package zygo

import (
	"errors"
	"fmt"
)

type SexpChannel struct {
	Val chan Sexp
	Typ *RegisteredType
}

func (ch *SexpChannel) SexpString(ps *PrintState) string {
	return "[chan]"
}

func (ch *SexpChannel) Type() *RegisteredType {
	return ch.Typ // TODO what should this be?
}

func MakeChanFunction(env *Zlisp, name string,
	args []Sexp) (Sexp, error) {
	if len(args) > 1 {
		return SexpNull, WrongNargs
	}

	size := 0
	if len(args) == 1 {
		switch t := args[0].(type) {
		case *SexpInt:
			size = int(t.Val)
		default:
			return SexpNull, errors.New(
				fmt.Sprintf("argument to %s must be int", name))
		}
	}

	return &SexpChannel{Val: make(chan Sexp, size)}, nil
}

func ChanTxFunction(env *Zlisp, name string,
	args []Sexp) (Sexp, error) {
	if len(args) < 1 {
		return SexpNull, WrongNargs
	}
	var channel chan Sexp
	switch t := args[0].(type) {
	case *SexpChannel:
		channel = chan Sexp(t.Val)
	default:
		return SexpNull, errors.New(
			fmt.Sprintf("argument 0 of %s must be channel", name))
	}

	if name == "send" {
		if len(args) != 2 {
			return SexpNull, WrongNargs
		}
		channel <- args[1]
		return SexpNull, nil
	}

	return <-channel, nil
}

func (env *Zlisp) ImportChannels() {
	env.AddFunction("makeChan", MakeChanFunction)
	env.AddFunction("send", ChanTxFunction)
	env.AddFunction("<!", ChanTxFunction)
}