// Package forge implements sort of a stack-based interpreter.
package forge

import (
	"io"
	"os"

	"git.sr.ht/~cco/go-scopes/common/ptr"
	"git.sr.ht/~cco/go-scopes/common/stack"
	"git.sr.ht/~cco/go-scopes/common/voc"
)

type fitem interface{}

type fptr = ptr.Ptr[fitem]
type fstack = stack.Stack[fitem]
type fvoc = voc.Vocabulary[XT]

type Callable func(*forgeEnv, XT)

type xitem struct {
	name      string
	immediate bool
	fct       Callable
	body      fptr
}

type XT = *xitem

type forgeEnv struct {
	ds, rs     fstack
	cp, ip, dp fptr
	voc        *fvoc
	latestXT   XT
	cstate     bool
	output     io.Writer
}

type FE = *forgeEnv

func NewVoc(parent *fvoc) *fvoc {
	return voc.NewVoc[XT](parent)
}

func NewFE() *forgeEnv {
	return newFE(NewVoc(nil))
}

func (f *forgeEnv) ChildFE() *forgeEnv {
	return newFE(NewVoc(f.voc))
}

func newFE(voc *fvoc) *forgeEnv {
	return &forgeEnv{
		ds:     stack.NewStack[fitem](),
		rs:     stack.NewStack[fitem](),
		ip:     ptr.NewSlice[fitem](),
		voc:    voc,
		output: os.Stdout,
	}
}

// basic functions and methods

func Register(voc *fvoc, name string, fct Callable) *xitem {
	it := xitem{
		name: name,
		fct:  fct,
	}
	voc.Register(name, &it)
	return &it
}

func (it *xitem) IsImmediate() bool {
	return it.immediate
}

func (it *xitem) Immediate() {
	it.immediate = true
}

func (it *xitem) Body() fptr {
	if it.body == nil {
		it.body = ptr.NewSlice[fitem]()
	}
	return it.body
}

func (it *xitem) Name() string {
	return it.name
}

// ForgeEnv methods

func (f *forgeEnv) Voc() *fvoc {
	return f.voc
}

func (f *forgeEnv) IP() fptr {
	return f.ip
}

func (f *forgeEnv) Exec(items ...fitem) {
	f.ip = ptr.NewSlice[fitem](items...)
	for f.ip.Next() != nil {
		it := f.ip.Value().(XT)
		it.fct(f, it)
	}
}

func (f *forgeEnv) Push(it fitem) {
	f.ds.Push(it)
}

func (f *forgeEnv) Pop() fitem {
	return f.ds.Pop()
}