//! Shared mobile authentication state; Swift only supplies input and presents results.

use std::{error::Error, fmt, sync::Mutex};

use crate::{
    authentication::{
        AuthenticationError, NativeAuthenticationHandle, NativeAuthenticationSession,
    },
    config::{Config, ConfigError},
    crypto::{CryptoError, KeyInfo, KeyStore, SecretProvider, SecretProviderError},
    document::{DocumentError, EntryDocument, EntryDocumentService, EntryFieldId},
    git::{AutomaticEntryCommitter, GitIdentity},
    mobile_entry::{MobileEntryPage, MobileEntryValueError, field_value},
    repository::{EntryPath, Repository, RepositoryError, SecretBytes},
    secret_store::{SecretProtectionPolicy, SecretStoreError},
};

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum MobileAuthenticationErrorKind {
    PassphraseRequired,
    InvalidPassphrase,
    Cancelled,
    BiometryUnavailable,
    Configuration,
    KeyMaterial,
    Entry,
    SecureStorage,
    Expired,
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct MobileAuthenticationError {
    kind: MobileAuthenticationErrorKind,
    title: String,
    detail: String,
}

impl MobileAuthenticationError {
    pub fn kind(&self) -> MobileAuthenticationErrorKind {
        self.kind
    }

    pub fn title(&self) -> &str {
        &self.title
    }

    pub fn detail(&self) -> &str {
        &self.detail
    }

    fn new(kind: MobileAuthenticationErrorKind, title: &str, detail: impl Into<String>) -> Self {
        Self {
            kind,
            title: title.to_owned(),
            detail: detail.into(),
        }
    }

    fn passphrase_required(detail: impl Into<String>) -> Self {
        Self::new(
            MobileAuthenticationErrorKind::PassphraseRequired,
            "Passphrase Required",
            detail,
        )
    }

    fn authentication(error: AuthenticationError) -> Self {
        match error {
            AuthenticationError::Cancelled => Self::new(
                MobileAuthenticationErrorKind::Cancelled,
                "Authentication Cancelled",
                "No protected content was unlocked.",
            ),
            AuthenticationError::Expired => Self::new(
                MobileAuthenticationErrorKind::Expired,
                "IronStorage Locked",
                "The authentication lease expired.",
            ),
            AuthenticationError::SecretStore(SecretStoreError::Missing) => {
                Self::passphrase_required("Enter the GPG key passphrase to continue.")
            }
            AuthenticationError::SecretStore(
                SecretStoreError::Denied
                | SecretStoreError::UnsupportedProtection
                | SecretStoreError::Unavailable,
            ) => Self::new(
                MobileAuthenticationErrorKind::BiometryUnavailable,
                "Biometric Unlock Unavailable",
                "Enter the GPG key passphrase to recover or continue without biometric unlock.",
            ),
            error => Self::new(
                MobileAuthenticationErrorKind::SecureStorage,
                "Secure Unlock Failed",
                error.to_string(),
            ),
        }
    }
}

impl fmt::Display for MobileAuthenticationError {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(formatter, "{}: {}", self.title, self.detail)
    }
}

impl Error for MobileAuthenticationError {}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct MobileAuthenticationState {
    unlocked: bool,
    biometric_unlock_enabled: bool,
    remaining_seconds: u64,
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct MobileEntryCopy {
    value: String,
    timeout_seconds: u64,
}

impl MobileEntryCopy {
    pub fn value(&self) -> &str {
        &self.value
    }

    pub fn timeout_seconds(&self) -> u64 {
        self.timeout_seconds
    }
}

impl MobileAuthenticationState {
    pub fn unlocked(self) -> bool {
        self.unlocked
    }

    pub fn biometric_unlock_enabled(self) -> bool {
        self.biometric_unlock_enabled
    }

    pub fn remaining_seconds(self) -> u64 {
        self.remaining_seconds
    }
}

struct ActiveMobileLease {
    handle: NativeAuthenticationHandle,
    key: KeyInfo,
}

struct MobileAuthenticationStatus {
    biometric_unlock_enabled: bool,
    active: Option<ActiveMobileLease>,
}

/// One process-wide mobile authentication lease shared by every tab and viewer.
pub struct MobileAuthentication {
    config: Config,
    repository: Repository,
    keys: KeyStore,
    session: NativeAuthenticationSession,
    status: Mutex<MobileAuthenticationStatus>,
}

impl MobileAuthentication {
    pub fn load() -> Result<Self, MobileAuthenticationError> {
        let config = Config::load(None).map_err(|error| {
            MobileAuthenticationError::new(
                MobileAuthenticationErrorKind::Configuration,
                "Authentication Is Unavailable",
                error.to_string(),
            )
        })?;
        let repository = Repository::open(config.vault()).map_err(entry_error)?;
        let keys = KeyStore::load(config.key_material()).map_err(key_error)?;
        let session = NativeAuthenticationSession::system(
            SecretProtectionPolicy::current_biometry_for_openpgp(),
            config.authentication_timeout(),
        )
        .map_err(MobileAuthenticationError::authentication)?;
        Ok(Self {
            status: Mutex::new(MobileAuthenticationStatus {
                biometric_unlock_enabled: config.biometric_unlock_enabled(),
                active: None,
            }),
            config,
            repository,
            keys,
            session,
        })
    }

    /// Validate an entry unlock and retain only the key passphrase for the shared lease.
    pub fn unlock_entry(
        &self,
        path: &str,
        passphrase: Option<SecretBytes>,
    ) -> Result<MobileAuthenticationState, MobileAuthenticationError> {
        let entry = EntryPath::parse(path).map_err(entry_error)?;
        let ciphertext = self.repository.read_entry(&entry).map_err(entry_error)?;
        let candidates = self.keys.decrypting_keys(&ciphertext).map_err(key_error)?;

        if let Some(active) = self.take_active()? {
            let mut provider = KeyOnlyProvider::new(active.handle.clone(), &active.key);
            if self.keys.decrypt(&ciphertext, &mut provider).is_ok() {
                self.restore_active(active)?;
                return self.state();
            }
            self.session
                .manual_lock()
                .map_err(MobileAuthenticationError::authentication)?;
        }

        let biometric_enabled = self.status()?.biometric_unlock_enabled;
        match passphrase {
            Some(passphrase) => {
                for key in &candidates {
                    let candidate = SecretBytes::new(passphrase.expose().to_vec());
                    let handle = self
                        .session
                        .authenticate_with_passphrase(key, candidate)
                        .map_err(MobileAuthenticationError::authentication)?;
                    let mut provider = KeyOnlyProvider::new(handle.clone(), key);
                    match self.keys.decrypt(&ciphertext, &mut provider) {
                        Ok(plaintext) => {
                            drop(plaintext);
                            if biometric_enabled {
                                handle
                                    .persist_passphrase(key)
                                    .map_err(MobileAuthenticationError::authentication)?;
                            }
                            self.set_active(handle, key.clone())?;
                            return self.state();
                        }
                        Err(CryptoError::DecryptionFailed) => {
                            self.session
                                .manual_lock()
                                .map_err(MobileAuthenticationError::authentication)?;
                        }
                        Err(error) => return Err(key_error(error)),
                    }
                }
                Err(MobileAuthenticationError::new(
                    MobileAuthenticationErrorKind::InvalidPassphrase,
                    "Incorrect Passphrase",
                    "The GPG key could not be unlocked.",
                ))
            }
            None if biometric_enabled => {
                for key in &candidates {
                    let handle = match self.session.authenticate(key) {
                        Ok(handle) => handle,
                        Err(AuthenticationError::Cancelled) => {
                            return Err(MobileAuthenticationError::authentication(
                                AuthenticationError::Cancelled,
                            ));
                        }
                        Err(_) => continue,
                    };
                    let mut provider = KeyOnlyProvider::new(handle.clone(), key);
                    if let Ok(plaintext) = self.keys.decrypt(&ciphertext, &mut provider) {
                        drop(plaintext);
                        self.set_active(handle, key.clone())?;
                        return self.state();
                    }
                    let _ = self.session.delete_key_passphrase(key);
                    let _ = self.session.manual_lock();
                }
                Err(MobileAuthenticationError::passphrase_required(
                    "Biometric unlock could not restore this key. Enter its GPG passphrase to recover.",
                ))
            }
            None => Err(MobileAuthenticationError::passphrase_required(
                "Enter the GPG key passphrase to continue.",
            )),
        }
    }

    pub fn set_biometric_unlock(
        &self,
        enabled: bool,
    ) -> Result<MobileAuthenticationState, MobileAuthenticationError> {
        if enabled {
            let status = self.status()?;
            if status.biometric_unlock_enabled {
                drop(status);
                return self.state();
            }
            let active = status.active.as_ref().ok_or_else(|| {
                MobileAuthenticationError::passphrase_required(
                    "Unlock a password entry before enabling biometric unlock.",
                )
            })?;
            active
                .handle
                .persist_passphrase(&active.key)
                .map_err(MobileAuthenticationError::authentication)?;
            drop(status);
            if let Err(error) = self.config.update_biometric_unlock(true) {
                let _ = self.delete_all_key_passphrases();
                let _ = self.manual_lock();
                return Err(config_error(error));
            }
            self.status()?.biometric_unlock_enabled = true;
        } else {
            self.delete_all_key_passphrases()?;
            self.config
                .update_biometric_unlock(false)
                .map_err(config_error)?;
            self.session
                .manual_lock()
                .map_err(MobileAuthenticationError::authentication)?;
            let mut status = self.status()?;
            status.biometric_unlock_enabled = false;
            status.active = None;
        }
        self.state()
    }

    pub fn state(&self) -> Result<MobileAuthenticationState, MobileAuthenticationError> {
        let remaining = self
            .session
            .remaining_time()
            .map_err(MobileAuthenticationError::authentication)?;
        let mut status = self.status()?;
        if remaining.is_none() {
            status.active = None;
        }
        Ok(MobileAuthenticationState {
            unlocked: status.active.is_some(),
            biometric_unlock_enabled: status.biometric_unlock_enabled,
            remaining_seconds: remaining.map_or(0, |duration| duration.as_secs()),
        })
    }

    pub fn touch_user_activity(&self) -> Result<(), MobileAuthenticationError> {
        let status = self.status()?;
        let active = status.active.as_ref().ok_or_else(|| {
            MobileAuthenticationError::new(
                MobileAuthenticationErrorKind::Expired,
                "IronStorage Locked",
                "Authenticate before using protected content.",
            )
        })?;
        active
            .handle
            .touch_user_activity()
            .map_err(MobileAuthenticationError::authentication)
    }

    pub fn entry_page(&self, path: &str) -> Result<MobileEntryPage, MobileAuthenticationError> {
        let document = self.open_active_document(path)?;
        Ok(MobileEntryPage::from_document(&document))
    }

    pub fn reveal_entry_field(
        &self,
        path: &str,
        field: u64,
    ) -> Result<String, MobileAuthenticationError> {
        let document = self.open_active_document(path)?;
        field_value(&document, field).map_err(value_error)
    }

    pub fn copy_entry_field(
        &self,
        path: &str,
        field: u64,
    ) -> Result<MobileEntryCopy, MobileAuthenticationError> {
        Ok(MobileEntryCopy {
            value: self.reveal_entry_field(path, field)?,
            timeout_seconds: self.config.clipboard_timeout().duration().as_secs(),
        })
    }

    pub fn replace_entry_field(
        &self,
        path: &str,
        field: u64,
        value: String,
    ) -> Result<MobileEntryPage, MobileAuthenticationError> {
        let mut document = self.open_active_document(path)?;
        document
            .replace_field_value(EntryFieldId::from_value(field), value.into_bytes())
            .map_err(document_error)?;
        let mut committer =
            AutomaticEntryCommitter::for_entry(&self.repository, path, GitIdentity::ironstorage())
                .map_err(|error| entry_detail("Password Entry Could Not Be Saved", error))?;
        EntryDocumentService::new(&self.repository, &self.keys)
            .save_recoverable(&document, None, &mut committer)
            .map_err(document_error)?;
        Ok(MobileEntryPage::from_document(&document))
    }

    pub fn manual_lock(&self) -> Result<(), MobileAuthenticationError> {
        self.session
            .manual_lock()
            .map_err(MobileAuthenticationError::authentication)?;
        self.status()?.active = None;
        Ok(())
    }

    pub fn cancel(&self) -> Result<(), MobileAuthenticationError> {
        self.session
            .cancel()
            .map_err(MobileAuthenticationError::authentication)?;
        self.status()?.active = None;
        Ok(())
    }

    fn delete_all_key_passphrases(&self) -> Result<(), MobileAuthenticationError> {
        for key in self.keys.infos().filter(KeyInfo::has_secret) {
            self.session
                .delete_key_passphrase(&key)
                .map_err(MobileAuthenticationError::authentication)?;
        }
        Ok(())
    }

    fn status(
        &self,
    ) -> Result<std::sync::MutexGuard<'_, MobileAuthenticationStatus>, MobileAuthenticationError>
    {
        self.status.lock().map_err(|_| {
            MobileAuthenticationError::new(
                MobileAuthenticationErrorKind::SecureStorage,
                "Authentication Is Unavailable",
                "The shared authentication state is unavailable.",
            )
        })
    }

    fn take_active(&self) -> Result<Option<ActiveMobileLease>, MobileAuthenticationError> {
        Ok(self.status()?.active.take())
    }

    fn restore_active(&self, active: ActiveMobileLease) -> Result<(), MobileAuthenticationError> {
        self.status()?.active = Some(active);
        Ok(())
    }

    fn set_active(
        &self,
        handle: NativeAuthenticationHandle,
        key: KeyInfo,
    ) -> Result<(), MobileAuthenticationError> {
        self.status()?.active = Some(ActiveMobileLease { handle, key });
        Ok(())
    }

    fn open_active_document(&self, path: &str) -> Result<EntryDocument, MobileAuthenticationError> {
        let (handle, key) = {
            let status = self.status()?;
            let active = status.active.as_ref().ok_or_else(locked_error)?;
            (active.handle.clone(), active.key.clone())
        };
        handle
            .ensure_active()
            .map_err(MobileAuthenticationError::authentication)?;
        let mut provider = KeyOnlyProvider::new(handle, &key);
        EntryDocumentService::new(&self.repository, &self.keys)
            .open(path, &mut provider)
            .map_err(document_error)
    }
}

struct KeyOnlyProvider<'a> {
    handle: NativeAuthenticationHandle,
    fingerprint: &'a str,
}

impl<'a> KeyOnlyProvider<'a> {
    fn new(handle: NativeAuthenticationHandle, key: &'a KeyInfo) -> Self {
        Self {
            handle,
            fingerprint: key.fingerprint().as_str(),
        }
    }
}

impl SecretProvider for KeyOnlyProvider<'_> {
    fn secret_for(&mut self, key: &KeyInfo) -> Result<SecretBytes, SecretProviderError> {
        if key.fingerprint().as_str() != self.fingerprint {
            return Err(SecretProviderError::Missing);
        }
        self.handle.secret_for(key)
    }
}

fn config_error(error: ConfigError) -> MobileAuthenticationError {
    MobileAuthenticationError::new(
        MobileAuthenticationErrorKind::Configuration,
        "Preference Was Not Saved",
        error.to_string(),
    )
}

fn entry_error(error: RepositoryError) -> MobileAuthenticationError {
    MobileAuthenticationError::new(
        MobileAuthenticationErrorKind::Entry,
        "Password Entry Is Unavailable",
        error.to_string(),
    )
}

fn key_error(error: CryptoError) -> MobileAuthenticationError {
    MobileAuthenticationError::new(
        MobileAuthenticationErrorKind::KeyMaterial,
        "GPG Key Unlock Failed",
        error.to_string(),
    )
}

fn locked_error() -> MobileAuthenticationError {
    MobileAuthenticationError::new(
        MobileAuthenticationErrorKind::Expired,
        "IronStorage Locked",
        "Authenticate before using protected content.",
    )
}

fn document_error(error: DocumentError) -> MobileAuthenticationError {
    entry_detail("Password Entry Is Unavailable", error)
}

fn value_error(error: MobileEntryValueError) -> MobileAuthenticationError {
    entry_detail("Field Value Is Unavailable", error)
}

fn entry_detail(title: &str, error: impl fmt::Display) -> MobileAuthenticationError {
    MobileAuthenticationError::new(
        MobileAuthenticationErrorKind::Entry,
        title,
        error.to_string(),
    )
}