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Scala library to handle form submission

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/*
 * Copyright 2022 Greenfossil Pte Ltd
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.greenfossil.data.mapping

/**
 * A form constraint.
 *
 * @tparam T type of values handled by this constraint
 * @param name the constraint name, to be displayed to final user
 * @param args the message arguments, to format the constraint name
 * @param f the validation function
 */
case class Constraint[-T](name: Option[String], args: Seq[Any])(f: T => ValidationResult):

  /**
   * Run the constraint validation.
   *
   * @param t the value to validate
   * @return the validation result
   */
  def apply(t: T): ValidationResult = f(t)

end Constraint


/**
 * This object provides helpers for creating `Constraint` values.
 *
 * For example:
 * {{{
 *   val negative = Constraint[Int] {
 *     case i if i < 0 => Valid
 *     case _ => Invalid("Must be a negative number.")
 *   }
 * }}}
 */
object Constraint:

  /**
   * Creates a new anonymous constraint from a validation function.
   *
   * @param f the validation function
   * @return a constraint
   */
  def apply[T](f: (T => ValidationResult)): Constraint[T] = apply(None, Nil)(f)

  /**
   * Creates a new named constraint from a validation function.
   *
   * @param name the constraint name
   * @param args the constraint arguments, used to format the constraint name
   * @param f the validation function
   * @return a constraint
   */
  def apply[T](name: String, args: Any*)(f: (T => ValidationResult)): Constraint[T] = apply(Some(name), args.toSeq)(f)

end Constraint