shader_type canvas_item;
uniform vec2 scale = vec2(1,1);
uniform float flip_param = 0.0;

vec2 Line2point(vec2 linePoint,vec2 lineDire,vec2 point) {
    lineDire = normalize(lineDire);
    vec2 line2Ori = - linePoint - dot(-linePoint,lineDire)*lineDire;
    vec2 p2Ori = - point - dot(-point,lineDire)*lineDire;
    return line2Ori-p2Ori;
}

vec4 ColorWithA(vec4 oldCol,vec4 newCol){
    vec4 finalCol;
    if((newCol.a + oldCol.a)>=1.) {
        finalCol.rgb = newCol.rgb;
        finalCol.a = 1.0;
    } else {
        finalCol.rgb = newCol.a/(newCol.a + oldCol.a)*newCol.rgb + oldCol.a/(newCol.a + oldCol.a)*oldCol.rgb;
        finalCol.a = oldCol.a + newCol.a;
    }
    return finalCol;
}

void fragment() {
	vec2 start_flip_pos = vec2(0.8, -0.2);
	vec2 end_flip_pos = vec2(0, 1);
    // Interpolate flip_pos based on flip_param
    vec2 flip_pos = mix(start_flip_pos, end_flip_pos, flip_param);

    vec2 uv = UV;
    vec4 finalColor = vec4(0.0); // Initialize with transparent color
    float scale_min = scale.x/scale.y;
    vec2 uv_max = vec2(scale_min,1.);
    float trueScale;
    if(scale.y < scale.x) {
        scale_min = scale.y/scale.x;
        uv.y = uv.y * scale_min;
        uv_max = vec2(1.,scale_min);
        trueScale = scale.x;
    } else {
        uv.x = uv.x * scale_min;
        trueScale = scale.y;
    }

    COLOR = texture(TEXTURE, uv);

    vec2 pPos = uv / TEXTURE_PIXEL_SIZE * trueScale;
    if (flip_pos.x > -0.0001) {
        vec2 left_bottom = vec2(0., uv_max.y / TEXTURE_PIXEL_SIZE.y * trueScale);
        vec2 midpoint = (flip_pos - left_bottom) / 2. + left_bottom;
        vec2 midDirect = normalize(vec2(-(flip_pos - left_bottom).y, (flip_pos - left_bottom).x));

        vec2 sharpPoint = vec2(0., midpoint.y - midDirect.y / midDirect.x * midpoint.x);
        vec2 flipEdgeDire = normalize(sharpPoint - flip_pos);

        vec2 sharpPointB = vec2(midpoint.x - midDirect.x / midDirect.y * (midpoint - left_bottom).y, left_bottom.y);
        vec2 flipEdgeDireB = normalize(sharpPointB - flip_pos);

        float cyOriOff = length(flip_pos - left_bottom);
        if (cyOriOff > 100.) cyOriOff = 100.;
        float cyR = cyOriOff * 2. / PI;
        float pageHDire = PI / 6.;
        vec2 midlineToP = Line2point(midpoint, midDirect, pPos);
        vec2 sideEdgeToP = Line2point(flip_pos, flipEdgeDire, pPos);
        vec2 BottomEdgeToP = Line2point(flip_pos, flipEdgeDireB, pPos);

        vec2 cyOriToP = midlineToP - normalize(flip_pos - left_bottom) * cyOriOff;
        vec2 cyEdgeToP = midlineToP - normalize(flip_pos - left_bottom) * (cyOriOff - cyR);

        bool atBG = (cyOriToP).x <= -0.01;
        bool atPageBack = !atBG && (sideEdgeToP.y > 0.) && (BottomEdgeToP.x <= 0.);
        bool atCy = cyEdgeToP.x >= 0. && (cyOriToP).x <= 0.;
        bool atCyPage = false;
        vec2 uvCy;
        vec2 uvCyB;

        float shadow = 1.;
        if (atCy) {
            vec2 cyOri = pPos - cyOriToP;
            vec2 trueDis = cyR * asin(length(cyOriToP) / cyR) * normalize(cyOriToP);
            vec2 truePos = cyOri + trueDis;

            vec2 sideEdgeToTP = Line2point(flip_pos, flipEdgeDire, truePos);
            vec2 BottomEdgeToTP = Line2point(flip_pos, flipEdgeDireB, truePos);
            uvCyB = truePos * TEXTURE_PIXEL_SIZE / trueScale;
            shadow *= 1. - pow(length(trueDis) / (cyR * PI / 2.), 3.);

            if ((BottomEdgeToTP.x < 0.) && (sideEdgeToTP.y > 0.)) {
                atCyPage = true;
                uvCy = vec2(length(sideEdgeToTP), left_bottom.y - length(BottomEdgeToTP)) * TEXTURE_PIXEL_SIZE / trueScale;
            }

            if ((uvCyB.x > uv_max.x) || (uvCyB.y > uv_max.y) || (uvCyB.x <= 0.) || (uvCyB.y <= 0.))
                atCy = false;
        }

        COLOR = vec4(0.);
        if (!atBG && !atCy) {
            vec4 color = texture(TEXTURE, uv);
            finalColor = color;
        }

        if (atCy) {
            vec4 cyColor = texture(TEXTURE, uvCyB);
            finalColor = cyColor;
        }

        if (atCyPage) {
            vec4 cyPageColor = texture(TEXTURE, uvCy);
            cyPageColor.xyz *= 0.8;
            finalColor = mix(finalColor, cyPageColor, cyPageColor.a);
        } else if (atPageBack) {
            uv = vec2(length(sideEdgeToP), left_bottom.y - length(BottomEdgeToP)) * TEXTURE_PIXEL_SIZE / trueScale;
            vec4 pageBackColor = texture(TEXTURE, uv);
            pageBackColor.xyz *= 0.8;
            finalColor = mix(finalColor, pageBackColor, pageBackColor.a);
        }

        COLOR = finalColor;
    }
}