Stepper

@using System.ComponentModel.DataAnnotations
@using System.Globalization
@inject NavigationManager Navigation

<Grid Template='new() { Base = "1fr", Lg = "1fr 18rem" }' Gap="8" Align="Align.Start" Grow>
    <Stack Gap="6">
        @* Finished steps link back; the step itself is ?step= in the address. *@
        <Stepper Current="Current" Label="Checkout progress">
            <Step Label="Cart" Href="@BackTo(1)" />
            <Step Label="Shipping" Href="@BackTo(2)" />
            <Step Label="Payment" Href="@BackTo(3)" />
            <Step Label="Review" />
        </Stepper>

        @switch (Current)
        {
            case 1:
                <Stack Gap="4">
                    <Heading Level="2" Size="TextSize.Xl">Your cart</Heading>
                    <TextBlock Color="Color.Muted">Both items are in stock and ready to ship.</TextBlock>
                    <Row><Button Href="@StepUrl(2)" EndIcon="Lucide.ArrowRight">Continue to shipping</Button></Row>
                </Stack>
                break;

            case 2:
                <Form Model="Shipping" FormName="checkout-shipping" OnValidSubmit="ToPayment" Columns="2">
                    <TextField @bind-Value="Shipping!.FullName" AutoComplete="name" ColSpan="GridSpan.Full" />
                    <TextField @bind-Value="Shipping!.Street" AutoComplete="street-address" ColSpan="GridSpan.Full" />
                    <TextField @bind-Value="Shipping!.City" AutoComplete="address-level2" />
                    <TextField @bind-Value="Shipping!.PostalCode" AutoComplete="postal-code" />
                    <RadioGroup @bind-Value="Shipping!.Delivery" ColSpan="GridSpan.Full" />
                    <FormActions Justify="Justify.Between">
                        <Button Href="@StepUrl(1)" Variant="ButtonVariant.Outline" Accent="Accent.Neutral" StartIcon="Lucide.ArrowLeft">Back</Button>
                        <Button Submit EndIcon="Lucide.ArrowRight">Continue to payment</Button>
                    </FormActions>
                </Form>
                break;

            case 3:
                <Form Model="Payment" FormName="checkout-payment" OnValidSubmit="ToReview" Columns="2">
                    <TextField @bind-Value="Payment!.NameOnCard" AutoComplete="cc-name" ColSpan="GridSpan.Full" />
                    <TextField @bind-Value="Payment!.CardNumber" AutoComplete="cc-number" Placeholder="4242 4242 4242 4242" ColSpan="GridSpan.Full" />
                    <TextField @bind-Value="Payment!.Expiry" AutoComplete="cc-exp" Placeholder="MM/YY" />
                    <TextField @bind-Value="Payment!.SecurityCode" AutoComplete="cc-csc" />
                    <FormActions Justify="Justify.Between">
                        <Button Href="@StepUrl(2)" Variant="ButtonVariant.Outline" Accent="Accent.Neutral" StartIcon="Lucide.ArrowLeft">Back</Button>
                        <Button Submit EndIcon="Lucide.ArrowRight">Review order</Button>
                    </FormActions>
                </Form>
                break;

            case 4:
                <Stack Gap="4">
                    <Heading Level="2" Size="TextSize.Xl">Review your order</Heading>
                    <DescriptionList Divided>
                        <DescriptionItem Term="Delivery">@(Express ? "Express, next day" : "Standard, 3 to 5 days")</DescriptionItem>
                        <DescriptionItem Term="Payment">Card, charged when the order ships</DescriptionItem>
                    </DescriptionList>
                    @* Placing the order is a post, not a link. *@
                    <form method="post" @formname="checkout-place" @onsubmit="Place">
                        <AntiforgeryToken />
                        <Row Gap="2" Justify="Justify.Between">
                            <Button Href="@StepUrl(3)" Variant="ButtonVariant.Outline" Accent="Accent.Neutral" StartIcon="Lucide.ArrowLeft">Back</Button>
                            <Button Submit StartIcon="Lucide.Lock">Place order</Button>
                        </Row>
                    </form>
                </Stack>
                break;

            default:
                <Alert Status="Status.Success" Title="Order placed">
                    Order #10482 is confirmed. We've emailed your receipt.
                </Alert>
                <Row><Button Href="@NewOrderUrl" Variant="ButtonVariant.Outline" Accent="Accent.Neutral">Start a new order</Button></Row>
                break;
        }
    </Stack>

    <Card Title="Order summary" TitleLevel="2">
        <Stack Gap="3">
            @foreach (var line in Lines)
            {
                <Row Gap="3" Justify="Justify.Between">
                    <TextBlock As="span">@line.Name <TextBlock As="span" Color="Color.Muted">× @line.Quantity</TextBlock></TextBlock>
                    <TextBlock As="span" TabularNums>@Money(line.Price * line.Quantity)</TextBlock>
                </Row>
            }
            <Divider />
            <Row Gap="3" Justify="Justify.Between">
                <TextBlock As="span" Color="Color.Muted">Delivery</TextBlock>
                <TextBlock As="span" TabularNums>@(Express ? Money(ExpressCost) : "Free")</TextBlock>
            </Row>
            <Row Gap="3" Justify="Justify.Between">
                <TextBlock As="span" Weight="FontWeight.Semibold">Total</TextBlock>
                <TextBlock As="span" Weight="FontWeight.Semibold" TabularNums>@Money(Total)</TextBlock>
            </Row>
        </Stack>
    </Card>
</Grid>

@code {
    private const int Steps = 4;

    [SupplyParameterFromQuery(Name = "step")]
    private int? StepQuery { get; set; }

    [SupplyParameterFromQuery(Name = "delivery")]
    private string? DeliveryQuery { get; set; }

    [SupplyParameterFromForm(FormName = "checkout-shipping")]
    private ShippingDetails? Shipping { get; set; }

    [SupplyParameterFromForm(FormName = "checkout-payment")]
    private PaymentDetails? Payment { get; set; }

    // Past the last step (5), every step shows as done.
    private int Current => Math.Clamp(StepQuery ?? 1, 1, Steps + 1);

    private bool Express => DeliveryQuery == "express";

    // A real checkout keeps the order on the server. This one keeps only the delivery choice, in
    // the address, so going back to Shipping shows it.
    // On an interactive page the component stays between steps, so the cart (step 1) starts a
    // new order.
    protected override void OnParametersSet()
    {
        if (Current == 1)
        {
            Shipping = null;
            Payment = null;
        }

        Shipping ??= new() { Delivery = Express ? DeliveryOption.Express : DeliveryOption.Standard };
        Payment ??= new();
    }

    private string StepUrl(int step) => Navigation.GetUriWithQueryParameter("step", step);

    private string? BackTo(int step) => step < Current && Current <= Steps ? StepUrl(step) : null;

    // On a static page this redirects after the post; on an interactive one it navigates.
    private void ToPayment() => Navigation.NavigateTo(Navigation.GetUriWithQueryParameters(new Dictionary<string, object?>
    {
        ["step"] = 3,
        ["delivery"] = Shipping!.Delivery == DeliveryOption.Express ? "express" : "standard",
    }));

    private void ToReview() => Navigation.NavigateTo(StepUrl(4));

    private void Place() => Navigation.NavigateTo(StepUrl(Steps + 1));

    private string NewOrderUrl => Navigation.GetUriWithQueryParameters(new Dictionary<string, object?> { ["step"] = 1, ["delivery"] = null });

}