web/DonateOptionsCard: add scroll buttons to the options container

cuz users without touchpads couldn't scroll it without tabbing

web/src/components/donate/DonateOptionsCard.svelte

@@ -1,5 +1,8 @@
 <script lang="ts">
+    import settings from "$lib/state/settings";
+
     import { donate } from "$lib/env";
+    import { device } from "$lib/device";
     import { t } from "$lib/i18n/translations";
 
     import DonateCardContainer from "$components/donate/DonateCardContainer.svelte";
@@ -11,7 +14,6 @@
     import IconPizza from "@tabler/icons-svelte/IconPizza.svelte";
     import IconToolsKitchen2 from "@tabler/icons-svelte/IconToolsKitchen2.svelte";
     import IconPaperBag from "@tabler/icons-svelte/IconPaperBag.svelte";
-    import IconArrowRight from "@tabler/icons-svelte/IconArrowRight.svelte";
     import IconSoup from "@tabler/icons-svelte/IconSoup.svelte";
     import IconFridge from "@tabler/icons-svelte/IconFridge.svelte";
     import IconArmchair from "@tabler/icons-svelte/IconArmchair.svelte";
@@ -20,7 +22,11 @@
     import IconPhoto from "@tabler/icons-svelte/IconPhoto.svelte";
     import IconWorldWww from "@tabler/icons-svelte/IconWorldWww.svelte";
     import IconBath from "@tabler/icons-svelte/IconBath.svelte";
-    import OuterLink from "$components/misc/OuterLink.svelte";
+
+    import IconArrowLeft from "@tabler/icons-svelte/IconArrowLeft.svelte";
+    import IconArrowRight from "@tabler/icons-svelte/IconArrowRight.svelte";
+
+    let donateList: HTMLElement;
 
     let customInput: HTMLInputElement;
     let customInputValue: number | null;
@@ -39,7 +45,7 @@
         4900: IconApple,
         7398: IconDeviceLaptop,
         8629: IconPhoto,
-        9433: IconBath
+        9433: IconBath,
     };
 
     type Processor = "stripe" | "liberapay";
@@ -66,7 +72,30 @@
         }
 
         const amount = Math.floor(Number(customInputValue) * 100);
-        return window.open(donationMethods[processor](amount), '_blank');
+        return window.open(donationMethods[processor](amount), "_blank");
+    };
+
+    const scrollBehavior = $settings.appearance.reduceMotion
+        ? "instant"
+        : "smooth";
+
+    $: showLeftScroll = false;
+    $: showRightScroll = true;
+
+    const scroll = (direction: "left" | "right") => {
+        const currentPos = donateList.scrollLeft;
+        const newPos = direction === "left" ? currentPos - 150 : currentPos + 150;
+        const maxPos = donateList.scrollWidth - donateList.getBoundingClientRect().width;
+
+        donateList.scroll({
+            left: newPos,
+            behavior: scrollBehavior,
+        });
+
+        setTimeout(() => {
+            showLeftScroll = newPos > 0;
+            showRightScroll = newPos < maxPos && newPos !== maxPos;
+        }, 150)
     };
 </script>
 
@@ -84,10 +113,11 @@
             <div class="donation-type-text">
                 <div class="donate-card-title">{$t("donate.card.once")}</div>
                 <div class="donate-card-subtitle">
-                    {$t("donate.card.processor", { value: 'stripe' })}
+                    {$t("donate.card.processor", { value: "stripe" })}
                 </div>
             </div>
         </button>
+
         <button
             id="donation-type-monthly"
             class="donation-type"
@@ -100,13 +130,48 @@
             <div class="donation-type-text">
                 <div class="donate-card-title">{$t("donate.card.monthly")}</div>
                 <div class="donate-card-subtitle">
-                    {$t("donate.card.processor", { value: 'liberapay' })}
+                    {$t("donate.card.processor", { value: "liberapay" })}
                 </div>
             </div>
         </button>
     </div>
-    <div id="donation-options">
+
-        {#each Object.entries(PRESET_DONATION_AMOUNTS) as [ amount, component ]}
+    <div
+        id="donation-options-container"
+        aria-hidden="true"
+        class:mask-both={!device.is.mobile && showLeftScroll && showRightScroll}
+        class:mask-left={!device.is.mobile && showLeftScroll && !showRightScroll}
+        class:mask-right={!device.is.mobile && showRightScroll && !showLeftScroll}
+    >
+        {#if !device.is.mobile}
+            <div id="donation-options-scroll">
+                <button
+                    class="scroll-button left"
+                    class:hidden={!showLeftScroll}
+                    on:click={() => {
+                        scroll("left");
+                    }}
+                >
+                    <IconArrowLeft />
+                </button>
+                <button
+                    class="scroll-button right"
+                    class:hidden={!showRightScroll}
+                    on:click={() => {
+                        scroll("right");
+                    }}
+                >
+                    <IconArrowRight />
+                </button>
+            </div>
+        {/if}
+
+        <div
+            id="donation-options"
+            bind:this={donateList}
+            on:scroll={(e) => {}}
+        >
+            {#each Object.entries(PRESET_DONATION_AMOUNTS) as [amount, component]}
                 <DonationOption
                     price={+amount}
                     desc={$t(`donate.card.option.${amount}`)}
@@ -116,11 +181,14 @@
                 </DonationOption>
             {/each}
         </div>
+    </div>
+
     <div id="donation-custom">
         <div id="input-container" class:focused={customFocused}>
             {#if customInputValue || customInput?.validity.badInput}
                 <span id="input-dollar-sign">$</span>
             {/if}
+
             <input
                 id="donation-custom-input"
                 type="number"
@@ -137,6 +205,7 @@
                 on:keydown={(e) => e.key === "Enter" && sendCustom()}
             />
         </div>
+
         <button
             id="donation-custom-submit"
             on:click={sendCustom}
@@ -146,6 +215,7 @@
             <IconArrowRight />
         </button>
     </div>
+
     <div class="donate-card-subtitle processor-mobile">
         {$t("donate.card.processor", { value: processor })}
     </div>
@@ -288,6 +358,79 @@
         text-align: center;
     }
 
+    #donation-options-container {
+        display: flex;
+        flex-direction: column;
+        gap: calc(var(--donate-card-main-padding) / 2);
+        position: relative;
+    }
+
+    #donation-options-scroll {
+        display: flex;
+        flex-direction: row;
+        justify-content: space-between;
+        align-items: center;
+        position: absolute;
+        pointer-events: none;
+        width: 100%;
+        height: 100%;
+        z-index: 3;
+        overflow: hidden;
+        opacity: 0;
+        transition: opacity 0.2s;
+    }
+
+    .scroll-button {
+        pointer-events: all;
+        color: white;
+        padding: 0 16px;
+        background-color: transparent;
+        height: 100%;
+        transition: opacity 0.2s;
+    }
+
+    #donation-options-container:hover #donation-options-scroll {
+        opacity: 1;
+    }
+
+    .scroll-button.hidden {
+        opacity: 0;
+        visibility: hidden;
+    }
+
+    #donation-options-container.mask-both:hover #donation-options {
+        mask-image: linear-gradient(
+            90deg,
+            rgba(0, 0, 0, 0) 0%,
+            rgba(0, 0, 0, 1) 20%,
+            rgba(0, 0, 0, 1) 50%,
+            rgba(0, 0, 0, 1) 80%,
+            rgba(0, 0, 0, 0) 100%
+        );
+    }
+
+    #donation-options-container.mask-left:hover #donation-options {
+        mask-image: linear-gradient(
+            90deg,
+            rgba(0, 0, 0, 0) 0%,
+            rgba(0, 0, 0, 1) 20%,
+            rgba(0, 0, 0, 1) 50%,
+            rgba(0, 0, 0, 1) 96%,
+            rgba(0, 0, 0, 0) 100%
+        );
+    }
+
+    #donation-options-container.mask-right:hover #donation-options {
+        mask-image: linear-gradient(
+            90deg,
+            rgba(0, 0, 0, 0) 0%,
+            rgba(0, 0, 0, 1) 4%,
+            rgba(0, 0, 0, 1) 50%,
+            rgba(0, 0, 0, 1) 80%,
+            rgba(0, 0, 0, 0) 100%
+        );
+    }
+
     @media screen and (max-width: 550px) {
         :global(#donation-box) {
             min-width: unset;