msy 0.4.6

// Bidirectional sync state tracking
//
// Stores filesystem state from prior sync to detect changes and conflicts.
// Uses text-based format for persistent state storage in ~/.cache/sy/bisync/

use crate::error::Result;
use std::collections::HashMap;
use std::fs;
use std::io::{BufRead, BufReader, Write};
use std::path::{Path, PathBuf};
use std::time::{SystemTime, UNIX_EPOCH};

/// Sync state for a single file
#[derive(Debug, Clone, PartialEq)]
pub struct SyncState {
	pub path: PathBuf,
	pub side: Side,
	pub mtime: SystemTime,
	pub size: u64,
	pub checksum: Option<u64>,
	pub last_sync: SystemTime,
}

/// Which side of the sync (source or destination)
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Side {
	Source,
	Dest,
}

/// Type alias for the state map returned by load_all()
/// Maps path to (source_state, dest_state) tuple
pub type StateMap = HashMap<PathBuf, (Option<SyncState>, Option<SyncState>)>;

impl Side {
	fn as_str(&self) -> &'static str {
		match self {
			Side::Source => "source",
			Side::Dest => "dest",
		}
	}

	fn from_str(s: &str) -> Option<Self> {
		match s {
			"source" => Some(Side::Source),
			"dest" => Some(Side::Dest),
			_ => None,
		}
	}
}

/// Bidirectional sync state database (text-based)
pub struct BisyncStateDb {
	state_file: PathBuf,
	source_path: PathBuf,
	dest_path: PathBuf,
	// In-memory cache for faster lookups
	states: StateMap,
}

impl BisyncStateDb {
	/// Format version
	const FORMAT_VERSION: &'static str = "v2";

	/// Generate unique hash for source+dest pair
	fn generate_sync_pair_hash(source: &Path, dest: &Path) -> String {
		use std::collections::hash_map::DefaultHasher;
		use std::hash::{Hash, Hasher};

		let mut hasher = DefaultHasher::new();
		source.to_string_lossy().hash(&mut hasher);
		dest.to_string_lossy().hash(&mut hasher);
		format!("{:x}", hasher.finish())
	}

	/// Get state directory (~/.cache/sy/bisync/)
	fn get_state_dir() -> Result<PathBuf> {
		let cache_dir = if let Ok(xdg_cache) = std::env::var("XDG_CACHE_HOME") {
			PathBuf::from(xdg_cache)
		} else if let Ok(home) = std::env::var("HOME") {
			PathBuf::from(home).join(".cache")
		} else {
			return Err(crate::error::SyncError::Config("Cannot determine cache directory (HOME not set)".to_string()));
		};

		let state_dir = cache_dir.join("sy").join("bisync");
		fs::create_dir_all(&state_dir)?;
		Ok(state_dir)
	}

	/// Open or create bisync state database for source/dest pair
	///
	/// If `force_resync` is true, deletes any existing corrupted state file
	/// and starts fresh (used for recovery from corruption)
	pub fn open(source: &Path, dest: &Path, force_resync: bool) -> Result<Self> {
		let sync_pair_hash = Self::generate_sync_pair_hash(source, dest);
		let state_dir = Self::get_state_dir()?;
		let state_file = state_dir.join(format!("{}.lst", sync_pair_hash));

		// If force_resync is true, delete the state file if it exists (corruption recovery)
		if force_resync && state_file.exists() {
			fs::remove_file(&state_file)?;
		}

		let states = if state_file.exists() {
			// Validate before loading to catch corruption early
			Self::validate_state_file(&state_file)?;
			Self::load_from_file(&state_file)?
		} else {
			HashMap::new()
		};

		Ok(Self { state_file, source_path: source.to_path_buf(), dest_path: dest.to_path_buf(), states })
	}

	/// Unescape a path string (handles \n, \", \\)
	fn unescape_path(s: &str) -> String {
		let mut result = String::with_capacity(s.len());
		let mut chars = s.chars();

		while let Some(c) = chars.next() {
			if c == '\\' {
				match chars.next() {
					Some('n') => result.push('\n'),
					Some('t') => result.push('\t'),
					Some('r') => result.push('\r'),
					Some('"') => result.push('"'),
					Some('\\') => result.push('\\'),
					Some(other) => {
						result.push('\\');
						result.push(other);
					}
					None => result.push('\\'),
				}
			} else {
				result.push(c);
			}
		}

		result
	}

	/// Validate state file for corruption before loading
	fn validate_state_file(path: &Path) -> Result<()> {
		let file = fs::File::open(path)?;
		let reader = BufReader::new(file);
		let lines: Vec<String> = reader.lines().collect::<std::io::Result<Vec<_>>>()?;

		// Check for completely empty file
		if lines.is_empty() {
			return Err(crate::error::SyncError::StateCorruption { path: path.to_path_buf(), reason: "State file is empty".to_string() });
		}

		// Check for valid header (should start with format version comment)
		let has_header = lines.iter().any(|line| line.trim().starts_with("# sy bisync"));

		if !has_header {
			return Err(crate::error::SyncError::StateCorruption { path: path.to_path_buf(), reason: "Missing or invalid format version header".to_string() });
		}

		// Count non-comment lines for basic sanity check
		let data_lines: Vec<&String> = lines
			.iter()
			.filter(|line| {
				let trimmed = line.trim();
				!trimmed.is_empty() && !trimmed.starts_with('#')
			})
			.collect();

		// If there are data lines, validate structure of first few
		if !data_lines.is_empty() {
			for (idx, line) in data_lines.iter().take(5).enumerate() {
				let parts: Vec<&str> = line.splitn(6, ' ').collect();
				if parts.len() != 5 && parts.len() != 6 {
					return Err(crate::error::SyncError::StateCorruption {
						path: path.to_path_buf(),
						reason: format!("Invalid field count at line {}: expected 5 or 6 fields, got {}", idx + 1, parts.len()),
					});
				}

				// Validate side field
				if parts[0] != "source" && parts[0] != "dest" {
					return Err(crate::error::SyncError::StateCorruption {
						path: path.to_path_buf(),
						reason: format!("Invalid side field '{}' at line {}: must be 'source' or 'dest'", parts[0], idx + 1),
					});
				}

				// Validate mtime is parseable number
				if parts[1].parse::<i64>().is_err() {
					return Err(crate::error::SyncError::StateCorruption {
						path: path.to_path_buf(),
						reason: format!("Invalid mtime '{}' at line {}: not a valid number", parts[1], idx + 1),
					});
				}

				// Validate size is parseable number
				if parts[2].parse::<u64>().is_err() {
					return Err(crate::error::SyncError::StateCorruption {
						path: path.to_path_buf(),
						reason: format!("Invalid size '{}' at line {}: not a valid number", parts[2], idx + 1),
					});
				}

				// Validate checksum format (hex or '-')
				let checksum = parts[3];
				if checksum != "-" && u64::from_str_radix(checksum, 16).is_err() {
					return Err(crate::error::SyncError::StateCorruption {
						path: path.to_path_buf(),
						reason: format!("Invalid checksum '{}' at line {}: must be hex or '-'", checksum, idx + 1),
					});
				}
			}
		}

		Ok(())
	}

	/// Load state from file
	fn load_from_file(path: &Path) -> Result<StateMap> {
		let file = fs::File::open(path)?;
		let reader = BufReader::new(file);
		let mut states: StateMap = HashMap::new();

		for (line_num, line) in reader.lines().enumerate() {
			let line = line?;
			let line = line.trim();

			// Skip comments and blank lines
			if line.is_empty() || line.starts_with('#') {
				continue;
			}

			// Parse: <side> <mtime_ns> <size> <checksum> <last_sync_ns> <path>
			let parts: Vec<&str> = line.splitn(6, ' ').collect();

			// Support both v1 (5 parts) and v2 (6 parts) formats
			let (side_str, mtime_str, size_str, checksum_str, last_sync_str, path_str) = if parts.len() == 6 {
				// v2 format
				(parts[0], parts[1], parts[2], parts[3], parts[4], parts[5])
			} else if parts.len() == 5 {
				// v1 format (backward compat): last_sync = mtime
				(parts[0], parts[1], parts[2], parts[3], parts[1], parts[4])
			} else {
				return Err(crate::error::SyncError::Config(format!(
					"Malformed state file line {}: expected 5 or 6 fields, got {}",
					line_num + 1,
					parts.len()
				)));
			};

			let side =
				Side::from_str(side_str).ok_or_else(|| crate::error::SyncError::Config(format!("Invalid side '{}' on line {}", side_str, line_num + 1)))?;

			let mtime_ns: i64 = mtime_str
				.parse()
				.map_err(|_| crate::error::SyncError::Config(format!("Invalid mtime '{}' on line {}", mtime_str, line_num + 1)))?;

			let size: u64 = size_str
				.parse()
				.map_err(|_| crate::error::SyncError::Config(format!("Invalid size '{}' on line {}", size_str, line_num + 1)))?;

			let checksum: Option<u64> = if checksum_str == "-" {
				None
			} else {
				Some(
					u64::from_str_radix(checksum_str, 16)
						.map_err(|_| crate::error::SyncError::Config(format!("Invalid checksum '{}' on line {}", checksum_str, line_num + 1)))?,
				)
			};

			let last_sync_ns: i64 = last_sync_str
				.parse()
				.map_err(|_| crate::error::SyncError::Config(format!("Invalid last_sync '{}' on line {}", last_sync_str, line_num + 1)))?;

			// Unquote and unescape path
			let path_unescaped = if path_str.starts_with('"') && path_str.ends_with('"') {
				Self::unescape_path(&path_str[1..path_str.len() - 1])
			} else {
				path_str.to_string()
			};

			let path = PathBuf::from(path_unescaped);

			// Convert i64 nanoseconds to SystemTime (clamp negative to 0)
			let mtime = UNIX_EPOCH + std::time::Duration::from_nanos(mtime_ns.max(0) as u64);
			let last_sync = UNIX_EPOCH + std::time::Duration::from_nanos(last_sync_ns.max(0) as u64);

			let state = SyncState { path: path.clone(), side, mtime, size, checksum, last_sync };

			let entry = states.entry(path).or_insert((None, None));
			match side {
				Side::Source => entry.0 = Some(state),
				Side::Dest => entry.1 = Some(state),
			}
		}

		Ok(states)
	}

	/// Save all state to file (atomic write)
	fn save_to_file(&self) -> Result<()> {
		let temp_file = self.state_file.with_extension("tmp");

		{
			let mut file = fs::File::create(&temp_file)?;

			// Write header
			writeln!(file, "# sy bisync {}", Self::FORMAT_VERSION)?;
			writeln!(file, "# sync_pair: {} <-> {}", self.source_path.display(), self.dest_path.display())?;
			let now = chrono::Utc::now();
			writeln!(file, "# last_sync: {}", now.to_rfc3339())?;

			// Collect and sort entries for deterministic output
			let mut entries: Vec<_> = self.states.iter().collect();
			entries.sort_by(|a, b| a.0.cmp(b.0));

			// Write each state
			for (_, (source_state, dest_state)) in entries {
				if let Some(state) = source_state {
					self.write_state(&mut file, state)?;
				}
				if let Some(state) = dest_state {
					self.write_state(&mut file, state)?;
				}
			}
		}

		// Atomic rename
		fs::rename(&temp_file, &self.state_file)?;

		Ok(())
	}

	/// Escape a path string (handles \n, \", \\, \t, \r)
	fn escape_path(s: &str) -> String {
		let mut result = String::with_capacity(s.len() + 10);
		result.push('"');

		for c in s.chars() {
			match c {
				'\\' => result.push_str("\\\\"),
				'"' => result.push_str("\\\""),
				'\n' => result.push_str("\\n"),
				'\t' => result.push_str("\\t"),
				'\r' => result.push_str("\\r"),
				_ => result.push(c),
			}
		}

		result.push('"');
		result
	}

	/// Convert SystemTime to nanoseconds since UNIX_EPOCH, clamped to valid i64 range
	fn system_time_to_nanos(time: SystemTime) -> i64 {
		time.duration_since(UNIX_EPOCH)
			.map(|d| {
				// Clamp to i64::MAX to avoid overflow (covers timestamps until year 2262)
				d.as_nanos().min(i64::MAX as u128) as i64
			})
			.unwrap_or(0) // Pre-epoch times become 0
	}

	/// Write a single state entry
	fn write_state(&self, file: &mut fs::File, state: &SyncState) -> Result<()> {
		let mtime_ns = Self::system_time_to_nanos(state.mtime);
		let last_sync_ns = Self::system_time_to_nanos(state.last_sync);

		let checksum_str = if let Some(cs) = state.checksum { format!("{:x}", cs) } else { "-".to_string() };

		let path_str = state.path.to_string_lossy();
		let path_escaped = Self::escape_path(&path_str);

		writeln!(file, "{} {} {} {} {} {}", state.side.as_str(), mtime_ns, state.size, checksum_str, last_sync_ns, path_escaped)?;

		Ok(())
	}

	/// Store state for a file
	pub fn store(&mut self, state: &SyncState) -> Result<()> {
		let entry = self.states.entry(state.path.clone()).or_insert((None, None));
		match state.side {
			Side::Source => entry.0 = Some(state.clone()),
			Side::Dest => entry.1 = Some(state.clone()),
		}
		self.save_to_file()?;
		Ok(())
	}

	/// Retrieve state for a specific file and side
	#[allow(dead_code)] // Used in tests and future features
	pub fn get(&self, path: &Path, side: Side) -> Result<Option<SyncState>> {
		if let Some((source_state, dest_state)) = self.states.get(path) {
			match side {
				Side::Source => Ok(source_state.clone()),
				Side::Dest => Ok(dest_state.clone()),
			}
		} else {
			Ok(None)
		}
	}

	/// Load all state records
	pub fn load_all(&self) -> Result<StateMap> {
		Ok(self.states.clone())
	}

	/// Delete state for a specific file
	pub fn delete(&mut self, path: &Path) -> Result<()> {
		self.states.remove(path);
		self.save_to_file()?;
		Ok(())
	}

	/// Clear all state (for --clear-bisync-state)
	pub fn clear_all(&mut self) -> Result<()> {
		self.states.clear();
		self.save_to_file()?;
		Ok(())
	}

	/// Prune deleted files (files not in recent syncs)
	#[allow(dead_code)] // Future feature: automatic state pruning
	pub fn prune_stale(&mut self, keep_syncs: usize) -> Result<usize> {
		// Not implemented yet - will add in follow-up
		// For now, just return 0 (no pruning)
		let _ = keep_syncs;
		Ok(0)
	}

	/// Get sync pair hash (for logging/debugging)
	#[allow(dead_code)] // Useful for debugging and future features
	pub fn sync_pair_hash(&self) -> String {
		Self::generate_sync_pair_hash(&self.source_path, &self.dest_path)
	}

	/// Log conflicts to history file for audit trail
	pub fn log_conflicts(&self, conflicts: &[crate::bisync::engine::ConflictInfo]) -> Result<()> {
		if conflicts.is_empty() {
			return Ok(());
		}

		let cache_dir = Self::get_state_dir()?;
		let hash = self.sync_pair_hash();
		let log_path = cache_dir.join(format!("{}.conflicts.log", hash));

		// Open in append mode to preserve history
		let mut file = fs::OpenOptions::new().create(true).append(true).open(&log_path)?;

		let now = SystemTime::now();
		let timestamp = now.duration_since(UNIX_EPOCH).map(|d| d.as_secs()).unwrap_or(0);

		for conflict in conflicts {
			// Determine winner based on resolution strategy
			let winner = determine_winner(conflict);

			// Format: timestamp | path | conflict_type | strategy | winner
			writeln!(
				file,
				"{} | {} | {} | {} | {}",
				timestamp,
				conflict.path.display(),
				conflict.action,
				format!("{:?}", conflict.resolution).to_lowercase(),
				winner
			)?;
		}

		Ok(())
	}
}

/// Determine winner for conflict logging
fn determine_winner(conflict: &crate::bisync::engine::ConflictInfo) -> String {
	use crate::bisync::resolver::ConflictResolution;

	match conflict.resolution {
		ConflictResolution::Source => "source".to_string(),
		ConflictResolution::Dest => "dest".to_string(),
		ConflictResolution::Rename => "both (renamed)".to_string(),
		ConflictResolution::Newer => {
			if let (Some(s_mtime), Some(d_mtime)) = (conflict.source_mtime, conflict.dest_mtime) {
				if s_mtime > d_mtime {
					"source (newer)".to_string()
				} else if d_mtime > s_mtime {
					"dest (newer)".to_string()
				} else {
					"both (tie)".to_string()
				}
			} else {
				"unknown".to_string()
			}
		}
		ConflictResolution::Larger => {
			if let (Some(s_size), Some(d_size)) = (conflict.source_size, conflict.dest_size) {
				if s_size > d_size {
					"source (larger)".to_string()
				} else if d_size > s_size {
					"dest (larger)".to_string()
				} else {
					"both (tie)".to_string()
				}
			} else {
				"unknown".to_string()
			}
		}
		ConflictResolution::Smaller => {
			if let (Some(s_size), Some(d_size)) = (conflict.source_size, conflict.dest_size) {
				if s_size < d_size {
					"source (smaller)".to_string()
				} else if d_size < s_size {
					"dest (smaller)".to_string()
				} else {
					"both (tie)".to_string()
				}
			} else {
				"unknown".to_string()
			}
		}
	}
}

#[cfg(test)]
mod tests {
	use super::*;
	use serial_test::serial;
	use std::time::Duration;

	fn temp_db() -> (BisyncStateDb, PathBuf) {
		let temp_dir = tempfile::tempdir().unwrap();
		let source = temp_dir.path().join("source");
		let dest = temp_dir.path().join("dest");
		let db = BisyncStateDb::open(&source, &dest, false).unwrap();
		let temp_path = temp_dir.path().to_path_buf();
		std::mem::forget(temp_dir); // Keep temp dir alive
		(db, temp_path)
	}

	#[test]
	#[serial]
	fn test_store_and_retrieve() {
		let (mut db, _temp) = temp_db();

		let state = SyncState {
			path: PathBuf::from("test.txt"),
			side: Side::Source,
			mtime: SystemTime::now(),
			size: 1024,
			checksum: Some(0x123456789abcdef0),
			last_sync: SystemTime::now(),
		};

		db.store(&state).unwrap();

		let retrieved = db.get(&state.path, Side::Source).unwrap().unwrap();
		assert_eq!(retrieved.path, state.path);
		assert_eq!(retrieved.side, state.side);
		assert_eq!(retrieved.size, state.size);
		assert_eq!(retrieved.checksum, state.checksum);
	}

	#[test]
	#[serial]
	fn test_store_both_sides() {
		let (mut db, _temp) = temp_db();

		let source_state = SyncState {
			path: PathBuf::from("test.txt"),
			side: Side::Source,
			mtime: SystemTime::now(),
			size: 1024,
			checksum: Some(0x111),
			last_sync: SystemTime::now(),
		};

		let dest_state = SyncState {
			path: PathBuf::from("test.txt"),
			side: Side::Dest,
			mtime: SystemTime::now() - Duration::from_secs(60),
			size: 2048,
			checksum: Some(0x222),
			last_sync: SystemTime::now(),
		};

		db.store(&source_state).unwrap();
		db.store(&dest_state).unwrap();

		let source_retrieved = db.get(&source_state.path, Side::Source).unwrap().unwrap();
		let dest_retrieved = db.get(&dest_state.path, Side::Dest).unwrap().unwrap();

		assert_eq!(source_retrieved.size, 1024);
		assert_eq!(dest_retrieved.size, 2048);
		assert_eq!(source_retrieved.checksum, Some(0x111));
		assert_eq!(dest_retrieved.checksum, Some(0x222));
	}

	#[test]
	#[serial]
	fn test_load_all() {
		let (mut db, _temp) = temp_db();

		let states = vec![
			SyncState {
				path: PathBuf::from("file1.txt"),
				side: Side::Source,
				mtime: SystemTime::now(),
				size: 100,
				checksum: None,
				last_sync: SystemTime::now(),
			},
			SyncState {
				path: PathBuf::from("file1.txt"),
				side: Side::Dest,
				mtime: SystemTime::now(),
				size: 100,
				checksum: None,
				last_sync: SystemTime::now(),
			},
			SyncState {
				path: PathBuf::from("file2.txt"),
				side: Side::Source,
				mtime: SystemTime::now(),
				size: 200,
				checksum: None,
				last_sync: SystemTime::now(),
			},
		];

		for state in &states {
			db.store(state).unwrap();
		}

		let all_states = db.load_all().unwrap();
		assert_eq!(all_states.len(), 2); // 2 unique paths

		let file1 = all_states.get(&PathBuf::from("file1.txt")).unwrap();
		assert!(file1.0.is_some()); // Source
		assert!(file1.1.is_some()); // Dest

		let file2 = all_states.get(&PathBuf::from("file2.txt")).unwrap();
		assert!(file2.0.is_some()); // Source
		assert!(file2.1.is_none()); // Dest
	}

	#[test]
	#[serial]
	fn test_delete() {
		let (mut db, _temp) = temp_db();

		let state = SyncState {
			path: PathBuf::from("test.txt"),
			side: Side::Source,
			mtime: SystemTime::now(),
			size: 1024,
			checksum: None,
			last_sync: SystemTime::now(),
		};

		db.store(&state).unwrap();
		assert!(db.get(&state.path, Side::Source).unwrap().is_some());

		db.delete(&state.path).unwrap();
		assert!(db.get(&state.path, Side::Source).unwrap().is_none());
	}

	#[test]
	#[serial]
	fn test_clear_all() {
		let (mut db, _temp) = temp_db();

		for i in 0..10 {
			let state = SyncState {
				path: PathBuf::from(format!("file{}.txt", i)),
				side: Side::Source,
				mtime: SystemTime::now(),
				size: 1024,
				checksum: None,
				last_sync: SystemTime::now(),
			};
			db.store(&state).unwrap();
		}

		let all_before = db.load_all().unwrap();
		assert_eq!(all_before.len(), 10);

		db.clear_all().unwrap();

		let all_after = db.load_all().unwrap();
		assert_eq!(all_after.len(), 0);
	}

	#[test]
	fn test_sync_pair_hash_uniqueness() {
		let temp_dir = tempfile::tempdir().unwrap();
		let source1 = temp_dir.path().join("source1");
		let source2 = temp_dir.path().join("source2");
		let dest = temp_dir.path().join("dest");

		let db1 = BisyncStateDb::open(&source1, &dest, false).unwrap();
		let db2 = BisyncStateDb::open(&source2, &dest, false).unwrap();

		// Different source → different hash
		assert_ne!(db1.sync_pair_hash(), db2.sync_pair_hash());
	}

	#[test]
	fn test_escape_unescape_quotes() {
		let original = r#"file"with"quotes.txt"#;
		let escaped = BisyncStateDb::escape_path(original);
		assert_eq!(escaped, r#""file\"with\"quotes.txt""#);

		let unescaped = BisyncStateDb::unescape_path(&escaped[1..escaped.len() - 1]);
		assert_eq!(unescaped, original);
	}

	#[test]
	fn test_escape_unescape_newlines() {
		let original = "file\nwith\nnewlines.txt";
		let escaped = BisyncStateDb::escape_path(original);
		assert_eq!(escaped, r#""file\nwith\nnewlines.txt""#);

		let unescaped = BisyncStateDb::unescape_path(&escaped[1..escaped.len() - 1]);
		assert_eq!(unescaped, original);
	}

	#[test]
	fn test_escape_unescape_backslashes() {
		let original = r"file\with\backslashes.txt";
		let escaped = BisyncStateDb::escape_path(original);
		assert_eq!(escaped, r#""file\\with\\backslashes.txt""#);

		let unescaped = BisyncStateDb::unescape_path(&escaped[1..escaped.len() - 1]);
		assert_eq!(unescaped, original);
	}

	#[test]
	fn test_escape_unescape_tabs() {
		let original = "file\twith\ttabs.txt";
		let escaped = BisyncStateDb::escape_path(original);
		assert_eq!(escaped, r#""file\twith\ttabs.txt""#);

		let unescaped = BisyncStateDb::unescape_path(&escaped[1..escaped.len() - 1]);
		assert_eq!(unescaped, original);
	}

	#[test]
	#[serial]
	fn test_edge_case_round_trip() {
		let (mut db, _temp) = temp_db();

		// Create state with edge-case filename
		let edge_case_path = PathBuf::from("file\"with\nnewline\tand\\backslash.txt");
		let state = SyncState {
			path: edge_case_path.clone(),
			side: Side::Source,
			mtime: SystemTime::now(),
			size: 1024,
			checksum: Some(0xdeadbeef),
			last_sync: SystemTime::now(),
		};

		// Store and retrieve
		db.store(&state).unwrap();
		let retrieved = db.get(&edge_case_path, Side::Source).unwrap().unwrap();

		// Path should round-trip correctly
		assert_eq!(retrieved.path, edge_case_path);
		assert_eq!(retrieved.size, 1024);
		assert_eq!(retrieved.checksum, Some(0xdeadbeef));
	}

	#[test]
	#[serial]
	fn test_last_sync_separate_from_mtime() {
		let (mut db, _temp) = temp_db();

		let now = SystemTime::now();
		let earlier = now - Duration::from_secs(3600);

		let state = SyncState {
			path: PathBuf::from("test.txt"),
			side: Side::Source,
			mtime: earlier, // File modified 1 hour ago
			size: 1024,
			checksum: None,
			last_sync: now, // But synced just now
		};

		db.store(&state).unwrap();
		let retrieved = db.get(&state.path, Side::Source).unwrap().unwrap();

		// last_sync should be preserved separately
		let mtime_diff = retrieved.mtime.duration_since(earlier).unwrap();
		let sync_diff = retrieved.last_sync.duration_since(now).unwrap();

		assert!(mtime_diff < Duration::from_millis(10)); // Close to earlier
		assert!(sync_diff < Duration::from_millis(10)); // Close to now
	}

	#[test]
	fn test_v1_backward_compatibility() {
		use std::io::Write;

		let temp_dir = tempfile::tempdir().unwrap();
		let _source = temp_dir.path().join("source");
		let _dest = temp_dir.path().join("dest");

		// Create a v1 format state file manually
		let state_dir = temp_dir.path().join("state");
		std::fs::create_dir_all(&state_dir).unwrap();
		let state_file = state_dir.join("test.lst");

		let mut file = std::fs::File::create(&state_file).unwrap();
		writeln!(file, "# sy bisync v1").unwrap();
		writeln!(file, "# sync_pair: /source <-> /dest").unwrap();
		writeln!(file, "# last_sync: 2025-01-01T00:00:00Z").unwrap();
		writeln!(file, "source 1730000000000000000 1024 abc123 test.txt").unwrap();

		// Load v1 file
		let states = BisyncStateDb::load_from_file(&state_file).unwrap();

		assert_eq!(states.len(), 1);
		let (source_state, _) = states.get(&PathBuf::from("test.txt")).unwrap();
		let state = source_state.as_ref().unwrap();

		// In v1, last_sync should equal mtime (backward compat)
		assert_eq!(state.mtime, state.last_sync);
	}

	#[test]
	fn test_parse_error_handling() {
		use std::io::Write;

		let temp_dir = tempfile::tempdir().unwrap();
		let state_file = temp_dir.path().join("bad.lst");

		// Create malformed state file
		let mut file = std::fs::File::create(&state_file).unwrap();
		writeln!(file, "# sy bisync v2").unwrap();
		writeln!(file, "source INVALID_NUMBER 1024 - 1730000000000000000 test.txt").unwrap();

		// Should error, not return 0/1970
		let result = BisyncStateDb::load_from_file(&state_file);
		assert!(result.is_err());
	}

	// --- Corruption Detection Tests ---

	#[test]
	fn test_detect_empty_state_file() {
		let temp_dir = tempfile::tempdir().unwrap();
		let state_file = temp_dir.path().join("empty.lst");

		// Create empty file
		std::fs::File::create(&state_file).unwrap();

		// Validation should catch empty file
		let result = BisyncStateDb::validate_state_file(&state_file);
		assert!(result.is_err());

		let err = result.unwrap_err();
		let err_str = format!("{}", err);
		assert!(err_str.contains("empty"));
	}

	#[test]
	fn test_detect_missing_header() {
		use std::io::Write;

		let temp_dir = tempfile::tempdir().unwrap();
		let state_file = temp_dir.path().join("no_header.lst");

		// Create file without proper header
		let mut file = std::fs::File::create(&state_file).unwrap();
		writeln!(file, "# some random comment").unwrap();
		writeln!(file, "source 1730000000000000000 1024 - 1730000000000000000 \"test.txt\"").unwrap();

		// Validation should catch missing header
		let result = BisyncStateDb::validate_state_file(&state_file);
		assert!(result.is_err());

		let err = result.unwrap_err();
		let err_str = format!("{}", err);
		assert!(err_str.contains("header"));
	}

	#[test]
	fn test_detect_invalid_side() {
		use std::io::Write;

		let temp_dir = tempfile::tempdir().unwrap();
		let state_file = temp_dir.path().join("bad_side.lst");

		// Create file with invalid side field
		let mut file = std::fs::File::create(&state_file).unwrap();
		writeln!(file, "# sy bisync v2").unwrap();
		writeln!(file, "invalid_side 1730000000000000000 1024 - 1730000000000000000 \"test.txt\"").unwrap();

		// Validation should catch invalid side
		let result = BisyncStateDb::validate_state_file(&state_file);
		assert!(result.is_err());

		let err = result.unwrap_err();
		let err_str = format!("{}", err);
		assert!(err_str.contains("side"));
	}

	#[test]
	fn test_detect_invalid_mtime() {
		use std::io::Write;

		let temp_dir = tempfile::tempdir().unwrap();
		let state_file = temp_dir.path().join("bad_mtime.lst");

		// Create file with non-numeric mtime
		let mut file = std::fs::File::create(&state_file).unwrap();
		writeln!(file, "# sy bisync v2").unwrap();
		writeln!(file, "source NOT_A_NUMBER 1024 - 1730000000000000000 \"test.txt\"").unwrap();

		// Validation should catch invalid mtime
		let result = BisyncStateDb::validate_state_file(&state_file);
		assert!(result.is_err());

		let err = result.unwrap_err();
		let err_str = format!("{}", err);
		assert!(err_str.contains("mtime"));
	}

	#[test]
	fn test_detect_invalid_size() {
		use std::io::Write;

		let temp_dir = tempfile::tempdir().unwrap();
		let state_file = temp_dir.path().join("bad_size.lst");

		// Create file with non-numeric size
		let mut file = std::fs::File::create(&state_file).unwrap();
		writeln!(file, "# sy bisync v2").unwrap();
		writeln!(file, "source 1730000000000000000 NOT_A_SIZE - 1730000000000000000 \"test.txt\"").unwrap();

		// Validation should catch invalid size
		let result = BisyncStateDb::validate_state_file(&state_file);
		assert!(result.is_err());

		let err = result.unwrap_err();
		let err_str = format!("{}", err);
		assert!(err_str.contains("size"));
	}

	#[test]
	fn test_detect_invalid_checksum() {
		use std::io::Write;

		let temp_dir = tempfile::tempdir().unwrap();
		let state_file = temp_dir.path().join("bad_checksum.lst");

		// Create file with invalid checksum (not hex or '-')
		let mut file = std::fs::File::create(&state_file).unwrap();
		writeln!(file, "# sy bisync v2").unwrap();
		writeln!(file, "source 1730000000000000000 1024 INVALID_HEX 1730000000000000000 \"test.txt\"").unwrap();

		// Validation should catch invalid checksum
		let result = BisyncStateDb::validate_state_file(&state_file);
		assert!(result.is_err());

		let err = result.unwrap_err();
		let err_str = format!("{}", err);
		assert!(err_str.contains("checksum"));
	}

	#[test]
	fn test_detect_wrong_field_count() {
		use std::io::Write;

		let temp_dir = tempfile::tempdir().unwrap();
		let state_file = temp_dir.path().join("wrong_fields.lst");

		// Create file with wrong number of fields
		let mut file = std::fs::File::create(&state_file).unwrap();
		writeln!(file, "# sy bisync v2").unwrap();
		writeln!(file, "source 1024").unwrap(); // Only 2 fields, need 5 or 6

		// Validation should catch field count mismatch
		let result = BisyncStateDb::validate_state_file(&state_file);
		assert!(result.is_err());

		let err = result.unwrap_err();
		let err_str = format!("{}", err);
		assert!(err_str.contains("field count"));
	}

	#[test]
	#[serial]
	fn test_force_resync_deletes_corrupt_state() {
		use std::io::Write;

		let temp_dir = tempfile::tempdir().unwrap();

		// Save original XDG_CACHE_HOME to restore later
		let original_cache_home = std::env::var("XDG_CACHE_HOME").ok();

		// Set cache dir BEFORE creating paths (so get_state_dir() uses it)
		unsafe {
			std::env::set_var("XDG_CACHE_HOME", temp_dir.path().join("cache"));
		};

		let source = temp_dir.path().join("source");
		let dest = temp_dir.path().join("dest");

		// Create a corrupt state file manually in the actual state directory
		let sync_pair_hash = BisyncStateDb::generate_sync_pair_hash(&source, &dest);
		let state_dir = BisyncStateDb::get_state_dir().unwrap();
		std::fs::create_dir_all(&state_dir).unwrap();
		let corrupt_file = state_dir.join(format!("{}.lst", sync_pair_hash));

		let mut file = std::fs::File::create(&corrupt_file).unwrap();
		writeln!(file, "CORRUPT DATA").unwrap(); // No header, totally corrupt
		drop(file);

		assert!(corrupt_file.exists());

		// Without force_resync, opening should fail
		let result = BisyncStateDb::open(&source, &dest, false);
		assert!(result.is_err());

		// Verify file still exists after failed open
		assert!(corrupt_file.exists());

		// With force_resync, corrupt file should be deleted and new db created
		let db = BisyncStateDb::open(&source, &dest, true).unwrap();

		// Corrupt file should be deleted
		assert!(!corrupt_file.exists());

		// DB should be empty (fresh start)
		assert_eq!(db.load_all().unwrap().len(), 0);

		// Restore original XDG_CACHE_HOME to avoid leaking to other tests
		match original_cache_home {
			Some(val) => unsafe { std::env::set_var("XDG_CACHE_HOME", val) },
			None => unsafe { std::env::remove_var("XDG_CACHE_HOME") },
		}
	}

	#[test]
	fn test_valid_state_passes_validation() {
		use std::io::Write;

		let temp_dir = tempfile::tempdir().unwrap();
		let state_file = temp_dir.path().join("valid.lst");

		// Create a properly formatted state file
		let mut file = std::fs::File::create(&state_file).unwrap();
		writeln!(file, "# sy bisync v2").unwrap();
		writeln!(file, "# sync_pair: /source <-> /dest").unwrap();
		writeln!(file, "source 1730000000000000000 1024 abc123 1730000000000000000 \"test.txt\"").unwrap();
		writeln!(file, "dest 1730000000000000000 1024 - 1730000000000000000 \"test2.txt\"").unwrap();

		// Validation should pass
		let result = BisyncStateDb::validate_state_file(&state_file);
		assert!(result.is_ok());
	}
}