use std::mem;
use std::time::Duration;
use crossbeam_channel::Sender;
use windows::{
    core::PCWSTR,
    Win32::Foundation::HANDLE,
    Win32::Storage::FileSystem::{
        CreateFileW, FILE_FLAG_BACKUP_SEMANTICS, FILE_SHARE_DELETE,
        FILE_SHARE_READ, FILE_SHARE_WRITE, OPEN_EXISTING,
    },
    Win32::System::Ioctl::{
        FSCTL_QUERY_USN_JOURNAL, FSCTL_READ_USN_JOURNAL,
        READ_USN_JOURNAL_DATA_V0, USN_JOURNAL_DATA_V0, USN_RECORD_V2,
        USN_REASON_FILE_CREATE, USN_REASON_FILE_DELETE,
        USN_REASON_RENAME_NEW_NAME, USN_REASON_RENAME_OLD_NAME,
    },
    Win32::System::IO::DeviceIoControl,
};
use crate::mft::types::{FileKind, FileRecord, IndexEvent, JournalCheckpoint, NtfsDrive};

const BUFFER_SIZE: usize = 64 * 1024;

pub struct UsnWatcher {
    handle: HANDLE,
    drive: NtfsDrive,
    sender: Sender<IndexEvent>,
    pub next_usn: i64,
    pub journal_id: u64,
}

impl UsnWatcher {
    pub fn new(
        drive: &NtfsDrive,
        sender: Sender<IndexEvent>,
    ) -> windows::core::Result<Self> {
        Self::new_from(drive, sender, None)
    }

    pub fn new_from(
        drive: &NtfsDrive,
        sender: Sender<IndexEvent>,
        checkpoint: Option<&JournalCheckpoint>,
    ) -> windows::core::Result<Self> {
        let path: Vec<u16> = drive.device_path.encode_utf16().chain(Some(0)).collect();

        let handle = unsafe {
            CreateFileW(
                PCWSTR(path.as_ptr()),
                0x0,
                FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
                None,
                OPEN_EXISTING,
                FILE_FLAG_BACKUP_SEMANTICS,
                None,
            )?
        };

        let mut journal_data: USN_JOURNAL_DATA_V0 = unsafe { mem::zeroed() };
        let mut bytes_returned = 0u32;

        unsafe {
            DeviceIoControl(
                handle,
                FSCTL_QUERY_USN_JOURNAL,
                None, 0,
                Some(&mut journal_data as *mut _ as *mut _),
                mem::size_of::<USN_JOURNAL_DATA_V0>() as u32,
                Some(&mut bytes_returned),
                None,
            )?;
        }

        // If checkpoint matches current journal and USN is still in range, resume.
        // Otherwise start from current position (don't replay old history).
        let next_usn = if let Some(cp) = checkpoint {
            if cp.journal_id != journal_data.UsnJournalID {
                return Err(windows::core::Error::new(
                    windows::Win32::Foundation::ERROR_JOURNAL_NOT_ACTIVE.into(),
                    "Journal ID mismatch — rescan needed",
                ));
            }
            if cp.next_usn < journal_data.FirstUsn || cp.next_usn > journal_data.NextUsn {
                return Err(windows::core::Error::new(
                    windows::Win32::Foundation::ERROR_JOURNAL_NOT_ACTIVE.into(),
                    "Saved USN outside journal range — rescan needed",
                ));
            }
            cp.next_usn
        } else {
            journal_data.NextUsn
        };

        Ok(Self {
            handle,
            drive: drive.clone(),
            sender,
            next_usn,
            journal_id: journal_data.UsnJournalID,
        })
    }

    pub fn checkpoint(&self) -> JournalCheckpoint {
        JournalCheckpoint {
            next_usn: self.next_usn,
            journal_id: self.journal_id,
            drive_letter: self.drive.letter,
        }
    }

    pub fn run(&mut self) {
        let mut buffer = vec![0u8; BUFFER_SIZE];
        loop {
            std::thread::sleep(Duration::from_millis(500));
            self.poll(&mut buffer);
        }
    }

    pub fn run_shared(&mut self, shared: std::sync::Arc<parking_lot::Mutex<Vec<JournalCheckpoint>>>) {
        let mut buffer = vec![0u8; BUFFER_SIZE];
        loop {
            std::thread::sleep(Duration::from_millis(500));
            self.poll(&mut buffer);
            let mut cps = shared.lock();
            cps.retain(|c| c.drive_letter != self.drive.letter);
            cps.push(self.checkpoint());
        }
    }

    /// Drain all pending journal entries — used for delta catch-up on startup
    pub fn drain(&mut self) -> usize {
        let mut buffer = vec![0u8; BUFFER_SIZE];
        let mut count = 0;
        loop {
            let before = self.next_usn;
            self.poll(&mut buffer);
            if self.next_usn == before {
                break;
            }
            count += 1;
        }
        count
    }

    fn poll(&mut self, buffer: &mut Vec<u8>) {
        let read_data = READ_USN_JOURNAL_DATA_V0 {
            StartUsn: self.next_usn,
            ReasonMask: USN_REASON_FILE_CREATE
                | USN_REASON_FILE_DELETE
                | USN_REASON_RENAME_NEW_NAME
                | USN_REASON_RENAME_OLD_NAME,
            ReturnOnlyOnClose: 0,
            Timeout: 0,
            BytesToWaitFor: 0,
            UsnJournalID: self.journal_id,
        };

        let mut bytes_returned = 0u32;
        let ok = unsafe {
            DeviceIoControl(
                self.handle,
                FSCTL_READ_USN_JOURNAL,
                Some(&read_data as *const _ as *const _),
                mem::size_of::<READ_USN_JOURNAL_DATA_V0>() as u32,
                Some(buffer.as_mut_ptr() as *mut _),
                BUFFER_SIZE as u32,
                Some(&mut bytes_returned),
                None,
            )
        };

        if ok.is_err() || bytes_returned <= 8 {
            return;
        }

        self.next_usn = i64::from_ne_bytes(buffer[0..8].try_into().unwrap());

        let mut offset = 8usize;
        while offset + mem::size_of::<USN_RECORD_V2>() <= bytes_returned as usize {
            let record = unsafe {
                &*(buffer.as_ptr().add(offset) as *const USN_RECORD_V2)
            };
            if record.RecordLength == 0 { break; }
            self.process_record(record, buffer, offset);
            offset += record.RecordLength as usize;
        }
    }

    fn process_record(&self, record: &USN_RECORD_V2, buffer: &[u8], offset: usize) {
        let name_offset = record.FileNameOffset as usize;
        let name_len = record.FileNameLength as usize / 2;
        let name_ptr = unsafe {
            buffer.as_ptr().add(offset + name_offset) as *const u16
        };
        let name_slice = unsafe { std::slice::from_raw_parts(name_ptr, name_len) };
        let name = String::from_utf16_lossy(name_slice);

        let is_dir = (record.FileAttributes & 0x10) != 0;
        let file_ref = record.FileReferenceNumber as u64;
        let parent_ref = record.ParentFileReferenceNumber as u64;
        let reason = record.Reason;

        if reason & USN_REASON_FILE_DELETE != 0 {
            let _ = self.sender.send(IndexEvent::Deleted(file_ref));
            return;
        }

        let kind = if is_dir { FileKind::Directory } else { FileKind::File };

        // Rename new name = could be a rename OR a move to different folder
        if reason & USN_REASON_RENAME_NEW_NAME != 0 {
            let _ = self.sender.send(IndexEvent::Moved {
                file_ref,
                new_parent_ref: parent_ref,
                name: name.clone(),
                kind: kind.clone(),
            });
            return;
        }

        if reason & USN_REASON_FILE_CREATE != 0 {
            let new_record = FileRecord {
                file_ref,
                parent_ref,
                name,
                kind,
            };
            let _ = self.sender.send(IndexEvent::Created(new_record));
        }
    }
}

impl Drop for UsnWatcher {
    fn drop(&mut self) {
        unsafe { windows::Win32::Foundation::CloseHandle(self.handle).ok() };
    }
}