refactor(editor): rename block-std to std (#11250)

Closes: BS-2946

blocksuite/framework/std/src/utils/fractional-indexing.ts

@@ -0,0 +1,66 @@
+import { generateKeyBetween } from 'fractional-indexing';
+
+function hasSamePrefix(a: string, b: string) {
+  return a.startsWith(b) || b.startsWith(a);
+}
+/**
+ * generate a key between a and b, the result key is always satisfied with a < result < b.
+ * the key always has a random suffix, so there is no need to worry about collision.
+ *
+ * make sure a and b are generated by this function.
+ *
+ * @param customPostfix custom postfix for the key, only letters and numbers are allowed
+ */
+export function generateKeyBetweenV2(a: string | null, b: string | null) {
+  const randomSize = 32;
+  function postfix(length: number = randomSize) {
+    const chars =
+      '123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
+    const values = new Uint8Array(length);
+    crypto.getRandomValues(values);
+    let result = '';
+    for (let i = 0; i < length; i++) {
+      result += chars.charAt(values[i] % chars.length);
+    }
+    return result;
+  }
+  if (a !== null && b !== null && a >= b) {
+    throw new Error('a should be smaller than b');
+  }
+  // get the subkey in full key
+  // e.g.
+  // a0xxxx -> a
+  // a0x0xxxx -> a0x
+  function subkey(key: string | null) {
+    if (key === null) {
+      return null;
+    }
+    if (key.length <= randomSize + 1) {
+      // no subkey
+      return key;
+    }
+    const splitAt = key.substring(0, key.length - randomSize - 1);
+    return splitAt;
+  }
+  const aSubkey = subkey(a);
+  const bSubkey = subkey(b);
+  if (aSubkey === null && bSubkey === null) {
+    // generate a new key
+    return generateKeyBetween(null, null) + '0' + postfix();
+  } else if (aSubkey === null && bSubkey !== null) {
+    // generate a key before b
+    return generateKeyBetween(null, bSubkey) + '0' + postfix();
+  } else if (bSubkey === null && aSubkey !== null) {
+    // generate a key after a
+    return generateKeyBetween(aSubkey, null) + '0' + postfix();
+  } else if (aSubkey !== null && bSubkey !== null) {
+    // generate a key between a and b
+    if (hasSamePrefix(aSubkey, bSubkey) && a !== null && b !== null) {
+      // conflict, if the subkeys are the same, generate a key between fullkeys
+      return generateKeyBetween(a, b) + '0' + postfix();
+    } else {
+      return generateKeyBetween(aSubkey, bSubkey) + '0' + postfix();
+    }
+  }
+  throw new Error('Never reach here');
+}