<?php

function wizard_page() {
  $steps = array(
    'step1',
    'step2',
    'step3',
  );

  return drupal_get_form('multistep_form', $steps)
       . 'Multistep form';
}

//function fpn_customer_become_customer_submit($form, &$form_state) {
//
//}


function multistep_form(&$form_state, $steps) {
  if (!$form_state['storage']['step']) {
    reset($steps);
    $form_state['storage']['steps']  = $steps;
    $form_state['storage']['step']   = $steps[key($steps)];
    $form_state['storage']['values'] = array();
  }

  $form = multistep_retrieve_step_form($form_state);
  settype($form['#submit'], 'array');
  $form['#submit'][] = 'multistep_process_submit';
  multistep_form_submit_buttons($form, $form_state);

  return $form;
}

function multistep_retrieve_step_form($form_state) {
  $step = $form_state['storage']['step'];
  $form = $step($form_state);

  if (!isset($form['#validate'])) {
    if (is_callable($step .'_validate'))
      $form['#validate'][] = $step .'_validate';
  }

  if (!isset($form['#submit'])) {
    if (is_callable($step .'_submit'))
      $form['#submit'][] = $step .'_submit';
  }
  dpm($form);
  return $form;
}


function multistep_process_submit($form, &$form_state) {
  $steps = $form_state['storage']['steps'];
  $step  = $form_state['storage']['step'];
  reset($steps); $first_step = current($steps);
  end($steps);   $last_step  = current($steps);

  $form_state['storage']['values'][$step] = $form_state['values'];

//  dpm($form_state);
  if ($form_state['values']['op'] == $form['multistep_buttons']['next']['#value']) {
    if ($step == $last_step) {
      unset($form_state['storage']);
    }
    else {
      $index = array_search($step, $steps);
      $form_state['storage']['step'] = $steps[$index + 1];
    }
  }
  else if ($form_state['values']['op'] == $form['multistep_buttons']['back']['#value']) {
    $index = array_search($step, $steps);
    $form_state['storage']['step'] = $steps[$index - 1];

  }
}

function multistep_form_submit_buttons(&$form, $form_state) {
  $steps = $form_state['storage']['steps'];
  $step  = $form_state['storage']['step'];
  reset($steps); $first_step = current($steps);
  end($steps);   $last_step  = current($steps);

  $buttons = array();
  if ($step != $first_step) {
    $buttons['back'] = array(
      '#type' => 'submit',
      '#value' => t('Back'),
    );
  }
  if ($step != $last_step) {
    $buttons['next'] = array(
      '#type' => 'submit',
      '#value' => t('Next'),
    );
  }
  else {
    $buttons['next'] = array(
      '#type' => 'submit',
      '#value' => t('Finish'),
    );
  }

  $form['multistep_buttons'] = $buttons;
  $form['multistep_buttons']['#tree'] = true;
}




function step1($form_state) {
  $form['input1'] = array(
    '#type' => 'textfield',
    '#title' => 'input1',
  );

  return $form;
}

function step1_submit($form_state) {
  dpm(__FUNCTION__);
}

function step1_validate($form_state) {
  dpm(__FUNCTION__);
}

function step2($form_state) {
  $form['input2'] = array(
    '#type' => 'textfield',
    '#title' => 'input2',
  );

  return $form;
}

function step2_submit($form_state) {
  dpm(__FUNCTION__);
}

function step2_validate($form_state) {
  dpm(__FUNCTION__);
}

function step3($form_state) {
  $form['input3'] = array(
    '#type' => 'textfield',
    '#title' => 'input3',
  );

  $form['#submit'][] = 'step3___submit';
  $form['#validate'][] = 'step3___validate';

  return $form;

}

function step3___submit($form_state) {
  dpm(__FUNCTION__);
}

function step3___validate($form_state) {
  dpm(__FUNCTION__);
}