/*
 * Amsterdam Web Communities System
 * Copyright (c) 2025-2026 Erbosoft Metaverse Design Solutions, All Rights Reserved
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 *
 * SPDX-License-Identifier: MPL-2.0
 */

// Package util contains utility definitions.
package util

import (
	crand "crypto/rand"
	"fmt"
	"io"
	"math/big"
	"strings"

	log "github.com/sirupsen/logrus"
)

// authAlphabet is the set of characters from which we generate auth strings.
const authAlphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz./"

// authStringLen is the standard lengtth of authentication strings.
const authStringLen = 32

// syllabary is used to generate random passwords.
var syllabary = [...]string{
	"ba", "be", "bi", "bo", "bu",
	"da", "de", "di", "do", "du",
	"cha", "chi", "cho", "chu",
	"fa", "fe", "fi", "fo", "fu",
	"ga", "ge", "gi", "go", "gu",
	"ha", "he", "hi", "ho", "hu",
	"ja", "je", "ji", "jo", "ju",
	"ka", "ke", "ki", "ko", "ku",
	"la", "le", "li", "lo", "lu",
	"ma", "me", "mi", "mo", "mu",
	"na", "ne", "ni", "no", "nu",
	"pa", "pe", "pi", "po", "pu",
	"ra", "re", "ri", "ro", "ru",
	"sa", "se", "si", "so", "su",
	"sha", "she", "sho", "shu",
	"ta", "te", "ti", "to", "tu",
	"va", "ve", "vi", "vo", "vu",
	"wa", "we", "wi", "wo", "wu",
	"ya", "ye", "yi", "yo", "yu",
	"za", "ze", "zi", "zo", "zu",
}

// RCN_BASE is the base for generating random confirmation numbers.
var RCN_BASE *big.Int = big.NewInt(9000000)

// RCN_OFFSET is what we add to a generated random number to get a proper confirmation number.
const RCN_OFFSET = 1000000

// RCN_MAX is the maximum value of a confirmation number.
const RCN_MAX = 9999999

// GenerateRandomAuthString generates a random authentication string.
func GenerateRandomAuthString() string {
	b := make([]byte, authStringLen)
	if _, err := io.ReadFull(crand.Reader, b); err != nil {
		// can't happen (at least on a modern OS)
		panic("failed to read random: " + err.Error())
	}
	for i := 0; i < authStringLen; i++ {
		b[i] = authAlphabet[int(b[i])%len(authAlphabet)]
	}
	return string(b)
}

// GenerateRandomConfirmationNumber generates a random 7-digit confirmation number.
func GenerateRandomConfirmationNumber() int32 {
	v1, err := crand.Int(crand.Reader, RCN_BASE)
	if err != nil {
		panic(fmt.Sprintf("GRCN ERR %v", err))
	}
	rc := int32(v1.Int64()) + RCN_OFFSET
	for rc < RCN_OFFSET || rc > RCN_MAX {
		log.Errorf("*** GRCN out of range error! %d", rc)
		v1, err = crand.Int(crand.Reader, RCN_BASE)
		if err != nil {
			panic(fmt.Sprintf("GRCN ERR %v", err))
		}
		rc = int32(v1.Int64()) + RCN_OFFSET
	}
	return rc
}

// GenerateRandomPassword generates a random password string.
func GenerateRandomPassword() string {
	var b strings.Builder
	rd := make([]byte, 7)
	if _, err := io.ReadFull(crand.Reader, rd); err != nil {
		// can't happen (at least on a modern OS)
		panic("failed to read random: " + err.Error())
	}
	for i := 0; i < 4; i++ { // add random syllables
		b.WriteString(syllabary[int(rd[i])%len(syllabary)])
	}
	for i := 4; i < 7; i++ { // add random digits
		b.WriteByte(byte('0' + int(rd[i])%10))
	}
	return b.String()
}