package api

import (
	"cmp"
	"context"
	"net/http"
	"slices"
	"strconv"

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

// noSuchChat answers a request naming a chat the bot does not have.
const noSuchChat = "no such chat"

// chat is how the API shows a chat. The bot talks to people only one to
// one, so its chats are its contacts, and a chat's id is its contact's.
type chat struct {
	ID             int64  `json:"id"`
	DisplayName    string `json:"display_name"`
	ContactDeleted bool   `json:"contact_deleted"`
}

// chats returns the bot's chats, ordered by id. GET /api/v1/chats
// answers with this list, and chatID accepts only an id in it.
func (h *handlers) chats(ctx context.Context) ([]chat, error) {
	contacts, err := h.client.Contacts(ctx, h.userID)
	if err != nil {
		return nil, err
	}

	chats := make([]chat, 0, len(contacts))
	for _, c := range contacts {
		chats = append(chats, chat{
			ID:             c.ContactID,
			DisplayName:    c.Profile.DisplayName,
			ContactDeleted: c.Deleted(),
		})
	}

	slices.SortFunc(chats, func(a, b chat) int { return cmp.Compare(a.ID, b.ID) })

	return chats, nil
}

// handleChats lists the bot's chats.
func (h *handlers) handleChats() http.HandlerFunc {
	type response struct {
		Chats []chat `json:"chats"`
	}

	return func(w http.ResponseWriter, r *http.Request) {
		chats, err := h.chats(r.Context())
		if err != nil {
			h.log.Error("listing the chats", "error", err)
			h.respondError(w, http.StatusInternalServerError,
				"the chats could not be read")

			return
		}

		h.respond(w, http.StatusOK, response{Chats: chats})
	}
}

// chatID returns the chat id in the request's path, if it is one of the
// bot's chats. Otherwise it answers the request itself, 404, or 500 if
// the chats could not be read, and returns false.
//
// The id is looked up rather than passed to the chat client, which also
// keeps contact records that are not chats, such as the bot's own
// profile, and would read or send in them.
func (h *handlers) chatID(w http.ResponseWriter, r *http.Request) (int64, bool) {
	id, err := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
	if err != nil {
		h.respondError(w, http.StatusNotFound, noSuchChat)

		return 0, false
	}

	chats, err := h.chats(r.Context())
	if err != nil {
		h.log.Error("looking up a chat", "error", err)
		h.respondError(w, http.StatusInternalServerError,
			"the chats could not be read")

		return 0, false
	}

	if !slices.ContainsFunc(chats, func(c chat) bool { return c.ID == id }) {
		h.respondError(w, http.StatusNotFound, noSuchChat)

		return 0, false
	}

	return id, true
}