package handlers

import (
	"net/http"

	"github.com/go-chi/chi"
	"gorm.io/gorm"
	"sneak.berlin/go/webhooker/internal/database"
)

// The outcomes of a replay POST, as the notice codes its redirect
// carries. noticeFor holds the line each one shows.
const (
	// replayQueued reports that a new delivery was created and handed
	// to the delivery engine.
	replayQueued noticeCode = "replay-queued"

	// replayTargetDeleted reports a target that once existed and has
	// since been deleted. Deletes are soft and deliveries carry no
	// foreign key to the target row, so the history survives its
	// target and this is the ordinary case for an old event. The
	// event log shows no Replay button for such a delivery, so only
	// a page loaded before the delete reaches this.
	replayTargetDeleted noticeCode = "replay-target-deleted"

	// replayTargetMissing reports a target id that names no row at
	// all, deleted or otherwise.
	replayTargetMissing noticeCode = "replay-target-missing"

	// replayTargetInactive reports a target the operator has
	// deactivated. A deactivated target receives no new deliveries, so
	// a replay to it would be a delivery they switched off.
	replayTargetInactive noticeCode = "replay-target-inactive"

	// replayNotTerminal reports a delivery the engine has not finished
	// with.
	replayNotTerminal noticeCode = "replay-not-terminal"

	// replayInFlight reports that an earlier replay of this event to
	// this target is still running.
	replayInFlight noticeCode = "replay-in-flight"
)

// HandleDeliveryReplay re-sends a finished delivery's event to its
// target.
//
// A replay never touches the delivery it repeats. The delivery engine
// creates a NEW pending delivery row for the same event and target and
// queues it as it queues the receiver's, so the original's status,
// attempts and timestamps stand as the record of what actually
// happened, and the replay is retried, SSRF-guarded and circuit-broken
// exactly as a first attempt is.
//
// What is re-sent is the stored EVENT body, never the response the
// original delivery received.
//
// The target's configuration is read now rather than as it stood when
// the original ran: a replay exists to deliver where the operator
// currently wants the event to go. That is also why a deleted target
// is refused rather than delivered to from stale configuration.
func (h *Handlers) HandleDeliveryReplay() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		webhook, ok := h.ownedWebhook(w, r)
		if !ok {
			return
		}

		// The body size cap is enforced by the MaxBodySize
		// middleware, which runs before CSRF parses the form.
		err := r.ParseForm()
		if err != nil {
			h.renderError(w, r, http.StatusBadRequest)

			return
		}

		h.replayDelivery(w, r, webhook)
	}
}

// replayDelivery performs the replay for a webhook the caller has
// already established the session's user owns.
func (h *Handlers) replayDelivery(
	w http.ResponseWriter,
	r *http.Request,
	webhook database.Webhook,
) {
	if !h.dbMgr.DBExists(webhook.ID) {
		h.renderError(w, r, http.StatusNotFound)

		return
	}

	webhookDB, err := h.dbMgr.GetDB(webhook.ID)
	if err != nil {
		h.serverError(w, r, "failed to get webhook database", err)

		return
	}

	original, ok := h.loadReplaySource(w, r, webhookDB)
	if !ok {
		return
	}

	if !original.Status.Terminal() {
		redirectToEventLog(w, r, webhook, replayNotTerminal)

		return
	}

	target, code := h.replayTarget(webhook.ID, original.TargetID)
	if target == nil {
		redirectToEventLog(w, r, webhook, code)

		return
	}

	h.queueReplay(w, r, webhookDB, webhook, original, target)
}

// loadReplaySource loads the delivery to be replayed, selecting only
// the columns the replay needs so no association is populated. A
// delivery id that names no row in this webhook's database is a 404.
func (h *Handlers) loadReplaySource(
	w http.ResponseWriter,
	r *http.Request,
	webhookDB *gorm.DB,
) (*database.Delivery, bool) {
	var original database.Delivery

	err := webhookDB.
		Select("id", "event_id", "target_id", "status").
		First(
			&original, "id = ?", chi.URLParam(r, "deliveryID"),
		).Error
	if err != nil {
		h.renderError(w, r, http.StatusNotFound)

		return nil, false
	}

	return &original, true
}

// queueReplay has the delivery engine create and queue the new
// delivery, unless an earlier replay is still in flight.
func (h *Handlers) queueReplay(
	w http.ResponseWriter,
	r *http.Request,
	webhookDB *gorm.DB,
	webhook database.Webhook,
	original *database.Delivery,
	target *database.Target,
) {
	inFlight, err := countInFlightDeliveries(
		webhookDB, original.EventID, target.ID,
	)
	if err != nil {
		h.serverError(
			w, r, "failed to count in-flight deliveries", err,
		)

		return
	}

	if inFlight > 0 {
		redirectToEventLog(w, r, webhook, replayInFlight)

		return
	}

	deliveryID, err := h.engine.CreateReplay(
		webhook.ID, original.EventID, target,
	)
	if err != nil {
		h.serverError(
			w, r, "failed to create replay delivery", err,
		)

		return
	}

	h.mtr.DeliveryReplayed(target.Type)

	h.log.Info(
		"delivery replay queued",
		"webhook_id", webhook.ID,
		"event_id", original.EventID,
		"target_id", target.ID,
		"replayed_delivery_id", original.ID,
		"delivery_id", deliveryID,
	)

	redirectToEventLog(w, r, webhook, replayQueued)
}

// replayTarget loads the delivery's target as it stands now.
//
// The load is Unscoped so that a soft-deleted row is still found:
// deletes are soft and a delivery carries no foreign key to its
// target, so a target's history outlives it, and without the deleted
// row there is no way to tell "you deleted this target" from "this id
// never named anything". A nil target means the replay is refused,
// with the returned code saying why.
func (h *Handlers) replayTarget(
	webhookID, targetID string,
) (*database.Target, noticeCode) {
	var target database.Target

	err := h.db.DB().Unscoped().Where(
		"id = ? AND webhook_id = ?", targetID, webhookID,
	).First(&target).Error
	if err != nil {
		return nil, replayTargetMissing
	}

	if target.DeletedAt.Valid {
		return nil, replayTargetDeleted
	}

	if !target.Active {
		return nil, replayTargetInactive
	}

	return &target, replayQueued
}

// countInFlightDeliveries reports how many deliveries of this event to
// this target the engine has not finished.
//
// It is the replay-storm guard: a replay is refused while an earlier
// one is still pending or retrying, so a held-down button or a scripted
// loop cannot stack copies of work already queued. It is a check and
// not a lock, so two simultaneous POSTs can still both pass it; the
// per-client rate limit on the route is what bounds that.
func countInFlightDeliveries(
	webhookDB *gorm.DB, eventID, targetID string,
) (int64, error) {
	var count int64

	err := webhookDB.Model(&database.Delivery{}).Where(
		"event_id = ? AND target_id = ? AND status IN ?",
		eventID, targetID,
		[]database.DeliveryStatus{
			database.DeliveryStatusPending,
			database.DeliveryStatusRetrying,
		},
	).Count(&count).Error

	return count, err
}

// redirectToEventLog redirects a replay or resubmit back to the event
// log it was triggered from, carrying the outcome as its notice. A
// Replay form carries the list it was pressed in as show, so a replay
// returns to the Failed or Pending list; a Resubmit form carries none,
// so a resubmit returns to the full log, where its new event is the
// newest.
func redirectToEventLog(
	w http.ResponseWriter,
	r *http.Request,
	webhook database.Webhook,
	code noticeCode,
) {
	location := withNotice("/hook/"+webhook.ID+"/events", code)

	show := r.PostFormValue(showParam)
	if eventLogStatuses(show) != nil {
		location += "&" + showParam + "=" + show
	}

	http.Redirect( //nolint:gosec // show is checked by eventLogStatuses
		w, r, location, http.StatusSeeOther,
	)
}