How calculate three phase kilowatt hour from time

My problem is I want to calculate three phase power from time sampled data of current and voltages.

My questions:

How can I calculate the energy (unit kilowatt hour) from time sampled data? Are any equations available?
Is it needed to take the phase shift in account? (How can I calculate the phase shift? How do I link this to calculating the three phase power?)
Is some better platform is available for solving my question?

I get the instantaneous sample value (not continuous). (I have some sensors that gives the current and voltage - I convert this to digital for processing). Around 50 samples are got per second. (Is it to be zero when we some up all the power of three phase - due to phase shift of 120?) How can I calculate total three phase energy from these sampled values? I am processing my data in Arduino.

(I don't know this is the place to ask my question (if I can get a better help from some where else please suggest me).)

Numerical calculus to the rescue.

If you have several samples of voltage and current, then you also have that many samples of momentary power: P(t) = U(t) * I(t).

Now you have power and you have time, you can integrate the power with respect to time. A simple numeric approach is the trapezoidal rule. This question is tagged "Arduino" and I know C reasonably well so here's some pseudo-C that illustrates the technique:

int n_samples = 1000; // or however many samples you have
double integral = 0.0;
for (int i = 0; i < n_samples - 1; i++) {
    integral += (samples[i] + samples[i + 1]) / 2;
}

integral *= (t_max - t_min) / n;

Where t_min and t_max are the beginning and ending time of the sampling, respectively, n_samples is the number of samples you got, samples is an array (presumably of double or so) that contains the calculated momentary power values. integral will hold the result.