Hilbish/golibs/bait/bait.go

// the event emitter
// Bait is the event emitter for Hilbish. Why name it bait? Why not.
// It throws hooks that you can catch. This is what you will use if
// you want to listen in on hooks to know when certain things have
// happened, like when you've changed directory, a command has failed,
// etc. To find all available hooks thrown by Hilbish, see doc hooks.
package bait

import (
	"errors"

	"hilbish/util"

	rt "github.com/arnodel/golua/runtime"
	"github.com/arnodel/golua/lib/packagelib"
)

type listenerType int
const (
	goListener listenerType = iota
	luaListener
)

// Recoverer is a function which is called when a panic occurs in an event.
type Recoverer func(event string, handler *Listener, err interface{})

// Listener is a struct that holds the handler for an event.
type Listener struct{
	typ listenerType
	once bool
	caller func(...interface{})
	luaCaller *rt.Closure
}

type Bait struct{
	Loader packagelib.Loader
	recoverer Recoverer
	handlers map[string][]*Listener
	rtm *rt.Runtime
}

// New creates a new Bait instance.
func New(rtm *rt.Runtime) *Bait {
	b := &Bait{
		handlers: make(map[string][]*Listener),
		rtm: rtm,
	}
	b.Loader = packagelib.Loader{
		Load: b.loaderFunc,
		Name: "bait",
	}

	return b
}

// Emit throws an event.
func (b *Bait) Emit(event string, args ...interface{}) {
	handles := b.handlers[event]
	if handles == nil {
		return
	}

	for idx, handle := range handles {
		defer func() {
			if err := recover(); err != nil {
				b.callRecoverer(event, handle, err)
			}
		}()

		if handle.typ == luaListener {
			funcVal := rt.FunctionValue(handle.luaCaller)
			var luaArgs []rt.Value
			for _, arg := range args {
				var luarg rt.Value
				switch arg.(type) {
					case rt.Value: luarg = arg.(rt.Value)
					default: luarg = rt.AsValue(arg)
				}
				luaArgs = append(luaArgs, luarg)
			}
			_, err := rt.Call1(b.rtm.MainThread(), funcVal, luaArgs...)
			if err != nil {
				if event != "error" {
					b.Emit("error", event, handle.luaCaller, err.Error())
					return
				}
				// if there is an error in an error event handler, panic instead
				// (calls the go recoverer function)
				panic(err)
			}
		} else {
			handle.caller(args...)
		}

		if handle.once {
			b.removeListener(event, idx)
		}
	}
}

// On adds a Go function handler for an event.
func (b *Bait) On(event string, handler func(...interface{})) *Listener {
	listener := &Listener{
		typ: goListener,
		caller: handler,
	}

	b.addListener(event, listener)
	return listener
}

// OnLua adds a Lua function handler for an event.
func (b *Bait) OnLua(event string, handler *rt.Closure) *Listener {
	listener :=&Listener{
		typ: luaListener,
		luaCaller: handler,
	}
	b.addListener(event, listener)

	return listener
}

// Off removes a Go function handler for an event.
func (b *Bait) Off(event string, listener *Listener) {
	handles := b.handlers[event]

	for i, handle := range handles {
		if handle == listener {
			b.removeListener(event, i)
		}
	}
}

// OffLua removes a Lua function handler for an event.
func (b *Bait) OffLua(event string, handler *rt.Closure) {
	handles := b.handlers[event]

	for i, handle := range handles {
		if handle.luaCaller == handler {
			b.removeListener(event, i)
		}
	}
}

// Once adds a Go function listener for an event that only runs once.
func (b *Bait) Once(event string, handler func(...interface{})) *Listener {
	listener := &Listener{
		typ: goListener,
		once: true,
		caller: handler,
	}
	b.addListener(event, listener)

	return listener
}

// OnceLua adds a Lua function listener for an event that only runs once.
func (b *Bait) OnceLua(event string, handler *rt.Closure) *Listener {
	listener := &Listener{
		typ: luaListener,
		once: true,
		luaCaller: handler,
	}
	b.addListener(event, listener)

	return listener
}

// SetRecoverer sets the function to be executed when a panic occurs in an event.
func (b *Bait) SetRecoverer(recoverer Recoverer) {
	b.recoverer = recoverer
}

func (b *Bait) addListener(event string, listener *Listener) {
	if b.handlers[event] == nil {
		b.handlers[event] = []*Listener{}
	}

	b.handlers[event] = append(b.handlers[event], listener)
}


func (b *Bait) removeListener(event string, idx int) {
	b.handlers[event][idx] = b.handlers[event][len(b.handlers[event]) - 1]

	b.handlers[event] = b.handlers[event][:len(b.handlers[event]) - 1]
}

func (b *Bait) callRecoverer(event string, handler *Listener, err interface{}) {
	if b.recoverer == nil {
		panic(err)
	}
	b.recoverer(event, handler, err)
}

func (b *Bait) loaderFunc(rtm *rt.Runtime) (rt.Value, func()) {
	exports := map[string]util.LuaExport{
		"catch": util.LuaExport{b.bcatch, 2, false},
		"catchOnce": util.LuaExport{b.bcatchOnce, 2, false},
		"throw": util.LuaExport{b.bthrow, 1, true},
		"release": util.LuaExport{b.brelease, 2, false},
		"hooks": util.LuaExport{b.bhooks, 1, false},
	}
	mod := rt.NewTable()
	util.SetExports(rtm, mod, exports)

	util.Document(mod,
`Bait is the event emitter for Hilbish. Why name it bait?
Because it throws hooks that you can catch (emits events
that you can listen to) and because why not, fun naming
is fun. This is what you will use if you want to listen
in on hooks to know when certain things have happened,
like when you've changed directory, a command has
failed, etc. To find all available hooks, see doc hooks.`)

	return rt.TableValue(mod), nil
}

func handleHook(t *rt.Thread, c *rt.GoCont, name string, catcher *rt.Closure, args ...interface{}) {
	funcVal := rt.FunctionValue(catcher)
	var luaArgs []rt.Value
	for _, arg := range args {
		var luarg rt.Value
		switch arg.(type) {
			case rt.Value: luarg = arg.(rt.Value)
			default: luarg = rt.AsValue(arg)
		}
		luaArgs = append(luaArgs, luarg)
	}
	_, err := rt.Call1(t, funcVal, luaArgs...)
	if err != nil {
		e := rt.NewError(rt.StringValue(err.Error()))
		e = e.AddContext(c.Next(), 1)
		// panicking here won't actually cause hilbish to panic and instead will
		// print the error and remove the hook (look at emission recover from above)
		panic(e)
	}
}

// throw(name, ...args)
// Throws a hook with `name` with the provided `args`
// --- @param name string
// --- @vararg any
func (b *Bait) bthrow(t *rt.Thread, c *rt.GoCont) (rt.Cont, error) {
	if err := c.Check1Arg(); err != nil {
		return nil, err
	}
	name, err := c.StringArg(0)
	if err != nil {
		return nil, err
	}
	ifaceSlice := make([]interface{}, len(c.Etc()))
	for i, v := range c.Etc() {
		ifaceSlice[i] = v
	}
	b.Emit(name, ifaceSlice...)

	return c.Next(), nil
}

// catch(name, cb)
// Catches a hook with `name`. Runs the `cb` when it is thrown
// --- @param name string
// --- @param cb function
func (b *Bait) bcatch(t *rt.Thread, c *rt.GoCont) (rt.Cont, error) {
	name, catcher, err := util.HandleStrCallback(t, c)
	if err != nil {
		return nil, err
	}

	b.OnLua(name, catcher)

	return c.Next(), nil
}

// catchOnce(name, cb)
// Same as catch, but only runs the `cb` once and then removes the hook
// --- @param name string
// --- @param cb function
func (b *Bait) bcatchOnce(t *rt.Thread, c *rt.GoCont) (rt.Cont, error) {
	name, catcher, err := util.HandleStrCallback(t, c)
	if err != nil {
		return nil, err
	}

	b.OnceLua(name, catcher)

	return c.Next(), nil
}

// release(name, catcher)
// Removes the `catcher` for the event with `name`
// For this to work, `catcher` has to be the same function used to catch
// an event, like one saved to a variable.
// --- @param name string
// --- @param catcher function
func (b *Bait) brelease(t *rt.Thread, c *rt.GoCont) (rt.Cont, error) {
	name, catcher, err := util.HandleStrCallback(t, c)
	if err != nil {
		return nil, err
	}

	b.OffLua(name, catcher)

	return c.Next(), nil
}

// hooks(name) -> {cb, cb...}
// Returns a table with hooks on the event with `name`.
// --- @param name string
// --- @returns table
func (b *Bait) bhooks(t *rt.Thread, c *rt.GoCont) (rt.Cont, error) {
	if err := c.Check1Arg(); err != nil {
		return nil, err
	}
	evName, err := c.StringArg(0)
	if err != nil {
		return nil, err
	}
	noHooks := errors.New("no hooks for event " + evName)

	handlers := b.handlers[evName]
	if handlers == nil {
		return nil, noHooks
	}

	luaHandlers := rt.NewTable()
	for _, handler := range handlers {
		if handler.typ != luaListener { continue }
		luaHandlers.Set(rt.IntValue(luaHandlers.Len() + 1), rt.FunctionValue(handler.luaCaller))
	}

	if luaHandlers.Len() == 0 {
		return nil, noHooks
	}

	return c.PushingNext1(t.Runtime, rt.TableValue(luaHandlers)), nil
}