package parsekit

// New takes an input string and a start state,
// and initializes the parser for it.
func New(input string, startState StateFn) *P {
	return &P{
		input:     input,
		len:       len(input),
		nextState: startState,
		items:     make(chan Item, 2),
	}
}

// Next retrieves the next parsed item.
// When a valid item was found, then the boolean return parameter will be true.
// On error or when successfully reaching the end of the input, false is returned.
// When an error occurred, it will be set in the error return value, nil otherwise.
func (p *P) Next() (Item, *Error, bool) {
	for {
		select {
		case i := <-p.items:
			switch {
			case i.Type == ItemEOF:
				return i, nil, false
			case i.Type == ItemError:
				p.err = &Error{i.Value, p.cursorRow, p.cursorColumn}
				return i, p.err, false
			default:
				p.item = i
				return i, nil, true
			}
		default:
			// When implementing a parser, it is mandatory to provide
			// a conscious state routing decision for every cycle.
			// This helps preventing bugs during implementation.
			if p.nextState == nil {
				panic("No next state was scheduled for the parser")
			}
			p.state, p.nextState = p.nextState, nil
			p.state(p)
		}
	}
}

// ToArray returns Parser items as an array (mainly intended for testing purposes)
// When an error occurs during scanning, a partial result will be
// returned, accompanied by the error that occurred.
func (p *P) ToArray() ([]Item, *Error) {
	var items []Item
	for {
		item, err, more := p.Next()
		if !more {
			return items, err
		}
		items = append(items, item)
	}
}