local ffi, discordRPClib = require "ffi"
local OS = love.system.getOS()
if OS == "Windows" then
	if love.filesystem.getInfo("lib/windows/discord-rpc.dll", "file") then
		discordRPClib = "lib/windows/discord-rpc"
	else
		discordRPClib = "discord-rpc"
	end
elseif OS == "Linux" then
	if love.filesystem.getInfo("lib/linux/libdiscord-rpc.so", "file") then
		discordRPClib = "lib/linux/libdiscord-rpc"
	else
		discordRPClib = "libdiscord-rpc"
	end
elseif OS == "OS X" then
	if love.filesystem.getInfo("lib/osx/libdiscord-rpc.dylib", "file") then
		discordRPClib = "lib/osx/libdiscord-rpc"
	else
		discordRPClib = "libdiscord-rpc"
	end
end

local success, v
if discordRPClib then success, v = pcall(ffi.load, discordRPClib) end
if success then
	discordRPClib = v
else
	local __NULL__ = function() end
	return setmetatable({}, {__index = function() return __NULL__ end})
end
ffi.cdef [[
typedef struct DiscordRichPresence {
    const char* state;   /* max 128 bytes */
    const char* details; /* max 128 bytes */
    int64_t startTimestamp;
    int64_t endTimestamp;
    const char* largeImageKey;  /* max 32 bytes */
    const char* largeImageText; /* max 128 bytes */
    const char* smallImageKey;  /* max 32 bytes */
    const char* smallImageText; /* max 128 bytes */
    const char* partyId;        /* max 128 bytes */
    int partySize;
    int partyMax;
    const char* matchSecret;    /* max 128 bytes */
    const char* joinSecret;     /* max 128 bytes */
    const char* spectateSecret; /* max 128 bytes */
    int8_t instance;
} DiscordRichPresence;

typedef struct DiscordUser {
    const char* userId;
    const char* username;
    const char* discriminator;
    const char* avatar;
} DiscordUser;

typedef void (*readyPtr)(const DiscordUser* request);
typedef void (*disconnectedPtr)(int errorCode, const char* message);
typedef void (*erroredPtr)(int errorCode, const char* message);
typedef void (*joinGamePtr)(const char* joinSecret);
typedef void (*spectateGamePtr)(const char* spectateSecret);
typedef void (*joinRequestPtr)(const DiscordUser* request);

typedef struct DiscordEventHandlers {
    readyPtr ready;
    disconnectedPtr disconnected;
    erroredPtr errored;
    joinGamePtr joinGame;
    spectateGamePtr spectateGame;
    joinRequestPtr joinRequest;
} DiscordEventHandlers;

void Discord_Initialize(const char* applicationId,
                        DiscordEventHandlers* handlers,
                        int autoRegister,
                        const char* optionalSteamId);

void Discord_Shutdown(void);

void Discord_RunCallbacks(void);

void Discord_UpdatePresence(const DiscordRichPresence* presence);

void Discord_ClearPresence(void);

void Discord_Respond(const char* userid, int reply);

void Discord_UpdateHandlers(DiscordEventHandlers* handlers);
]]

local discordRPC = {} -- module table

-- proxy to detect garbage collection of the module
discordRPC.gcDummy = newproxy(true)

local function unpackDiscordUser(request)
	return ffi.string(request.userId), ffi.string(request.username),
		ffi.string(request.discriminator), ffi.string(request.avatar)
end

-- callback proxies
-- note: callbacks are not JIT compiled (= SLOW), try to avoid doing performance critical tasks in them
-- luajit.org/ext_ffi_semantics.html
local ready_proxy = ffi.cast("readyPtr", function(request)
	if discordRPC.ready then
		discordRPC.ready(unpackDiscordUser(request))
	end
end)

local disconnected_proxy = ffi.cast("disconnectedPtr", function(errorCode, message)
	if discordRPC.disconnected then
		discordRPC.disconnected(errorCode, ffi.string(message))
	end
end)

local errored_proxy = ffi.cast("erroredPtr", function(errorCode, message)
	if discordRPC.errored then
		discordRPC.errored(errorCode, ffi.string(message))
	end
end)

local joinGame_proxy = ffi.cast("joinGamePtr", function(joinSecret)
	if discordRPC.joinGame then
		discordRPC.joinGame(ffi.string(joinSecret))
	end
end)

local spectateGame_proxy = ffi.cast("spectateGamePtr", function(spectateSecret)
	if discordRPC.spectateGame then
		discordRPC.spectateGame(ffi.string(spectateSecret))
	end
end)

local joinRequest_proxy = ffi.cast("joinRequestPtr", function(request)
	if discordRPC.joinRequest then
		discordRPC.joinRequest(unpackDiscordUser(request))
	end
end)

-- helpers
local function checkArg(arg, argType, argName, func, maybeNil)
	assert(type(arg) == argType or (maybeNil and arg == nil),
		string.format("Argument \"%s\" to function \"%s\" has to be of type \"%s\"",
			argName, func, argType))
end

local function checkStrArg(arg, maxLen, argName, func, maybeNil)
	if maxLen then
		assert(type(arg) == "string" and arg:len() <= maxLen or (maybeNil and arg == nil),
			string.format("Argument \"%s\" of function \"%s\" has to be of type string with maximum length %d",
				argName, func, maxLen))
	else
		checkArg(arg, "string", argName, func, true)
	end
end

local function checkIntArg(arg, maxBits, argName, func, maybeNil)
	maxBits = math.min(maxBits or 32, 52) -- lua number (double) can only store integers < 2^53
	local maxVal = 2 ^ (maxBits - 1)   -- assuming signed integers, which, for now, are the only ones in use
	assert(type(arg) == "number" and math.floor(arg) == arg
		and arg < maxVal and arg >= -maxVal
		or (maybeNil and arg == nil),
		string.format("Argument \"%s\" of function \"%s\" has to be a whole number <= %d",
			argName, func, maxVal))
end

-- function wrappers
function discordRPC.initialize(applicationId, autoRegister, optionalSteamId)
	local func = "discordRPC.Initialize"
	checkStrArg(applicationId, nil, "applicationId", func)
	checkArg(autoRegister, "boolean", "autoRegister", func)
	if optionalSteamId ~= nil then
		checkStrArg(optionalSteamId, nil, "optionalSteamId", func)
	end

	local eventHandlers = ffi.new("struct DiscordEventHandlers")
	eventHandlers.ready = ready_proxy
	eventHandlers.disconnected = disconnected_proxy
	eventHandlers.errored = errored_proxy
	eventHandlers.joinGame = joinGame_proxy
	eventHandlers.spectateGame = spectateGame_proxy
	eventHandlers.joinRequest = joinRequest_proxy

	discordRPClib.Discord_Initialize(applicationId, eventHandlers,
		autoRegister and 1 or 0, optionalSteamId)
end

function discordRPC.shutdown()
	discordRPClib.Discord_Shutdown()
end

function discordRPC.runCallbacks()
	discordRPClib.Discord_RunCallbacks()
end

-- http://luajit.org/ext_ffi_semantics.html#callback :
-- It is not allowed, to let an FFI call into a C function (runCallbacks)
-- get JIT-compiled, which in turn calls a callback, calling into Lua again (e.g. discordRPC.ready).
-- Usually this attempt is caught by the interpreter first and the C function
-- is blacklisted for compilation.
-- solution:
-- "Then you'll need to manually turn off JIT-compilation with jit.off() for
-- the surrounding Lua function that invokes such a message polling function."
jit.off(discordRPC.runCallbacks)

function discordRPC.updatePresence(presence)
	local func = "discordRPC.updatePresence"
	checkArg(presence, "table", "presence", func)

	-- -1 for string length because of 0-termination
	checkStrArg(presence.state, 127, "presence.state", func, true)
	checkStrArg(presence.details, 127, "presence.details", func, true)

	checkIntArg(presence.startTimestamp, 64, "presence.startTimestamp", func, true)
	checkIntArg(presence.endTimestamp, 64, "presence.endTimestamp", func, true)

	checkStrArg(presence.largeImageKey, 31, "presence.largeImageKey", func, true)
	checkStrArg(presence.largeImageText, 127, "presence.largeImageText", func, true)
	checkStrArg(presence.smallImageKey, 31, "presence.smallImageKey", func, true)
	checkStrArg(presence.smallImageText, 127, "presence.smallImageText", func, true)
	checkStrArg(presence.partyId, 127, "presence.partyId", func, true)

	checkIntArg(presence.partySize, 32, "presence.partySize", func, true)
	checkIntArg(presence.partyMax, 32, "presence.partyMax", func, true)

	checkStrArg(presence.matchSecret, 127, "presence.matchSecret", func, true)
	checkStrArg(presence.joinSecret, 127, "presence.joinSecret", func, true)
	checkStrArg(presence.spectateSecret, 127, "presence.spectateSecret", func, true)

	checkIntArg(presence.instance, 8, "presence.instance", func, true)

	local cpresence = ffi.new("struct DiscordRichPresence")
	cpresence.state = presence.state
	cpresence.details = presence.details
	cpresence.startTimestamp = presence.startTimestamp or 0
	cpresence.endTimestamp = presence.endTimestamp or 0
	cpresence.largeImageKey = presence.largeImageKey
	cpresence.largeImageText = presence.largeImageText
	cpresence.smallImageKey = presence.smallImageKey
	cpresence.smallImageText = presence.smallImageText
	cpresence.partyId = presence.partyId
	cpresence.partySize = presence.partySize or 0
	cpresence.partyMax = presence.partyMax or 0
	cpresence.matchSecret = presence.matchSecret
	cpresence.joinSecret = presence.joinSecret
	cpresence.spectateSecret = presence.spectateSecret
	cpresence.instance = presence.instance or 0

	discordRPClib.Discord_UpdatePresence(cpresence)
end

function discordRPC.clearPresence()
	discordRPClib.Discord_ClearPresence()
end

local replyMap = {
	no = 0,
	yes = 1,
	ignore = 2
}

-- maybe let reply take ints too (0, 1, 2) and add constants to the module
function discordRPC.respond(userId, reply)
	checkStrArg(userId, nil, "userId", "discordRPC.respond")
	assert(replyMap[reply], "Argument 'reply' to discordRPC.respond has to be one of \"yes\", \"no\" or \"ignore\"")
	discordRPClib.Discord_Respond(userId, replyMap[reply])
end

-- garbage collection callback
getmetatable(discordRPC.gcDummy).__gc = function()
	discordRPC.shutdown()
	ready_proxy:free()
	disconnected_proxy:free()
	errored_proxy:free()
	joinGame_proxy:free()
	spectateGame_proxy:free()
	joinRequest_proxy:free()
end

return discordRPC
