package typeset

import "image"
import "unicode"
import "image/draw"
import "image/color"
import "golang.org/x/image/math/fixed"

// Drawer is an extended TypeSetter that is able to draw text. Much like
// TypeSetter, It has no constructor and its zero value can be used safely.
type Drawer struct { TypeSetter }

// Draw draws the drawer's text onto the specified canvas at the given offset.
func (drawer Drawer) Draw (
	destination draw.Image,
	col         color.Color,
	offset      image.Point,
) (
	updatedRegion image.Rectangle,
) {
	source := image.NewUniform(col)
	
	drawer.ForRunes (func (
		index    int,
		char     rune,
		position fixed.Point26_6,
	) bool {
		// leave empty space for space characters
		if unicode.IsSpace(char) {
			return true
		}
		
		dot := fixed.P (
			offset.X + position.X.Round(),
			offset.Y + position.Y.Round())
		destinationRectangle,
		mask, maskPoint, _, ok := drawer.face.Glyph(dot, char)
		// tofu
		if !ok {
			drawer.drawTofu(char, destination, col, dot)
			return true
		}

		// FIXME:? clip destination rectangle if we are on the cusp of
		// the maximum height.

		draw.DrawMask (
			destination,
			destinationRectangle,
			source, image.Point { },
			mask, maskPoint,
			draw.Over)

		updatedRegion = updatedRegion.Union(destinationRectangle)
		return true
	})
	return
}

func (drawer Drawer) drawTofu (
	char rune,
	destination draw.Image,
	col         color.Color,
	position    fixed.Point26_6,
) {
	bounds, _ := tofuBounds(drawer.face)
	rectBounds := image.Rect (
		bounds.Min.X.Round(),
		bounds.Min.Y.Round(),
		bounds.Max.X.Round(),
		bounds.Max.Y.Round()).Add(image.Pt(
			position.X.Round(),
			position.Y.Round()))
	for x := rectBounds.Min.X; x < rectBounds.Max.X; x ++ {
		destination.Set(x, rectBounds.Min.Y, col)
	}
	for y := rectBounds.Min.Y; y < rectBounds.Max.Y; y ++ {
		destination.Set(rectBounds.Min.X, y, col)
		destination.Set(rectBounds.Max.X - 1, y, col)
	}
	for x := rectBounds.Min.X; x < rectBounds.Max.X; x ++ {
		destination.Set(x, rectBounds.Max.Y - 1, col)
	}
}