shader_type canvas_item;

// Scale and mouse position as input parameters
const vec2 scale = vec2(1, 1);

uniform float dim_color_scale : hint_range(0.0, 1.0) = 0.5;
uniform float pos_x : hint_range(0.0, 1.0) = 0.0001 ;
uniform float pos_y : hint_range(0.0, 1.0) = 0.05;

// Helper function to calculate the distance between a point and a line
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;
}

// Function to blend two colors based on their alpha values
vec4 ColorWithA(vec4 oldCol, vec4 newCol) {
    vec4 finalCol;
    if ((newCol.a + oldCol.a) >= 1.0) {
        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() {
    // Initialize mouse position and final color
    vec2 mouse_pos = vec2(-1., -1.);
    vec2 uv = UV;
    vec4 finalColor = vec4(0.0); // Transparent color initially

    // Adjust scale to maintain aspect ratio of the sprite
    float scale_min = scale.x / scale.y;
    vec2 uv_max = vec2(scale_min, 1.0);
    float trueScale;

    if (scale.y < scale.x) {
        scale_min = scale.y / scale.x;
        uv.y = uv.y * scale_min;
        uv_max = vec2(1.0, scale_min);
        trueScale = scale.x;
    } else {
        uv.x = uv.x * scale_min;
        trueScale = scale.y;
    }

    // Normalize mouse position based on the texture pixel size
    mouse_pos.x = pos_x * (1.0 / TEXTURE_PIXEL_SIZE.x);
    mouse_pos.y = pos_y * (1.0 / TEXTURE_PIXEL_SIZE.y);
    vec2 normalized_mouse = mouse_pos * uv_max;

    // Default texture color assignment
    COLOR = texture(TEXTURE, uv);

    // Calculate sprite's position relative to the mouse
    vec2 pPos = uv / TEXTURE_PIXEL_SIZE * trueScale;
    
    // Only process if the mouse position is valid
    if (normalized_mouse.x > -0.0001) {
        vec2 left_bottom = vec2(0.0, uv_max.y / TEXTURE_PIXEL_SIZE.y * trueScale);
        vec2 midpoint = (normalized_mouse - left_bottom) / 2.0 + left_bottom;
        vec2 midDirect = normalize(vec2(-(normalized_mouse - left_bottom).y, (normalized_mouse - left_bottom).x));

        // Calculate flip interactions
        vec2 sharpPoint = vec2(0.0, midpoint.y - midDirect.y / midDirect.x * midpoint.x);
        vec2 flipEdgeDire = normalize(sharpPoint - normalized_mouse);

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

        // Flip logic based on mouse distance and angle
        float cyOriOff = length(normalized_mouse - left_bottom);
        if (cyOriOff > 100.0) cyOriOff = 100.0;
        float cyR = cyOriOff * 2.0 / PI;

        vec2 midlineToP = Line2point(midpoint, midDirect, pPos);
        vec2 sideEdgeToP = Line2point(normalized_mouse, flipEdgeDire, pPos);
        vec2 BottomEdgeToP = Line2point(normalized_mouse, flipEdgeDireB, pPos);

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

        bool atBG = (cyOriToP).x <= -0.01;
        bool atPageBack = !atBG && (sideEdgeToP.y > 0.0) && (BottomEdgeToP.x <= 0.0);
        bool atCy = cyEdgeToP.x >= 0.0 && (cyOriToP).x <= 0.0;
        bool atCyPage = false;

        float shadow = 1.0;
        vec2 uvCy, uvCyB;

        // Handle flip state and apply shadow effect
        if (atCy) {
            vec2 cyOri = pPos - cyOriToP;
            vec2 trueDis = cyR * asin(length(cyOriToP) / cyR) * normalize(cyOriToP);
            vec2 truePos = cyOri + trueDis;

            uvCyB = truePos * TEXTURE_PIXEL_SIZE / trueScale;
            shadow *= 1.0 - pow(length(trueDis) / (cyR * PI / 2.0), 3.0);

            // Determine if we are on the flip side of the page
            if ((BottomEdgeToP.x < 0.0) && (sideEdgeToP.y > 0.0)) {
                atCyPage = true;
                uvCy = vec2(length(sideEdgeToP), left_bottom.y - length(BottomEdgeToP)) * TEXTURE_PIXEL_SIZE / trueScale;
            }

            if (uvCyB.x > uv_max.x || uvCyB.y > uv_max.y || uvCyB.x <= 0.0 || uvCyB.y <= 0.0) {
                atCy = false;
            }
        }

        // Blend final color based on conditions
        COLOR = vec4(0.0); // Reset COLOR

        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 *= dim_color_scale; // Dim the color slightly
            finalColor = mix(finalColor, cyPageColor, cyPageColor.a);
        } else if (atPageBack) { // If the fragment is on the flipped page, adjust the color for the back of the page
            uv = vec2(length(sideEdgeToP), left_bottom.y - length(BottomEdgeToP)) * TEXTURE_PIXEL_SIZE / trueScale;
            vec4 pageBackColor = texture(TEXTURE, uv);
            pageBackColor.xyz *= dim_color_scale; // Dim the back page color
            finalColor = mix(finalColor, pageBackColor, pageBackColor.a);
        }

        COLOR = finalColor;
    }
	else{
		
	}
}