package handlers

import (
	"errors"
	"net/http"

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

// HandleSourceDelete handles webhook deletion.
func (h *Handlers) HandleSourceDelete() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		userID, ok := h.getUserID(r)
		if !ok {
			http.Redirect(
				w, r, "/pages/login", http.StatusSeeOther,
			)

			return
		}

		sourceID := chi.URLParam(r, "sourceID")

		var webhook database.Webhook

		err := h.db.DB().Where(
			"id = ? AND user_id = ?", sourceID, userID,
		).First(&webhook).Error
		if err != nil {
			h.renderError(w, r, http.StatusNotFound)

			return
		}

		h.deleteWebhookResources(w, r, webhook, userID)
	}
}

// The messages deleteWebhookResources logs when a file of the event
// database cannot be removed: the database file itself, or only a
// sidecar once the database file is gone.
const (
	eventDBLeftMsg = "webhook deleted, but its event database file is " +
		"still on disk; remove it by hand"
	sidecarLeftMsg = "webhook deleted and its events are gone, but a " +
		"-wal or -shm sidecar of its event database is " +
		"still on disk; remove it by hand"
)

// deleteWebhookResources soft-deletes config and hard-deletes
// the per-webhook event database.
func (h *Handlers) deleteWebhookResources(
	w http.ResponseWriter,
	r *http.Request,
	webhook database.Webhook,
	userID string,
) {
	// The configuration delete commits before the event database
	// is touched. No transaction spans the main database and the
	// filesystem, so one side has to go first: committing the
	// configuration first means a later failure leaves an unused
	// event database file on disk, while removing the event
	// database first would mean a failed commit destroys the
	// history of a webhook that still exists. A leftover file can
	// be removed by hand; deleted history cannot be recovered.
	err := h.commitWebhookDeletion(&webhook)
	if err != nil {
		h.serverError(w, r, "failed to delete webhook", err)

		return
	}

	h.log.Info(
		"webhook deleted",
		"webhook_id", webhook.ID,
		"user_id", userID,
	)

	// Release the delivery engine's per-webhook archiving state
	// so a deleted webhook's archive writer (and any handle open
	// within its debounce window) does not linger for the
	// process lifetime. The archive file itself is deliberately
	// left on disk; see evictArchiveWriter.
	h.evictArchiveWriter(webhook.ID)

	err = h.dbMgr.DeleteDB(webhook.ID)
	if err != nil {
		// The configuration is committed, so the webhook is gone,
		// but a file of its event database is still on disk with
		// nothing referencing it. Report the failure rather than
		// redirecting as though everything succeeded: the file
		// needs removing by hand, and the logged error names it.
		// When only a sidecar is left, the events are already
		// gone, and the message must not suggest they survive.
		msg := eventDBLeftMsg
		if errors.Is(err, database.ErrSidecarNotRemoved) {
			msg = sidecarLeftMsg
		}

		h.serverError(w, r, msg, err)

		return
	}

	http.Redirect(
		w, r, withNotice("/hooks", webhookDeleted), http.StatusSeeOther,
	)
}

// commitWebhookDeletion soft-deletes a webhook's entrypoints,
// targets and the webhook row in one transaction. Every
// statement is checked and any failure rolls the whole
// transaction back, so a caller that gets an error knows the
// configuration is untouched and the event database must be
// left alone.
func (h *Handlers) commitWebhookDeletion(
	webhook *database.Webhook,
) error {
	tx := h.db.DB().Begin()
	if tx.Error != nil {
		return tx.Error
	}

	err := tx.Where(
		"webhook_id = ?", webhook.ID,
	).Delete(&database.Entrypoint{}).Error
	if err != nil {
		tx.Rollback()

		return err
	}

	err = tx.Where(
		"webhook_id = ?", webhook.ID,
	).Delete(&database.Target{}).Error
	if err != nil {
		tx.Rollback()

		return err
	}

	err = tx.Delete(webhook).Error
	if err != nil {
		tx.Rollback()

		return err
	}

	return tx.Commit().Error
}

// evictArchiveWriter asks the delivery engine to drop the cached
// archive writers of a webhook's database targets, closing their
// archive file handles.
//
// The archive database files are NOT deleted. Unlike the event
// database — which is per-webhook working storage and is
// hard-deleted with the webhook — an archive is explicitly
// long-term storage that an operator may want to keep or move
// away for offline retention. Destroying it as a side effect of
// deleting a webhook would be a surprising and unrecoverable
// data loss, so the file is left for the operator to handle.
func (h *Handlers) evictArchiveWriter(webhookID string) {
	if h.archives == nil {
		return
	}

	h.archives.EvictWebhook(webhookID)
}