"use client";

import { useEffect, useReducer, useState } from "react";
import type { Appliance, CookingStyle, Cuisine, ItemId, ItemPreference, MealPlanState } from "@/app/types";
import { toggle, withoutVisibleSlots } from "./plan";
import { DEFAULT_STATE, sanitizeState } from "./sanitize";

// ---------------------------------------------------------------------------
// All plan state lives in one reducer, persisted to localStorage.
//
// Why a reducer: a dozen controls each change one field, and the slot grid
// needs swap/replace operations. One switch statement is easier to follow
// than a dozen useStates.
// ---------------------------------------------------------------------------

const STORAGE_KEY = "budget-meal-planner:v2";

export type PlanAction =
  | { type: "setBudget"; value: number }
  | { type: "setDays"; value: number }
  | { type: "setMealsPerDay"; value: number }
  | { type: "setHouseholdSize"; value: number }
  | { type: "toggleAppliance"; value: Appliance }
  | { type: "toggleCuisine"; value: Cuisine }
  | { type: "toggleStyle"; value: CookingStyle }
  | { type: "setItemPreference"; itemIds: ItemId[]; preference: ItemPreference }
  | { type: "setSlot"; key: string; recipeId: string | null }
  | { type: "swapSlots"; from: string; to: string }
  | { type: "replaceSlots"; slots: Record<string, string> }
  | { type: "clearSlots" };

/** Exported for tests. */
export function planReducer(state: MealPlanState, action: PlanAction): MealPlanState {
  switch (action.type) {
    case "setBudget":
      return { ...state, targetBudget: action.value };
    case "setDays":
      return { ...state, daysCount: action.value };
    case "setMealsPerDay":
      // Slots don't move: meal numbers are fixed (see visibleMeals in plan.ts).
      return { ...state, mealsPerDay: action.value };
    case "setHouseholdSize":
      return { ...state, householdSize: action.value };
    case "toggleAppliance":
      return { ...state, selectedAppliances: toggle(state.selectedAppliances, action.value) };
    case "toggleCuisine":
      return { ...state, preferredCuisines: toggle(state.preferredCuisines, action.value) };
    case "toggleStyle":
      return { ...state, preferredStyles: toggle(state.preferredStyles, action.value) };
    case "setItemPreference": {
      // An item lives in at most one list: avoided, on hand, or neither ("use").
      const ids = new Set(action.itemIds);
      const avoidedItems = state.avoidedItems.filter((id) => !ids.has(id));
      const onHandItems = state.onHandItems.filter((id) => !ids.has(id));
      if (action.preference === "avoid") avoidedItems.push(...ids);
      if (action.preference === "have") onHandItems.push(...ids);
      return { ...state, avoidedItems, onHandItems };
    }
    case "setSlot": {
      const slots = { ...state.slots };
      if (action.recipeId) slots[action.key] = action.recipeId;
      else delete slots[action.key];
      return { ...state, slots };
    }
    case "swapSlots": {
      const slots = { ...state.slots };
      const from = slots[action.from];
      const to = slots[action.to];
      if (to) slots[action.from] = to;
      else delete slots[action.from];
      if (from) slots[action.to] = from;
      else delete slots[action.to];
      return { ...state, slots };
    }
    case "replaceSlots":
      return { ...state, slots: action.slots };
    case "clearSlots":
      // Clears what you can see; meals on hidden days/meals survive.
      return { ...state, slots: withoutVisibleSlots(state) };
  }
}

export type SyncStatus = "saved" | "error";

/** Read the saved plan. Only call in the browser (the planner is client-only, see page.tsx). */
function loadSavedState(): MealPlanState {
  try {
    const raw = window.localStorage.getItem(STORAGE_KEY);
    if (raw) return sanitizeState(JSON.parse(raw));
    return DEFAULT_STATE;
  } catch {
    return DEFAULT_STATE; // corrupt JSON or blocked storage
  }
}

function storageWorks(): boolean {
  try {
    window.localStorage.setItem(`${STORAGE_KEY}:probe`, "1");
    window.localStorage.removeItem(`${STORAGE_KEY}:probe`);
    return true;
  } catch {
    return false; // e.g. some private-browsing modes
  }
}

export function usePlanState() {
  // Lazy initializers run once, on first render, so the saved plan shows immediately.
  const [state, dispatch] = useReducer(planReducer, undefined, loadSavedState);
  const [canSave] = useState(storageWorks);

  // Persist every change. (Writing to an external system is exactly what effects are for.)
  useEffect(() => {
    if (!canSave) return;
    window.localStorage.setItem(STORAGE_KEY, JSON.stringify(state));
  }, [state, canSave]);

  const syncStatus: SyncStatus = canSave ? "saved" : "error";
  return { state, dispatch, syncStatus };
}