package gigaparsec

//go:generate go run ./internal/bindgen -output bind.go -max 5 -pkg gigaparsec
import (
	"errors"
	"fmt"
	"io"
	"slices"

	"git.codemonkeysoftware.net/b/gigaparsec/cursor"
)

type Result[In, Out any] struct {
	consumed, succeeded bool
	value               Out
	next                State[In]
	message             Message
}

func Fail[In, Out any](consumed bool, msg Message) Result[In, Out] {
	return Result[In, Out]{
		consumed:  consumed,
		succeeded: false,
		message:   msg,
	}
}

func (r Result[In, Out]) Failed() (failed, consumed bool, msg Message) {
	failed = !r.succeeded
	if failed {
		consumed = r.consumed
		msg = r.message
	}
	return
}

func Succeed[In, Out any](consumed bool, value Out, next State[In], msg Message) Result[In, Out] {
	return Result[In, Out]{
		succeeded: true,
		value:     value,
		consumed:  consumed,
		next:      next,
		message:   msg,
	}
}

func (r Result[In, Out]) Succeeded() (succeeded, consumed bool, value Out, next State[In], msg Message) {
	succeeded = r.succeeded
	if succeeded {
		consumed = r.consumed
		value = r.value
		next = r.next
		msg = r.message
	}
	return
}

func (r Result[In, Out]) Consumed() bool {
	return r.consumed
}

func (r Result[In, Out]) Consume(consumed bool) Result[In, Out] {
	r.consumed = consumed
	return r
}

func MakeMessage(pos uint64, got string, expected ...string) Message {
	return Message{
		pos:      pos,
		got:      got,
		expected: expected,
	}
}

type Message struct {
	pos      uint64
	got      string
	expected []string
}

func (m Message) PosMethod() uint64 {
	return m.pos
}

func (m Message) GotMethod() string {
	return m.got
}

func (m Message) ExpectedMethod() []string {
	return m.expected
}

func (m Message) expect(s string) Message {
	m.expected = []string{s}
	return m
}

func MessageOK(pos uint64) Message { return Message{pos: pos} }

func MessageEnd(pos uint64) Message { return Message{pos: pos, got: "end of input"} }

func MakeState[In any](c cursor.Cursor[In]) State[In] {
	return State[In]{cursor: c}
}

type State[In any] struct {
	cursor cursor.Cursor[In]
}

func (s State[In]) Cursor() cursor.Cursor[In] {
	return s.cursor
}

func (s State[In]) Read(dst []In) (n uint64, next State[In], err error) {
	n, c, err := s.cursor.Read(dst)
	return n, State[In]{cursor: c}, err
}

func (s State[In]) Pos() uint64 {
	return s.cursor.Pos()
}

func (s State[In]) At(pos uint64) State[In] {
	return State[In]{cursor: s.cursor.At(pos)}
}

type Parser[In, Out any] func(State[In]) (Result[In, Out], error)

func (p Parser[In, Out]) Label(label string) Parser[In, Out] {
	return func(input State[In]) (Result[In, Out], error) {
		result, err := p(input)
		if err != nil || result.Consumed() {
			return result, err
		}
		if succeeded, _, value, next, msg := result.Succeeded(); succeeded {
			return Succeed(false, value, next, msg.expect(label)), nil
		}
		_, _, msg := result.Failed()
		return Fail[In, Out](false, msg.expect(label)), nil
	}
}

func Return[In, Out any](value Out) Parser[In, Out] {
	return func(state State[In]) (Result[In, Out], error) {
		return Succeed(false, value, state, MessageOK(state.Pos())), nil
	}
}

func Satisfy[T any](pred func(T) bool) Parser[T, T] {
	return func(state State[T]) (Result[T, T], error) {
		token := make([]T, 1)
		n, next, err := state.Read(token)
		if errors.Is(err, io.EOF) {
			return Fail[T, T](false, MessageEnd(state.Pos())), nil
		}
		if err != nil {
			return Result[T, T]{}, err
		}
		if n != 1 {
			panic(fmt.Sprintf("expected 1 element from Read, but got %d", n))
		}
		if pred(token[0]) {
			return Succeed(true, token[0], next, MessageOK(state.Pos())), nil
		}
		return Fail[T, T](false, MakeMessage(state.Pos(), fmt.Sprint(token))), nil
	}
}

func Slice[T comparable](s []T) Parser[T, []T] {
	expected := fmt.Sprint(s)
	return func(state State[T]) (Result[T, []T], error) {
		token := make([]T, len(s))
		_, next, err := state.Read(token)
		if errors.Is(err, io.EOF) {
			return Fail[T, []T](false, MessageEnd(state.Pos())), nil
		}
		if err != nil {
			return Result[T, []T]{}, err
		}
		if !slices.Equal(s, token) {
			return Fail[T, []T](false, MakeMessage(state.Pos(), fmt.Sprint(token), expected)), nil
		}
		return Succeed(true, token, next, MessageOK(state.Pos())), nil
	}
}

func Choose[In, Out any](p Parser[In, Out], ps ...Parser[In, Out]) Parser[In, Out] {
	// TODO Check this against the Parsec paper again, and simplify it.
	all := append([]Parser[In, Out]{p}, ps...)
	return func(input State[In]) (Result[In, Out], error) {
		expecteds := make([][]string, 0, len(all))
		var value Out
		var got string
		var failed bool
		for _, q := range all {
			result, err := q(input)
			if err != nil {
				return Result[In, Out]{}, err
			}
			if result.Consumed() {
				return result, nil
			}
			var qMsg Message
			if isFailure, _, msg := result.Failed(); isFailure {
				qMsg = msg
				failed = true
			} else {
				_, _, qValue, _, msg := result.Succeeded()
				if failed {
					value = qValue
					failed = false
				}
				qMsg = msg
			}
			if got == "" {
				got = qMsg.got
			}
		}
		msg := MakeMessage(input.Pos(), got, slices.Concat(expecteds...)...)
		if failed {
			return Fail[In, Out](false, msg), nil
		}
		return Succeed(false, value, input, msg), nil
	}
}

// Try behaves identically to p, except that if p returns an error,
// Try will pretend that no input was consumed. This allows infinite
// lookahead: Since Choose only calls another parser when the previous
// parser consumed nothing, Try will allow backing out of a complex
// parser that partially succeeded.
func Try[In, Out any](p Parser[In, Out]) Parser[In, Out] {
	return func(input State[In]) (Result[In, Out], error) {
		result, err := p(input)
		if err != nil {
			return result, err
		}
		if failed, _, msg := result.Failed(); failed {
			return Fail[In, Out](false, msg), nil
		}
		return result, nil
	}
}

func Map[In, Out1, Out2 any](p Parser[In, Out1], f func(Out1) Out2) Parser[In, Out2] {
	return Bind(p, func(out Out1) Parser[In, Out2] {
		return Return[In](f(out))
	})
}

func end[In any](s State[In]) (Result[In, struct{}], error) {
	_, _, err := s.cursor.Read([]In{})
	if errors.Is(err, io.EOF) {
		return Succeed(true, struct{}{}, s, MessageOK(s.Pos())), nil
	}
	if err != nil {
		return Result[In, struct{}]{}, fmt.Errorf("End: unexpected error: %w", err)
	}
	return Fail[In, struct{}](false, MakeMessage(s.Pos(), "", "end of input")), nil
}

func End[In any]() Parser[In, struct{}] {
	return end
}