// Package security provides password hashing and JWT issuing/verification
// shared across auth modules.
package security

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/base64"
	"fmt"
	"strings"

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

const (
	argon2Time    = 3
	argon2Memory  = 64 * 1024 // 64 MB
	argon2Threads = 2
	argon2SaltLen = 16
	argon2KeyLen  = 32
)

// HashPassword hashes a plaintext password using argon2id and returns the
// PHC-formatted string ($argon2id$v=19$m=...,t=...,p=...$salt$hash).
func HashPassword(password string) (string, error) {
	salt := make([]byte, argon2SaltLen)
	if _, err := rand.Read(salt); err != nil {
		return "", fmt.Errorf("generate salt: %w", err)
	}

	hash := argon2.IDKey([]byte(password), salt, argon2Time, argon2Memory, argon2Threads, argon2KeyLen)

	encoded := fmt.Sprintf(
		"$argon2id$v=%d$m=%d,t=%d,p=%d$%s$%s",
		argon2.Version,
		argon2Memory,
		argon2Time,
		argon2Threads,
		base64.RawStdEncoding.EncodeToString(salt),
		base64.RawStdEncoding.EncodeToString(hash),
	)
	return encoded, nil
}

// VerifyPassword checks a plaintext password against a PHC-formatted argon2id hash.
func VerifyPassword(encodedHash, password string) (bool, error) {
	parts := strings.Split(encodedHash, "$")
	if len(parts) != 6 || parts[1] != "argon2id" {
		return false, fmt.Errorf("invalid hash format")
	}

	var version int
	if _, err := fmt.Sscanf(parts[2], "v=%d", &version); err != nil {
		return false, fmt.Errorf("invalid hash version segment: %w", err)
	}
	if version != argon2.Version {
		return false, fmt.Errorf("unsupported argon2 version: %d", version)
	}

	var memory uint32
	var time uint32
	var threads uint8
	if _, err := fmt.Sscanf(parts[3], "m=%d,t=%d,p=%d", &memory, &time, &threads); err != nil {
		return false, fmt.Errorf("invalid hash params segment: %w", err)
	}

	salt, err := base64.RawStdEncoding.DecodeString(parts[4])
	if err != nil {
		return false, fmt.Errorf("decode salt: %w", err)
	}
	wantHash, err := base64.RawStdEncoding.DecodeString(parts[5])
	if err != nil {
		return false, fmt.Errorf("decode hash: %w", err)
	}

	gotHash := argon2.IDKey([]byte(password), salt, time, memory, threads, uint32(len(wantHash)))

	if subtle.ConstantTimeCompare(gotHash, wantHash) == 1 {
		return true, nil
	}
	return false, nil
}