// Package gomatrix implements the Matrix Client-Server API.
//
// Specification can be found at http://matrix.org/docs/spec/client_server/r0.2.0.html
//
// Example usage of this library: (blocking version)
// 	cli, _ := gomatrix.NewClient("https://matrix.org", "@example:matrix.org", "MDAefhiuwehfuiwe")
//	syncer := cli.Syncer.(*gomatrix.DefaultSyncer)
//	syncer.OnEventType("m.room.message", func(ev *gomatrix.Event) {
//		fmt.Println("Message: ", ev)
//	})
//	if err := cli.Sync(); err != nil {
//		fmt.Println("Sync() returned ", err)
//	}
//
// To make the example non-blocking, call Sync() in a goroutine.
package gomatrix

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"net/http"
	"net/url"
	"path"
	"strconv"
	"sync"
	"time"
)

// Client represents a Matrix client.
type Client struct {
	HomeserverURL *url.URL     // The base homeserver URL
	Prefix        string       // The API prefix eg '/_matrix/client/r0'
	UserID        string       // The user ID of the client. Used for forming HTTP paths which use the client's user ID.
	AccessToken   string       // The access_token for the client.
	syncingMutex  sync.Mutex   // protects syncingID
	syncingID     uint32       // Identifies the current Sync. Only one Sync can be active at any given time.
	Client        *http.Client // The underlying HTTP client which will be used to make HTTP requests.
	Syncer        Syncer       // The thing which can process /sync responses
}

// HTTPError An HTTP Error response, which may wrap an underlying native Go Error.
type HTTPError struct {
	WrappedError error
	Message      string
	Code         int
}

func (e HTTPError) Error() string {
	var wrappedErrMsg string
	if e.WrappedError != nil {
		wrappedErrMsg = e.WrappedError.Error()
	}
	return fmt.Sprintf("%s: %d: %s", e.Message, e.Code, wrappedErrMsg)
}

// BuildURL builds a URL with the Client's homserver/prefix/access_token set already.
func (cli *Client) BuildURL(urlPath ...string) string {
	ps := []string{cli.Prefix}
	for _, p := range urlPath {
		ps = append(ps, p)
	}
	return cli.BuildBaseURL(ps...)
}

// BuildBaseURL builds a URL with the Client's homeserver/access_token set already. You must
// supply the prefix in the path.
func (cli *Client) BuildBaseURL(urlPath ...string) string {
	// copy the URL. Purposefully ignore error as the input is from a valid URL already
	hsURL, _ := url.Parse(cli.HomeserverURL.String())
	parts := []string{hsURL.Path}
	parts = append(parts, urlPath...)
	hsURL.Path = path.Join(parts...)
	query := hsURL.Query()
	query.Set("access_token", cli.AccessToken)
	hsURL.RawQuery = query.Encode()
	return hsURL.String()
}

// BuildURLWithQuery builds a URL with query paramters in addition to the Client's homeserver/prefix/access_token set already.
func (cli *Client) BuildURLWithQuery(urlPath []string, urlQuery map[string]string) string {
	u, _ := url.Parse(cli.BuildURL(urlPath...))
	q := u.Query()
	for k, v := range urlQuery {
		q.Set(k, v)
	}
	u.RawQuery = q.Encode()
	return u.String()
}

// Sync starts syncing with the provided Homeserver. This function will block until a fatal /sync error occurs, so should
// almost always be started as a new goroutine. If Sync() is called twice then the first sync will be stopped.
func (cli *Client) Sync() error {
	// Mark the client as syncing.
	// We will keep syncing until the syncing state changes. Either because
	// Sync is called or StopSync is called.
	syncingID := cli.incrementSyncingID()
	nextBatch := cli.Syncer.NextBatchStorer().LoadNextBatch(cli.UserID)
	filterID := cli.Syncer.FilterStorer().LoadFilter(cli.UserID)
	if filterID == "" {
		filterJSON := cli.Syncer.FilterStorer().GetFilterJSON(cli.UserID)
		resFilter, err := cli.CreateFilter(filterJSON)
		if err != nil {
			return err
		}
		filterID = resFilter.FilterID
		cli.Syncer.FilterStorer().SaveFilter(cli.UserID, filterID)
	}

	for {
		resSync, err := cli.SyncRequest(30000, nextBatch, filterID, false, "")
		if err != nil {
			duration, err2 := cli.Syncer.OnFailedSync(resSync, err)
			if err2 != nil {
				return err2
			}
			time.Sleep(duration)
			continue
		}

		// Check that the syncing state hasn't changed
		// Either because we've stopped syncing or another sync has been started.
		// We discard the response from our sync.
		if cli.getSyncingID() != syncingID {
			return nil
		}

		// Save the token now *before* processing it. This means it's possible
		// to not process some events, but it means that we won't get constantly stuck processing
		// a malformed/buggy event which keeps making us panic.
		cli.Syncer.NextBatchStorer().SaveNextBatch(cli.UserID, resSync.NextBatch)
		if err = cli.Syncer.ProcessResponse(resSync, nextBatch); err != nil {
			return err
		}

		nextBatch = resSync.NextBatch
	}
}

func (cli *Client) incrementSyncingID() uint32 {
	cli.syncingMutex.Lock()
	defer cli.syncingMutex.Unlock()
	cli.syncingID++
	return cli.syncingID
}

func (cli *Client) getSyncingID() uint32 {
	cli.syncingMutex.Lock()
	defer cli.syncingMutex.Unlock()
	return cli.syncingID
}

// StopSync stops the ongoing sync started by Sync.
func (cli *Client) StopSync() {
	// Advance the syncing state so that any running Syncs will terminate.
	cli.incrementSyncingID()
}

// SendJSON sends JSON to the given URL. Returns an error if the response is not 2xx.
func (cli *Client) SendJSON(method string, httpURL string, contentJSON interface{}) ([]byte, error) {
	jsonStr, err := json.Marshal(contentJSON)
	if err != nil {
		return nil, err
	}
	req, err := http.NewRequest(method, httpURL, bytes.NewBuffer(jsonStr))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/json")
	res, err := cli.Client.Do(req)
	if res != nil {
		defer res.Body.Close()
	}
	if err != nil {
		return nil, err
	}
	contents, err := ioutil.ReadAll(res.Body)
	if res.StatusCode >= 300 || res.StatusCode < 200 {
		return nil, HTTPError{
			Code:    res.StatusCode,
			Message: "Failed to " + method + " JSON: HTTP " + strconv.Itoa(res.StatusCode),
		}
	}
	if err != nil {
		return nil, err
	}
	return contents, nil
}

// CreateFilter makes an HTTP request according to http://matrix.org/docs/spec/client_server/r0.2.0.html#post-matrix-client-r0-user-userid-filter
func (cli *Client) CreateFilter(filter json.RawMessage) (*RespCreateFilter, error) {
	urlPath := cli.BuildURL("user", cli.UserID, "filter")
	resBytes, err := cli.SendJSON("POST", urlPath, &filter)
	if err != nil {
		return nil, err
	}
	var filterResponse RespCreateFilter
	if err = json.Unmarshal(resBytes, &filterResponse); err != nil {
		return nil, err
	}
	return &filterResponse, nil
}

// SyncRequest makes an HTTP request according to http://matrix.org/docs/spec/client_server/r0.2.0.html#get-matrix-client-r0-sync
func (cli *Client) SyncRequest(timeout int, since, filterID string, fullState bool, setPresence string) (*RespSync, error) {
	query := map[string]string{
		"timeout": strconv.Itoa(timeout),
	}
	if since != "" {
		query["since"] = since
	}
	if filterID != "" {
		query["filter"] = filterID
	}
	if setPresence != "" {
		query["set_presence"] = setPresence
	}
	if fullState {
		query["full_state"] = "true"
	}
	urlPath := cli.BuildURLWithQuery([]string{"sync"}, query)
	req, err := http.NewRequest("GET", urlPath, nil)
	if err != nil {
		return nil, err
	}
	res, err := cli.Client.Do(req)
	if res != nil {
		defer res.Body.Close()
	}
	if err != nil {
		return nil, err
	}

	var syncResponse RespSync
	err = json.NewDecoder(res.Body).Decode(&syncResponse)
	return &syncResponse, err
}

// NewClient creates a new Matrix Client ready for syncing
func NewClient(homeserverURL, userID, accessToken string) (*Client, error) {
	hsURL, err := url.Parse(homeserverURL)
	if err != nil {
		return nil, err
	}
	cli := Client{
		AccessToken:   accessToken,
		HomeserverURL: hsURL,
		UserID:        userID,
		Prefix:        "/_matrix/client/r0",
		Syncer: NewDefaultSyncer(
			userID,
			// By default, use an in-memory next_batch storer which will never save tokens to disk.
			// The client will work with this storer: it just won't
			// remember the token across restarts. In practice, a database backend should be used.
			&InMemoryNextBatchStore{make(map[string]string)},
			// By default, use an in-memory filter storer which will never save the filter ID to disk.
			// The client will work with this storer: it just won't remember the filter
			// ID across restarts and hence request a new one. In practice, a database backend should be used.
			&InMemoryFilterStore{
				Filter:       json.RawMessage(`{"room":{"timeline":{"limit":50}}}`),
				UserToFilter: make(map[string]string),
			},
		),
	}
	// By default, use the default HTTP client.
	cli.Client = http.DefaultClient

	return &cli, nil
}