package ids

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

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

type Prefix string

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

func New(prefix Prefix) string {
	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 string(prefix) + string(out)
}

func Derive(prefix Prefix, parts ...string) string {
	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 string(prefix) + string(out)
}