package parsekit

import (
	"fmt"
	"reflect"
	"runtime"
)

// 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, a state function must provide
			// a routing decision in every state function execution.
			// When no route is specified, then it is considered a but
			// in the parser implementation.
			// An exception is when a function specified its expectation
			// using the Expects() method. In that case, an unexpected
			// input error is emitted.
			if p.nextState == nil {
				if p.expecting != "" {
					p.UnexpectedInput()
					continue
				} else {
					name := runtime.FuncForPC(reflect.ValueOf(p.state).Pointer()).Name()
					panic(fmt.Sprintf("StateFn implementation bug: %s did not set next state or input expectation", name))
				}
			}
			p.state = p.nextState
			p.nextState = nil
			p.expecting = ""
			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)
	}
}