package state

import (
	"errors"

	"github.com/diamondburned/arikawa/v2/discord"
)

// Store is the state storage. It should handle mutex itself, and it should only
// concern itself with the local state.
type Store interface {
	StoreGetter
	StoreModifier
}

// All methods in StoreGetter will be wrapped by the State. If the State can't
// find anything in the storage, it will call the API itself and automatically
// add what's missing into the storage.
//
// Methods that return with a slice should pay attention to race conditions that
// would mutate the underlying slice (and as a result the returned slice as
// well). The best way to avoid this is to copy the whole slice, like
// DefaultStore does.
//
// These methods should not care about returning slices in order, unless
// explicitly stated against.
type StoreGetter interface {
	Me() (*discord.User, error)

	// Channel should check for both DM and guild channels.
	Channel(id discord.ChannelID) (*discord.Channel, error)
	Channels(guildID discord.GuildID) ([]discord.Channel, error)

	// same API as (*api.Client)
	CreatePrivateChannel(recipient discord.UserID) (*discord.Channel, error)
	PrivateChannels() ([]discord.Channel, error)

	Emoji(guildID discord.GuildID, emojiID discord.EmojiID) (*discord.Emoji, error)
	Emojis(guildID discord.GuildID) ([]discord.Emoji, error)

	Guild(id discord.GuildID) (*discord.Guild, error)
	Guilds() ([]discord.Guild, error)

	Member(guildID discord.GuildID, userID discord.UserID) (*discord.Member, error)
	Members(guildID discord.GuildID) ([]discord.Member, error)

	Message(channelID discord.ChannelID, messageID discord.MessageID) (*discord.Message, error)
	// Messages should return messages ordered from latest to earliest.
	Messages(channelID discord.ChannelID) ([]discord.Message, error)
	MaxMessages() int // used to know if the state is filled or not.

	// These don't get fetched from the API, it's Gateway only.
	Presence(guildID discord.GuildID, userID discord.UserID) (*discord.Presence, error)
	Presences(guildID discord.GuildID) ([]discord.Presence, error)

	Role(guildID discord.GuildID, roleID discord.RoleID) (*discord.Role, error)
	Roles(guildID discord.GuildID) ([]discord.Role, error)

	VoiceState(guildID discord.GuildID, userID discord.UserID) (*discord.VoiceState, error)
	VoiceStates(guildID discord.GuildID) ([]discord.VoiceState, error)
}

type StoreModifier interface {
	MyselfSet(me discord.User) error

	// ChannelSet should switch on Type to know if it's a private channel or
	// not.
	ChannelSet(discord.Channel) error
	ChannelRemove(discord.Channel) error

	// EmojiSet should delete all old emojis before setting new ones.
	EmojiSet(guildID discord.GuildID, emojis []discord.Emoji) error

	GuildSet(discord.Guild) error
	GuildRemove(id discord.GuildID) error

	MemberSet(guildID discord.GuildID, member discord.Member) error
	MemberRemove(guildID discord.GuildID, userID discord.UserID) error

	// MessageSet should prepend messages into the slice, the latest being in
	// front.
	MessageSet(discord.Message) error
	MessageRemove(channelID discord.ChannelID, messageID discord.MessageID) error

	PresenceSet(guildID discord.GuildID, presence discord.Presence) error
	PresenceRemove(guildID discord.GuildID, userID discord.UserID) error

	RoleSet(guildID discord.GuildID, role discord.Role) error
	RoleRemove(guildID discord.GuildID, roleID discord.RoleID) error

	VoiceStateSet(guildID discord.GuildID, voiceState discord.VoiceState) error
	VoiceStateRemove(guildID discord.GuildID, userID discord.UserID) error
}

// StoreResetter is used by the state to reset the store on every Ready event.
type StoreResetter interface {
	// Reset resets the store to a new valid instance.
	Reset() error
}

// ErrStoreNotFound is an error that a store can use to return when something
// isn't in the storage. There is no strict restrictions on what uses this (the
// default one does, though), so be advised.
var ErrStoreNotFound = errors.New("item not found in store")

// DiffMessage fills non-empty fields from src to dst.
func DiffMessage(src discord.Message, dst *discord.Message) {
	// Thanks, Discord.
	if src.Content != "" {
		dst.Content = src.Content
	}
	if src.EditedTimestamp.IsValid() {
		dst.EditedTimestamp = src.EditedTimestamp
	}
	if src.Mentions != nil {
		dst.Mentions = src.Mentions
	}
	if src.Embeds != nil {
		dst.Embeds = src.Embeds
	}
	if src.Attachments != nil {
		dst.Attachments = src.Attachments
	}
	if src.Timestamp.IsValid() {
		dst.Timestamp = src.Timestamp
	}
	if src.Author.ID.IsValid() {
		dst.Author = src.Author
	}
	if src.Reactions != nil {
		dst.Reactions = src.Reactions
	}
}