package handlers

import (
	"net/http"
	"strconv"
	"time"

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

// recentEventColumns is the recent events list's projection. It
// reads the body's size and never the body itself, for the reason
// maxRenderedBodyBytes gives; the cast to blob makes length count
// bytes rather than characters.
const recentEventColumns = "id, created_at, method, content_type, " +
	"resubmitted_from_id, length(cast(body as blob)) AS body_bytes"

// RecentEventView is one row of the recent events list on a
// webhook's page.
type RecentEventView struct {
	Method      string
	ContentType string

	// ResubmittedFromID names the event this one was copied from,
	// empty for an event that arrived on the receiver.
	ResubmittedFromID string

	// Received is how long ago the event arrived, and ReceivedUTC
	// the full timestamp the page shows on hover.
	Received    string
	ReceivedUTC string

	// Size is the size of the stored body.
	Size string

	// ProcessingTime is how long the event's slowest delivery
	// took; see processingTime.
	ProcessingTime string

	// Status is what the webhook's HTTP target answered, and
	// StatusClass its colour; see targetStatus. Both are empty
	// unless the webhook has exactly one HTTP target.
	Status      string
	StatusClass string
}

// recentEventRow is one row of recentEventColumns.
type recentEventRow struct {
	ID                string
	CreatedAt         time.Time
	Method            string
	ContentType       string
	ResubmittedFromID *string
	BodyBytes         uint64
}

// singleHTTPTargetID returns the ID of the webhook's HTTP target
// when it has exactly one, and "" when it has none or several.
func singleHTTPTargetID(targets []database.Target) string {
	id := ""
	count := 0

	for i := range targets {
		if targets[i].Type == database.TargetTypeHTTP {
			id = targets[i].ID
			count++
		}
	}

	if count != 1 {
		return ""
	}

	return id
}

// loadRecentEvents loads the webhook's recentEventLimit newest
// events for its page, newest first. statusTargetID is the
// webhook's only HTTP target, or "" when the list shows no status.
func (h *Handlers) loadRecentEvents(
	webhookDB *gorm.DB, webhookID, statusTargetID string,
) ([]RecentEventView, error) {
	var rows []recentEventRow

	err := webhookDB.Model(&database.Event{}).
		Select(recentEventColumns).
		Where("webhook_id = ?", webhookID).
		Order("created_at DESC").
		Limit(recentEventLimit).
		Find(&rows).Error
	if err != nil {
		return nil, err
	}

	eventIDs := make([]string, len(rows))
	for i := range rows {
		eventIDs[i] = rows[i].ID
	}

	// Oldest first, so an event's last delivery to a target is its
	// newest: a replay adds a delivery rather than changing the
	// earlier one.
	var deliveries []database.Delivery

	err = webhookDB.
		Select("id, event_id, target_id, status, created_at").
		Where("event_id IN ?", eventIDs).
		Order("created_at ASC").
		Find(&deliveries).Error
	if err != nil {
		return nil, err
	}

	byEvent := make(map[string][]database.Delivery, len(rows))
	deliveryIDs := make([]string, len(deliveries))

	for i := range deliveries {
		eventID := deliveries[i].EventID
		byEvent[eventID] = append(byEvent[eventID], deliveries[i])
		deliveryIDs[i] = deliveries[i].ID
	}

	attempts, err := h.loadDeliveryResults(webhookDB, deliveryIDs)
	if err != nil {
		return nil, err
	}

	views := make([]RecentEventView, len(rows))
	for i := range rows {
		views[i] = rows[i].view(
			byEvent[rows[i].ID], attempts, statusTargetID,
		)
	}

	return views, nil
}

// view projects a loaded row for rendering. deliveries is the
// event's deliveries, oldest first, and attempts their recorded
// attempts keyed by delivery ID.
func (r *recentEventRow) view(
	deliveries []database.Delivery,
	attempts map[string][]deliveryResultRow,
	statusTargetID string,
) RecentEventView {
	v := RecentEventView{
		Method:         r.Method,
		ContentType:    r.ContentType,
		Received:       humanize.Time(r.CreatedAt),
		ReceivedUTC:    r.CreatedAt.UTC().Format(time.DateTime) + " UTC",
		Size:           humanize.Bytes(r.BodyBytes),
		ProcessingTime: processingTime(deliveries, attempts),
	}

	if r.ResubmittedFromID != nil {
		v.ResubmittedFromID = *r.ResubmittedFromID
	}

	if statusTargetID != "" {
		v.Status, v.StatusClass = targetStatus(
			deliveries, attempts, statusTargetID,
		)
	}

	return v
}

// processingTime is how long the event's slowest delivery took,
// from being queued to its last recorded attempt, time spent
// waiting between retries included. A delivery is queued when its
// event is received, or when an operator replays it, so a replay
// is timed from the replay rather than from the event's arrival.
// It is "in progress" while any delivery is pending or retrying,
// and empty for an event with no deliveries.
func processingTime(
	deliveries []database.Delivery,
	attempts map[string][]deliveryResultRow,
) string {
	if len(deliveries) == 0 {
		return ""
	}

	var slowest time.Duration

	for i := range deliveries {
		if !deliveries[i].Status.Terminal() {
			return "in progress"
		}

		tries := attempts[deliveries[i].ID]
		if len(tries) == 0 {
			continue
		}

		last := tries[len(tries)-1].CreatedAt
		slowest = max(slowest, last.Sub(deliveries[i].CreatedAt))
	}

	return slowest.Round(time.Millisecond).String()
}

// targetStatus is what the target answered for the event, and the
// colour to show it in: the HTTP status code of the last attempt of
// the event's newest delivery to the target. Without a code it is
// "no response" when that attempt failed before a response
// arrived, the delivery's status ("pending") before any attempt,
// and "not sent" when the event has no delivery to the target.
func targetStatus(
	deliveries []database.Delivery,
	attempts map[string][]deliveryResultRow,
	targetID string,
) (string, string) {
	newest := -1

	for i := range deliveries {
		if deliveries[i].TargetID == targetID {
			newest = i
		}
	}

	if newest < 0 {
		return "not sent", "text-gray-400"
	}

	tries := attempts[deliveries[newest].ID]
	if len(tries) == 0 {
		return string(deliveries[newest].Status), "text-gray-400"
	}

	code := tries[len(tries)-1].StatusCode

	switch {
	case code == 0:
		return "no response", "text-red-600"
	case code >= http.StatusInternalServerError:
		return strconv.Itoa(code), "text-red-600"
	case code >= http.StatusBadRequest:
		return strconv.Itoa(code), "text-yellow-600"
	case code >= http.StatusMultipleChoices:
		return strconv.Itoa(code), "text-gray-500"
	case code >= http.StatusOK:
		return strconv.Itoa(code), "text-green-600"
	default:
		return strconv.Itoa(code), "text-gray-500"
	}
}