package api

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

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

	"geniusrun/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 activityResponse `json:"activity"`
	Laps     []lapResponse    `json:"laps"`
	Samples  []store.Sample   `json:"samples"`
}

// handleReviewQueue backs the Activities page: every activity that has been
// classified at least once, not just ones still needing review, so the page
// can show each activity's current kind (or "Unclassified") and let the user
// lock/unlock it. It's cursor-paginated: fetching every 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. The optional kind_id/unclassified filters are applied before
// that cursor slicing too, so a filtered view still only loads (and
// chart-renders) one page at a time instead of the whole matching backlog.
func (s *Server) handleReviewQueue(w http.ResponseWriter, r *http.Request) {
	userID := userIDFromContext(r.Context())
	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

	var kindIDFilter *int64
	if v := r.URL.Query().Get("kind_id"); v != "" {
		if n, err := strconv.ParseInt(v, 10, 64); err == nil {
			kindIDFilter = &n
		}
	}
	unclassifiedOnly := r.URL.Query().Get("unclassified") == "true"

	queue, err := s.DB.AllCurrentAssignments(r.Context(), userID)
	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 {
		if kindIDFilter != nil && (a.WorkoutKindID == nil || *a.WorkoutKindID != *kindIDFilter) {
			continue
		}
		if unclassifiedOnly && a.WorkoutKindID != nil {
			continue
		}
		activity, ok, err := s.DB.GetActivity(r.Context(), userID, 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(), userID, 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(), userID, wa.assignment.ActivityID)
		if err != nil {
			writeError(w, http.StatusInternalServerError, err.Error())
			return
		}
		items = append(items, reviewQueueItem{
			KindAssignment: wa.assignment,
			Activity:       toActivityResponse(wa.activity),
			Laps:           toLapResponses(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) {
	userID := userIDFromContext(r.Context())
	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(), userID, 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(), userID, 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"})
}

// handleUnassignReview manually clears an activity's kind back to
// Unclassified. Like handleResolveReview, it's a deliberate manual choice --
// recorded as source=manual (with no kind) so the rule engine leaves it alone
// on a later reclassify pass, exactly as it would for a manual kind
// assignment. The frontend only offers this while the activity is unlocked
// (locked activities must be unlocked first, same precondition as picking a
// different kind), but the backend doesn't re-enforce that here, matching
// handleResolveReview's own lack of a lock precondition check.
func (s *Server) handleUnassignReview(w http.ResponseWriter, r *http.Request) {
	userID := userIDFromContext(r.Context())
	activityID, err := strconv.ParseInt(chi.URLParam(r, "activityID"), 10, 64)
	if err != nil {
		writeError(w, http.StatusBadRequest, "invalid activity id")
		return
	}

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

// handleUnlockReview reverts a manual assignment back to rule_engine
// sourcing, keeping the same kind, so a later reclassify pass (which always
// skips manual assignments) is free to change it again. It's the inverse of
// handleResolveReview, not a delete: the kind stays visible as-is until
// something actually reclassifies it.
func (s *Server) handleUnlockReview(w http.ResponseWriter, r *http.Request) {
	userID := userIDFromContext(r.Context())
	activityID, err := strconv.ParseInt(chi.URLParam(r, "activityID"), 10, 64)
	if err != nil {
		writeError(w, http.StatusBadRequest, "invalid activity id")
		return
	}

	current, ok, err := s.DB.CurrentAssignment(r.Context(), userID, activityID)
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}
	if !ok {
		writeError(w, http.StatusNotFound, "activity has no assignment yet")
		return
	}
	if current.AssignmentSource != store.AssignmentSourceManual {
		writeError(w, http.StatusBadRequest, "activity is not manually locked")
		return
	}

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