//! SFTP service — high-level file operations over an existing SSH connection.
//!
//! SFTP sessions are created from SSH handles via a separate subsystem channel
//! (not the PTY channel). One `SftpSession` is stored per SSH session ID and
//! provides all file operations needed by the frontend.

use std::sync::Arc;
use std::time::{Duration, UNIX_EPOCH};

use dashmap::DashMap;
use log::{debug, info};
use russh_sftp::client::SftpSession;
use russh_sftp::protocol::OpenFlags;
use serde::{Deserialize, Serialize};
use tokio::io::{AsyncReadExt, AsyncWriteExt};
use tokio::sync::Mutex as TokioMutex;

// ── file entry ───────────────────────────────────────────────────────────────

/// Metadata about a single remote file or directory, returned to the frontend.
#[derive(Debug, Serialize, Deserialize, Clone)]
#[serde(rename_all = "camelCase")]
pub struct FileEntry {
    pub name: String,
    pub path: String,
    pub size: u64,
    pub is_dir: bool,
    /// Unix permission string, e.g. "0755"
    pub permissions: String,
    /// Human-readable modification time, e.g. "Mar 17 14:30"
    pub mod_time: String,
}

// ── helpers ──────────────────────────────────────────────────────────────────

/// Format a Unix timestamp (seconds since epoch) as "Mon DD HH:MM".
fn format_mtime(unix_secs: u32) -> String {
    // Build a SystemTime from the raw epoch value.
    let st = UNIX_EPOCH + Duration::from_secs(unix_secs as u64);

    // Convert to seconds-since-epoch for manual formatting.  We avoid pulling
    // in chrono just for this; a simple manual decomposition is sufficient for
    // the "Mar 17 14:30" display format expected by the frontend.
    let secs = unix_secs as i64;

    // Days since epoch → calendar date (Gregorian, ignoring leap seconds).
    let days = secs / 86_400;
    let time_of_day = secs % 86_400;
    let hours = time_of_day / 3_600;
    let minutes = (time_of_day % 3_600) / 60;

    // Gregorian calendar calculation (Zeller / Julian Day approach).
    let z = days + 719_468;
    let era = if z >= 0 { z } else { z - 146_096 } / 146_097;
    let doe = z - era * 146_097;
    let yoe = (doe - doe / 1_460 + doe / 36_524 - doe / 146_096) / 365;
    let y = yoe + era * 400;
    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
    let mp = (5 * doy + 2) / 153;
    let d = doy - (153 * mp + 2) / 5 + 1;
    let m = if mp < 10 { mp + 3 } else { mp - 9 };
    let _y = if m <= 2 { y + 1 } else { y };

    let month = match m {
        1 => "Jan",
        2 => "Feb",
        3 => "Mar",
        4 => "Apr",
        5 => "May",
        6 => "Jun",
        7 => "Jul",
        8 => "Aug",
        9 => "Sep",
        10 => "Oct",
        11 => "Nov",
        12 => "Dec",
        _ => "???",
    };

    // Suppress unused variable warning — st is only used as a sanity anchor.
    let _ = st;

    format!("{} {:2} {:02}:{:02}", month, d, hours, minutes)
}

/// Convert raw permission bits to a "0755"-style octal string.
fn format_permissions(raw: Option<u32>) -> String {
    match raw {
        Some(p) => format!("{:04o}", p & 0o7777),
        None => "----".to_string(),
    }
}

// ── SFTP service ─────────────────────────────────────────────────────────────

/// Manages SFTP sessions keyed by SSH session ID.
#[derive(Clone)]
pub struct SftpService {
    /// One `SftpSession` per SSH session, behind a mutex so async commands can
    /// take a shared reference to the `SftpService` and still mutably borrow
    /// individual sessions.
    clients: DashMap<String, Arc<TokioMutex<SftpSession>>>,
}

impl SftpService {
    pub fn new() -> Self {
        Self {
            clients: DashMap::new(),
        }
    }

    /// Store an SFTP client for the given session.
    pub fn register_client(&self, session_id: &str, client: SftpSession) {
        info!("SFTP client registered for session {}", session_id);
        self.clients
            .insert(session_id.to_string(), Arc::new(TokioMutex::new(client)));
    }

    /// Remove and drop the SFTP client for a session (called on SSH disconnect).
    pub fn remove_client(&self, session_id: &str) {
        if self.clients.remove(session_id).is_some() {
            info!("SFTP client removed for session {}", session_id);
        }
    }

    /// List the contents of a remote directory.
    ///
    /// Returns entries sorted: directories first (alphabetically), then files
    /// (alphabetically).
    pub async fn list(&self, session_id: &str, path: &str) -> Result<Vec<FileEntry>, String> {
        let arc = self.get_client(session_id)?;
        let client = arc.lock().await;

        let read_dir = client
            .read_dir(path)
            .await
            .map_err(|e| format!("SFTP list '{}' failed: {}", path, e))?;

        let mut entries: Vec<FileEntry> = read_dir
            .map(|entry| {
                let meta = entry.metadata();
                let name = entry.file_name();
                let full_path = if path.ends_with('/') {
                    format!("{}{}", path, name)
                } else {
                    format!("{}/{}", path, name)
                };
                let is_dir = meta.is_dir();
                FileEntry {
                    name,
                    path: full_path,
                    size: meta.size.unwrap_or(0),
                    is_dir,
                    permissions: format_permissions(meta.permissions),
                    mod_time: meta.mtime.map(format_mtime).unwrap_or_default(),
                }
            })
            .collect();

        // Sort: directories first, then files; each group alphabetical.
        entries.sort_by(|a, b| match (a.is_dir, b.is_dir) {
            (true, false) => std::cmp::Ordering::Less,
            (false, true) => std::cmp::Ordering::Greater,
            _ => a.name.to_lowercase().cmp(&b.name.to_lowercase()),
        });

        debug!(
            "SFTP list '{}' for session {}: {} entries",
            path,
            session_id,
            entries.len()
        );
        Ok(entries)
    }

    /// Read a remote file as a UTF-8 string.
    ///
    /// Enforces a 5 MB guard — returns an error for larger files.
    pub async fn read_file(&self, session_id: &str, path: &str) -> Result<String, String> {
        const MAX_BYTES: u64 = 5 * 1024 * 1024;

        let arc = self.get_client(session_id)?;
        let client = arc.lock().await;

        // Stat first to check size before pulling bytes.
        let meta = client
            .metadata(path)
            .await
            .map_err(|e| format!("SFTP stat '{}' failed: {}", path, e))?;

        if let Some(size) = meta.size {
            if size > MAX_BYTES {
                return Err(format!(
                    "File '{}' is {} bytes — exceeds 5 MB read limit",
                    path, size
                ));
            }
        }

        let mut file = client
            .open(path)
            .await
            .map_err(|e| format!("SFTP open '{}' failed: {}", path, e))?;

        let mut buf = Vec::new();
        file.read_to_end(&mut buf)
            .await
            .map_err(|e| format!("SFTP read '{}' failed: {}", path, e))?;

        String::from_utf8(buf)
            .map_err(|_| format!("File '{}' is not valid UTF-8", path))
    }

    /// Write a UTF-8 string to a remote file (create or truncate).
    pub async fn write_file(
        &self,
        session_id: &str,
        path: &str,
        content: &str,
    ) -> Result<(), String> {
        let arc = self.get_client(session_id)?;
        let client = arc.lock().await;

        let mut file = client
            .open_with_flags(
                path,
                OpenFlags::CREATE | OpenFlags::TRUNCATE | OpenFlags::WRITE,
            )
            .await
            .map_err(|e| format!("SFTP open '{}' for write failed: {}", path, e))?;

        file.write_all(content.as_bytes())
            .await
            .map_err(|e| format!("SFTP write '{}' failed: {}", path, e))?;

        file.flush()
            .await
            .map_err(|e| format!("SFTP flush '{}' failed: {}", path, e))?;

        debug!("SFTP wrote {} bytes to '{}'", content.len(), path);
        Ok(())
    }

    /// Create a remote directory.
    pub async fn mkdir(&self, session_id: &str, path: &str) -> Result<(), String> {
        let arc = self.get_client(session_id)?;
        let client = arc.lock().await;

        client
            .create_dir(path)
            .await
            .map_err(|e| format!("SFTP mkdir '{}' failed: {}", path, e))
    }

    /// Delete a remote file or directory.
    ///
    /// Tries `remove_file` first; falls back to `remove_dir` if that fails.
    pub async fn delete(&self, session_id: &str, path: &str) -> Result<(), String> {
        let arc = self.get_client(session_id)?;
        let client = arc.lock().await;

        match client.remove_file(path).await {
            Ok(()) => Ok(()),
            Err(_) => client
                .remove_dir(path)
                .await
                .map_err(|e| format!("SFTP delete '{}' failed: {}", path, e)),
        }
    }

    /// Rename (or move) a remote path.
    pub async fn rename(
        &self,
        session_id: &str,
        old_path: &str,
        new_path: &str,
    ) -> Result<(), String> {
        let arc = self.get_client(session_id)?;
        let client = arc.lock().await;

        client
            .rename(old_path, new_path)
            .await
            .map_err(|e| format!("SFTP rename '{}' → '{}' failed: {}", old_path, new_path, e))
    }

    /// Stat a single remote path and return its metadata as a `FileEntry`.
    pub async fn stat(&self, session_id: &str, path: &str) -> Result<FileEntry, String> {
        let arc = self.get_client(session_id)?;
        let client = arc.lock().await;

        let meta = client
            .metadata(path)
            .await
            .map_err(|e| format!("SFTP stat '{}' failed: {}", path, e))?;

        // Extract the file name from the path.
        let name = path
            .rsplit('/')
            .next()
            .unwrap_or(path)
            .to_string();

        Ok(FileEntry {
            name,
            path: path.to_string(),
            size: meta.size.unwrap_or(0),
            is_dir: meta.is_dir(),
            permissions: format_permissions(meta.permissions),
            mod_time: meta.mtime.map(format_mtime).unwrap_or_default(),
        })
    }

    // ── private helpers ───────────────────────────────────────────────────────

    fn get_client(
        &self,
        session_id: &str,
    ) -> Result<Arc<TokioMutex<SftpSession>>, String> {
        self.clients
            .get(session_id)
            .map(|r| r.clone())
            .ok_or_else(|| format!("No SFTP client for session {}", session_id))
    }
}