// m05 game: one `update` function turns every action into a new state; replay is a fold over actions.
import { turn } from './rules.js'
import { tick } from './spawn.js'

/** Tick and Turn are handled here; other actions leave the state alone (m10 adds more). */
export const update = (state, action) => {
  switch (action.tag) {
    case 'Tick': return tick(state)
    case 'Turn': return turn(state, action.dir)
    default: return state
  }
}

/** Fold the actions over the state, left to right. */
export const replay = (state, actions) => actions.reduce(update, state)

/** Like replay, but keeps each intermediate state. Recursion instead of mutation: no array is ever pushed to. */
export const history = (state, actions) =>
  actions.length === 0
    ? [state]
    : [state, ...history(update(state, actions[0]), actions.slice(1))]