how to add refraction to a water shader?

shader_type spatial;

uniform sampler2D DEPTH_TEXTURE : hint_depth_texture, repeat_disable, filter_nearest; 
uniform sampler2D SCREEN_TEXTURE : hint_screen_texture, filter_linear_mipmap;
uniform float refraction = 0.075;
varying mat4 inv_mvp; 
uniform float absorbance : hint_range(0.0, 10.0) = 2.0;

uniform vec3 shallow_color : source_color = vec3(0.22, 0.66, 1.0);
uniform vec3 deep_color : source_color = vec3(0.0, 0.25, 0.45);

uniform float foam_amount : hint_range(0.0, 2.0) = 0.2;
uniform vec3 foam_color : source_color = vec3(1);
uniform sampler2D caustic_texture : hint_default_white,repeat_enable,filter_linear_mipmap;
uniform sampler2D foam_texture : hint_default_white,repeat_enable,filter_linear_mipmap;

uniform float roughness : hint_range(0.0, 1.0) = 0.05;
uniform float wave_scale = 4.0;

varying vec3 uv_world_pos;

uniform sampler2D normal1 : hint_normal,repeat_enable,filter_linear_mipmap;
uniform vec2 wave_dir1 = vec2(1.0, 0.0);
uniform sampler2D normal2 :hint_normal,repeat_enable,filter_linear_mipmap;
uniform vec2 wave_dir2 = vec2(0.0, 1.0);
uniform float wave_speed : hint_range(0.0, 0.2) = 0.015;

vec3 screen(vec3 base, vec3 blend){
	return 1.0 - (1.0 - base) * (1.0 - blend);
}
void vertex() {
	uv_world_pos = (MODEL_MATRIX * vec4(VERTEX, 1.0)).xyz;
	inv_mvp = inverse(PROJECTION_MATRIX * MODELVIEW_MATRIX);
}

void fragment()
{
	vec2 normal_offset1 = (TIME * wave_dir1) * wave_speed;
	vec2 normal_offset2 = (TIME * wave_dir2) * wave_speed;
	vec3 normal_blend = mix(texture(normal1, uv_world_pos.xz / wave_scale + normal_offset1), texture(normal2, uv_world_pos.xz / wave_scale + normal_offset2), 0.5).rgb;
	vec3 ref_normalmap = normal_blend * 2.0 - 1.0;
	ref_normalmap = normalize(TANGENT * ref_normalmap.x + BINORMAL * ref_normalmap.y + NORMAL *ref_normalmap.z);
	vec2 ref_uv = SCREEN_UV + (ref_normalmap.xy);
	float depth_raw = texture(DEPTH_TEXTURE, ref_uv).r * 2.0 - 1.0;
	float depth = PROJECTION_MATRIX[3][2] / (depth_raw + PROJECTION_MATRIX[2][2]);
	float depth_blend = exp((depth+VERTEX.z + absorbance) * -absorbance);
	depth_blend = clamp(1.0-depth_blend, 0.0, 1.0);
	float depth_blend_pow = clamp(pow(depth_blend, 2.5), 0.0, 1.0);
	float depth1 = texture(DEPTH_TEXTURE, SCREEN_UV, 0.0).r;
  	vec3 ndc = vec3(SCREEN_UV * 2.0 - 1.0, depth1);
	vec4 world = INV_VIEW_MATRIX * INV_PROJECTION_MATRIX * vec4(ndc, 1.0);
	float depth_texture_y = world.y / world.w;
	float vertex_y = (INV_VIEW_MATRIX * vec4(VERTEX, 1.0)).y;
	float vertical_depth = vertex_y - depth_texture_y;
	
	
	// Makes the water more transparent as it gets more shallow
	float alpha_blend = -vertical_depth * absorbance;
	alpha_blend = clamp(1.0 - exp(alpha_blend), 0.0, 1.0);
	vec2 distortUV = (ref_normalmap.xy + SCREEN_UV) * refraction * 2.0;
	vec3 refractiontex = texture(SCREEN_TEXTURE, distortUV).xyz;
	vec3 screen_color = refractiontex;
	
		
	// Small layer of foam
	float foam_blend = clamp(1.0 - (vertical_depth / foam_amount), 0.0,1.0);
	vec4 foamtex = texture(foam_texture,uv_world_pos.xz / wave_scale + normal_offset1 + normal_offset2);
	vec3 foam = foam_blend * foam_color * foamtex.rgb;
	
	// Mix them all together
	vec3 color_out = mix(deep_color, shallow_color, alpha_blend);
	color_out = screen(color_out, foam);
	color_out = mix(color_out, screen_color, .5);
	mediump float fresnel = sqrt(1.0 - dot(NORMAL, VIEW));
	
	// Caustic screen projection
	vec4 caustic_screenPos = vec4(ref_uv*2.0-1.0, depth_raw, 1.0);
	vec4 caustic_localPos = inv_mvp * caustic_screenPos;
	caustic_localPos = vec4(caustic_localPos.xyz/caustic_localPos.w, caustic_localPos.w);
	
	vec2 caustic_Uv = caustic_localPos.xz / vec2(1024.0) + 0.5;
	vec4 caustic_color = texture(caustic_texture, caustic_Uv*300.0);

	color_out *= 1.0 + pow(caustic_color.r, 1.50) * (1.0-alpha_blend) * 6.0;



	// Set all values:
	ALBEDO = color_out;
	METALLIC = 0.05;
	ROUGHNESS = roughness;
	SPECULAR = 0.2 + depth_blend_pow * fresnel;
	NORMAL_MAP = normal_blend;
	ALPHA = alpha_blend;
	
}