package apple2

import (
	"image"
	"image/color"
	"time"
)

const (
	charWidth        = 7
	charHeight       = 8
	textColumns      = 40
	textLines        = 24
	textLinesMix     = 4
	textPage1Address = uint16(0x0400)
	textPage2Address = uint16(0x0800)
)

func getTextCharOffset(col int, line int) uint16 {

	// See "Understanding the Apple II", page 5-10
	// http://www.applelogic.org/files/UNDERSTANDINGTHEAII.pdf
	section := line / 8 // Top, middle and bottom
	eigth := line % 8
	return uint16(section*40 + eigth*0x80 + col)
}

func getTextChar(a *Apple2, col int, line int, page int) uint8 {
	address := textPage1Address
	if page == 1 {
		address = textPage2Address
	}
	address += getTextCharOffset(col, line)
	return a.mmu.internalPeek(address)
}

func snapshotTextMode(a *Apple2, page int, mixMode bool, light color.Color) *image.RGBA {
	// Flash mode is 2Hz
	isFlashedFrame := time.Now().Nanosecond() > (1 * 1000 * 1000 * 1000 / 2)

	lineStart := 0
	if mixMode {
		lineStart = textLines - textLinesMix
	}

	width := textColumns * charWidth
	height := (textLines - lineStart) * charHeight
	size := image.Rect(0, 0, width, height)
	img := image.NewRGBA(size)

	for x := 0; x < width; x++ {
		for y := 0; y < height; y++ {
			line := y/charHeight + lineStart
			col := x / charWidth
			rowInChar := y % charHeight
			colInChar := x % charWidth
			char := getTextChar(a, col, line, page)
			topBits := char >> 6
			isInverse := topBits == 0
			isFlash := topBits == 1

			pixel := a.cg.getPixel(char, rowInChar, colInChar)
			pixel = pixel != (isInverse || (isFlash && isFlashedFrame))
			var colour color.Color
			if pixel {
				colour = light
			} else {
				colour = color.Black
			}
			img.Set(x, y, colour)
		}
	}

	return img
}