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All right.

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So now we're going to add the reducer function to add an item to the cart.

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So let's go down to our cart slice and this reducers object.

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And what we're going to do is add a new function called Add to Cart.

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So we'll set that to an arrow function.

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And I shut off GitHub copilot just because it was starting to get annoying.

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Now that we're writing more code, it just gets a little confusing as to what I already wrote and what

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it's recommending.

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So in add to Cart, since this is a reducer function, it's going to take in two things a state and

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an action.

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So the state is just whatever the current state is of the cart.

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And then an action will include any data inside of a payload.

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So basically in this case, we're going to be sending an item to add to the cart which we can access

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with action dot payload action dot payload.

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So let's create a variable called item and set that to action dot payload.

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So that'll be the item, including the fields or whatever.

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Now we want to check to see if the item is already in the cart.

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So we'll say let's say exist.

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Item and we'll say state, and then we can access anything that's in the state.

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Right now.

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We just have an initial state of cart items, which is an empty array, but that's what we want to check

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is cart items.

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So we'll say cart items dot find.

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So we want to find a specific item and that's the one that matches whatever the ID of this.

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So in find we'll pass in a function, we'll say we'll use X here for whatever the current item is because

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it's going to loop through, just like with any high order array method.

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And we'll say if that current item, if the dot underscore ID is equal to the item from the action from

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the payload ID, right?

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So if those match, then that's going to put that particular item into this variable.

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All right.

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And we want to update the basically we'll just update the quantity.

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So let's say if.

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So if exist item.

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Then we're going to take our state cart items.

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And we're going to set that to state dot.

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Cart items dot map because we're going to map through.

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And I'll use X here again.

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So we'll map through.

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And then what we want to do is have a condition.

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We'll say if x, if x dot underscore ID is equal to the exist item dot underscore id.

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Then we'll return that item.

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Else we'll just.

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It'll just be whatever the item is that we're looping through.

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Okay.

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Else.

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Then we just want to add the new item so we can say state dot cart items and we'll set that to an array

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and then we'll just spread across what's already there.

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So state dot cart items because remember, we're not going to use dot push, you know, state dot cart

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items dot push because state the state is immutable.

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So we're basically just making a copy of it by setting an array and putting everything in it and then

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also adding.

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The new item.

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So now what we need to do is, is do some calculations for the price we want to store the items, price,

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shipping, price, tax, price.

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And when we add those together, that will give us the total price.

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So let's go under the if statement here.

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And let's say calc calculate item's price.

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All right.

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So we want to calculate the item's price.

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We're also going to get the shipping price.

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We're going to get the tax price.

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And then all of those together will be the total price.

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All right.

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So let's start with the item's price.

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So we're just going to take our state and we're going to add on to that an item's price value.

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And we can get that by just taking all of the price values for each item in the cart and adding them

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together.

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And this is a good case for the reduce method, which is a high order array method, and we can use

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that to to add all the prices together.

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So let's take the cart items.

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So state dot cart items and let's say dot reduce.

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Let's just close that up for now.

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So we're going to reduce and that takes in a function.

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And the what we're going to pass in here is the accumulator and then the item itself.

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Okay.

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And that accumulator, we're going to set that to to zero.

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And basically it'll start from there and then we can add the prices together.

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So let's take the accumulator, add on the item dot price, and then we also need to take into account

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the quantity, right?

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Because if you have two or more of an item, then you need to add that to the price.

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So we're going to say times item dot Qty.

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Okay.

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And then the next argument we pass in is the default for the accumulator, which is going to be zero.

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So this starts at zero.

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It'll loop through, it'll add the item price multiply by the quantity and we should end up with the

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total item price.

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Now we have some stuff to add on to that shipping and tax.

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So, but before we do that, I want to make sure that we have the right amount of decimals and it's

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formatted correctly.

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So I'm actually going to create a helper function up here called Add decimals.

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Okay.

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And then that's going to take in a number.

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And what?

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I want this to return.

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Is going to be.

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Let's use the math object here.

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We're going to round.

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Say math.round.

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The num.

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Times 100 and then just divide that by 100.

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Actually, let's put.

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This in parentheses, this whole thing.

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Like that.

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And then we want two decimal places.

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So I'm going to say two fixed.

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And pass in two.

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So I just want to use this helper function for all of our pricing.

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So let's wrap this right here.

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Where we have our let's see state item price.

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Yeah, we're going to set that to add.

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Decimals.

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And we're just going to wrap this entire thing.

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All right.

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So now for the shipping price.

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Let's do that.

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So we're going to say state dot.

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Shipping price.

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And what I'm going to do for shipping.

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I'll put it up here actually.

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So shipping will be, let's say, if.

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If order is over $100, then free.

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Else it'll be $10 shipping.

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Okay.

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And you can have any shipping policy you want.

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That's just what we're going to do.

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All right.

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So we're going to use Add decimals here as well.

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And then let's pass in here.

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We'll take our state dot items, price that we just calculated above and we'll say if that is greater

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than 100, then it'll be zero.

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Else it'll be ten.

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Okay.

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So shipping price, it's always going to be either 0 or 10 based on the amount of the order.

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Now for the tax price, it's going to be 15%.

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So let's just say 15% tax.

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So state and then tax price.

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And we want to use add decimals here as well.

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And let's just make sure that this is a number.

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So we're going to wrap it in number and then in parentheses we'll say 0.15.

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And we want to multiply that by the item's price.

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So state dot item's price.

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So that will give us 15% of that.

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And then let's just add on to this to fixed.

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With two decibels.

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All right.

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Now for the total price, basically, we just need to to add all that stuff together.

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So let's say state dot and then total.

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Price, and we're going to set that.

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Let's wrap this in parentheses and we'll say number.

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Just make sure everything is formatted as a number so the state dot items.

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Items.

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Price And then we want to add.

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See number.

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State dot.

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Shipping price.

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State dot.

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And then let's see.

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Tax price.

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And I think that should do it.

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And then we'll just add to fixed.

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To now all of this that we have this state items price shipping, price tax, total price.

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I want this all saved in local storage.

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So we're going to go right under the line that we just finished and we're going to save to local storage.

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So let's say local storage dot set item, save it as cart and we're going to save the entire state.

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We just need to run it through Json.stringify.

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And then state.

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Okay.

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Now, in order to use this add to cart, which we're going to be using from our component, we need

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to export it as an action.

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So even though we already exported the reducer to put that in the store JS file, any function we create

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here we need to export as an action.

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So let's say.

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Export, const.

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And then.

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Add to cart.

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And that's going to be from cart slice.

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So cart slice dot actions.

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And then we should be able to bring that in and we should be able to use it, which is what we're going

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to do in the next video is hook this button up so that we can actually add these items to the cart.