PHP Form Builder

array.php

<?php

function assoc_array_map($cb, $arr) {
  $new_array = array();

  foreach ($arr as $key => $value) {
    array_push($new_array, $cb($key, $value));
  }

  return $new_array;
}

function is_assoc($arr) {
  return array_keys($arr) !== range(0, count($arr) - 1);
}

example.php

<?php
  require "form.php";

  form_builder("/test", function() {
    ?>
    
    <legend>Example</legend>

    <?php
    label("Username");
    text_field("username");

    label("Password");
    password_field("password");

    checkbox_field("tos", "Check if you understand the terms of service", true);

    label("Message", "message_body");
    textarea_field("message_body");

    select_field("preference", function() {
      select_options(array(1 => "Category 1", 2 => "Category 2", 3 => "Category 3"));
    });

    radio_field("service", array("Full time", "Part time", "Whenever"));

    radio_field("category", array(1 => "Category 1", 2 => "Category 2", 3 => "Category 3"));

    hidden_field("id", 54);

    submit_button("Submit");
  });

?>

form.php

<?php

require "array.php";
require "string.php";

function form_builder($arg, $block=null) {
  $options = array();

  if (is_string($arg)) {
    $options["action"] = $arg;
    $options["method"] = "post";
  } else {
    $options = $arg;
  }

  // form open
  echo "<form " . html_options($options) . ">";

  // form body
  if (is_callable($block)) {
    $block();
  }

  // form close
  echo "</form>";
}

function label($text, $for=NULL) {
  if ($for === NULL) {
    $for = snake_case($text);
  }

  echo '<label for="' . $for . '">' . $text . '</label>';
}

function text_field($args) {
  $options = array();

  if (is_string($args)) {
    $options["name"] = $args;
    $options["id"] = $args;
    $options["type"] = "text";
  } else {
    $options = $args;
  }

  echo '<input ' . html_options($options) . '>';
}

function password_field($args) {
  $options = array();

  if (is_string($args)) {
    $options["name"] = $args;
    $options["id"] = $args;
  } else {
    $options = $args;
  }

  $options["type"] = "password";

  echo '<input ' . html_options($options) . '>';
}

function hidden_field($args, $value=NULL) {
  $options = array();

  if (is_string($args) && $value !== NULL) {
    $options["name"] = $args;
    $options["id"] = $args;
    $options["value"] = $value;
  } else {
    $options = $args;
  }

  $options["type"] = "hidden";

  echo '<input ' . html_options($options) . '>';
}

function checkbox_field($args, $text, $checked=false) {
  $options = array();

  if (is_string($args)) {
    $options["name"] = $args;
    $options["id"] = $args;
    if ($checked) {
      $options["checked"] = "checked";
    }
  } else {
    $options = $args;
  }

  $options["type"] = "checkbox";

  // label open
  echo '<label class="checkbox">';
  echo '<input ' . html_options($options) . '> ';
  echo $text;
  echo '</label>';
}

function radio_field($args, $collection=NULL) {
  $options = array();

  if (is_string($args)) {
    $options["name"] = $args;
    
  } else {
    $options = $args;
  }

  $options["type"] = "radio";

  if (is_array($collection)) {
    if (is_assoc($collection)) {
      foreach($collection as $value => $text) {
        echo '<label>';
        echo '<input ' . html_options($options) . ' value="' . $value . '"> ';
        echo $text;
        echo '</label>';
      }
    } else {
      foreach ($collection as $text) {
        echo '<label>';
        echo '<input ' . html_options($options) . ' value="' . $text . '"> ';
        echo $text;
        echo '</label>';
      }
    }
  } else {
    echo '<label>';
    echo '<input ' . html_options($options) . '>';
    echo $collection;
    echo '</label>';
  }
}

function select_field($args, $block=NULL) {
  $options = array();

  if (is_string($args)) {
    $options["name"] = $args;
    $options["id"] = $args;
  } else {
    $options = $args;
  }

  // select open
  echo '<select ' . html_options($options) . '>';

  // select body
  if (is_callable($block)) {
    $block();
  }

  // select close
  echo '</select>';
}

function select_options($collection) {
  if (is_assoc($collection)) {
    assoc_array_map(function($value, $text) {
      echo '<option value="' . $value . '">' . $text . '</option>';
    }, $collection);
  } else {
    array_map(function($text) {
      echo '<option>' . $text . '</option>';
    }, $collection);
  }
}

function textarea_field($args, $value=NULL) {
  $options = array();

  if (is_string($args)) {
    $options["name"] = $args;
  } else {
    $options = $args;
  }

  // textarea open
  echo '<textarea ' . html_options($options) . '>';

  // conditional value
  if (is_string($value)) { echo $value; }

  // close textarea
  echo '</textarea>';
}

function submit_button($args) {
  $options = array();

  if (is_string($args)) {
    $options["name"] = snake_case($args);
    $options["id"] = snake_case($args);
    $options["value"] = $args;
    $options["class"] = "btn";
  } else {
    $options = $args;
  }

  $options["type"] = "submit";

  echo '<input ' . html_options($options) . '>';
}

function html_options($opts) {
  $mapped = assoc_array_map(function($attr, $value) {
    return $attr . '="' . $value . '"';
  }, $opts);

  return implode(" ", $mapped);
}

sample_output.html

<form action="/test" method="post">            
  <legend>Example</legend>

  <label for="username">Username</label>
  <input name="username" id="username" type="text">

  <label for="password">Password</label>
  <input name="password" id="password" type="password">

  <label class="checkbox"><input name="tos" id="tos" checked="checked" type="checkbox"> Check if you understand the terms of service</label>

  <label for="message_body">Message</label>
  <textarea name="message_body"></textarea>
  
  <select name="preference" id="preference">
    <option value="1">Category 1</option>
    <option value="2">Category 2</option>
    <option value="3">Category 3</option>
  </select>

  <label><input name="service" type="radio" value="Full time"> Full time</label>
  <label><input name="service" type="radio" value="Part time"> Part time</label>
  <label><input name="service" type="radio" value="Whenever"> Whenever</label>

  <label><input name="category" type="radio" value="1"> Category 1</label>
  <label><input name="category" type="radio" value="2"> Category 2</label>
  <label><input name="category" type="radio" value="3"> Category 3</label>

  <input name="id" id="id" value="54" type="hidden">

  <input name="submit" id="submit" value="Submit" class="btn" type="submit">

</form>

string.php

<?php

function snake_case($str) {
  return strtolower(str_replace(" ", "_", $str));
}