package main

import (
	"fmt"
	"strconv"
	"strings"
)

// Context is a set of Dictionary + Stacks + Flags representing a runtime environment
type Context struct {
	Dictionary Dictionary
	Stack      *Stack
	RStack     *Stack
	Flags      Flags
	Words      []string
}

// Eval evaulates a given line, recursively descending into given words as needed
func (c *Context) Eval(line string) error {
	// state
	var word []byte

	for i := 0; i < len(line); i = i + 1 {
		switch line[i] {
		case ' ':
			sword := strings.TrimSpace(string(word))
			if len(word) == 0 {
				// empty space, just continue...
				continue
			}
			// Is this a word we know?
			w, _ := c.Dictionary.GetWord(sword)
			// check if it's an IMMEDIATE mode toggle word
			if !c.Flags.GetFlag("Immediate") {
				c.Flags.SetFlag("Immediate", w.Immediate)
			}

			if !c.Flags.GetFlag("Immediate") {
				if !c.Flags.GetFlag("Comment") {
					c.Words = append(c.Words, sword)
				}
				word = []byte{}
				continue
			}

			int, err := strconv.Atoi(sword)
			if err == nil {
				// it was a number! put it on the stack.
				c.Stack.Push(int)
				word = []byte{}
				continue
			}

			// it wasn't a number. Is it a word we know?
			w, err = c.Dictionary.GetWord(sword)
			if err != nil {
				return fmt.Errorf("could not parse %s; %v", w.Name, err)
			}
			// run word
			c.RStack.Push(i)
			if err = c.Exec(w); err != nil {
				return err
			}
			i, err = c.RStack.Pop()
			if err != nil {
				return fmt.Errorf("error while popping from return stack: %v", err)
			}
			word = []byte{}
		default:
			word = append(word, line[i])
		}
	}

	return nil
}

// Exec wraps the branched execution of words (either built-in or user-defined)
func (c *Context) Exec(w Word) error {
	if w.Impl != nil {
		// we have an implementation for that word. Run it.
		err := w.Impl()
		if err != nil {
			return err
		}
	} else if len(w.Source) != 0 {
		// user-defined word; let's descend...
		err := c.Eval(strings.Join(w.Source, " ") + " ")
		if err != nil {
			return err
		}
	}
	return nil
}