//! Cryptographic key module.

use std::collections::BTreeMap;
use std::fmt;
use std::io::Cursor;

use anyhow::{Context as _, Result, bail, ensure};
use base64::Engine as _;
use deltachat_contact_tools::EmailAddress;
use pgp::composed::Deserializable;
pub use pgp::composed::{SignedPublicKey, SignedSecretKey};
use pgp::ser::Serialize;
use pgp::types::{KeyDetails, KeyId, Password};
use tokio::runtime::Handle;

use crate::context::Context;
use crate::events::EventType;
use crate::log::LogExt;
use crate::pgp::KeyPair;
use crate::tools::{self, time_elapsed};

/// Convenience trait for working with keys.
///
/// This trait is implemented for rPGP's [SignedPublicKey] and
/// [SignedSecretKey] types and makes working with them a little
/// easier in the deltachat world.
pub trait DcKey: Serialize + Deserializable + Clone {
    /// Create a key from some bytes.
    fn from_slice(bytes: &[u8]) -> Result<Self> {
        let res = <Self as Deserializable>::from_bytes(Cursor::new(bytes));
        if let Ok(res) = res {
            return Ok(res);
        }

        // Workaround for keys imported using
        // Delta Chat core < 1.0.0.
        // Old Delta Chat core had a bug
        // that resulted in treating CRC24 checksum
        // as part of the key when reading ASCII Armor.
        // Some users that started using Delta Chat in 2019
        // have such corrupted keys with garbage bytes at the end.
        //
        // Garbage is at least 3 bytes long
        // and may be longer due to padding
        // at the end of the real key data
        // and importing the key multiple times.
        //
        // If removing 10 bytes is not enough,
        // the key is likely actually corrupted.
        for garbage_bytes in 3..std::cmp::min(bytes.len(), 10) {
            let res = <Self as Deserializable>::from_bytes(Cursor::new(
                bytes
                    .get(..bytes.len().saturating_sub(garbage_bytes))
                    .unwrap_or_default(),
            ));
            if let Ok(res) = res {
                return Ok(res);
            }
        }

        // Removing garbage bytes did not help, return the error.
        Ok(res?)
    }

    /// Create a key from a base64 string.
    fn from_base64(data: &str) -> Result<Self> {
        // strip newlines and other whitespace
        let cleaned: String = data.split_whitespace().collect();
        let bytes = base64::engine::general_purpose::STANDARD.decode(cleaned.as_bytes())?;
        Self::from_slice(&bytes)
    }

    /// Create a key from an ASCII-armored string.
    fn from_asc(data: &str) -> Result<Self> {
        let bytes = data.as_bytes();
        let res = Self::from_armor_single(Cursor::new(bytes));
        let (key, _headers) = match res {
            Err(pgp::errors::Error::NoMatchingPacket { .. }) => match Self::is_private() {
                true => bail!("No private key packet found"),
                false => bail!("No public key packet found"),
            },
            _ => res.context("rPGP error")?,
        };
        Ok(key)
    }

    /// Serialise the key as bytes.
    fn to_bytes(&self) -> Vec<u8> {
        // Not using Serialize::to_bytes() to make clear *why* it is
        // safe to ignore this error.
        // Because we write to a Vec<u8> the io::Write impls never
        // fail and we can hide this error.
        let mut buf = Vec::new();
        self.to_writer(&mut buf).unwrap();
        buf
    }

    /// Serialise the key to a base64 string.
    fn to_base64(&self) -> String {
        base64::engine::general_purpose::STANDARD.encode(DcKey::to_bytes(self))
    }

    /// Serialise the key to ASCII-armored representation.
    ///
    /// Each header line must be terminated by `\r\n`.  Only allows setting one
    /// header as a simplification since that's the only way it's used so far.
    // Since .to_armored_string() are actual methods on SignedPublicKey and
    // SignedSecretKey we can not generically implement this.
    fn to_asc(&self, header: Option<(&str, &str)>) -> String;

    /// The fingerprint for the key.
    fn dc_fingerprint(&self) -> Fingerprint;

    /// Whether the key is private (or public).
    fn is_private() -> bool;

    /// Returns the OpenPGP Key ID.
    fn key_id(&self) -> KeyId;
}

/// Attempts to load own public key.
///
/// Returns `None` if no key is generated yet.
pub(crate) async fn load_self_public_key_opt(context: &Context) -> Result<Option<SignedPublicKey>> {
    let Some(public_key_bytes) = context
        .sql
        .query_row_optional(
            "SELECT public_key
             FROM keypairs
             WHERE id=(SELECT value FROM config WHERE keyname='key_id')",
            (),
            |row| {
                let bytes: Vec<u8> = row.get(0)?;
                Ok(bytes)
            },
        )
        .await?
    else {
        return Ok(None);
    };
    let public_key = SignedPublicKey::from_slice(&public_key_bytes)?;
    Ok(Some(public_key))
}

/// Loads own public key.
///
/// If no key is generated yet, generates a new one.
pub(crate) async fn load_self_public_key(context: &Context) -> Result<SignedPublicKey> {
    match load_self_public_key_opt(context).await? {
        Some(public_key) => Ok(public_key),
        None => {
            let keypair = generate_keypair(context).await?;
            Ok(keypair.public)
        }
    }
}

/// Returns our own public keyring.
pub(crate) async fn load_self_public_keyring(context: &Context) -> Result<Vec<SignedPublicKey>> {
    let keys = context
        .sql
        .query_map_vec(
            r#"SELECT public_key
               FROM keypairs
               ORDER BY id=(SELECT value FROM config WHERE keyname='key_id') DESC"#,
            (),
            |row| {
                let public_key_bytes: Vec<u8> = row.get(0)?;
                Ok(public_key_bytes)
            },
        )
        .await?
        .into_iter()
        .filter_map(|bytes| SignedPublicKey::from_slice(&bytes).log_err(context).ok())
        .collect();
    Ok(keys)
}

/// Returns own public key fingerprint in (not human-readable) hex representation.
/// This is the fingerprint format that is used in the database.
///
/// If no key is generated yet, generates a new one.
///
/// For performance reasons, the fingerprint is cached after the first invocation.
pub(crate) async fn self_fingerprint(context: &Context) -> Result<&str> {
    if let Some(fp) = context.self_fingerprint.get() {
        Ok(fp)
    } else {
        let fp = load_self_public_key(context).await?.dc_fingerprint().hex();
        Ok(context.self_fingerprint.get_or_init(|| fp))
    }
}

/// Returns own public key fingerprint in (not human-readable) hex representation.
/// This is the fingerprint format that is used in the database.
///
/// Returns `None` if no key is generated yet.
///
/// For performance reasons, the fingerprint is cached after the first invocation.
pub(crate) async fn self_fingerprint_opt(context: &Context) -> Result<Option<&str>> {
    if let Some(fp) = context.self_fingerprint.get() {
        Ok(Some(fp))
    } else if let Some(key) = load_self_public_key_opt(context).await? {
        let fp = key.dc_fingerprint().hex();
        Ok(Some(context.self_fingerprint.get_or_init(|| fp)))
    } else {
        Ok(None)
    }
}

pub(crate) async fn load_self_secret_key(context: &Context) -> Result<SignedSecretKey> {
    let private_key = context
        .sql
        .query_row_optional(
            "SELECT private_key
             FROM keypairs
             WHERE id=(SELECT value FROM config WHERE keyname='key_id')",
            (),
            |row| {
                let bytes: Vec<u8> = row.get(0)?;
                Ok(bytes)
            },
        )
        .await?;
    match private_key {
        Some(bytes) => SignedSecretKey::from_slice(&bytes),
        None => {
            let keypair = generate_keypair(context).await?;
            Ok(keypair.secret)
        }
    }
}

pub(crate) async fn load_self_secret_keyring(context: &Context) -> Result<Vec<SignedSecretKey>> {
    let keys = context
        .sql
        .query_map_vec(
            r#"SELECT private_key
               FROM keypairs
               ORDER BY id=(SELECT value FROM config WHERE keyname='key_id') DESC"#,
            (),
            |row| {
                let bytes: Vec<u8> = row.get(0)?;
                Ok(bytes)
            },
        )
        .await?
        .into_iter()
        .filter_map(|bytes| SignedSecretKey::from_slice(&bytes).log_err(context).ok())
        .collect();
    Ok(keys)
}

impl DcKey for SignedPublicKey {
    fn to_asc(&self, header: Option<(&str, &str)>) -> String {
        // Not using .to_armored_string() to make clear *why* it is
        // safe to ignore this error.
        // Because we write to a Vec<u8> the io::Write impls never
        // fail and we can hide this error.
        let headers =
            header.map(|(key, value)| BTreeMap::from([(key.to_string(), vec![value.to_string()])]));
        let mut buf = Vec::new();
        self.to_armored_writer(&mut buf, headers.as_ref().into())
            .unwrap_or_default();
        std::string::String::from_utf8(buf).unwrap_or_default()
    }

    fn is_private() -> bool {
        false
    }

    fn dc_fingerprint(&self) -> Fingerprint {
        self.fingerprint().into()
    }

    fn key_id(&self) -> KeyId {
        KeyDetails::key_id(self)
    }
}

impl DcKey for SignedSecretKey {
    fn to_asc(&self, header: Option<(&str, &str)>) -> String {
        // Not using .to_armored_string() to make clear *why* it is
        // safe to do these unwraps.
        // Because we write to a Vec<u8> the io::Write impls never
        // fail and we can hide this error.  The string is always ASCII.
        let headers =
            header.map(|(key, value)| BTreeMap::from([(key.to_string(), vec![value.to_string()])]));
        let mut buf = Vec::new();
        self.to_armored_writer(&mut buf, headers.as_ref().into())
            .unwrap_or_default();
        std::string::String::from_utf8(buf).unwrap_or_default()
    }

    fn is_private() -> bool {
        true
    }

    fn dc_fingerprint(&self) -> Fingerprint {
        self.fingerprint().into()
    }

    fn key_id(&self) -> KeyId {
        KeyDetails::key_id(&**self)
    }
}

/// Deltachat extension trait for secret keys.
///
/// Provides some convenience wrappers only applicable to [SignedSecretKey].
pub(crate) trait DcSecretKey {
    /// Create a public key from a private one.
    fn split_public_key(&self) -> Result<SignedPublicKey>;
}

impl DcSecretKey for SignedSecretKey {
    fn split_public_key(&self) -> Result<SignedPublicKey> {
        self.verify()?;
        let unsigned_pubkey = self.public_key();
        let mut rng = rand_old::thread_rng();
        let signed_pubkey = unsigned_pubkey.sign(
            &mut rng,
            &self.primary_key,
            self.primary_key.public_key(),
            &Password::empty(),
        )?;
        Ok(signed_pubkey)
    }
}

async fn generate_keypair(context: &Context) -> Result<KeyPair> {
    let addr = context.get_primary_self_addr().await?;
    let addr = EmailAddress::new(&addr)?;
    let _guard = context.generating_key_mutex.lock().await;

    // Check if the key appeared while we were waiting on the lock.
    match load_keypair(context).await? {
        Some(key_pair) => Ok(key_pair),
        None => {
            let start = tools::Time::now();
            info!(context, "Generating keypair.");
            let keypair = Handle::current()
                .spawn_blocking(move || crate::pgp::create_keypair(addr))
                .await??;

            store_self_keypair(context, &keypair).await?;
            info!(
                context,
                "Keypair generated in {:.3}s.",
                time_elapsed(&start).as_secs(),
            );
            Ok(keypair)
        }
    }
}

pub(crate) async fn load_keypair(context: &Context) -> Result<Option<KeyPair>> {
    let res = context
        .sql
        .query_row_optional(
            "SELECT public_key, private_key
             FROM keypairs
             WHERE id=(SELECT value FROM config WHERE keyname='key_id')",
            (),
            |row| {
                let pub_bytes: Vec<u8> = row.get(0)?;
                let sec_bytes: Vec<u8> = row.get(1)?;
                Ok((pub_bytes, sec_bytes))
            },
        )
        .await?;

    Ok(if let Some((pub_bytes, sec_bytes)) = res {
        Some(KeyPair {
            public: SignedPublicKey::from_slice(&pub_bytes)?,
            secret: SignedSecretKey::from_slice(&sec_bytes)?,
        })
    } else {
        None
    })
}

/// Store the keypair as an owned keypair for addr in the database.
///
/// This will save the keypair as keys for the given address.  The
/// "self" here refers to the fact that this DC instance owns the
/// keypair.  Usually `addr` will be [Config::ConfiguredAddr].
///
/// If either the public or private keys are already present in the
/// database, this entry will be removed first regardless of the
/// address associated with it.  Practically this means saving the
/// same key again overwrites it.
///
/// [Config::ConfiguredAddr]: crate::config::Config::ConfiguredAddr
pub(crate) async fn store_self_keypair(context: &Context, keypair: &KeyPair) -> Result<()> {
    let mut config_cache_lock = context.sql.config_cache.write().await;
    let new_key_id = context
        .sql
        .transaction(|transaction| {
            let public_key = DcKey::to_bytes(&keypair.public);
            let secret_key = DcKey::to_bytes(&keypair.secret);

            // private_key and public_key columns
            // are UNIQUE since migration 107,
            // so this fails if we already have this key.
            transaction
                .execute(
                    "INSERT INTO keypairs (public_key, private_key)
                     VALUES (?,?)",
                    (&public_key, &secret_key),
                )
                .context("Failed to insert keypair")?;

            let new_key_id = transaction.last_insert_rowid();

            // This will fail if we already have `key_id`.
            //
            // Setting default key is only possible if we don't
            // have a key already.
            transaction.execute(
                "INSERT INTO config (keyname, value) VALUES ('key_id', ?)",
                (new_key_id,),
            )?;
            Ok(new_key_id)
        })
        .await?;
    context.emit_event(EventType::AccountsItemChanged);
    config_cache_lock.insert("key_id".to_string(), Some(new_key_id.to_string()));
    Ok(())
}

/// Saves a keypair as the default keys.
///
/// This API is used for testing purposes
/// to avoid generating the key in tests.
/// Use import/export APIs instead.
pub async fn preconfigure_keypair(context: &Context, secret_data: &str) -> Result<()> {
    let secret = SignedSecretKey::from_asc(secret_data)?;
    let public = secret.split_public_key()?;
    let keypair = KeyPair { public, secret };
    store_self_keypair(context, &keypair).await?;
    Ok(())
}

/// A key fingerprint
#[derive(Clone, Eq, PartialEq, Hash, serde::Serialize, serde::Deserialize)]
pub struct Fingerprint(Vec<u8>);

impl Fingerprint {
    /// Creates new 160-bit (20 bytes) fingerprint.
    pub fn new(v: Vec<u8>) -> Fingerprint {
        debug_assert_eq!(v.len(), 20);
        Fingerprint(v)
    }

    /// Make a hex string from the fingerprint.
    ///
    /// Use [std::fmt::Display] or [ToString::to_string] to get a
    /// human-readable formatted string.
    pub fn hex(&self) -> String {
        hex::encode_upper(&self.0)
    }
}

impl From<pgp::types::Fingerprint> for Fingerprint {
    fn from(fingerprint: pgp::types::Fingerprint) -> Fingerprint {
        Self::new(fingerprint.as_bytes().into())
    }
}

impl fmt::Debug for Fingerprint {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Fingerprint")
            .field("hex", &self.hex())
            .finish()
    }
}

/// Make a human-readable fingerprint.
impl fmt::Display for Fingerprint {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // Split key into chunks of 4 with space and newline at 20 chars
        for (i, c) in self.hex().chars().enumerate() {
            if i > 0 && i % 20 == 0 {
                writeln!(f)?;
            } else if i > 0 && i % 4 == 0 {
                write!(f, " ")?;
            }
            write!(f, "{c}")?;
        }
        Ok(())
    }
}

/// Parse a human-readable or otherwise formatted fingerprint.
impl std::str::FromStr for Fingerprint {
    type Err = anyhow::Error;

    fn from_str(input: &str) -> Result<Self> {
        let hex_repr: String = input
            .to_uppercase()
            .chars()
            .filter(|&c| c.is_ascii_hexdigit())
            .collect();
        let v: Vec<u8> = hex::decode(&hex_repr)?;
        ensure!(v.len() == 20, "wrong fingerprint length: {hex_repr}");
        let fp = Fingerprint::new(v);
        Ok(fp)
    }
}

#[cfg(test)]
mod tests {
    use std::sync::{Arc, LazyLock};

    use super::*;
    use crate::config::Config;
    use crate::test_utils::{TestContext, alice_keypair};

    static KEYPAIR: LazyLock<KeyPair> = LazyLock::new(alice_keypair);

    #[test]
    fn test_from_armored_string() {
        let private_key = SignedSecretKey::from_asc(
            "-----BEGIN PGP PRIVATE KEY BLOCK-----

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XsV31J215HfYBh/Nkru8fawiVxr+sJG2IDAeA9SBjsDCogfzW4PwLXgTXRqNFLVr
fK6hf6wpF56STV2U2D60b9xJeSAbBWlZFzCCQw3mPtGf/EGMHFxnJUE7MLEaaTEf
V2Fclh+G0sWp7F2ZS3nt0vX1hYG8TMIzM8Bj2eMsdXATOji9ST7EUxk/BpFax86D
i8pcjGO+IZffvyZJVRWfVooBJmWWbPB1pueo3tx8w3+fcuzpxz+RLFKaPyqXO+dD
7yPJeQ==
=KZk/
-----END PGP PRIVATE KEY BLOCK-----",
        )
        .expect("failed to decode");
        let binary = DcKey::to_bytes(&private_key);
        SignedSecretKey::from_slice(&binary).expect("invalid private key");
    }

    #[test]
    fn test_asc_roundtrip() {
        let key = KEYPAIR.public.clone();
        let asc = key.to_asc(Some(("spam", "ham")));
        let key2 = SignedPublicKey::from_asc(&asc).unwrap();
        assert_eq!(key, key2);

        let key = KEYPAIR.secret.clone();
        let asc = key.to_asc(Some(("spam", "ham")));
        let key2 = SignedSecretKey::from_asc(&asc).unwrap();
        assert_eq!(key, key2);
    }

    #[test]
    fn test_from_slice_roundtrip() {
        let public_key = KEYPAIR.public.clone();
        let private_key = KEYPAIR.secret.clone();

        let binary = DcKey::to_bytes(&public_key);
        let public_key2 = SignedPublicKey::from_slice(&binary).expect("invalid public key");
        assert_eq!(public_key, public_key2);

        let binary = DcKey::to_bytes(&private_key);
        let private_key2 = SignedSecretKey::from_slice(&binary).expect("invalid private key");
        assert_eq!(private_key, private_key2);
    }

    #[test]
    fn test_from_slice_bad_data() {
        let mut bad_data: [u8; 4096] = [0; 4096];
        for (i, v) in bad_data.iter_mut().enumerate() {
            *v = (i & 0xff) as u8;
        }
        for j in 0..(4096 / 40) {
            let slice = &bad_data.get(j..j + 4096 / 2 + j).unwrap();
            assert!(SignedPublicKey::from_slice(slice).is_err());
            assert!(SignedSecretKey::from_slice(slice).is_err());
        }
    }

    /// Tests workaround for Delta Chat core < 1.0.0
    /// which parsed CRC24 at the end of ASCII Armor
    /// as the part of the key.
    /// Depending on the alignment and the number of
    /// `=` characters at the end of the key,
    /// this resulted in various number of garbage
    /// octets at the end of the key, starting from 3 octets,
    /// but possibly 4 or 5 and maybe more octets
    /// if the key is imported or transferred
    /// using Autocrypt Setup Message multiple times.
    #[test]
    fn test_ignore_trailing_garbage() {
        // Test several variants of garbage.
        for garbage in [
            b"\x02\xfc\xaa\x38\x4b\x5c".as_slice(),
            b"\x02\xfc\xaa".as_slice(),
            b"\x01\x02\x03\x04\x05".as_slice(),
        ] {
            let private_key = KEYPAIR.secret.clone();

            let mut binary = DcKey::to_bytes(&private_key);
            binary.extend(garbage);

            let private_key2 =
                SignedSecretKey::from_slice(&binary).expect("Failed to ignore garbage");

            assert_eq!(private_key.dc_fingerprint(), private_key2.dc_fingerprint());
        }
    }

    #[test]
    fn test_base64_roundtrip() {
        let key = KEYPAIR.public.clone();
        let base64 = key.to_base64();
        let key2 = SignedPublicKey::from_base64(&base64).unwrap();
        assert_eq!(key, key2);
    }

    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
    async fn test_load_self_generate_public() {
        let t = TestContext::new().await;
        t.set_config(Config::ConfiguredAddr, Some("alice@example.org"))
            .await
            .unwrap();
        let key = load_self_public_key(&t).await;
        assert!(key.is_ok());
    }

    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
    async fn test_load_self_generate_secret() {
        let t = TestContext::new().await;
        t.set_config(Config::ConfiguredAddr, Some("alice@example.org"))
            .await
            .unwrap();
        let key = load_self_secret_key(&t).await;
        assert!(key.is_ok());
    }

    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
    async fn test_load_self_generate_concurrent() {
        use std::thread;

        let t = TestContext::new().await;
        t.set_config(Config::ConfiguredAddr, Some("alice@example.org"))
            .await
            .unwrap();
        let thr0 = {
            let ctx = t.clone();
            thread::spawn(move || {
                tokio::runtime::Runtime::new()
                    .unwrap()
                    .block_on(load_self_public_key(&ctx))
            })
        };
        let thr1 = {
            let ctx = t.clone();
            thread::spawn(move || {
                tokio::runtime::Runtime::new()
                    .unwrap()
                    .block_on(load_self_public_key(&ctx))
            })
        };
        let res0 = thr0.join().unwrap();
        let res1 = thr1.join().unwrap();
        assert_eq!(res0.unwrap(), res1.unwrap());
    }

    #[test]
    fn test_split_key() {
        let pubkey = KEYPAIR.secret.split_public_key().unwrap();
        assert_eq!(pubkey.primary_key, KEYPAIR.public.primary_key);
    }

    /// Tests that setting a default key second time is not allowed.
    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
    async fn test_save_self_key_twice() {
        // Saving the same key twice should result in only one row in
        // the keypairs table.
        let t = TestContext::new().await;
        let ctx = Arc::new(t);

        let nrows = || async {
            ctx.sql
                .count("SELECT COUNT(*) FROM keypairs;", ())
                .await
                .unwrap()
        };
        assert_eq!(nrows().await, 0);
        store_self_keypair(&ctx, &KEYPAIR).await.unwrap();
        assert_eq!(nrows().await, 1);

        // Saving a second key fails.
        let res = store_self_keypair(&ctx, &KEYPAIR).await;
        assert!(res.is_err());

        assert_eq!(nrows().await, 1);
    }

    #[test]
    fn test_fingerprint_from_str() {
        let res = Fingerprint::new(vec![
            1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,
        ]);

        let fp: Fingerprint = "0102030405060708090A0B0c0d0e0F1011121314".parse().unwrap();
        assert_eq!(fp, res);

        let fp: Fingerprint = "zzzz 0102 0304 0506\n0708090a0b0c0D0E0F1011121314 yyy"
            .parse()
            .unwrap();
        assert_eq!(fp, res);

        assert!("1".parse::<Fingerprint>().is_err());
    }

    #[test]
    fn test_fingerprint_hex() {
        let fp = Fingerprint::new(vec![
            1, 2, 4, 8, 16, 32, 64, 128, 255, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,
        ]);
        assert_eq!(fp.hex(), "0102040810204080FF0A0B0C0D0E0F1011121314");
    }

    #[test]
    fn test_fingerprint_to_string() {
        let fp = Fingerprint::new(vec![
            1, 2, 4, 8, 16, 32, 64, 128, 255, 1, 2, 4, 8, 16, 32, 64, 128, 255, 19, 20,
        ]);
        assert_eq!(
            fp.to_string(),
            "0102 0408 1020 4080 FF01\n0204 0810 2040 80FF 1314"
        );
    }
}
