package handler

import (
	"encoding/json"
	"errors"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/prabhupadasays/spsays-bff/internal/repository"
	"github.com/prabhupadasays/spsays-bff/internal/service"
	"github.com/prabhupadasays/spsays-bff/pkg/response"
)

// VaniHandler serves the public "Vāṇī of the Day" pick for the home page.
type VaniHandler struct {
	svc *service.VaniService
}

func NewVaniHandler(svc *service.VaniService) *VaniHandler {
	return &VaniHandler{svc: svc}
}

// Today — GET /vani/today. Public; the same pick is returned to everyone for
// the current UTC day. Responds with `data: null` if there's no content.
type setVaniReq struct {
	// Day as YYYY-MM-DD (UTC). Empty means today.
	Day  string `json:"day"`
	Kind string `json:"kind"`
	// RefID is the content's Mongo _id hex, which search returns as doc_id.
	RefID string `json:"ref_id"`
}

// Set — POST /admin/vani. Pins a specific item as a day's Vāṇī.
func (h *VaniHandler) Set(w http.ResponseWriter, r *http.Request) {
	var req setVaniReq
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		response.Error(w, http.StatusBadRequest, "invalid JSON body")
		return
	}
	day, err := parseVaniDay(req.Day)
	if err != nil {
		response.Error(w, http.StatusBadRequest, "day must be YYYY-MM-DD")
		return
	}
	pick, err := h.svc.SetForDay(r.Context(), day, req.Kind, req.RefID)
	if err != nil {
		writeVaniError(w, err)
		return
	}
	response.JSON(w, http.StatusOK, map[string]any{
		"day":     pick.Day.Format("2006-01-02"),
		"kind":    pick.Kind,
		"ref_id":  pick.RefID,
		"payload": pick.Payload,
	})
}

// Clear — DELETE /admin/vani/{day}. Hands the day back to the random picker.
func (h *VaniHandler) Clear(w http.ResponseWriter, r *http.Request) {
	day, err := parseVaniDay(chi.URLParam(r, "day"))
	if err != nil {
		response.Error(w, http.StatusBadRequest, "day must be YYYY-MM-DD")
		return
	}
	if err := h.svc.ClearForDay(r.Context(), day); err != nil {
		writeVaniError(w, err)
		return
	}
	response.NoContent(w)
}

// Schedule — GET /admin/vani. Decided days from today onward.
func (h *VaniHandler) Schedule(w http.ResponseWriter, r *http.Request) {
	limit, _ := strconv.Atoi(r.URL.Query().Get("limit"))
	picks, err := h.svc.Schedule(r.Context(), limit)
	if err != nil {
		writeVaniError(w, err)
		return
	}
	out := make([]map[string]any, 0, len(picks))
	for _, p := range picks {
		out = append(out, map[string]any{
			"day":     p.Day.Format("2006-01-02"),
			"kind":    p.Kind,
			"ref_id":  p.RefID,
			"payload": p.Payload,
		})
	}
	response.JSON(w, http.StatusOK, out)
}

// parseVaniDay accepts YYYY-MM-DD, or empty for today (UTC — the pick is
// keyed on a UTC calendar day so everyone sees the same item).
func parseVaniDay(s string) (time.Time, error) {
	if strings.TrimSpace(s) == "" {
		return time.Now().UTC().Truncate(24 * time.Hour), nil
	}
	return time.Parse("2006-01-02", strings.TrimSpace(s))
}

func writeVaniError(w http.ResponseWriter, err error) {
	switch {
	case errors.Is(err, repository.ErrVaniRefInvalid), errors.Is(err, service.ErrVaniBadKind):
		response.Error(w, http.StatusBadRequest, err.Error())
	case errors.Is(err, repository.ErrVaniRefNotFound):
		response.Error(w, http.StatusNotFound, err.Error())
	default:
		response.Error(w, http.StatusInternalServerError, "vāṇī request failed")
	}
}

func (h *VaniHandler) Today(w http.ResponseWriter, r *http.Request) {
	payload, err := h.svc.Today(r.Context())
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "could not load vāṇī of the day")
		return
	}
	response.JSON(w, http.StatusOK, payload)
}