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skunk-tables
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/*
 * Copyright 2023 Foldables
 *
 * 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 skunk.tables

import skunk.Fragment

/** Descendants of this trait represnet the last stage of a query, ready to be executed in Skunk
  * session. All these actions need to have at least some input (a type, its value and a
  * `Fragment`).
  *
  * The descendants however can be seen as a combination of all necessary query components:
  *   - `Fragment` (to prepare SQL, coming from `Action`)
  *   - user-provided values (to fulfill prepared SQL, also coming from `Action`)
  *   - `Query` and `Decoder` (to decode output, coming from `Query` descendant and present only
  *     there)
  *   - statically known info about cardinality of the query
  *
  * Typically, `Action` contains some kind of a `Query` (like `SELECT`) underneath, but also can be
  * an `Command` (like `INSERT`).
  *
  * @tparam F
  *   \- an effect, such as `IO`
  * @tparam S
  *   \- special `Size` label, telling user how many items the query would return, as we know this
  *   information statically
  * @tparam O
  *   \- returned output value of the action
  */
private[tables] trait Action[F[_], S <: Action.Size, O]:
  /** Input is whatever provided via `Fragment`, i.e. a Twiddle list For `SELECT` it will be
    * whatever values provided for `WHERE` for `INSERT` it will be whatever provided for `VALUES`
    * for static tables (`COUNT`, `SELECT *`) it will be `Void`
    *
    * It's hidden as type member because user-generally doesn't care what was passed in to construct
    * the query, unlike `O` which is going to be an output type
    */
  type Input

  /** The actual user-provided values as Twiddle list */
  def input: Input

  /** The original fragment. All descendants only prepend/append SQL to it */
  def fragment: Fragment[Input]

object Action:

  type Size = Query.Size | "none"