Generic GLSL Lighting Shader

Pixel based lighting is a common issue in many OpenGL applications, as the standard OpenGL lighting has very poor quality.

I want to use a GLSL program to have per-pixel based lighting in my OpenGL program instead of per-vertex. Just Diffuse lighting, but with fog, texture and texture-alpha at least.

I started with this shader:

texture.vert:

varying vec3 position;
varying vec3 normal; 

void main(void) 
{
  gl_Position       = gl_ModelViewProjectionMatrix * gl_Vertex;
  gl_FrontColor     = gl_Color;
  gl_TexCoord[0]    = gl_MultiTexCoord0; 
  normal        = normalize(gl_NormalMatrix * gl_Normal);
  position      = vec3(gl_ModelViewMatrix * gl_Vertex);
}

texture.frag:

uniform sampler2D Texture0;
uniform int ActiveLights;

varying vec3 position;
varying vec3 normal; 

void main(void) 
{
  vec3 lightDir;
  float  attenFactor;
  vec3 eyeDir           = normalize(-position); // camera is at (0,0,0) in ModelView space
  vec4 lightAmbientDiffuse  = vec4(0.0,0.0,0.0,0.0);
  vec4 lightSpecular        = vec4(0.0,0.0,0.0,0.0);    

  // iterate all lights
  for (int i=0; i<ActiveLights; ++i)
  {
    // attenuation and light direction
    if (gl_LightSource[i].position.w != 0.0)
    {
        // positional light source
        float dist  = distance(gl_LightSource[i].position.xyz, position);
        attenFactor = 1.0/( gl_LightSource[i].constantAttenuation + 
                    gl_LightSource[i].linearAttenuation * dist +
                    gl_LightSource[i].quadraticAttenuation * dist * dist );
        lightDir    = normalize(gl_LightSource[i].position.xyz - position);
    }       
    else 
    {           
        // directional light source         
        attenFactor = 1.0;          
        lightDir    = gl_LightSource[