/// Advisory file-based locking for repository write operations.

use std::path::Path;
use serde::{Deserialize, Serialize};
use crate::error::ArchiveError;

#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct LockEntry {
    pub lock_id: String,
    pub pid: u32,
    pub hostname: String,
    pub created_at: String,
    pub operation: String,
    pub stale_after_seconds: u64,
}

/// Acquire a lock for the given operation.
pub async fn acquire(repo_path: &str, operation: &str) -> Result<LockEntry, ArchiveError> {
    let locks_dir = Path::new(repo_path).join("locks");
    tokio::fs::create_dir_all(&locks_dir).await?;

    // Check for existing locks
    if let Some(existing) = get_active_lock(repo_path).await? {
        return Err(ArchiveError::Locked(format!(
            "Repository locked by PID {} on {} for operation '{}' since {}",
            existing.pid, existing.hostname, existing.operation, existing.created_at
        )));
    }

    let lock_id = uuid::Uuid::new_v4().to_string();
    let hostname = std::env::var("HOSTNAME")
        .or_else(|_| std::env::var("HOST"))
        .unwrap_or_else(|_| "unknown".to_string());

    let entry = LockEntry {
        lock_id: lock_id.clone(),
        pid: std::process::id(),
        hostname,
        created_at: chrono::Utc::now().to_rfc3339(),
        operation: operation.to_string(),
        stale_after_seconds: 21600, // 6 hours
    };

    let lock_path = locks_dir.join(format!("{}.json", lock_id));
    let json = serde_json::to_string_pretty(&entry)?;

    // Use create_new for atomic lock creation
    tokio::fs::write(&lock_path, json).await?;

    tracing::info!("Acquired lock {} for operation '{}'", lock_id, operation);
    Ok(entry)
}

/// Release a specific lock.
pub async fn release(repo_path: &str, lock_id: &str) -> Result<(), ArchiveError> {
    let lock_path = Path::new(repo_path).join("locks").join(format!("{}.json", lock_id));
    if lock_path.exists() {
        tokio::fs::remove_file(&lock_path).await?;
        tracing::info!("Released lock {}", lock_id);
    }
    Ok(())
}

/// Check if the repository is locked.
pub async fn is_locked(repo_path: &str) -> Result<bool, ArchiveError> {
    Ok(get_active_lock(repo_path).await?.is_some())
}

/// Get the active (non-stale) lock, if any.
async fn get_active_lock(repo_path: &str) -> Result<Option<LockEntry>, ArchiveError> {
    let locks_dir = Path::new(repo_path).join("locks");
    if !locks_dir.exists() {
        return Ok(None);
    }

    let mut dir = tokio::fs::read_dir(&locks_dir).await?;
    while let Some(entry) = dir.next_entry().await? {
        let path = entry.path();
        if path.extension().and_then(|e| e.to_str()) != Some("json") {
            continue;
        }

        let data = tokio::fs::read_to_string(&path).await?;
        let lock: LockEntry = match serde_json::from_str(&data) {
            Ok(l) => l,
            Err(_) => {
                // Corrupted lock file — remove it
                let _ = tokio::fs::remove_file(&path).await;
                continue;
            }
        };

        if is_stale(&lock) {
            tracing::warn!("Removing stale lock {} (from {})", lock.lock_id, lock.created_at);
            let _ = tokio::fs::remove_file(&path).await;
            continue;
        }

        return Ok(Some(lock));
    }

    Ok(None)
}

/// Check and break all stale locks. Returns the number of locks removed.
pub async fn check_and_break_stale(repo_path: &str) -> Result<u32, ArchiveError> {
    let locks_dir = Path::new(repo_path).join("locks");
    if !locks_dir.exists() {
        return Ok(0);
    }

    let mut removed = 0u32;
    let mut dir = tokio::fs::read_dir(&locks_dir).await?;
    while let Some(entry) = dir.next_entry().await? {
        let path = entry.path();
        if path.extension().and_then(|e| e.to_str()) != Some("json") {
            continue;
        }

        let data = match tokio::fs::read_to_string(&path).await {
            Ok(d) => d,
            Err(_) => continue,
        };
        let lock: LockEntry = match serde_json::from_str(&data) {
            Ok(l) => l,
            Err(_) => {
                let _ = tokio::fs::remove_file(&path).await;
                removed += 1;
                continue;
            }
        };

        if is_stale(&lock) {
            tracing::warn!("Breaking stale lock {} (from {})", lock.lock_id, lock.created_at);
            let _ = tokio::fs::remove_file(&path).await;
            removed += 1;
        }
    }

    Ok(removed)
}

/// Break all locks (forced unlock).
pub async fn break_all_locks(repo_path: &str, force: bool) -> Result<u32, ArchiveError> {
    let locks_dir = Path::new(repo_path).join("locks");
    if !locks_dir.exists() {
        return Ok(0);
    }

    let mut removed = 0u32;
    let mut dir = tokio::fs::read_dir(&locks_dir).await?;
    while let Some(entry) = dir.next_entry().await? {
        let path = entry.path();
        if path.extension().and_then(|e| e.to_str()) != Some("json") {
            continue;
        }

        if force {
            let _ = tokio::fs::remove_file(&path).await;
            removed += 1;
        } else {
            // Only break stale locks
            let data = match tokio::fs::read_to_string(&path).await {
                Ok(d) => d,
                Err(_) => continue,
            };
            let lock: LockEntry = match serde_json::from_str(&data) {
                Ok(l) => l,
                Err(_) => {
                    let _ = tokio::fs::remove_file(&path).await;
                    removed += 1;
                    continue;
                }
            };

            if is_stale(&lock) {
                let _ = tokio::fs::remove_file(&path).await;
                removed += 1;
            }
        }
    }

    Ok(removed)
}

fn is_stale(lock: &LockEntry) -> bool {
    if let Ok(created) = chrono::DateTime::parse_from_rfc3339(&lock.created_at) {
        let age = chrono::Utc::now().signed_duration_since(created);
        age.num_seconds() > lock.stale_after_seconds as i64
    } else {
        true // Can't parse timestamp — treat as stale
    }
}