// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
// See License.txt for license information.

package plugin

import (
	"io"
	"net/http"

	"github.com/mattermost/mattermost-server/model"
)

// These assignments are part of the wire protocol used to trigger hook events in plugins.
//
// Feel free to add more, but do not change existing assignments. Follow the naming convention of
// <HookName>Id as the autogenerated glue code depends on that.
const (
	OnActivateId            = 0
	OnDeactivateId          = 1
	ServeHTTPId             = 2
	OnConfigurationChangeId = 3
	ExecuteCommandId        = 4
	MessageWillBePostedId   = 5
	MessageWillBeUpdatedId  = 6
	MessageHasBeenPostedId  = 7
	MessageHasBeenUpdatedId = 8
	UserHasJoinedChannelId  = 9
	UserHasLeftChannelId    = 10
	UserHasJoinedTeamId     = 11
	UserHasLeftTeamId       = 12
	ChannelHasBeenCreatedId = 13
	FileWillBeUploadedId    = 14
	UserWillLogInId         = 15
	UserHasLoggedInId       = 16
	TotalHooksId            = iota
)

// Hooks describes the methods a plugin may implement to automatically receive the corresponding
// event.
//
// A plugin only need implement the hooks it cares about. The MattermostPlugin provides some
// default implementations for convenience but may be overridden.
type Hooks interface {
	// OnActivate is invoked when the plugin is activated. If an error is returned, the plugin
	// will be terminated. The plugin will not receive hooks until after OnActivate returns
	// without error.
	OnActivate() error

	// Implemented returns a list of hooks that are implemented by the plugin.
	// Plugins do not need to provide an implementation. Any given will be ignored.
	Implemented() ([]string, error)

	// OnDeactivate is invoked when the plugin is deactivated. This is the plugin's last chance to
	// use the API, and the plugin will be terminated shortly after this invocation. The plugin
	// will stop receiving hooks just prior to this method being called.
	OnDeactivate() error

	// OnConfigurationChange is invoked when configuration changes may have been made. Any
	// returned error is logged, but does not stop the plugin. You must be prepared to handle
	// a configuration failure gracefully.
	OnConfigurationChange() error

	// ServeHTTP allows the plugin to implement the http.Handler interface. Requests destined for
	// the /plugins/{id} path will be routed to the plugin.
	//
	// The Mattermost-User-Id header will be present if (and only if) the request is by an
	// authenticated user.
	ServeHTTP(c *Context, w http.ResponseWriter, r *http.Request)

	// ExecuteCommand executes a command that has been previously registered via the RegisterCommand
	// API.
	ExecuteCommand(c *Context, args *model.CommandArgs) (*model.CommandResponse, *model.AppError)

	// MessageWillBePosted is invoked when a message is posted by a user before it is committed
	// to the database. If you also want to act on edited posts, see MessageWillBeUpdated.
	//
	// To reject a post, return an non-empty string describing why the post was rejected.
	// To modify the post, return the replacement, non-nil *model.Post and an empty string.
	// To allow the post without modification, return a nil *model.Post and an empty string.
	//
	// If you don't need to modify or reject posts, use MessageHasBeenPosted instead.
	//
	// Note that this method will be called for posts created by plugins, including the plugin that
	// created the post.
	MessageWillBePosted(c *Context, post *model.Post) (*model.Post, string)

	// MessageWillBeUpdated is invoked when a message is updated by a user before it is committed
	// to the database. If you also want to act on new posts, see MessageWillBePosted.
	// Return values should be the modified post or nil if rejected and an explanation for the user.
	// On rejection, the post will be kept in its previous state.
	//
	// If you don't need to modify or rejected updated posts, use MessageHasBeenUpdated instead.
	//
	// Note that this method will be called for posts updated by plugins, including the plugin that
	// updated the post.
	MessageWillBeUpdated(c *Context, newPost, oldPost *model.Post) (*model.Post, string)

	// MessageHasBeenPosted is invoked after the message has been committed to the database.
	// If you need to modify or reject the post, see MessageWillBePosted
	// Note that this method will be called for posts created by plugins, including the plugin that
	// created the post.
	MessageHasBeenPosted(c *Context, post *model.Post)

	// MessageHasBeenUpdated is invoked after a message is updated and has been updated in the database.
	// If you need to modify or reject the post, see MessageWillBeUpdated
	// Note that this method will be called for posts created by plugins, including the plugin that
	// created the post.
	MessageHasBeenUpdated(c *Context, newPost, oldPost *model.Post)

	// ChannelHasBeenCreated is invoked after the channel has been committed to the database.
	ChannelHasBeenCreated(c *Context, channel *model.Channel)

	// UserHasJoinedChannel is invoked after the membership has been committed to the database.
	// If actor is not nil, the user was invited to the channel by the actor.
	UserHasJoinedChannel(c *Context, channelMember *model.ChannelMember, actor *model.User)

	// UserHasLeftChannel is invoked after the membership has been removed from the database.
	// If actor is not nil, the user was removed from the channel by the actor.
	UserHasLeftChannel(c *Context, channelMember *model.ChannelMember, actor *model.User)

	// UserHasJoinedTeam is invoked after the membership has been committed to the database.
	// If actor is not nil, the user was added to the team by the actor.
	UserHasJoinedTeam(c *Context, teamMember *model.TeamMember, actor *model.User)

	// UserHasLeftTeam is invoked after the membership has been removed from the database.
	// If actor is not nil, the user was removed from the team by the actor.
	UserHasLeftTeam(c *Context, teamMember *model.TeamMember, actor *model.User)

	// UserWillLogIn before the login of the user is returned. Returning a non empty string will reject the login event.
	// If you don't need to reject the login event, see UserHasLoggedIn
	UserWillLogIn(c *Context, user *model.User) string

	// UserHasLoggedIn is invoked after a user has logged in.
	UserHasLoggedIn(c *Context, user *model.User)

	// FileWillBeUploaded is invoked when a file is uploaded, but before it is committed to backing store.
	// Read from file to retrieve the body of the uploaded file.
	//
	// To reject a file upload, return an non-empty string describing why the file was rejected.
	// To modify the file, write to the output and/or return a non-nil *model.FileInfo, as well as an empty string.
	// To allow the file without modification, do not write to the output and return a nil *model.FileInfo and an empty string.
	//
	// Note that this method will be called for files uploaded by plugins, including the plugin that uploaded the post.
	// FileInfo.Size will be automatically set properly if you modify the file.
	FileWillBeUploaded(c *Context, info *model.FileInfo, file io.Reader, output io.Writer) (*model.FileInfo, string)
}