Init

1 files changed, 59 insertions, 0 deletions

diff --git a/src/scripts/lib/dom.ts b/src/scripts/lib/dom.ts
new file mode 100644
index 0000000..a88686a
--- /dev/null
+++ b/src/scripts/lib/dom.ts
@@ -0,0 +1,59 @@
+function isAbove(a: HTMLElement, b: HTMLElement) {
+        return a.offsetTop + a.clientHeight < b.offsetTop;
+}
+
+export function getVerticalNeighbor(
+        dir: -1 | 1,
+        items: Iterable<HTMLElement>,
+        current: HTMLElement,
+) {
+        let candidates: HTMLElement[] = [];
+
+        if (dir === -1) {
+                let adjacentY = Number.MIN_SAFE_INTEGER;
+
+                for (const item of items) {
+                        if (!isAbove(item, current)) {
+                                continue;
+                        }
+
+                        if (item.offsetTop > adjacentY) {
+                                adjacentY = item.offsetTop;
+                                candidates = [item];
+                        } else if (item.offsetTop === adjacentY) {
+                                candidates.push(item);
+                        }
+                }
+        } else {
+                let adjacentY = Number.MAX_SAFE_INTEGER;
+
+                for (const item of items) {
+                        if (!isAbove(current, item)) {
+                                continue;
+                        }
+
+                        if (item.offsetTop < adjacentY) {
+                                adjacentY = item.offsetTop;
+                                candidates = [item];
+                        } else if (item.offsetTop === adjacentY) {
+                                candidates.push(item);
+                        }
+                }
+        }
+
+        const currentX = current.offsetLeft + 0.5 * current.clientWidth;
+        let match = candidates[0];
+        let bestDist = Number.MAX_SAFE_INTEGER;
+
+        for (const candidate of candidates) {
+                const candidateX = candidate.offsetLeft + 0.5 * candidate.clientWidth;
+                const dist = Math.abs(currentX - candidateX);
+
+                if (dist < bestDist) {
+                        bestDist = dist;
+                        match = candidate;
+                }
+        }
+
+        return match;
+}