package api

import (
	"encoding/json"
	"net/http"
	"sort"
	"strconv"

	"github.com/go-chi/chi/v5"

	"smartrun/backend/internal/store"
)

// defaultReviewQueuePageSize matches the frontend's initial/incremental
// page size for its infinite-scroll list.
const defaultReviewQueuePageSize = 10

type reviewQueueItem struct {
	store.KindAssignment
	Activity store.Activity `json:"activity"`
	Laps     []store.Lap    `json:"laps"`
	Samples  []store.Sample `json:"samples"`
}

// handleReviewQueue is cursor-paginated: fetching every needs_review
// activity's laps and (especially) per-second samples is expensive once
// there are many of them, so that work only happens for the requested page,
// not the full backlog. Sorting/cursor filtering still needs each
// activity's summary row (a cheap indexed lookup, no laps/samples), which
// happens for the whole backlog -- only the heavy per-item fetches are
// deferred to the page actually being returned.
func (s *Server) handleReviewQueue(w http.ResponseWriter, r *http.Request) {
	limit := defaultReviewQueuePageSize
	if v := r.URL.Query().Get("limit"); v != "" {
		if n, err := strconv.Atoi(v); err == nil && n > 0 {
			limit = n
		}
	}
	cursor := r.URL.Query().Get("before") // activity StartTimeUTC of the last item on the previous page

	queue, err := s.DB.ReviewQueue(r.Context())
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}

	type withActivity struct {
		assignment store.KindAssignment
		activity   store.Activity
	}
	all := make([]withActivity, 0, len(queue))
	for _, a := range queue {
		activity, ok, err := s.DB.GetActivity(r.Context(), a.ActivityID)
		if err != nil {
			writeError(w, http.StatusInternalServerError, err.Error())
			return
		}
		if !ok {
			continue
		}
		all = append(all, withActivity{assignment: a, activity: activity})
	}

	// Most recent run first, by when the activity actually happened (not
	// when the rule engine flagged it), so the queue reads like a log.
	sort.Slice(all, func(i, j int) bool {
		return all[i].activity.StartTimeUTC > all[j].activity.StartTimeUTC
	})

	total := len(all)

	if cursor != "" {
		idx := 0
		for idx < len(all) && all[idx].activity.StartTimeUTC >= cursor {
			idx++
		}
		all = all[idx:]
	}
	hasMore := len(all) > limit
	if len(all) > limit {
		all = all[:limit]
	}

	items := make([]reviewQueueItem, 0, len(all))
	for _, wa := range all {
		laps, err := s.DB.LapsForActivity(r.Context(), wa.assignment.ActivityID)
		if err != nil {
			writeError(w, http.StatusInternalServerError, err.Error())
			return
		}
		// Per-second telemetry, not just per-lap averages, so the chart can
		// show real within-lap variation instead of one flat segment per lap
		// (most activities only have a handful of laps).
		samples, err := s.DB.SamplesForActivity(r.Context(), wa.assignment.ActivityID)
		if err != nil {
			writeError(w, http.StatusInternalServerError, err.Error())
			return
		}
		items = append(items, reviewQueueItem{KindAssignment: wa.assignment, Activity: wa.activity, Laps: laps, Samples: samples})
	}

	var nextCursor *string
	if hasMore && len(items) > 0 {
		c := items[len(items)-1].Activity.StartTimeUTC
		nextCursor = &c
	}

	writeJSON(w, http.StatusOK, map[string]any{
		"items":       items,
		"next_cursor": nextCursor,
		"total":       total,
	})
}

func (s *Server) handleResolveReview(w http.ResponseWriter, r *http.Request) {
	activityID, err := strconv.ParseInt(chi.URLParam(r, "activityID"), 10, 64)
	if err != nil {
		writeError(w, http.StatusBadRequest, "invalid activity id")
		return
	}

	var body struct {
		WorkoutKindID int64 `json:"workout_kind_id"`
	}
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
		writeError(w, http.StatusBadRequest, "invalid request body")
		return
	}
	if body.WorkoutKindID == 0 {
		writeError(w, http.StatusBadRequest, "workout_kind_id is required")
		return
	}

	kind, ok, err := s.DB.GetWorkoutKind(r.Context(), body.WorkoutKindID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	} else if !ok {
		writeError(w, http.StatusBadRequest, "workout kind not found")
		return
	}
	if kind.Name == "Race" {
		writeError(w, http.StatusBadRequest, "Race is assigned automatically from Garmin metadata and cannot be set manually")
		return
	}

	kindID := body.WorkoutKindID
	if _, err := s.DB.InsertKindAssignment(r.Context(), store.KindAssignment{
		ActivityID:         activityID,
		WorkoutKindID:      &kindID,
		AssignmentSource:   store.AssignmentSourceManual,
		Status:             store.AssignmentStatusAssigned,
		CandidateKindsJSON: "[]",
	}); err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}
	writeJSON(w, http.StatusOK, map[string]string{"status": "resolved"})
}