<div class="container" id="container">
    <div class="image-container">
        <img src="/photos/japan-day/7.jpg" alt="Image" class="image" />
        <img
            src="/photos/japan-day/7.jpg"
            alt="Image in black and white"
            class="image overlay"
            id="overlay"
        />
    </div>

    <div class="slider" id="slider" tabindex="0">
        <div class="handle">
            <svg
                xmlns="http://www.w3.org/2000/svg"
                width="24"
                height="24"
                viewBox="0 0 24 24"
                fill="none"
                stroke="currentColor"
                stroke-width="2"
                stroke-linecap="round"
                stroke-linejoin="round"
            >
                <path d="m18 8 4 4-4 4" />
                <path d="m6 8-4 4 4 4" />
                <path d="M8 12h.01" />
                <path d="M12 12h.01" />
                <path d="M16 12h.01" />
            </svg>
        </div>
    </div>
</div>

<script type="module">
    const { animate, transform, clamp, frame } = window.Motion

    const step = 50
    const elastic = 0.1

    const container = document.getElementById("container")
    const slider = document.getElementById("slider")
    const overlay = document.getElementById("overlay")

    // State
    let x = 0
    let boundary = 300
    let mixClipPath
    let mixSliderColor

    // Initialize
    function init() {
        boundary = container.clientWidth / 2

        mixClipPath = transform(
            [-boundary, boundary],
            ["inset(0% 0% 0% 0%)", "inset(0% 0% 0% 100%)"]
        )

        mixSliderColor = transform(
            [-boundary + 20, -boundary + 60, boundary - 60, boundary - 20],
            [
                "rgba(255, 255, 255, 0)",
                "rgba(255, 255, 255, 1)",
                "rgba(255, 255, 255, 1)",
                "rgba(255, 255, 255, 0)",
            ]
        )

        moveSlider(0)
    }

    // Update slider position and clip path
    function moveSlider(newX) {
        x = newX
        overlay.style.clipPath = mixClipPath(x)
        slider.style.transform = `translateX(${x}px)`
        slider.style.backgroundColor = mixSliderColor(x)
    }

    // Keyboard navigation
    function handleKeyDown(event) {
        let moveBy = 0

        if (event.key === "ArrowLeft") {
            moveBy = -step
        } else if (event.key === "ArrowRight") {
            moveBy = step
        } else {
            return
        }

        animate(x, clamp(-boundary, boundary, x + moveBy), {
            onUpdate: (value) => moveSlider(value),
            type: "spring",
            stiffness: 900,
            damping: 40,
            // Manually setting velocity is what allows the slider
            // to give a little tug at the boundary.
            velocity: moveBy * 10,
        })
    }

    function setupDrag() {
        let startX = 0
        let newX = 0

        function updateX() {
            moveSlider(newX)
        }

        slider.addEventListener("pointerdown", (e) => {
            startX = x - e.clientX
            document.body.style.cursor = "grabbing"
            slider.style.cursor = "grabbing"
            slider.classList.add("active")
            slider.setPointerCapture(e.pointerId)
        })

        slider.addEventListener("pointermove", (e) => {
            if (!slider.hasPointerCapture(e.pointerId)) return

            newX = startX + e.clientX

            // Apply elastic resistance when dragging beyond boundaries
            if (newX < -boundary) {
                newX = -boundary + (newX + boundary) * elastic
            } else if (newX > boundary) {
                newX = boundary + (newX - boundary) * elastic
            }

            frame.render(updateX)
        })

        slider.addEventListener("pointerup", (e) => {
            if (!slider.hasPointerCapture(e.pointerId)) return

            slider.releasePointerCapture(e.pointerId)
            document.body.style.cursor = "default"
            slider.style.cursor = "grab"
            slider.classList.remove("active")

            // If x is outside boundary, animate to the nearest boundary
            if (x < -boundary || x > boundary) {
                const targetX = x < -boundary ? -boundary : boundary
                animate(x, targetX, {
                    onUpdate: (value) => moveSlider(value),
                    type: "spring",
                    stiffness: 900,
                    damping: 40,
                })
            }
        })
    }

    // Setup event listeners
    slider.addEventListener("focus", () => {
        document.addEventListener("keydown", handleKeyDown)
    })

    slider.addEventListener("blur", () => {
        document.removeEventListener("keydown", handleKeyDown)
    })

    window.addEventListener("resize", () => {
        init()
        moveSlider(clamp(-boundary, boundary, x))
    })

    setupDrag()
    init()
</script>

<style>
    .container {
        position: relative;
    }

    .image-container {
        position: relative;
        background-color: var(--layer);
        border: 1px solid var(--border);
        border-radius: 12px;
        overflow: hidden;
        aspect-ratio: 4/3;
        height: 300px;
    }

    .image {
        position: absolute;
        width: 100%;
        height: 100%;
        object-fit: cover;
        will-change: clip-path;
    }

    .overlay {
        top: 0;
        left: 0;
        filter: grayscale(100%);
    }

    .slider {
        position: absolute;
        top: 0;
        bottom: 0;
        width: 2px;
        background-color: white;
        cursor: grab;
        left: 50%;
        transform: translateX(-50%);
        filter: drop-shadow(2px 0 3px rgba(0, 0, 0, 0.4));
        will-change: transform, background-color;
    }

    .handle {
        position: absolute;
        top: 50%;
        left: 50%;
        transform: translate(-50%, -50%);
        width: 40px;
        height: 40px;
        background-color: white;
        border-radius: 50%;
        display: flex;
        align-items: center;
        justify-content: center;
        color: #0f1115;
        cursor: grab;
    }

    .slider:focus-visible {
        outline: none;
    }

    .slider:focus-visible .handle {
        outline: 4px solid #ff0088;
        outline-offset: 2px;
    }

    .handle:active {
        cursor: grabbing;
    }
</style>