coreason-runtime 0.1.0

// Copyright (c) 2026 CoReason, Inc.
// All rights reserved.

//! Structural Integrity — Zero-trust module self-checksumming.
//!
//! Replaces `coreason_runtime/execution_plane/integrity.py`.
//!
//! Enforces the zero-trust structural integrity of the runtime by providing
//! self-checksumming capabilities. Mathematically hashes source content at
//! runtime to detect "Fork-and-Patch" attacks where critical cryptographic
//! components (like the license verifier) might have been tampered with.
//!
//! Zero Waste: SHA-256 delegated to `sha2` (MIT/Apache-2.0).
//! Ed25519 signature verification delegated to `ed25519-dalek` (BSD-3-Clause).
//! Memory-mapped file I/O delegated to `memmap2` (MIT/Apache-2.0).
//! Thread-safe caching delegated to `dashmap` (MIT).

use dashmap::DashMap;
use ed25519_dalek::{Signature, Verifier, VerifyingKey};
use sha2::{Digest, Sha256};
use std::convert::TryInto;
use std::sync::OnceLock;

/// Thread-safe module integrity verification cache.
///
/// Once a module is verified, its hash is cached to avoid redundant
/// disk I/O on hot paths.
fn verified_cache() -> &'static DashMap<String, String> {
    static CACHE: OnceLock<DashMap<String, String>> = OnceLock::new();
    CACHE.get_or_init(DashMap::new)
}

/// Raised when structural integrity verification fails.
#[derive(Debug, Clone)]
pub struct IntegrityViolationError {
    pub message: String,
}

impl std::fmt::Display for IntegrityViolationError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "IntegrityViolation: {}", self.message)
    }
}

impl std::error::Error for IntegrityViolationError {}

/// Check if a module has already been verified (cache hit).
pub fn check_cache(module_name: &str, expected_hash: &str) -> bool {
    verified_cache()
        .get(module_name)
        .map_or(false, |v| v.value() == expected_hash)
}

/// Store a successful verification result in the cache.
pub fn update_cache(module_name: &str, expected_hash: &str) {
    verified_cache().insert(module_name.to_string(), expected_hash.to_string());
}

/// Clear the entire verification cache.
pub fn clear_cache() {
    verified_cache().clear();
}

/// Verify source code integrity via SHA-256 checksum.
///
/// Normalizes CRLF → LF before hashing for cross-platform consistency.
/// Zero Waste: SHA-256 delegated to `sha2`.
pub fn verify_module_integrity(source_code: &str, expected_sha256: &str) -> bool {
    let normalized = source_code.replace("\r\n", "\n");
    let mut hasher = Sha256::new();
    hasher.update(normalized.as_bytes());
    let actual_hash = format!("{:x}", hasher.finalize());
    actual_hash == expected_sha256
}

/// Verify a file's SHA-256 hash using memory-mapped I/O.
///
/// Zero Waste: Uses `memmap2` for zero-copy file reading and `sha2` for hashing.
pub fn verify_file_hash(file_path: &str, expected_sha256: &str) -> Result<bool, String> {
    use memmap2::Mmap;
    use std::fs::File;

    let file = File::open(file_path).map_err(|e| format!("Failed to open file: {}", e))?;
    let mmap = unsafe { Mmap::map(&file).map_err(|e| format!("Failed to mmap file: {}", e))? };

    // Normalize CRLF → LF on the fly
    let mut normalized = Vec::with_capacity(mmap.len());
    let mut i = 0;
    while i < mmap.len() {
        if i + 1 < mmap.len() && mmap[i] == b'\r' && mmap[i + 1] == b'\n' {
            normalized.push(b'\n');
            i += 2;
        } else {
            normalized.push(mmap[i]);
            i += 1;
        }
    }

    let mut hasher = Sha256::new();
    hasher.update(&normalized);
    let actual_hash = format!("{:x}", hasher.finalize());
    Ok(actual_hash == expected_sha256)
}

/// Verify an Ed25519 signature over a message.
///
/// Zero Waste: Ed25519 delegated to `ed25519-dalek` (BSD-3-Clause).
pub fn verify_signature(
    message: &str,
    signature_hex: &str,
    public_key_hex: &str,
) -> Result<bool, String> {
    let public_bytes = hex::decode(public_key_hex).map_err(|e| e.to_string())?;
    let signature_bytes = hex::decode(signature_hex).map_err(|e| e.to_string())?;

    let public_array: [u8; 32] = public_bytes
        .as_slice()
        .try_into()
        .map_err(|_| "Public key must be 32 bytes".to_string())?;
    let signature_array: [u8; 64] = signature_bytes
        .as_slice()
        .try_into()
        .map_err(|_| "Signature must be 64 bytes".to_string())?;

    let verifying_key = VerifyingKey::from_bytes(&public_array)
        .map_err(|e| format!("Invalid public key: {}", e))?;
    let signature = Signature::from_bytes(&signature_array);

    Ok(verifying_key.verify(message.as_bytes(), &signature).is_ok())
}

/// Full module integrity check with caching.
///
/// First checks the cache, then verifies the source code hash.
/// Updates the cache on successful verification.
pub fn assert_module_integrity(
    module_name: &str,
    source_code: &str,
    expected_hash: &str,
) -> Result<(), IntegrityViolationError> {
    // Check cache first
    if check_cache(module_name, expected_hash) {
        return Ok(());
    }

    // Verify hash
    if !verify_module_integrity(source_code, expected_hash) {
        let normalized = source_code.replace("\r\n", "\n");
        let mut hasher = Sha256::new();
        hasher.update(normalized.as_bytes());
        let actual_hash = format!("{:x}", hasher.finalize());

        return Err(IntegrityViolationError {
            message: format!(
                "CRITICAL INTEGRITY VIOLATION: Module {} has been tampered with! \
                 Expected hash {}... but got {}...",
                module_name,
                &expected_hash[..expected_hash.len().min(8)],
                &actual_hash[..actual_hash.len().min(8)],
            ),
        });
    }

    // Cache successful verification
    update_cache(module_name, expected_hash);
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_verify_module_integrity() {
        let source = "fn main() { println!(\"hello\"); }";
        let mut hasher = Sha256::new();
        hasher.update(source.as_bytes());
        let expected = format!("{:x}", hasher.finalize());

        assert!(verify_module_integrity(source, &expected));
        assert!(!verify_module_integrity(source, "badhash"));
    }

    #[test]
    fn test_verify_module_normalizes_crlf() {
        let source_lf = "line1\nline2";
        let source_crlf = "line1\r\nline2";

        let mut hasher = Sha256::new();
        hasher.update(source_lf.as_bytes());
        let expected = format!("{:x}", hasher.finalize());

        assert!(verify_module_integrity(source_lf, &expected));
        assert!(verify_module_integrity(source_crlf, &expected));
    }

    #[test]
    fn test_cache_operations() {
        let test_key = "test_mod_ops_unique";
        // Do not clear cache to avoid interfering with other parallel tests
        update_cache(test_key, "hash123");
        assert!(check_cache(test_key, "hash123"));
        assert!(!check_cache(test_key, "wrong_hash"));
    }

    #[test]
    fn test_assert_module_integrity_valid() {
        let test_key = "test_mod_valid_unique";
        let source = "test source code";
        let mut hasher = Sha256::new();
        hasher.update(source.as_bytes());
        let expected = format!("{:x}", hasher.finalize());

        assert!(assert_module_integrity(test_key, source, &expected).is_ok());
        // Should be cached now
        assert!(check_cache(test_key, &expected));
    }

    #[test]
    fn test_assert_module_integrity_tampered() {
        let test_key = "test_mod_tampered_unique";
        let source = "original source";
        let result = assert_module_integrity(test_key, source, "badhash0000");
        assert!(result.is_err());
        assert!(result
            .unwrap_err()
            .message
            .contains("CRITICAL INTEGRITY VIOLATION"));
    }

    #[test]
    fn test_assert_module_integrity_cached() {
        // Use a unique key with timestamp to avoid any parallel test interference
        let unique_key = format!(
            "cached_mod_{}_{}",
            std::process::id(),
            std::time::SystemTime::now()
                .duration_since(std::time::UNIX_EPOCH)
                .unwrap()
                .as_nanos()
        );
        // Insert directly and immediately verify
        update_cache(&unique_key, "known_hash");
        assert!(check_cache(&unique_key, "known_hash"));
        // The assert_module_integrity should hit the cache and skip hash verification
        assert!(assert_module_integrity(&unique_key, "doesn't matter", "known_hash").is_ok());
    }

    #[test]
    fn test_hex_decode() {
        assert_eq!(hex::decode("48656c6c6f").unwrap(), b"Hello");
        assert!(hex::decode("abc").is_err()); // Odd length
        assert!(hex::decode("zz").is_err()); // Invalid hex
    }
}