MVP, no mod tools or anything but it works

resources/snowflakes/LICENSE

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+MIT License
+
+Copyright (c) 2017 Arke Works
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

resources/snowflakes/NOTICE

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+You can find the original generator at https://github.com/arke-works/arke/blob/master/snowflakes/generator.go

resources/snowflakes/generator.go

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+package snowflakes
+
+import (
+	"errors"
+	"sync"
+	"time"
+)
+
+const (
+	counterLen  = 10
+	counterMask = -1 ^ (-1 << counterLen)
+)
+
+var (
+	errNoFuture = errors.New("Start Time cannot be set in the future")
+)
+
+// Generator is a fountain for new snowflakes. StartTime must be
+// initialized to a past point in time and Instance ID can be any
+// positive value or 0.
+//
+// If any value is not correctly set, new IDs cannot be produced.
+type Generator struct {
+	StartTime int64
+	mutex     *sync.Mutex
+	sequence  int32
+	now       int64
+}
+
+// NewID generates a new, unique snowflake value
+//
+// Up to 8192 snowflakes per second can be requested
+// If exhausted, it blocks and sleeps until a new second
+// of unix time starts.
+//
+// The return value is signed but always positive.
+//
+// Additionally, the return value is monotonic for a single
+// instance and weakly monotonic for many instances.
+func (g *Generator) NewID() (int64, error) {
+	if g.mutex == nil {
+		g.mutex = new(sync.Mutex)
+	}
+	if g.StartTime > time.Now().Unix() {
+		return 0, errNoFuture
+	}
+	g.mutex.Lock()
+	defer g.mutex.Unlock()
+
+	var (
+		now   int64
+		flake int64
+	)
+	now = int64(time.Now().Unix())
+
+	if now == g.now {
+		g.sequence = (g.sequence + 1) & counterMask
+		if g.sequence == 0 {
+			for now <= g.now {
+				now = int64(time.Now().Unix())
+				time.Sleep(time.Microsecond * 100)
+			}
+		}
+	} else {
+		g.sequence = 0
+	}
+
+	g.now = now
+
+	flake = int64(
+		((now - g.StartTime) << counterLen) |
+			int64(g.sequence))
+
+	return flake, nil
+}