package api

import (
	"encoding/json"
	"errors"
	"io"
	"net/http"
	"net/url"
	"strconv"
	"time"

	"sneak.berlin/go/simplexcalc/internal/simplex"
)

const (
	// defaultCount and maxCount bound how many of a chat's last items a
	// request for its messages reads.
	defaultCount = 20
	maxCount     = 100
)

// message is how the API shows a message, wherever it shows one.
type message struct {
	ID        int64     `json:"id"`
	Direction string    `json:"direction"`
	Type      string    `json:"type"`
	Text      string    `json:"text"`
	Time      time.Time `json:"time"`
}

// newMessage returns the message a chat item holds, and false for an
// item that holds none: the chat client also records events in a chat,
// such as the contact connecting.
func newMessage(item simplex.ChatItem) (message, bool) {
	var direction string

	switch item.Content.Type {
	case "rcvMsgContent":
		direction = "received"
	case "sndMsgContent":
		direction = "sent"
	default:
		return message{}, false
	}

	content := item.Content.MsgContent
	if content == nil {
		return message{}, false
	}

	return message{
		ID:        item.Meta.ItemID,
		Direction: direction,
		Type:      content.Type,
		Text:      content.Text,
		Time:      item.Meta.ItemTs,
	}, true
}

// handleMessages answers with the messages among a chat's last count
// items, oldest first.
func (h *handlers) handleMessages() http.HandlerFunc {
	type response struct {
		Messages []message `json:"messages"`
	}

	return func(w http.ResponseWriter, r *http.Request) {
		contactID, ok := h.chatID(w, r)
		if !ok {
			return
		}

		count, ok := messageCount(r)
		if !ok {
			h.respondError(w, http.StatusBadRequest,
				"count must be a whole number from 1 to "+strconv.Itoa(maxCount))

			return
		}

		items, err := h.client.ChatItems(r.Context(), contactID, count)
		if err != nil {
			h.respondChatError(w, err, "reading a chat's messages",
				"the messages could not be read")

			return
		}

		messages := make([]message, 0, len(items))

		for _, item := range items {
			if m, ok := newMessage(item); ok {
				messages = append(messages, m)
			}
		}

		h.respond(w, http.StatusOK, response{Messages: messages})
	}
}

// handleSend sends the text in the request's body to a chat, and answers
// with the message sent.
func (h *handlers) handleSend() http.HandlerFunc {
	type request struct {
		Text string `json:"text"`
	}

	type response struct {
		Message message `json:"message"`
	}

	return func(w http.ResponseWriter, r *http.Request) {
		contactID, ok := h.chatID(w, r)
		if !ok {
			return
		}

		body, err := io.ReadAll(r.Body)

		var tooLarge *http.MaxBytesError
		if errors.As(err, &tooLarge) {
			h.respondError(w, http.StatusRequestEntityTooLarge, "the body is too large")

			return
		}

		var req request

		if err != nil || json.Unmarshal(body, &req) != nil {
			h.respondError(w, http.StatusBadRequest,
				`the body must be JSON such as {"text":"hello"}`)

			return
		}

		if req.Text == "" {
			h.respondError(w, http.StatusBadRequest, "text is empty")

			return
		}

		item, err := h.client.SendMessage(r.Context(), contactID, req.Text)
		if err != nil {
			h.respondChatError(w, err, "sending a message",
				"the message could not be sent")

			return
		}

		sent, ok := newMessage(item)
		if !ok {
			h.log.Error("sending a message: the answer holds no message",
				"content_type", item.Content.Type)
			h.respondError(w, http.StatusInternalServerError,
				"the chat client's answer could not be read")

			return
		}

		h.respond(w, http.StatusCreated, response{Message: sent})
	}
}

// respondChatError answers a request the chat client did not serve: 404
// for a contact removed after chatID found it, 409 for one who cannot
// receive messages, 413 for a text too long to send, and 500 with
// sentence for anything else, which is logged as what.
func (h *handlers) respondChatError(
	w http.ResponseWriter, err error, what, sentence string,
) {
	switch {
	case errors.Is(err, simplex.ErrNoContact):
		h.respondError(w, http.StatusNotFound, noSuchChat)
	case errors.Is(err, simplex.ErrContactNotReady):
		h.respondError(w, http.StatusConflict, "the contact cannot receive messages")
	case errors.Is(err, simplex.ErrMessageTooLarge):
		h.respondError(w, http.StatusRequestEntityTooLarge, "the text is too long")
	default:
		h.log.Error(what, "error", err)
		h.respondError(w, http.StatusInternalServerError, sentence)
	}
}

// messageCount returns the request's count, defaultCount if it has none,
// and false if it is anything but a whole number from 1 to maxCount. The
// query is parsed here because r.URL.Query drops a pair it cannot
// decode, which would turn count=1% into the default.
func messageCount(r *http.Request) (int, bool) {
	query, err := url.ParseQuery(r.URL.RawQuery)
	if err != nil {
		return 0, false
	}

	if !query.Has("count") {
		return defaultCount, true
	}

	count, err := strconv.Atoi(query.Get("count"))

	return count, err == nil && count >= 1 && count <= maxCount
}