package main

import (
	"crypto/rand"
	"crypto/sha256"
	"crypto/subtle"
	"encoding/base64"
	"errors"
	"fmt"
	"strconv"
	"strings"

	"golang.org/x/crypto/argon2"
)

const (
	RoleViewer        = "viewer"
	RoleOperator      = "operator"
	RoleAdministrator = "administrator"
)

type User struct {
	ID       string `json:"id"`
	Username string `json:"username"`
	Role     string `json:"role"`
}

func HashPassword(password string) (string, error) {
	if len(password) < 12 || len(password) > 1024 {
		return "", errors.New("password must be between 12 and 1024 bytes")
	}
	salt := make([]byte, 16)
	if _, err := rand.Read(salt); err != nil {
		return "", err
	}
	const memory = 64 * 1024
	const iterations = 3
	const parallelism = 2
	hash := argon2.IDKey([]byte(password), salt, iterations, memory, parallelism, 32)
	return fmt.Sprintf("$argon2id$v=19$m=%d,t=%d,p=%d$%s$%s", memory, iterations, parallelism,
		base64.RawStdEncoding.EncodeToString(salt), base64.RawStdEncoding.EncodeToString(hash)), nil
}

func VerifyPassword(encoded, password string) bool {
	parts := strings.Split(encoded, "$")
	if len(parts) != 6 || parts[1] != "argon2id" || parts[2] != "v=19" {
		return false
	}
	var memory uint32
	var iterations uint32
	var parallelism uint8
	if _, err := fmt.Sscanf(parts[3], "m=%d,t=%d,p=%d", &memory, &iterations, &parallelism); err != nil {
		return false
	}
	if memory > 128*1024 || iterations > 10 || parallelism > 8 {
		return false
	}
	salt, err := base64.RawStdEncoding.DecodeString(parts[4])
	if err != nil || len(salt) < 16 {
		return false
	}
	expected, err := base64.RawStdEncoding.DecodeString(parts[5])
	if err != nil || len(expected) != 32 {
		return false
	}
	actual := argon2.IDKey([]byte(password), salt, iterations, memory, parallelism, uint32(len(expected)))
	return subtle.ConstantTimeCompare(actual, expected) == 1
}

func randomToken() (string, []byte, error) {
	raw := make([]byte, 32)
	if _, err := rand.Read(raw); err != nil {
		return "", nil, err
	}
	token := base64.RawURLEncoding.EncodeToString(raw)
	digest := sha256.Sum256([]byte(token))
	return token, digest[:], nil
}

func tokenHash(token string) []byte {
	digest := sha256.Sum256([]byte(token))
	return digest[:]
}

func validRole(role string) bool {
	return role == RoleViewer || role == RoleOperator || role == RoleAdministrator
}

func permits(role, required string) bool {
	rank := map[string]int{RoleViewer: 1, RoleOperator: 2, RoleAdministrator: 3}
	return rank[role] >= rank[required] && rank[required] > 0
}

func validUsername(username string) bool {
	if len(username) < 3 || len(username) > 64 {
		return false
	}
	for _, char := range username {
		if !(char >= 'a' && char <= 'z') && !(char >= 'A' && char <= 'Z') &&
			!(char >= '0' && char <= '9') && !strings.ContainsRune("._-", char) {
			return false
		}
	}
	return true
}

func parseInt(value string, fallback int) int {
	parsed, err := strconv.Atoi(value)
	if err != nil {
		return fallback
	}
	return parsed
}