//! Plugin signature verification using Ed25519 + BLAKE3
//!
//! Each plugin directory may contain a `plugin.sig` file alongside its
//! `plugin.toml`. The signature covers the BLAKE3 hash of the WASM binary
//! referenced by the manifest. Verification uses Ed25519 public keys
//! configured as trusted in the server's plugin settings.
//!
//! When `allow_unsigned` is false, plugins _must_ carry a valid signature
//! from one of the trusted keys or they will be rejected at load time.

use std::path::Path;

use anyhow::{Result, anyhow};
use ed25519_dalek::{Signature, Verifier, VerifyingKey};

/// Outcome of a signature check on a plugin package.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum SignatureStatus {
  /// Signature is present and valid against a trusted key.
  Valid,
  /// No signature file found.
  Unsigned,
  /// Signature file exists but does not match any trusted key.
  Invalid(String),
}

/// Verify the signature of a plugin's WASM binary.
///
/// Reads `plugin.sig` from `plugin_dir`, computes the BLAKE3 hash of the
/// WASM binary at `wasm_path`, and verifies the signature against each of
/// the `trusted_keys`. The signature file is raw 64-byte Ed25519 signature
/// over the 32-byte BLAKE3 digest.
///
/// # Errors
///
/// Returns an error only on I/O failures, never for cryptographic rejection,
/// which is reported via [`SignatureStatus`] instead.
pub fn verify_plugin_signature(
  plugin_dir: &Path,
  wasm_path: &Path,
  trusted_keys: &[VerifyingKey],
) -> Result<SignatureStatus> {
  let sig_path = plugin_dir.join("plugin.sig");
  if !sig_path.exists() {
    return Ok(SignatureStatus::Unsigned);
  }

  let sig_bytes = std::fs::read(&sig_path)
    .map_err(|e| anyhow!("failed to read plugin.sig: {e}"))?;

  let signature = Signature::from_slice(&sig_bytes).map_err(|e| {
    // Malformed signature file is an invalid signature, not an I/O error
    tracing::warn!(path = %sig_path.display(), "malformed plugin.sig: {e}");
    anyhow!("malformed plugin.sig: {e}")
  });
  let Ok(signature) = signature else {
    return Ok(SignatureStatus::Invalid(
      "malformed signature file".to_string(),
    ));
  };

  // BLAKE3 hash of the WASM binary is the signed message
  let wasm_bytes = std::fs::read(wasm_path)
    .map_err(|e| anyhow!("failed to read WASM binary for verification: {e}"))?;
  let digest = blake3::hash(&wasm_bytes);
  let message = digest.as_bytes();

  for key in trusted_keys {
    if key.verify(message, &signature).is_ok() {
      return Ok(SignatureStatus::Valid);
    }
  }

  Ok(SignatureStatus::Invalid(
    "signature did not match any trusted key".to_string(),
  ))
}

/// Parse a hex-encoded Ed25519 public key (64 hex characters = 32 bytes).
///
/// # Errors
///
/// Returns an error if the string is not valid hex or is the wrong length.
pub fn parse_public_key(hex_str: &str) -> Result<VerifyingKey> {
  let hex_str = hex_str.trim();
  if hex_str.len() != 64 {
    return Err(anyhow!(
      "expected 64 hex characters for Ed25519 public key, got {}",
      hex_str.len()
    ));
  }

  let mut bytes = [0u8; 32];
  for (i, byte) in bytes.iter_mut().enumerate() {
    *byte = u8::from_str_radix(&hex_str[i * 2..i * 2 + 2], 16)
      .map_err(|e| anyhow!("invalid hex in public key: {e}"))?;
  }

  VerifyingKey::from_bytes(&bytes)
    .map_err(|e| anyhow!("invalid Ed25519 public key: {e}"))
}

#[cfg(test)]
mod tests {
  use ed25519_dalek::{Signer, SigningKey};
  use rand::RngExt;

  use super::*;

  fn make_keypair() -> (SigningKey, VerifyingKey) {
    let secret_bytes: [u8; 32] = rand::rng().random();
    let signing = SigningKey::from_bytes(&secret_bytes);
    let verifying = signing.verifying_key();
    (signing, verifying)
  }

  #[test]
  fn test_verify_unsigned_plugin() {
    let dir = tempfile::tempdir().unwrap();
    let wasm_path = dir.path().join("plugin.wasm");
    std::fs::write(&wasm_path, b"\0asm\x01\x00\x00\x00").unwrap();

    let (_, vk) = make_keypair();
    let status =
      verify_plugin_signature(dir.path(), &wasm_path, &[vk]).unwrap();
    assert_eq!(status, SignatureStatus::Unsigned);
  }

  #[test]
  fn test_verify_valid_signature() {
    let dir = tempfile::tempdir().unwrap();
    let wasm_path = dir.path().join("plugin.wasm");
    let wasm_bytes = b"\0asm\x01\x00\x00\x00some_code_here";
    std::fs::write(&wasm_path, wasm_bytes).unwrap();

    let (sk, vk) = make_keypair();

    // Sign the BLAKE3 hash of the WASM binary
    let digest = blake3::hash(wasm_bytes);
    let signature = sk.sign(digest.as_bytes());
    std::fs::write(dir.path().join("plugin.sig"), signature.to_bytes())
      .unwrap();

    let status =
      verify_plugin_signature(dir.path(), &wasm_path, &[vk]).unwrap();
    assert_eq!(status, SignatureStatus::Valid);
  }

  #[test]
  fn test_verify_wrong_key() {
    let dir = tempfile::tempdir().unwrap();
    let wasm_path = dir.path().join("plugin.wasm");
    let wasm_bytes = b"\0asm\x01\x00\x00\x00some_code";
    std::fs::write(&wasm_path, wasm_bytes).unwrap();

    let (sk, _) = make_keypair();
    let (_, wrong_vk) = make_keypair();

    let digest = blake3::hash(wasm_bytes);
    let signature = sk.sign(digest.as_bytes());
    std::fs::write(dir.path().join("plugin.sig"), signature.to_bytes())
      .unwrap();

    let status =
      verify_plugin_signature(dir.path(), &wasm_path, &[wrong_vk]).unwrap();
    assert!(matches!(status, SignatureStatus::Invalid(_)));
  }

  #[test]
  fn test_verify_tampered_wasm() {
    let dir = tempfile::tempdir().unwrap();
    let wasm_path = dir.path().join("plugin.wasm");
    let original = b"\0asm\x01\x00\x00\x00original";
    std::fs::write(&wasm_path, original).unwrap();

    let (sk, vk) = make_keypair();
    let digest = blake3::hash(original);
    let signature = sk.sign(digest.as_bytes());
    std::fs::write(dir.path().join("plugin.sig"), signature.to_bytes())
      .unwrap();

    // Tamper with the WASM file after signing
    std::fs::write(&wasm_path, b"\0asm\x01\x00\x00\x00tampered").unwrap();

    let status =
      verify_plugin_signature(dir.path(), &wasm_path, &[vk]).unwrap();
    assert!(matches!(status, SignatureStatus::Invalid(_)));
  }

  #[test]
  fn test_verify_malformed_sig_file() {
    let dir = tempfile::tempdir().unwrap();
    let wasm_path = dir.path().join("plugin.wasm");
    std::fs::write(&wasm_path, b"\0asm\x01\x00\x00\x00").unwrap();

    // Write garbage to plugin.sig (wrong length)
    std::fs::write(dir.path().join("plugin.sig"), b"not a signature").unwrap();

    let (_, vk) = make_keypair();
    let status =
      verify_plugin_signature(dir.path(), &wasm_path, &[vk]).unwrap();
    assert!(matches!(status, SignatureStatus::Invalid(_)));
  }

  #[test]
  fn test_verify_multiple_trusted_keys() {
    let dir = tempfile::tempdir().unwrap();
    let wasm_path = dir.path().join("plugin.wasm");
    let wasm_bytes = b"\0asm\x01\x00\x00\x00multi_key_test";
    std::fs::write(&wasm_path, wasm_bytes).unwrap();

    let (sk2, vk2) = make_keypair();
    let (_, vk1) = make_keypair();
    let (_, vk3) = make_keypair();

    // Sign with key 2
    let digest = blake3::hash(wasm_bytes);
    let signature = sk2.sign(digest.as_bytes());
    std::fs::write(dir.path().join("plugin.sig"), signature.to_bytes())
      .unwrap();

    // Verify against [vk1, vk2, vk3]; should find vk2
    let status =
      verify_plugin_signature(dir.path(), &wasm_path, &[vk1, vk2, vk3])
        .unwrap();
    assert_eq!(status, SignatureStatus::Valid);
  }

  #[test]
  fn test_parse_public_key_valid() {
    let (_, vk) = make_keypair();
    let hex = hex_encode(vk.as_bytes());
    let parsed = parse_public_key(&hex).unwrap();
    assert_eq!(parsed, vk);
  }

  #[test]
  fn test_parse_public_key_wrong_length() {
    assert!(parse_public_key("abcdef").is_err());
  }

  #[test]
  fn test_parse_public_key_invalid_hex() {
    let bad =
      "zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz";
    assert!(parse_public_key(bad).is_err());
  }

  fn hex_encode(bytes: &[u8]) -> String {
    bytes.iter().map(|b| format!("{b:02x}")).collect()
  }
}