package interp

import (
	"fmt"
	"unsafe"
)

var err_num_args *error_t = &error_t{msg: "wrong number of arguments"}

/*
	   value stack (p.vstack)

		           <--- SP (p.vsp)
		    ARG1
		    ARG0
		    NAME
			RET

		evaluation stack (p.ctx)
*/

func (p *process_t) push_cnode_value(val *Cnode_t) error {
	if p.vsp >= cap(p.vstack) {
		return fmt.Errorf("stack full")
	}

	// TODO: using the last bit won't be compatible with go's GC.
	// CHANGE to use inteface{} or devise a different scheme...
	p.vstack[p.vsp] = unsafe.Pointer(uintptr(unsafe.Pointer(val)) | 1)
	p.vsp++
	p.ctx.count++

	return nil
}

func (p *process_t) push_string_value(val string) error {
	if p.vsp >= cap(p.vstack) {
		return fmt.Errorf("stack full")
	}

	p.vstack[p.vsp] = unsafe.Pointer(&val)
	p.vsp++
	p.ctx.count++

	return nil
}

func (p *process_t) merge_top_values() error {
	var new_val string

	if p.vsp < 2 {
		return fmt.Errorf("stack corrupt")
	}
	new_val = *(*string)(p.vstack[p.vsp-2]) + *(*string)(p.vstack[p.vsp-1])
	p.vsp--
	p.vstack[p.vsp] = nil
	p.vstack[p.vsp-1] = unsafe.Pointer(&new_val)
	p.ctx.count--
	return nil
}

func (p *process_t) pop_value() unsafe.Pointer {
	var v unsafe.Pointer
	p.vsp--
	v = p.vstack[p.vsp]
	p.vstack[p.vsp] = nil
	return v
}

func (p *process_t) call() error {
	var (
		proc   func(*process_t) error
		callee *string
	)

	callee = p.GetCalleeName()
	// TODO: use a map
	switch *callee {
	case "if":
		proc = proc_if
	case "puts":
		proc = proc_puts
	default:
		proc = proc_unknown
	}
	return proc(p)
}

func (p *process_t) GetCalleeName() *string {
	return (*string)(p.vstack[p.vsp-p.ctx.count+1])
}

func (p *process_t) GetArg(idx int) unsafe.Pointer {
	return (p.vstack[p.vsp-p.ctx.count+2+idx])
}

func (p *process_t) GetNumArgs() int {
	return p.ctx.count - 2
}

func (p *process_t) Return(val string) {
	p.vstack[p.vsp-p.ctx.count] = unsafe.Pointer(&val)
}

func (p *process_t) push_context(node *Cnode_t, container_node *Cnode_t) {
	p.ctx = &context_t{count: 0, parent_ctx: p.ctx, parent_node: node, container_node: container_node}
}

func (p *process_t) pop_context() (*Cnode_t, *Cnode_t) {
	var (
		i         int
		node      *Cnode_t
		container *Cnode_t
	)

	node = p.ctx.parent_node
	container = p.ctx.container_node

	// clean up the unused part of the stack
	for i = 1; i < p.ctx.count; i++ {
		p.vstack[p.vsp-p.ctx.count+i] = nil
	}

	// pop off the cleaned arguments
	p.vsp -= p.ctx.count - 1 // keep the return value in the stack
	p.ctx = p.ctx.parent_ctx

	if p.ctx != nil {
		p.ctx.count++ // let the return value be the argument to the caller
	}

	return node, container
}

func (interp *Interp) eval_node_child(container_node *Cnode_t) (*string, error) {
	var (
		p          process_t
		v          *string
		stmt_node  *Cnode_t
		inner_node *Cnode_t
		err        error
	)

	v = new(string) // TODO: change new(string) to a const

	p.interp = interp
	stmt_node = container_node.child

	//interp.dump_cnodes(container_node, true)
	//fmt.Printf("--------------\n")
	//interp.dump_cnodes(stmt_node, true)
	//fmt.Printf("--------------\n")

	fmt.Printf("START p.sp = %d\n", p.vsp)
	for stmt_node != nil {
		if stmt_node.code != CNODE_STMT {
			panic("internal error - not statement node")
		}

		p.push_context(stmt_node, nil)
		p.push_string_value("") // placeholder for return value

	start_over:
		inner_node = stmt_node.child
	resume:
		for inner_node != nil {
			switch inner_node.code {
			case CNODE_BRACKET:
			case CNODE_DQUOTE:
				if inner_node.child != nil {
					stmt_node = inner_node.child // first statement inside []
					p.push_context(stmt_node, inner_node)
					p.push_string_value("")
					goto start_over
				} else {
					// no statements inside []. treat it like an empty string
					p.push_string_value("")
				}

			case CNODE_BRACE:
				p.push_cnode_value(inner_node)

			case CNODE_TEXT:

				//fmt.Printf("XXXXXXXXXXXXXXXXXXXx[%s]\n", string(inner_node.token))
				err = p.push_string_value(string(inner_node.token))
				if err != nil {
					goto oops
				}

				// TODO: many more types...
			}

			inner_node = inner_node.next
		}

		fmt.Printf("CALLING for %d\n", p.ctx.parent_node.code)
		if p.ctx.parent_node.code == CNODE_STMT {
			err = p.call()
			if err != nil {
				goto oops
			}
		} else {
			fmt.Printf("DDDDDDDDDDDDBVVVVVVVVVVVDDDd\n")
		}

		stmt_node, inner_node = p.pop_context()
		if inner_node != nil {
			inner_node = inner_node.next
			goto resume
		}

		v = (*string)(p.pop_value()) // get the return value of the statement.
		stmt_node = stmt_node.next
	}

	fmt.Printf("END p.sp = %d\n", p.vsp)
	return v, nil

oops:
	return nil, err
}

/*
func (interp *Interp) eval_atom_node_old(node *Cnode_t) (*string, error) {

	var (
		p   process_t
		v   *string
		err error
	)

	p.interp = interp
	p.push_context(nil)
	p.push_string_value("") // placeholder for return value

	for node != nil {
		switch node.code {
		case CNODE_BRACKET: // this is a container
			if node.child != nil {
				p.push_context(node)
				err = p.push_string_value("") // placeholder for return value
				if err != nil {
					goto oops
				}
				node = node.child
				continue
			} else {
				err = p.push_string_value("")
				if err != nil {
					goto oops
				}
			}

		case CNODE_BRACE: // this is a container
			err = p.push_cnode_value(node)
			if err != nil {
				goto oops
			}

		case CNODE_DQUOTE: // this is a container
			// TODO: at the feed layer, recompose CNODE_DQUOTE item to
			// successive ATOM item
			// "abc $ddd [xx 11]" must be TEXT("abc ") + VAR("ddd") + BRACKET["xx 11"]  without SEP in between

			// this is not right.....
			if node.child != nil {
				// TODO:  something is not right here. handle inner stuffs
				//fmt.Printf("pushing [%s]\n", string(node.child.token))
				err = p.push_string_value(string(node.child.token))
			} else {
				err = p.push_string_value("")
			}
			if err != nil {
				goto oops
			}

		case CNODE_VAR:

		case CNODE_TEXT:
			//fmt.Printf("pushing [%s]\n", string(node.token))
			err = p.push_string_value(string(node.token))
			if err != nil {
				goto oops
			}

		default:
			err = fmt.Errorf("internal error - non-atom node - %d", node.code)
			goto oops
		}

		node = node.next
	check_end:
		if node == nil { // reached the last node
			err = p.call()
			if err != nil {
				goto oops
			}
			if p.ctx.parent_ctx != nil {
				node = p.pop_context()
				if node.seqno > 0 {
					// merge the top 2 values (return from [] + previous argument)
					// for instance,  the expression `aa[qq 11]` must product a single word
					// `aa` concatenated of the result of `qq 11`
					err = p.merge_top_values()
					if err != nil {
						goto oops
					}
				}
				node = node.next

				// take `aa 11 22 [dd [bb cc]]` as an example
				// after [bb cc] is called, it must call `[dd]`` followed by `aa`.
				// this goto loop is to handle successive calls when a nested call is the
				// last argument
				goto check_end
			}
		}
	}

	v = (*string)(p.pop_value())
	p.pop_context()
	if p.ctx != nil {
		err = fmt.Errorf("internal error - dangling process context")
		goto oops
	}

	return v, nil

oops:
	return nil, err
}
*/

func (interp *Interp) eval_arg(p *process_t, pos int) (*string, error) {
	var (
		ptr uintptr
	)

	ptr = uintptr(p.GetArg(pos))
	if ptr&1 == 1 { // cnode
		ptr &= ^uintptr(1)
		//interp.dump_cnodes((*Cnode_t)(unsafe.Pointer(ptr)), true)
		//return interp.eval_atom_node((*Cnode_t)(unsafe.Pointer(ptr)).child)
		return interp.eval_node_child((*Cnode_t)(unsafe.Pointer(ptr)))
	} else {
		return (*string)(unsafe.Pointer(ptr)), nil
	}
}

func (interp *Interp) eval_arg_literally(p *process_t, pos int) (*string, error) {
	var (
		ptr uintptr
		//cnode *Cnode_t
	)

	ptr = uintptr(p.GetArg(pos))
	if ptr&1 == 1 { // cnode
		ptr &= ^uintptr(1)
		//cnode = (*Cnode_t)(unsafe.Pointer(ptr))
		//cnode.child i hate this portion....
		return nil, fmt.Errorf("not supported - unable to evaluate {} literally")
	} else {
		return (*string)(unsafe.Pointer(ptr)), nil
	}
}

func (interp *Interp) EvalText(text []rune) (*string, error) {
	var (
		v    *string
		node *Cnode_t
		err  error
	)

	interp.BeginFeed() // this resets the feed stack to the initial state

	err = interp.FeedRunes(text)
	if err != nil {
		goto oops
	}

	node, err = interp.EndFeed()
	if err != nil {
		goto oops
	}

	//fmt.Printf("--------------------\n")
	//interp.dump_cnodes(node, true)
	//fmt.Printf("--------------------\n")

	v, err = interp.Execute(node)
	if err != nil {
		goto oops
	}

	return v, nil

oops:
	return nil, err
}