package bufr

import (
	"bufio"
	"io"
	"strings"

	"git.milar.in/milarin/ds"
)

type Reader struct {
	buf ds.Stack[posRune]
	src *bufio.Reader
	pos *Position
}

func New(r io.Reader) *Reader {
	return &Reader{
		buf: ds.NewArrayStack[posRune](),
		src: bufio.NewReader(r),
		pos: &Position{Index: 0, Line: 1, Column: 1},
	}
}

func NewFromString(str string) *Reader {
	return New(strings.NewReader(str))
}

func (r *Reader) psrn(rn rune) posRune {
	return posRune{
		Rune: rn,
		Pos:  *r.pos,
	}
}

func (r *Reader) Pos() Position {
	return *r.pos
}

// Rune returns the next rune in r
func (r *Reader) Rune() (rune, error) {
	rn, _, err := r.src.ReadRune()
	if err == nil {
		r.buf.Push(r.psrn(rn))
		r.pos.Advance(rn)
	}
	return rn, err
}

func (r *Reader) Buffered() int {
	return r.src.Buffered()
}

// PeekRune returns the next rune in r without advancing reader position.
// The next read will return the same rune again.
func (r *Reader) PeekRune() (rune, error) {
	rn, err := r.Rune()
	if err != nil {
		return 0, err
	}

	if err := r.UnreadRune(); err != nil {
		return 0, err
	}

	return rn, nil
}

// String returns the next len runes in r as a string.
// If an error occurs, both the already read string and the error will be returned
func (r *Reader) String(len int) (string, error) {
	str := ""

	for i := 0; i < len; i++ {
		rn, err := r.Rune()
		if err != nil {
			return str, err
		}
		str += string(rn)
	}

	return str, nil
}

// UnreadRune unreads the last rune.
// The next read will include the unread rune.
// It returns ErrNothingToUnread if there wasn't any read yet
func (r *Reader) UnreadRune() error {
	if r.buf.Empty() {
		return ErrNothingToUnread.New()
	}

	if err := r.src.UnreadRune(); err == nil {
		rn := r.buf.Pop()
		*r.pos = rn.Pos
	} else {
		rn := r.buf.Pop()
		*r.pos = rn.Pos
		r.src = prependRune(rn.Rune, r.src)
	}

	return nil
}

// UnreadString calls UnreadRune for each rune in str + one addtional rune for the separator rune
// The actual runes in str are irrelevant.
// Only the rune count of str determines the amount of UnreadRune calls.
// The first error occured will be returned immediately.
func (r *Reader) UnreadString(str string) error {
	for range str {
		err := r.UnreadRune()
		if err != nil {
			return err
		}
	}
	return r.UnreadRune()
}

// UnreadRunes calls UnreadRune n times
func (r *Reader) UnreadRunes(n int) error {
	for i := 0; i < n; i++ {
		err := r.UnreadRune()
		if err != nil {
			return err
		}
	}
	return nil
}

// StringWhile reads runes and calls all functions for each one.
// It returns all runes as a string for which any function returned true.
// It stops when all functions returned false or an error occured.
// The rune for which that function returned false will not be unread.
func (r *Reader) StringWhile(f ...RuneFunc) (string, error) {
	s := new(strings.Builder)

	var rn rune
	var err error
	for rn, err = r.Rune(); err == nil && findFirstTrue(rn, f); rn, err = r.Rune() {
		s.WriteRune(rn)
	}

	return s.String(), err
}

// PeekStringWhile acts as StringWhile but does not advance reader position
func (r *Reader) PeekStringWhile(f ...RuneFunc) (string, error) {
	str, err := r.StringWhile(f...)
	if err != nil {
		return "", err
	}

	if err := r.UnreadString(str); err != nil {
		return "", err
	}

	return str, nil
}

// StringUntil reads runes and calls all functions for each one.
// It returns all runes as a string for which all functions returned true.
// It stops when any function returns false or an error occured.
// The rune for which that function returned false will not be unread.
func (r *Reader) StringUntil(f ...RuneFunc) (string, error) {
	return r.StringWhile(func(rn rune) bool { return !findFirstTrue(rn, f) })
}

// PeekStringUntil acts as StringUntil but does not advance reader position
func (r *Reader) PeekStringUntil(f ...RuneFunc) (string, error) {
	str, err := r.StringUntil(f...)
	if err != nil {
		return "", err
	}

	if err := r.UnreadString(str); err != nil {
		return "", err
	}

	return str, nil
}

// SkipUntil acts as StringUntil but discards the string
// The rune for which that function returned false will be unread.
func (r *Reader) SkipUntil(f ...RuneFunc) error {
	_, err := r.StringUntil(f...)
	if err != nil {
		return err
	}
	return r.UnreadRune()
}

// SkipWhile acts as StringWhile but discards the string.
// The rune for which that function returned false will be unread.
func (r *Reader) SkipWhile(f ...RuneFunc) error {
	_, err := r.StringWhile(f...)
	if err != nil {
		return err
	}
	return r.UnreadRune()
}

// ExpectRune returns true if any function returns true for the next rune read from r
func (r *Reader) ExpectRune(f ...RuneFunc) (bool, error) {
	rn, err := r.Rune()
	if err != nil {
		return false, err
	}
	return findFirstTrue(rn, f), nil
}

// ExpectString calls ExpectRune for each rune in str successively.
// If the expected string was not found, all read runes will be unread
func (r *Reader) ExpectString(str string) (bool, error) {
	read := 0
	for _, rn := range str {
		ok, err := r.ExpectRune(Is(rn))
		if err != nil {
			return false, err
		}

		read++

		if !ok {
			if err := r.UnreadRunes(read); err != nil {
				return false, err
			}
			return false, nil
		}
	}

	return true, nil
}

// ExpectOneOfString calls ExpectString for each string successively
// and returns the string which first matched.
// The returned string will not be unread.
// If no string matches, ErrNoMatchFound is returned
func (r *Reader) ExpectOneOfString(str ...string) (string, error) {
	for _, s := range str {
		ok, err := r.ExpectString(s)
		if err != nil {
			return "", err
		}

		if ok {
			return s, nil
		}
	}

	return "", ErrNoMatchFound.New()
}

// Commit clears the internal buffer and therefore removes all data which were already read.
// After calling Commit any unreads will return ErrNothingToUnread until another read occured.
func (r *Reader) Commit() {
	r.buf.Clear()
}