package config

import (
	"encoding/hex"
	"encoding/xml"
	"errors"
	"fmt"
	"os"
	"strings"

	"git.wxccs.org/iceking2nd/winauth-go/internal/crypto"
	"git.wxccs.org/iceking2nd/winauth-go/internal/global"
)

// LegacyAuthenticator is the partial WinAuth XML element we care about.
// Fields not relevant to migration are ignored.
type LegacyAuthenticator struct {
	XMLName  xml.Name `xml:"WinAuthAuthenticator"`
	Type     string   `xml:"type,attr"`
	Name     string   `xml:"name"`
	AuthData struct {
		Encrypted      string `xml:"encrypted,attr"`
		SecretData     string `xml:"secretdata"`
		ServerTimeDiff string `xml:"servertimediff"`
	} `xml:"authenticatordata"`
}

// legacyRoot matches the outer <WinAuth ...><authenticator>...</authenticator>
// container the original WinAuthHelper.SaveAuthenticator writes.
type legacyRoot struct {
	XMLName        xml.Name              `xml:"WinAuth"`
	Authenticators []LegacyAuthenticator `xml:"authenticator>WinAuthAuthenticator"`
}

// LegacyPasswordType encodes the per-entry encryption layering of an old
// WinAuth config. Multiple bits may be set: the original app supported
// chained encryption like "yum" (password → user-DPAPI → machine-DPAPI).
type LegacyPasswordType int

const (
	LegacyPasswordNone     LegacyPasswordType = 0
	LegacyPasswordExplicit LegacyPasswordType = 1 << iota // 'y' — PBKDF2-SHA1 + Blowfish
	LegacyPasswordUser                                    // 'u' — User-scope DPAPI
	LegacyPasswordMachine                                 // 'm' — Machine-scope DPAPI
)

// ErrLegacyPasswordRequired is returned by LoadLegacyXML when at least
// one entry has the 'y' bit set but the caller did not supply a
// passphrase. The caller is expected to prompt the user and retry.
var ErrLegacyPasswordRequired = errors.New("legacy XML: password required")

// ErrLegacyPasswordWrong is returned when the supplied passphrase
// successfully unprotects DPAPI layers but the resulting Blowfish output
// fails to look like sensible UTF-8 secret data — almost always a wrong
// password since the legacy format has no MAC.
var ErrLegacyPasswordWrong = errors.New("legacy XML: wrong password")

// parseLegacyEncryptionFlags maps the encrypted-attribute string ("y",
// "ymu", "um", ...) to a flag bitmask. Unknown letters are ignored.
func parseLegacyEncryptionFlags(s string) LegacyPasswordType {
	var f LegacyPasswordType
	for _, c := range strings.ToLower(strings.TrimSpace(s)) {
		switch c {
		case 'y':
			f |= LegacyPasswordExplicit
		case 'u':
			f |= LegacyPasswordUser
		case 'm':
			f |= LegacyPasswordMachine
		}
	}
	return f
}

// LegacyXMLNeedsPassword reports whether any entry in the file uses the
// 'y' password layer, so the UI knows to prompt before calling
// LoadLegacyXML with the user-supplied password.
func LegacyXMLNeedsPassword(path string) (bool, error) {
	raw, err := os.ReadFile(path)
	if err != nil {
		return false, err
	}
	var root legacyRoot
	if err := xml.Unmarshal(raw, &root); err != nil {
		return false, fmt.Errorf("legacy XML: %w", err)
	}
	for _, a := range root.Authenticators {
		if parseLegacyEncryptionFlags(a.AuthData.Encrypted)&LegacyPasswordExplicit != 0 {
			return true, nil
		}
	}
	return false, nil
}

// LoadLegacyXML reads an old WinAuth XML config (the one stored at
// %APPDATA%\WinAuth\winauth.xml). password may be nil if the file is
// fully unencrypted, but it must be supplied if any entry carries the
// 'y' password bit, otherwise ErrLegacyPasswordRequired is returned.
//
// Entries that cannot be decrypted (e.g. DPAPI blob produced by a
// different Windows user / on a different machine) are logged and
// skipped — partial migration is better than aborting.
func LoadLegacyXML(path string, password []byte) (*Config, error) {
	const fn = "internal.config.LoadLegacyXML"
	logger := global.Log.WithField("func", fn).WithField("path", path)

	raw, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}
	var root legacyRoot
	if err := xml.Unmarshal(raw, &root); err != nil {
		return nil, fmt.Errorf("legacy XML: %w", err)
	}

	// Pre-flight: refuse early so the UI can switch to password prompt
	// without us having partially decrypted some unprotected entries.
	for _, a := range root.Authenticators {
		flags := parseLegacyEncryptionFlags(a.AuthData.Encrypted)
		if flags&LegacyPasswordExplicit != 0 && len(password) == 0 {
			return nil, ErrLegacyPasswordRequired
		}
	}

	cfg := &Config{Version: 1}
	for _, a := range root.Authenticators {
		entryLogger := logger.WithField("name", a.Name)
		flags := parseLegacyEncryptionFlags(a.AuthData.Encrypted)

		plaintext, err := decryptLegacySecretData(a.AuthData.SecretData, flags, password)
		if err != nil {
			entryLogger.WithError(err).Warn("skip entry: decrypt failed")
			continue
		}

		entry, err := convertLegacyEntry(a, plaintext)
		if err != nil {
			entryLogger.WithError(err).Warn("skip entry: conversion failed")
			continue
		}
		cfg.Entries = append(cfg.Entries, entry)
	}
	logger.WithField("entries", len(cfg.Entries)).Debug("legacy config imported")
	return cfg, nil
}

// decryptLegacySecretData reverses the layered encryption WinAuth wrote.
// Each layer expects a hex string and produces a hex string (the final
// layer's hex decodes to UTF-8 secret data). Order of removal is the
// reverse of the original encryption order: User-DPAPI, then
// Machine-DPAPI, then explicit Password.
func decryptLegacySecretData(data string, flags LegacyPasswordType, password []byte) (string, error) {
	data = strings.TrimSpace(data)
	if data == "" || flags == LegacyPasswordNone {
		return data, nil
	}

	if flags&LegacyPasswordUser != 0 {
		blob, err := hex.DecodeString(data)
		if err != nil {
			return "", fmt.Errorf("user-DPAPI: hex decode: %w", err)
		}
		out, err := crypto.Unprotect(blob, nil, crypto.DPAPIScopeCurrentUser)
		if err != nil {
			return "", fmt.Errorf("user-DPAPI: %w", err)
		}
		data = hex.EncodeToString(out)
	}

	if flags&LegacyPasswordMachine != 0 {
		blob, err := hex.DecodeString(data)
		if err != nil {
			return "", fmt.Errorf("machine-DPAPI: hex decode: %w", err)
		}
		out, err := crypto.Unprotect(blob, nil, crypto.DPAPIScopeLocalMachine)
		if err != nil {
			return "", fmt.Errorf("machine-DPAPI: %w", err)
		}
		data = hex.EncodeToString(out)
	}

	if flags&LegacyPasswordExplicit != 0 {
		// First 16 hex chars = 8-byte salt; rest is Blowfish ciphertext.
		const saltHexLen = 16
		if len(data) < saltHexLen {
			return "", errors.New("explicit: payload shorter than salt")
		}
		saltHex, bodyHex := data[:saltHexLen], data[saltHexLen:]
		salt, err := hex.DecodeString(saltHex)
		if err != nil {
			return "", fmt.Errorf("explicit: salt hex decode: %w", err)
		}
		key := crypto.DerivePBKDF2SHA1(password, salt)
		defer func() {
			for i := range key {
				key[i] = 0
			}
		}()
		plain, err := crypto.LegacyDecryptBlowfish(bodyHex, key)
		if err != nil {
			return "", fmt.Errorf("explicit: %w", err)
		}
		// The Blowfish output should itself be a hex string representing
		// the next inner layer (or the UTF-8 secret data). A wrong
		// password almost always lands here producing garbage bytes;
		// check that the result is printable ASCII to reject it.
		if !looksLikeLegacyPlaintext(plain) {
			return "", ErrLegacyPasswordWrong
		}
		data = string(plain)
	}

	return data, nil
}

// looksLikeLegacyPlaintext returns true if buf reads as a printable
// ASCII string of the kind WinAuth writes for SecretData (tab-separated
// hex, pipe-separated serial, or JSON). Non-printable bytes nearly
// always indicate a bad password since legacy Blowfish has no MAC.
func looksLikeLegacyPlaintext(buf []byte) bool {
	if len(buf) == 0 {
		return false
	}
	for _, b := range buf {
		if b == '\t' || b == '\n' || b == '\r' || (b >= 0x20 && b < 0x7f) {
			continue
		}
		return false
	}
	return true
}

// convertLegacyEntry takes one parsed authenticator block and its
// decrypted secret-data payload and turns it into a modern Entry.
// Vendor-specific quirks (Battle.Net serial trailer, Steam JSON, ...)
// live in the per-vendor helpers in legacy_secretdata.go.
func convertLegacyEntry(a LegacyAuthenticator, secret string) (Entry, error) {
	vendor := detectLegacyVendor(a.Type)
	raw, err := normalizeLegacySecretData(vendor, secret)
	if err != nil {
		return Entry{}, err
	}
	return Entry{
		Name:      a.Name,
		Vendor:    vendor,
		SecretRaw: raw,
	}, nil
}

func detectLegacyVendor(typeAttr string) string {
	t := strings.ToLower(typeAttr)
	switch {
	case strings.Contains(t, "battlenet"):
		return "battlenet"
	case strings.Contains(t, "steam"):
		return "steam"
	case strings.Contains(t, "microsoft"):
		return "microsoft"
	case strings.Contains(t, "oktaverify"):
		return "okta"
	case strings.Contains(t, "hotp"):
		return "hotp"
	default:
		return "google"
	}
}