package braille

import (
	"errors"
	"unicode/utf8"
)

// displayMasks is shared by the BrlAPI writer and cell export. A zero AND mask
// makes a Unicode Braille cell independent of BRLTTY's text translation table.
// Dots are attributes to OR into the cell, not a replacement cell array.
func displayMasks(text string, dots []byte) ([]byte, []byte, error) {
	if !utf8.ValidString(text) {
		return nil, nil, errors.New("invalid braille text")
	}
	length := utf8.RuneCountInString(text)
	if len(dots) != 0 && len(dots) != length {
		return nil, nil, errors.New("invalid braille indicator length")
	}
	andMask, orMask := make([]byte, length), make([]byte, length)
	for index, cell := range []rune(text) {
		andMask[index] = 0xff
		if len(dots) != 0 {
			orMask[index] = dots[index]
		}
		if cell >= 0x2800 && cell <= 0x28ff {
			andMask[index] = 0
			orMask[index] |= byte(cell - 0x2800)
		}
	}
	return andMask, orMask, nil
}

// rawCells exports a translated viewport without opening a display. It shares
// the physical writer's cell/attribute handling and the existing viewport's
// translation, wrapping and routing maps. The caller owns this viewport and
// serializes all access, independently of any physical viewport.
//
// Ordinary text needs BRLTTY translation and is deliberately rejected. Callers
// must first use the existing liblouis path with an explicitly chosen table.
// Spaces here are blank padding or the synthetic end-of-line cursor cell.
// cursorDots is an explicit, static overlay; this does not reproduce BRLTTY's
// configured cursor shape or blink timing. No native routing metadata is exported.
func (v *viewport) rawCells(cursorDots byte) ([]byte, error) {
	if _, err := (Geometry{Columns: v.width, Rows: 1}).Cells(); err != nil {
		return nil, err
	}
	text := []rune(v.frame())
	for index, cell := range text {
		if cell == ' ' {
			text[index] = '\u2800'
		} else if cell < 0x2800 || cell > 0x28ff {
			return nil, errors.New("raw braille export requires translated cells")
		}
	}
	_, cells, err := displayMasks(string(text), v.displayDots())
	if err != nil {
		return nil, err
	}
	if cursor := v.displayCursor(); cursor > 0 {
		cells[cursor-1] |= cursorDots
	}
	return cells, nil
}