use std::ffi::{c_int, c_void, CStr};
use std::mem::MaybeUninit;
use std::num::NonZeroU32;
use std::ptr::null_mut;

use libsql_ffi::{
    libsql_wal, libsql_wal_manager, sqlite3_wal, sqlite3_wal_manager, Error, SQLITE_OK,
    WAL_SAVEPOINT_NDATA,
};

use super::{
    BusyHandler, CheckpointCallback, CheckpointMode, PageHeaders, Result, Sqlite3Db, Sqlite3File,
    UndoHandler, Vfs, Wal, WalManager,
};

/// SQLite3 default wal_manager implementation.
#[derive(Clone, Copy)]
pub struct Sqlite3WalManager {
    inner: libsql_wal_manager,
}

/// Safety: the create pointer is an immutable global pointer
unsafe impl Send for Sqlite3WalManager {}
unsafe impl Sync for Sqlite3WalManager {}

impl Sqlite3WalManager {
    pub fn new() -> Self {
        Self {
            inner: unsafe { sqlite3_wal_manager },
        }
    }
}

impl Default for Sqlite3WalManager {
    fn default() -> Self {
        Self::new()
    }
}

impl WalManager for Sqlite3WalManager {
    type Wal = Sqlite3Wal;

    fn use_shared_memory(&self) -> bool {
        self.inner.bUsesShm != 0
    }

    fn open(
        &self,
        vfs: &mut Vfs,
        file: &mut Sqlite3File,
        no_shm_mode: c_int,
        max_log_size: i64,
        db_path: &CStr,
    ) -> Result<Self::Wal> {
        let mut wal: MaybeUninit<libsql_wal> = MaybeUninit::uninit();
        let rc = unsafe {
            (self.inner.xOpen.unwrap())(
                self.inner.pData,
                vfs.as_ptr(),
                file.as_ptr(),
                no_shm_mode,
                max_log_size,
                db_path.as_ptr(),
                wal.as_mut_ptr(),
            )
        };

        if rc != 0 {
            Err(Error::new(rc))?
        }

        let inner = unsafe { wal.assume_init() };

        Ok(Sqlite3Wal { inner })
    }

    fn close(
        &self,
        wal: &mut Self::Wal,
        db: &mut Sqlite3Db,
        sync_flags: c_int,
        scratch: Option<&mut [u8]>,
    ) -> Result<()> {
        let scratch_len = scratch.as_ref().map(|s| s.len()).unwrap_or(0);
        let scratch_ptr = scratch.map(|s| s.as_mut_ptr()).unwrap_or(null_mut());
        let rc = unsafe {
            (self.inner.xClose.unwrap())(
                self.inner.pData,
                wal.inner.pData,
                db.as_ptr(),
                sync_flags,
                scratch_len as _,
                scratch_ptr as _,
            )
        };

        if rc != 0 {
            Err(Error::new(rc))?
        } else {
            Ok(())
        }
    }

    fn destroy_log(&self, vfs: &mut Vfs, db_path: &CStr) -> Result<()> {
        let rc = unsafe {
            (self.inner.xLogDestroy.unwrap())(self.inner.pData, vfs.as_ptr(), db_path.as_ptr())
        };

        if rc != 0 {
            Err(Error::new(rc))?
        } else {
            Ok(())
        }
    }

    fn log_exists(&self, vfs: &mut Vfs, db_path: &CStr) -> Result<bool> {
        let mut out: c_int = 0;
        let rc = unsafe {
            (self.inner.xLogExists.unwrap())(
                self.inner.pData,
                vfs.as_ptr(),
                db_path.as_ptr(),
                &mut out,
            )
        };

        if rc != 0 {
            Err(Error::new(rc))?
        } else {
            Ok(out != 0)
        }
    }

    fn destroy(self)
    where
        Self: Sized,
    {
        unsafe { (self.inner.xDestroy.unwrap())(self.inner.pData) }
    }
}

unsafe impl Send for Sqlite3Wal {}

/// SQLite3 wal implementation
pub struct Sqlite3Wal {
    inner: libsql_wal,
}

impl Wal for Sqlite3Wal {
    fn limit(&mut self, size: i64) {
        unsafe {
            (self.inner.methods.xLimit.unwrap())(self.inner.pData, size);
        }
    }

    fn begin_read_txn(&mut self) -> Result<bool> {
        let mut out: c_int = 0;
        let rc = unsafe {
            (self.inner.methods.xBeginReadTransaction.unwrap())(
                self.inner.pData,
                &mut out as *mut _,
            )
        };
        if rc != 0 {
            Err(Error::new(rc))
        } else {
            Ok(out != 0)
        }
    }

    fn end_read_txn(&mut self) {
        unsafe {
            (self.inner.methods.xEndReadTransaction.unwrap())(self.inner.pData);
        }
    }

    fn find_frame(&mut self, page_no: NonZeroU32) -> Result<Option<NonZeroU32>> {
        let mut out: u32 = 0;
        let rc = unsafe {
            (self.inner.methods.xFindFrame.unwrap())(self.inner.pData, page_no.into(), &mut out)
        };

        if rc != 0 {
            Err(Error::new(rc))
        } else {
            Ok(NonZeroU32::new(out))
        }
    }

    fn read_frame(&mut self, frame_no: NonZeroU32, buffer: &mut [u8]) -> Result<()> {
        let rc = unsafe {
            (self.inner.methods.xReadFrame.unwrap())(
                self.inner.pData,
                frame_no.into(),
                buffer.len() as _,
                buffer.as_mut_ptr(),
            )
        };
        if rc != 0 {
            Err(Error::new(rc))
        } else {
            Ok(())
        }
    }

    fn db_size(&self) -> u32 {
        unsafe { (self.inner.methods.xDbsize.unwrap())(self.inner.pData) }
    }

    fn begin_write_txn(&mut self) -> Result<()> {
        let rc = unsafe { (self.inner.methods.xBeginWriteTransaction.unwrap())(self.inner.pData) };
        if rc != 0 {
            Err(Error::new(rc))
        } else {
            Ok(())
        }
    }

    fn end_write_txn(&mut self) -> Result<()> {
        let rc = unsafe { (self.inner.methods.xEndWriteTransaction.unwrap())(self.inner.pData) };
        if rc != 0 {
            Err(Error::new(rc))
        } else {
            Ok(())
        }
    }

    fn undo<U: UndoHandler>(&mut self, undo_handler: Option<&mut U>) -> Result<()> {
        unsafe extern "C" fn call_handler<U: UndoHandler>(p: *mut c_void, page_no: u32) -> c_int {
            let this = &mut *(p as *mut U);
            match this.handle_undo(page_no) {
                Ok(_) => SQLITE_OK,
                Err(e) => e.extended_code,
            }
        }

        let handler = undo_handler
            .is_some()
            .then_some(call_handler::<U> as unsafe extern "C" fn(*mut c_void, u32) -> i32);
        let handler_data = undo_handler
            .map(|d| d as *mut _ as *mut _)
            .unwrap_or(std::ptr::null_mut());

        let rc =
            unsafe { (self.inner.methods.xUndo.unwrap())(self.inner.pData, handler, handler_data) };
        if rc != 0 {
            Err(Error::new(rc))
        } else {
            Ok(())
        }
    }

    fn savepoint(&mut self, rollback_data: &mut [u32]) {
        assert_eq!(rollback_data.len(), WAL_SAVEPOINT_NDATA as usize);
        unsafe {
            (self.inner.methods.xSavepoint.unwrap())(self.inner.pData, rollback_data.as_mut_ptr());
        }
    }

    fn savepoint_undo(&mut self, rollback_data: &mut [u32]) -> Result<()> {
        assert_eq!(rollback_data.len(), WAL_SAVEPOINT_NDATA as usize);
        let rc = unsafe {
            (self.inner.methods.xSavepointUndo.unwrap())(
                self.inner.pData,
                rollback_data.as_mut_ptr(),
            )
        };
        if rc != 0 {
            Err(Error::new(rc))
        } else {
            Ok(())
        }
    }

    fn insert_frames(
        &mut self,
        page_size: c_int,
        page_headers: &mut PageHeaders,
        size_after: u32,
        is_commit: bool,
        sync_flags: c_int,
    ) -> Result<usize> {
        let mut frames = 0;
        let rc = unsafe {
            (self.inner.methods.xFrames.unwrap())(
                self.inner.pData,
                page_size,
                page_headers.as_mut_ptr(),
                size_after,
                is_commit as _,
                sync_flags,
                &mut frames,
            )
        };
        if rc != 0 {
            Err(Error::new(rc))
        } else {
            Ok(frames as _)
        }
    }

    fn checkpoint(
        &mut self,
        db: &mut Sqlite3Db,
        mode: CheckpointMode,
        mut busy_handler: Option<&mut dyn BusyHandler>,
        sync_flags: u32,
        // temporary scratch buffer
        buf: &mut [u8],
        mut checkpoint_cb: Option<&mut dyn CheckpointCallback>,
        in_wal: Option<&mut i32>,
        backfilled: Option<&mut i32>,
    ) -> Result<()> {
        unsafe extern "C" fn call_handler(p: *mut c_void) -> c_int {
            let this = &mut *(p as *mut &mut dyn BusyHandler);
            this.handle_busy() as _
        }

        unsafe extern "C" fn call_cb(
            data: *mut c_void,
            max_safe_frame_no: c_int,
            page: *const u8,
            page_len: c_int,
            page_no: c_int,
            frame_no: c_int,
        ) -> c_int {
            let this = &mut *(data as *mut &mut dyn CheckpointCallback);
            let ret = if page.is_null() {
                this.finish()
            } else {
                this.frame(
                    max_safe_frame_no as _,
                    std::slice::from_raw_parts(page, page_len as _),
                    NonZeroU32::new(page_no as _).unwrap(),
                    NonZeroU32::new(frame_no as _).unwrap(),
                )
            };

            match ret {
                Ok(()) => 0,
                Err(e) => e.extended_code,
            }
        }

        let handler = busy_handler
            .is_some()
            .then_some(call_handler as unsafe extern "C" fn(*mut c_void) -> i32);
        let handler_data = busy_handler
            .as_mut()
            .map(|d| d as *mut _ as *mut _)
            .unwrap_or(std::ptr::null_mut());

        let checkpoint_cb_fn = checkpoint_cb.is_some().then_some(call_cb as _);
        let checkpoint_cb_data = checkpoint_cb
            .as_mut()
            .map(|d| d as *mut &mut dyn CheckpointCallback as *mut _)
            .unwrap_or(std::ptr::null_mut());

        let out_log_num_frames = in_wal.map(|ptr| ptr as _).unwrap_or(std::ptr::null_mut());
        let out_backfilled = backfilled
            .map(|ptr| ptr as _)
            .unwrap_or(std::ptr::null_mut());

        let rc = unsafe {
            (self.inner.methods.xCheckpoint.unwrap())(
                self.inner.pData,
                db.as_ptr(),
                mode as _,
                handler,
                handler_data,
                sync_flags as _,
                buf.len() as _,
                buf.as_mut_ptr(),
                out_log_num_frames,
                out_backfilled,
                checkpoint_cb_fn,
                checkpoint_cb_data,
            )
        };

        if rc != 0 {
            Err(Error::new(rc))
        } else {
            Ok(())
        }
    }

    fn exclusive_mode(&mut self, op: c_int) -> Result<()> {
        let rc = unsafe { (self.inner.methods.xExclusiveMode.unwrap())(self.inner.pData, op) };

        if rc != 0 {
            Err(Error::new(rc))
        } else {
            Ok(())
        }
    }

    fn uses_heap_memory(&self) -> bool {
        unsafe { (self.inner.methods.xHeapMemory.unwrap())(self.inner.pData) != 0 }
    }

    fn set_db(&mut self, db: &mut Sqlite3Db) {
        unsafe {
            (self.inner.methods.xDb.unwrap())(self.inner.pData, db.as_ptr());
        }
    }

    fn callback(&self) -> i32 {
        unsafe { (self.inner.methods.xCallback.unwrap())(self.inner.pData) }
    }

    fn frames_in_wal(&self) -> u32 {
        unsafe {
            let wal = &*(self.inner.pData as *const sqlite3_wal);
            wal.hdr.mxFrame
        }
    }

    fn db_file(&self) -> &Sqlite3File {
        unsafe {
            let ptr = &mut (*(self.inner.pData as *mut sqlite3_wal)).pDbFd;
            std::mem::transmute(ptr)
        }
    }

    fn backfilled(&self) -> u32 {
        unsafe {
            let ptr = &mut (*(self.inner.pData as *mut sqlite3_wal));
            if ptr.apWiData.is_null() {
                panic!("unititialized wal")
            }
            return libsql_ffi::sqlite3_wal_backfilled(ptr) as _;
        }
    }

    /// ported from wal.c
    /// returns the page_no corresponding to a given frame_no
    fn frame_page_no(&self, frame_no: NonZeroU32) -> Option<NonZeroU32> {
        unsafe {
            let ptr = &mut (*(self.inner.pData as *mut sqlite3_wal));
            NonZeroU32::new(libsql_ffi::sqlite3_wal_frame_page_no(ptr, frame_no.get()))
        }
    }
}