package interp

import (
	"fmt"
	"unsafe"
)

var debug bool = true

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
	case "true":
		proc = proc_true
	case "false":
		proc = proc_false
	case "null":
		proc = proc_null
	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(clear_vstack bool) (*Cnode_t, *Cnode_t) {
	var (
		i         int
		node      *Cnode_t
		container *Cnode_t
	)

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

	if clear_vstack {
		// 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) dump_vstack(p *process_t) {
	fmt.Printf("p.VSP => %d\n", p.vsp)
	for i := 0; i < p.vsp; i++ {
		x := uintptr(p.vstack[i])
		if x&1 == 0 {
			// string value
			fmt.Printf(" %d => [%s]\n", i, *(*string)(p.vstack[i]))
		} else {
			// cnode value
			fmt.Printf(" %d => cnode %p", i, p.vstack[i]) // TODO: strip 1 off
		}
	}
}

/*
puts "hello" world

	[STMT]
		[TEXT|puts] [DQUOTE] [TEXT|world]
	                     [TEXT|hello]

[puts 1 2; puts 1] 999

	[STMT]
	    [BRACKET] [TEXT|999]
		   [STMT]
		      [TEXT|puts] [TEXT|1] [TEXT|2]
		   [STMT]
		      [TEXT|puts] [TEXT|1]

"pu[null 1]ts" 10 20

	[STMT]
	     [DQUOTE] [TEXT|10] [TEXT|20]
		    [TEXT|pu] [BRACKET] [JOIN] [TEXT|ts] [JOIN]
			         [STMT]
					    [TEXT|null] [TEXT|1]
*/
func (interp *Interp) eval_stmt_nodes(container_node *Cnode_t) (*string, error) {
	var (
		p          process_t
		v          *string
		stmt_node  *Cnode_t
		upper_node *Cnode_t
		inner_node *Cnode_t
		is_stmt    bool
		err        error
	)

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

	p.interp = interp
	upper_node = container_node
	stmt_node = upper_node.child // the first statement

	fmt.Printf("START p.sp = %d\n", p.vsp)

	for stmt_node != nil {
	start_over_0:
		if stmt_node.code != CNODE_STMT {
			panic("internal error - not statement node")
		}

		//fmt.Printf("PUSHING CONTEXT.....\n")
		p.push_context(stmt_node, upper_node)
		p.push_string_value("") // placeholder for return value

		//start_over:
		inner_node = stmt_node.child
	resume:
		for inner_node != nil {
			//fmt.Printf("handling %d\n", inner_node.code)
			switch inner_node.code {
			case CNODE_BRACKET:
				if inner_node.child != nil {
					upper_node = inner_node
					stmt_node = upper_node.child
					if debug {
						fmt.Printf("going to start over\n")
						interp.dump_cnodes(stmt_node, true)
						fmt.Printf("\n--\n")
					}
					goto start_over_0
				} else {
					// no statements inside []. treat it like an empty string
					p.push_string_value("")
				}

			case CNODE_DQUOTE:
				if inner_node.child != nil {
					//fmt.Printf("PUSHING CONTEXT.....\n")
					p.push_context(stmt_node, inner_node)
					//p.push_string_value("") // no placeholder for return value is needed
					inner_node = inner_node.child
					if debug {
						fmt.Printf("going to start over\n")
						interp.dump_cnodes(stmt_node, true)
						fmt.Printf("\n--\n")
					}
					goto resume
				} 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...
			case CNODE_JOIN:
				p.merge_top_values()
			}

			inner_node = inner_node.next
		}

		if debug {
			interp.dump_vstack(&p)
		}
		//fmt.Printf("p.ctx.parent_node.code %d p.ctx.container_node.code %d CNODE_STMT %d CNODE_DQUOTE %d CNODE_BRACKET %d\n", p.ctx.parent_node.code, p.ctx.container_node.code, CNODE_STMT, CNODE_DQUOTE, CNODE_BRACKET)
		if p.ctx.container_node.code == CNODE_INIT || p.ctx.container_node.code == CNODE_BRACKET {
			if debug {
				fmt.Printf("calling..... [%s]\n", *p.GetCalleeName())
			}
			err = p.call()
			if err != nil {
				goto oops
			}

			is_stmt = true
		} else {
			is_stmt = false
		}

		//fmt.Printf("POPPING CONTEXT.....is_stmt[%v]\n", is_stmt)
		stmt_node, upper_node = p.pop_context(is_stmt)
		if upper_node != container_node {
			if debug {
				fmt.Printf("resuming... %d upper_node.next %p\n", p.vsp, upper_node.next)
			}
			inner_node = upper_node.next // as if it hit the bottom of the innner for loop
			goto resume
		}

		//fmt.Printf("POPPING VALUE...\n")
		v = (*string)(p.pop_value()) // get the return value of the statement.
		if debug {
			interp.dump_vstack(&p)
		}
		stmt_node = stmt_node.next
	}

	if debug {
		interp.dump_vstack(&p)
		fmt.Printf("END p.sp = %d\n", p.vsp)
	}
	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_stmt_nodes((*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
}