package ids

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/binary"
	"fmt"
	"strings"
)

const (
	alphabet     = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
	randomLength = 11
)

const (
	Project            = "prj"
	Task               = "tsk"
	Session            = "ses"
	Snapshot           = "snp"
	Review             = "rev"
	InboxItem          = "inb"
	InboxResponse      = "rsp"
	Blob               = "blb"
	LeadNote           = "not"
	WorkflowDefinition = "wfd"
	WorkflowRun        = "run"
	Send               = "snd"
	Client             = "cli"
	ClientRequest      = "req"
	Transfer           = "xfr"
)

var prefixes = map[string]bool{
	Project: true, Task: true, Session: true, Snapshot: true, Review: true,
	InboxItem: true, InboxResponse: true, Blob: true, LeadNote: true,
	WorkflowDefinition: true, WorkflowRun: true, Send: true,
	Client: true, ClientRequest: true, Transfer: true,
}

func New(prefix string) string {
	check(prefix)
	out := make([]byte, randomLength)
	buf := make([]byte, 1)
	for i := 0; i < len(out); {
		rand.Read(buf)
		if int(buf[0]) >= 256/len(alphabet)*len(alphabet) {
			continue
		}
		out[i] = alphabet[int(buf[0])%len(alphabet)]
		i++
	}
	return prefix + string(out)
}

func Derive(prefix string, parts ...string) string {
	check(prefix)
	sum := sha256.Sum256([]byte(strings.Join(parts, "\x00")))
	n := binary.BigEndian.Uint64(sum[:8])
	out := make([]byte, randomLength)
	for i := range out {
		out[i] = alphabet[n%uint64(len(alphabet))]
		n /= uint64(len(alphabet))
	}
	return prefix + string(out)
}

func check(prefix string) {
	if !prefixes[prefix] {
		panic(fmt.Sprintf("no id prefix %q", prefix))
	}
}