trackingId"))
	if trackingID == "" {
		return utils.CxNotFound(c, "We could not find that order")
	}

	var dest models.BookingDestination
	if err := db.DB.Where("trackingno = ?", trackingID).First(&dest).Error; err != nil {
		return utils.CxNotFound(c, "We could not find that order")
	}

	var booking models.PickupBooking
	if err := db.DB.Where("bookingid = ? AND appcustomerid = ?", dest.Bookingid, customerID).
		First(&booking).Error; err != nil {
		// The tracking number exists but belongs to someone else. Answered as
		// not-found rather than forbidden: confirming that a tracking number is
		// real tells an enumerating caller something they should not learn.
		return utils.CxNotFound(c, "We could not find that order")
	}

	bundle := loadCxBundle([]models.PickupBooking{booking})
	return utils.CxOK(c, renderCxBooking(&booking, bundle))
}

// CancelCxBooking cancels the whole pickup.
//
// Allowed through arrived and refused from picked_up onward. `cancellable` on
// the booking mirrors the same policy so the UI can hide the button, but this
// re-checks — the button state is a hint the client renders from a response
// that may be seconds old, never the authority.
func CancelCxBooking(c *fiber.Ctx) error {
	customerID := c.Locals("userid").(int)
	reference := strings.TrimSpace(c.Params("reference"))

	var req struct {
		Reason string `json:"reason"`
	}
	_ = c.BodyParser(&req)

	booking, err := cxLoadBooking(customerID, reference)
	if err != nil {
		return utils.CxNotFound(c, "We could not find that pickup")
	}

	if booking.Customerstatus == constants.CxStatusCancelled ||
		booking.Status == constants.BookingCancelled {
		// Already cancelled. Answered as success rather than as a conflict: the
		// customer asked for a state the booking is already in, and a retry
		// over a flaky network must not read as a failure.
		return utils.CxOK(c, fiber.Map{
			"reference":    booking.Bookingno,
			"status":       constants.CxStatusCancelled,
			"cancelReason": booking.Cancelreason,
		})
	}

	stage := booking.Customerstage
	if stage == "" {
		stage = deriveStageFromStatus(booking)
	}
	if !constants.CxCancellable(stage) {
		return utils.CxConflict(c, "This pickup can no longer be cancelled")
	}

	reason := strings.TrimSpace(req.Reason)

	tx := db.DB.Begin()
	if err := cxstage.Cancel(tx, booking.Bookingid, reason,
		constants.CxActorCustomer, &customerID, "POST /customer/bookings/{reference}/cancel"); err != nil {
		tx.Rollback()
		utils.Error("CancelCxBooking: cancel failed", "booking_id", booking.Bookingid, "error", err)
		return utils.CxInternal(c)
	}

	// Release the rider. Without this the assignment stays open, the rider
	// keeps a stop they must not attempt, and MilerEndDuty refuses to let them
	// go off duty while any assignment is still Assigned or Accepted.
	if err := tx.Model(&models.BookingAssignment{}).
		Where("bookingid = ? AND assignmentstatus IN ?", booking.Bookingid,
			[]string{constants.AssignmentAssigned, constants.AssignmentAccepted}).
		Updates(map[string]interface{}{
			"assignmentstatus": constants.AssignmentCancelled,
			"remarks":          "cancelled by customer",
		}).Error; err != nil {
		tx.Rollback()
		utils.Error("CancelCxBooking: could not release assignment", "booking_id", booking.Bookingid, "error", err)
		return utils.CxInternal(c)
	}
	if booking.Assignedmileruserid != nil {
		if err := tx.Model(&models.MilerProfile{}).
			Where("userid = ? AND availabilitystatus IN ?", *booking.Assignedmileruserid,
				[]string{constants.MilerAssigned, constants.MilerOnPickup, constants.MilerAtCustomer}).
			Update("availabilitystatus", constants.MilerAvailable).Error; err != nil {
			tx.Rollback()
			utils.Error("CancelCxBooking: could not free the rider", "booking_id", booking.Bookingid, "error", err)
			return utils.CxInternal(c)
		}
	}

	if err := tx.Commit().Error; err != nil {
		utils.Error("CancelCxBooking: commit failed", "booking_id", booking.Bookingid, "error", err)
		return utils.CxInternal(c)
	}

	publishCxBookingCancelled(booking, reason)

	return utils.CxOK(c, fiber.Map{
		"reference":    booking.Bookingno,
		"status":       constants.CxStatusCancelled,
		"cancelReason": reason,
	})
}

// PatchCxDestination fills in the parts of an address the customer left out.
//
// Accepted until the parcels are collected. After that the shipment's addresses
// are frozen on the consignment and an edit here would change what the customer
// sees without changing where the parcel is going — which is worse than
// refusing.
//
// Writes land on the same booking row the miler app reads addresses from, so a
// correction made while the rider is on their way reaches them.
func PatchCxDestination(c *fiber.Ctx) error {
	customerID := c.Locals("userid").(int)
	reference := strings.TrimSpace(c.Params("reference"))

	index, err := strconv.Atoi(c.Params("index"))
	if err != nil || index < 0 {
		return utils.CxNotFound(c, "We could not find that destination")
	}

	booking, err := cxLoadBooking(customerID, reference)
	if err != nil {
		return utils.CxNotFound(c, "We could not find that pickup")
	}

	stage := booking.Customerstage
	if stage == "" {
		stage = deriveStageFromStatus(booking)
	}
	if constants.CxStageRank(stage) >= constants.CxStageOrder[constants.CxStagePickedUp] {
		return utils.CxConflict(c, "Your packages have been collected — these details can no longer be changed")
	}
	if booking.Customerstatus == constants.CxStatusCancelled || booking.Status == constants.BookingCancelled {
		return utils.CxConflict(c, "This pickup was cancelled")
	}

	var dest models.BookingDestination
	if err := db.DB.Where("bookingid = ? AND seq = ?", booking.Bookingid, index).
		First(&dest).Error; err != nil {
		return utils.CxNotFound(c, "We could not find that destination")
	}

	var req cxDetailsInput
	if err := c.BodyParser(&req); err != nil {
		return utils.CxBadRequest(c, "We could not read that request")
	}

	applyCxDetails(&dest, &req)
	dest.Updatedat = utils.DBNow()

	tx := db.DB.Begin()
	if err := tx.Save(&dest).Error; err != nil {
		tx.Rollback()
		utils.Error("PatchCxDestination: save failed", "destination_id", dest.Bookingdestinationid, "error", err)
		return utils.CxInternal(c)
	}

	// Destination 0 mirrors onto the booking's flat delivery columns, which is
	// where the miler app and the routing code look. An edit that only landed
	// on bookingdestinations would be invisible to the rider standing at the
	// door, which is precisely who it was made for.
	if dest.Seq == 0 {
		updates := map[string]interface{}{
			"deliveryaddress": cxDestinationAddressFromRow(&dest),
			"updatedat":       utils.DBNow(),
		}
		if dest.Pinlatitude != nil && dest.Pinlongitude != nil {
			updates["deliverylatitude"] = *dest.Pinlatitude
			updates["deliverylongitude"] = *dest.Pinlongitude
		}
		if err := tx.Model(&models.PickupBooking{}).
			Where("bookingid = ?", booking.Bookingid).Updates(updates).Error; err != nil {
			tx.Rollback()
			utils.Error("PatchCxDestination: could not mirror onto booking", "booking_id", booking.Bookingid, "error", err)
			return utils.CxInternal(c)
		}
	}

	if err := tx.Commit().Error; err != nil {
		utils.Error("PatchCxDestination: commit failed", "booking_id", booking.Bookingid, "error", err)
		return utils.CxInternal(c)
	}

	return cxRespondWithBooking(c, booking.Bookingid, fiber.StatusOK)
}

// ── Helpers ──────────────────────────────────────────────────────────────────

// cxLoadBooking finds a booking by its customer-facing reference, scoped to the
// caller. Ownership is part of the lookup, not a check afterwards — a query
// that can return someone else's row is one forgotten `if` away from leaking it.
func cxLoadBooking(customerID int, reference string) (*models.PickupBooking, error) {
	if reference == "" {
		return nil, gorm.ErrRecordNotFound
	}
	var booking models.PickupBooking
	if err := db.DB.Where("bookingno = ? AND appcustomerid = ?", reference, customerID).
		First(&booking).Error; err != nil {
		return nil, err
	}
	return &booking, nil
}

// cxRespondWithBooking re-reads and renders, so a create or a patch answers in
// exactly the shape a later GET will.
func cxRespondWithBooking(c *fiber.Ctx, bookingID, status int) error {
	var booking models.PickupBooking
	if err := db.DB.First(&booking, bookingID).Error; err != nil {
		utils.Error("cxRespondWithBooking: reload failed", "booking_id", bookingID, "error", err)
		return utils.CxInternal(c)
	}
	bundle := loadCxBundle([]models.PickupBooking{booking})
	payload := renderCxBooking(&booking, bundle)
	if status == fiber.StatusCreated {
		return utils.CxCreated(c, payload)
	}
	return utils.CxOK(c, payload)
}

// applyCxDetails writes only the fields actually present in the request. An
// omitted key leaves the stored value alone; an explicit null clears it, which
// is how the customer removes a landmark they no longer want the rider to use.
func applyCxDetails(dest *models.BookingDestination, in *cxDetailsInput) {
	if in == nil {
		return
	}
	if in.Street != nil {
		dest.Street = strings.TrimSpace(*in.Street)
	}
	if in.Building != nil {
		dest.Building = strings.TrimSpace(*in.Building)
	}
	if in.Landmark != nil {
		dest.Landmark = strings.TrimSpace(*in.Landmark)
	}
	if in.RecipientName != nil {
		dest.Recipientname = strings.TrimSpace(*in.RecipientName)
	}
	if in.RecipientPhone != nil {
		if phone, _, ok := normalizePhone(*in.RecipientPhone); ok {
			dest.Recipientphone = phone
		} else {
			dest.Recipientphone = strings.TrimSpace(*in.RecipientPhone)
		}
	}
	if in.Instructions != nil {
		dest.Instructions = strings.TrimSpace(*in.Instructions)
	}
	if in.Pin != nil {
		lat, lng := in.Pin.Lat, in.Pin.Lng
		if lat == 0 && lng == 0 {
			dest.Pinlatitude, dest.Pinlongitude = nil, nil
		} else {
			dest.Pinlatitude, dest.Pinlongitude = &lat, &lng
		}
	}
	if in.CodAmount != nil {
		dest.Codamount = *in.CodAmount
	}
}

func cxFirstPin(in *cxDetailsInput) *[2]float64 {
	if in == nil || in.Pin == nil {
		return nil
	}
	if in.Pin.Lat == 0 && in.Pin.Lng == 0 {
		return nil
	}
	return &[2]float64{in.Pin.Lat, in.Pin.Lng}
}

// cxDestinationAddress builds the flat address string the rest of the system
// stores, from whatever the customer supplied. It always resolves to something
// non-empty — pickupbookings.deliveryaddress is NOT NULL, and a booking with
// only a state and a district is a legitimate booking.
func cxDestinationAddress(in *cxDetailsInput, district models.ServiceableDistrict) string {
	parts := []string{}
	if in != nil {
		if in.Building != nil {
			parts = append(parts, *in.Building)
		}
		if in.Street != nil {
			parts = append(parts, *in.Street)
		}
		if in.Landmark != nil {
			parts = append(parts, *in.Landmark)
		}
	}
	parts = append(parts, district.Districtname)
	address := joinNonEmpty(", ", parts...)
	if address == "" {
		return district.Districtcode
	}
	return address
}

func cxDestinationAddressFromRow(d *models.BookingDestination) string {
	address := joinNonEmpty(", ", d.Building, d.Street, d.Landmark, d.Districtname)
	if address == "" {
		return d.Districtcode
	}
	return address
}

// cxStateNames resolves display names for the states a set of districts belong
// to, in one query.
func cxStateNames(districts []models.ServiceableDistrict) (map[string]string, error) {
	codes := make([]string, 0, len(districts))
	seen := map[string]bool{}
	for _, d := range districts {
		if d.Statecode != "" && !seen[d.Statecode] {
			seen[d.Statecode] = true
			codes = append(codes, d.Statecode)
		}
	}
	names := make(map[string]string, len(codes))
	if len(codes) == 0 {
		return names, nil
	}
	var states []models.ServiceableState
	if err := db.DB.Where("statecode IN ?", codes).Find(&states).Error; err != nil {
		return names, err
	}
	for _, s := range states {
		names[s.Statecode] = s.Statename
	}
	return names, nil
}

// cxToDBTime converts an IST wall clock into the shape this database stores —
// the same digits, tagged UTC so the driver writes them verbatim. See
// utils.DBNow: comparing a container's UTC clock against IST-stamped rows is
// what made date-range reports undercount.
func cxToDBTime(t time.Time) time.Time {
	ist := t.In(utils.ISTLocation())
	return time.Date(ist.Year(), ist.Month(), ist.Day(), ist.Hour(), ist.Minute(), ist.Second(), 0, time.UTC)
}

// ── Events ───────────────────────────────────────────────────────────────────

// publishCxBookingCreated and publishCxBookingCancelled mirror the existing
// booking events onto NATS. Best-effort and nil-checked, like every other
// publish in this codebase: the event bus is never allowed to fail a booking.
func publishCxBookingCreated(b *models.PickupBooking, destinationCount int) {
	if db.Js == nil {
		return
	}
	payload := map[string]interface{}{
		"booking_id":        b.Bookingid,
		"booking_no":        b.Bookingno,
		"customer_id":       b.Appcustomerid,
		"pickup_address":    b.Pickupaddress,
		"pickup_pincode":    b.Pickuppincode,
		"destination_count": destinationCount,
		"slot_id":           b.Slotid,
		"status":            constants.BookingPendingPickup,
		"created_at":        utils.EpochMillis(b.Createdat),
	}
	data, err := json.Marshal(payload)
	if err != nil {
		return
	}
	if _, err := db.Js.Publish("api.v1.bookings.create", data); err != nil {
		utils.Warn("Failed to publish booking.create to NATS", "booking_id", b.Bookingid, "error", err)
	}
}

func publishCxBookingCancelled(b *models.PickupBooking, reason string) {
	if db.Js == nil {
		return
	}
	payload := map[string]interface{}{
		"booking_id":   b.Bookingid,
		"booking_no":   b.Bookingno,
		"customer_id":  b.Appcustomerid,
		"status":       "Cancelled",
		"reason":       reason,
		"cancelled_at": time.Now().UnixMilli(),
	}
	data, err := json.Marshal(payload)
	if err != nil {
		return
	}
	if _, err := db.Js.Publish("api.v1.bookings.cancel", data); err != nil {
		utils.Warn("Failed to publish booking.cancel to NATS", "booking_id", b.Bookingid, "error", err)
	}
}