//! Federated Policy & Trust Packs.
//!
//! A Trust Pack is a cryptographically signed bundle of assertions and aliases
//! that can be exported from one project and imported into another.
//! This enables organizations to distribute security policies, exceptions,
//! and patterns without manual reconfiguration.

use std::fs;
use std::path::Path;

use ed25519_dalek::{Signer, SigningKey, VerifyingKey};
use rkyv::{Archive, Deserialize, Serialize};
use stemedb_core::types::{Assertion, ConceptAlias};
use tracing::{info, instrument};

use crate::types::PredicateAliasSet;
use crate::{current_timestamp, AphoriaError};

/// Record of a signature for audit trail.
///
/// When a Trust Pack is re-signed (key rotation), the previous signature
/// is preserved in the signature chain for audit purposes.
#[derive(Archive, Deserialize, Serialize, Debug, Clone)]
#[archive(check_bytes)]
pub struct SignatureRecord {
    /// Public key of the signer (32 bytes).
    pub issuer_id: [u8; 32],
    /// Ed25519 signature.
    pub signature: [u8; 64],
    /// Timestamp when this signature was created.
    pub signed_at: u64,
    /// Optional reason for re-signing (e.g., "Key rotation", "Security incident").
    pub reason: Option<String>,
}

/// Serializable predicate alias set for Trust Packs.
///
/// This is a serializable version of PredicateAliasSet that can be
/// included in Trust Pack archives.
#[derive(Archive, Deserialize, Serialize, Debug, Clone)]
#[archive(check_bytes)]
pub struct PackPredicateAliasSet {
    /// Canonical predicate name.
    pub canonical: String,
    /// Aliases that map to the canonical name.
    pub aliases: Vec<String>,
}

impl From<&PredicateAliasSet> for PackPredicateAliasSet {
    fn from(set: &PredicateAliasSet) -> Self {
        Self { canonical: set.canonical.clone(), aliases: set.aliases.clone() }
    }
}

impl From<&PackPredicateAliasSet> for PredicateAliasSet {
    fn from(set: &PackPredicateAliasSet) -> Self {
        Self { canonical: set.canonical.clone(), aliases: set.aliases.clone() }
    }
}

/// A signed bundle of assertions and aliases.
#[derive(Archive, Deserialize, Serialize, Debug, Clone)]
#[archive(check_bytes)]
pub struct TrustPack {
    /// Metadata about the pack.
    pub header: PackHeader,
    /// Assertions (e.g., acknowledgments, custom rules).
    pub assertions: Vec<Assertion>,
    /// Aliases (e.g., mapping custom code paths to RFCs).
    pub aliases: Vec<ConceptAlias>,
    /// Predicate aliases for semantic matching.
    pub predicate_aliases: Vec<PackPredicateAliasSet>,
    /// Ed25519 signature of the serialized content (excluding signature field).
    pub signature: [u8; 64],
    /// Chain of previous signatures for audit trail (key rotation history).
    pub signature_chain: Vec<SignatureRecord>,
}

/// Metadata header for a Trust Pack.
#[derive(Archive, Deserialize, Serialize, Debug, Clone)]
#[archive(check_bytes)]
pub struct PackHeader {
    /// Human-readable name of the policy pack.
    pub name: String,
    /// Version string (semver recommended).
    pub version: String,
    /// Public key of the issuer (32 bytes).
    pub issuer_id: [u8; 32],
    /// Creation timestamp (Unix epoch).
    pub timestamp: u64,
}

impl TrustPack {
    /// Create a new Trust Pack.
    ///
    /// Signs the content automatically.
    pub fn new(
        name: String,
        version: String,
        assertions: Vec<Assertion>,
        aliases: Vec<ConceptAlias>,
        signing_key: &SigningKey,
    ) -> Result<Self, AphoriaError> {
        Self::new_with_predicate_aliases(
            name,
            version,
            assertions,
            aliases,
            Vec::new(),
            signing_key,
        )
    }

    /// Create a new Trust Pack with predicate aliases.
    ///
    /// Signs the content automatically.
    pub fn new_with_predicate_aliases(
        name: String,
        version: String,
        assertions: Vec<Assertion>,
        aliases: Vec<ConceptAlias>,
        predicate_aliases: Vec<PackPredicateAliasSet>,
        signing_key: &SigningKey,
    ) -> Result<Self, AphoriaError> {
        let timestamp = current_timestamp();

        let issuer_id = signing_key.verifying_key().to_bytes();

        let header = PackHeader { name, version, issuer_id, timestamp };

        // Create temporary pack with zeroed signature to compute hash
        let temp_pack = TrustPack {
            header: header.clone(),
            assertions: assertions.clone(),
            aliases: aliases.clone(),
            predicate_aliases: predicate_aliases.clone(),
            signature: [0u8; 64],
            signature_chain: Vec::new(),
        };

        // Serialize to bytes for signing
        let bytes = rkyv::to_bytes::<_, 1024>(&temp_pack)
            .map_err(|e| AphoriaError::Storage(format!("Serialization failed: {}", e)))?;

        // Sign the bytes
        let signature = signing_key.sign(&bytes).to_bytes();

        Ok(TrustPack {
            header,
            assertions,
            aliases,
            predicate_aliases,
            signature,
            signature_chain: Vec::new(),
        })
    }

    /// Save the Trust Pack to a file.
    pub fn save(&self, path: &Path) -> Result<(), AphoriaError> {
        let bytes = rkyv::to_bytes::<_, 1024>(self)
            .map_err(|e| AphoriaError::Storage(format!("Serialization failed: {}", e)))?;
        fs::write(path, bytes).map_err(|e| {
            AphoriaError::Storage(format!("Failed to write policy to {}: {e}", path.display()))
        })?;
        Ok(())
    }

    /// Load a Trust Pack from a file and verify signature.
    pub fn load(path: &Path) -> Result<Self, AphoriaError> {
        let bytes = fs::read(path).map_err(|e| {
            AphoriaError::Storage(format!("Failed to read policy from {}: {e}", path.display()))
        })?;
        let pack: TrustPack = rkyv::from_bytes(&bytes)
            .map_err(|e| AphoriaError::Storage(format!("Deserialization failed: {}", e)))?;

        // Verify signature
        pack.verify()?;

        Ok(pack)
    }

    /// Verify the signature of the Trust Pack.
    pub fn verify(&self) -> Result<(), AphoriaError> {
        use ed25519_dalek::{Signature, Verifier};

        // Reconstruct the zero-signature version to check against
        let temp_pack = TrustPack {
            header: self.header.clone(),
            assertions: self.assertions.clone(),
            aliases: self.aliases.clone(),
            predicate_aliases: self.predicate_aliases.clone(),
            signature: [0u8; 64],
            signature_chain: self.signature_chain.clone(),
        };

        let bytes = rkyv::to_bytes::<_, 1024>(&temp_pack)
            .map_err(|e| AphoriaError::Storage(format!("Serialization failed: {}", e)))?;

        let verifying_key = VerifyingKey::from_bytes(&self.header.issuer_id)
            .map_err(|e| AphoriaError::Storage(format!("Invalid issuer key: {}", e)))?;

        let signature = Signature::from_bytes(&self.signature);

        verifying_key
            .verify(&bytes, &signature)
            .map_err(|_| AphoriaError::Storage("Invalid policy signature".to_string()))?;

        Ok(())
    }

    /// Load a Trust Pack from a file WITHOUT verifying signature.
    ///
    /// Used for key rotation when the old key is no longer available.
    pub fn load_unverified(path: &Path) -> Result<Self, AphoriaError> {
        let bytes = fs::read(path).map_err(|e| {
            AphoriaError::Storage(format!("Failed to read policy from {}: {e}", path.display()))
        })?;
        let pack: TrustPack = rkyv::from_bytes(&bytes)
            .map_err(|e| AphoriaError::Storage(format!("Deserialization failed: {}", e)))?;
        Ok(pack)
    }

    /// Re-sign a Trust Pack with a new key, preserving the signature chain.
    ///
    /// This is used for key rotation. The old signature is added to the
    /// signature chain for audit purposes.
    pub fn resign(
        name: String,
        version: String,
        assertions: Vec<Assertion>,
        aliases: Vec<ConceptAlias>,
        predicate_aliases: Vec<PackPredicateAliasSet>,
        signing_key: &SigningKey,
        signature_chain: Vec<SignatureRecord>,
    ) -> Result<Self, AphoriaError> {
        let timestamp = current_timestamp();

        let issuer_id = signing_key.verifying_key().to_bytes();

        let header = PackHeader { name, version, issuer_id, timestamp };

        // Create temporary pack with zeroed signature to compute hash
        let temp_pack = TrustPack {
            header: header.clone(),
            assertions: assertions.clone(),
            aliases: aliases.clone(),
            predicate_aliases: predicate_aliases.clone(),
            signature: [0u8; 64],
            signature_chain: signature_chain.clone(),
        };

        // Serialize to bytes for signing
        let bytes = rkyv::to_bytes::<_, 1024>(&temp_pack)
            .map_err(|e| AphoriaError::Storage(format!("Serialization failed: {}", e)))?;

        // Sign the bytes
        let signature = signing_key.sign(&bytes).to_bytes();

        Ok(TrustPack { header, assertions, aliases, predicate_aliases, signature, signature_chain })
    }
}

/// Manager for loading and resolving policies.
pub struct PolicyManager {
    cache_dir: std::path::PathBuf,
}

impl PolicyManager {
    /// Create a new policy manager with the specified cache directory.
    ///
    /// The cache directory is used for storing downloaded remote policies.
    pub fn new(cache_dir: &Path) -> Self {
        Self { cache_dir: cache_dir.to_path_buf() }
    }

    /// Resolve and load a list of policy URIs.
    ///
    /// Supports:
    /// - Local paths: `file://./policies/security.pack` or just `./policies/security.pack`
    /// - HTTP(S): `https://example.com/policies/security.pack`
    #[instrument(skip(self))]
    pub fn load_policies(&self, uris: &[String]) -> Result<Vec<TrustPack>, AphoriaError> {
        let mut packs = Vec::new();

        for uri in uris {
            let pack = if uri.starts_with("http://") || uri.starts_with("https://") {
                self.fetch_remote(uri)?
            } else {
                let path = if let Some(p) = uri.strip_prefix("file://") {
                    Path::new(p)
                } else {
                    Path::new(uri)
                };
                TrustPack::load(path)?
            };

            info!(name = %pack.header.name, version = %pack.header.version, "Loaded policy");
            packs.push(pack);
        }

        Ok(packs)
    }

    fn fetch_remote(&self, url: &str) -> Result<TrustPack, AphoriaError> {
        // Hash URL for cache filename
        let hash = blake3::hash(url.as_bytes());
        let filename = format!("{}.pack", hash.to_hex());
        let cache_path = self.cache_dir.join(filename);

        if !cache_path.exists() {
            info!(url, "Fetching remote policy");
            let resp = ureq::get(url)
                .call()
                .map_err(|e| AphoriaError::Storage(format!("Network error: {}", e)))?;

            let mut reader = resp.into_reader();
            let mut file = fs::File::create(&cache_path).map_err(|e| {
                AphoriaError::Storage(format!(
                    "Failed to create cache file {}: {e}",
                    cache_path.display()
                ))
            })?;
            std::io::copy(&mut reader, &mut file).map_err(|e| {
                AphoriaError::Storage(format!(
                    "Failed to write to cache file {}: {e}",
                    cache_path.display()
                ))
            })?;
        }

        TrustPack::load(&cache_path)
    }
}