package subsonic

import (
	"crypto/md5"
	"database/sql"
	"encoding/hex"
	"strconv"
	"strings"

	vsauth "git.noroutes.net/NoRoutes/vibetunes/internal/auth"
	"git.noroutes.net/NoRoutes/vibetunes/internal/database"
)

// authenticate implements original Subsonic authentication: either
// token/salt (t = md5(password + salt), the modern recommended mode) or
// password (p=<plaintext> or p=enc:<hex>, kept for older clients).
//
// This never touches VibeSonic's Argon2id-hashed password directly for
// token auth — that hash is one-way by design. Token auth is instead
// verified against a separately maintained, AES-GCM-encrypted copy of
// the password (see internal/auth/subsonic_secret.go); the /rest/*
// surface never reintroduces MD5 or plaintext as VibeSonic's own storage
// format, it only speaks it on the wire where the protocol requires it.
func authenticate(db *sql.DB, encryptionKey []byte, p params) (*database.User, *apiError) {
	apiKey := p.Get("apiKey")
	username := p.Get("u")

	if apiKey != "" {
		// The apiKeyAuthentication extension requires a client not send
		// 'u' alongside 'apiKey' — accepting both would leave it
		// ambiguous which identity the caller actually intended, so this
		// is rejected outright rather than silently preferring one.
		if username != "" {
			return nil, errConflictingAuth
		}
		return authenticateAPIKey(db, apiKey)
	}

	if username == "" {
		return nil, errMissingParameter("u")
	}

	user, err := database.GetUserByUsername(db, username)
	if err != nil || user.Disabled {
		return nil, errWrongCredentials
	}

	token := p.Get("t")
	salt := p.Get("s")
	password := p.Get("p")

	switch {
	case token != "" && salt != "":
		if !user.SubsonicAuthSecret.Valid {
			return nil, errTokenAuthNotSupported
		}
		plaintext, derr := vsauth.DecryptPassword(encryptionKey, user.SubsonicAuthSecret.String)
		if derr != nil {
			return nil, errWrongCredentials
		}
		sum := md5.Sum([]byte(plaintext + salt))
		expected := hex.EncodeToString(sum[:])
		if !strings.EqualFold(expected, token) {
			return nil, errWrongCredentials
		}

	case password != "":
		plaintext := password
		if strings.HasPrefix(password, "enc:") {
			decoded, herr := hex.DecodeString(strings.TrimPrefix(password, "enc:"))
			if herr != nil {
				return nil, errWrongCredentials
			}
			plaintext = string(decoded)
		}
		if !user.PasswordHash.Valid {
			return nil, errWrongCredentials
		}
		ok, verr := vsauth.VerifyPassword(plaintext, user.PasswordHash.String)
		if verr != nil || !ok {
			return nil, errWrongCredentials
		}

	default:
		return nil, errMissingParameter("p or t/s")
	}

	return user, nil
}

// authenticateAPIKey implements the OpenSubsonic apiKeyAuthentication
// extension: the key is hashed the same way as VibeSonic's own web
// settings API keys (they are exactly the same keys — one system, not a
// parallel one) and looked up by hash, never by scanning stored keys in
// plaintext.
func authenticateAPIKey(db *sql.DB, rawKey string) (*database.User, *apiError) {
	key, err := database.GetAPIKeyByHash(db, vsauth.HashAPIKey(rawKey))
	if err != nil {
		return nil, errInvalidAPIKey
	}
	user, err := database.GetUserByID(db, key.UserID)
	if err != nil || user.Disabled {
		return nil, errInvalidAPIKey
	}
	_ = database.TouchAPIKey(db, key.ID)
	return user, nil
}

// checkVersion rejects clients whose declared protocol version is newer
// than what this server implements. A missing or unparsable v is
// tolerated (treated as compatible) rather than rejected outright, to
// stay lenient with tooling that omits it — the protocol is additive, so
// there is no reason to reject an old client either.
func checkVersion(v string) *apiError {
	if v == "" {
		return nil
	}
	client, ok := parseVersion(v)
	if !ok {
		return nil
	}
	server, _ := parseVersion(ServerVersion)
	if versionGreater(client, server) {
		return errClientMustUpgrade
	}
	return nil
}

type semver struct{ major, minor, patch int }

func parseVersion(v string) (semver, bool) {
	parts := strings.SplitN(v, ".", 3)
	if len(parts) == 0 {
		return semver{}, false
	}
	var s semver
	var err error
	s.major, err = strconv.Atoi(parts[0])
	if err != nil {
		return semver{}, false
	}
	if len(parts) > 1 {
		s.minor, _ = strconv.Atoi(parts[1])
	}
	if len(parts) > 2 {
		s.patch, _ = strconv.Atoi(parts[2])
	}
	return s, true
}

func versionGreater(a, b semver) bool {
	if a.major != b.major {
		return a.major > b.major
	}
	if a.minor != b.minor {
		return a.minor > b.minor
	}
	return a.patch > b.patch
}