use std::ffi::CStr;
use std::os::raw::{c_char, c_int};
#[cfg(feature = "load_extension")]
use std::path::Path;
use std::ptr;
use std::str;
use std::sync::{Arc, Mutex};

use super::ffi;
use super::str_for_sqlite;
use super::{Connection, InterruptHandle, OpenFlags, PrepFlags, Result};
use crate::error::{
    decode_result_raw, error_from_handle, error_from_sqlite_code, error_with_offset, Error,
};
use crate::raw_statement::RawStatement;
use crate::statement::Statement;
use crate::version_number;

pub struct InnerConnection {
    pub db: *mut ffi::sqlite3,
    // It's unsafe to call `sqlite3_close` while another thread is performing
    // a `sqlite3_interrupt`, and vice versa, so we take this mutex during
    // those functions. This protects a copy of the `db` pointer (which is
    // cleared on closing), however the main copy, `db`, is unprotected.
    // Otherwise, a long-running query would prevent calling interrupt, as
    // interrupt would only acquire the lock after the query's completion.
    interrupt_lock: Arc<Mutex<*mut ffi::sqlite3>>,
    #[cfg(feature = "hooks")]
    pub free_commit_hook: Option<unsafe fn(*mut std::os::raw::c_void)>,
    #[cfg(feature = "hooks")]
    pub free_rollback_hook: Option<unsafe fn(*mut std::os::raw::c_void)>,
    #[cfg(feature = "hooks")]
    pub free_update_hook: Option<unsafe fn(*mut std::os::raw::c_void)>,
    #[cfg(feature = "hooks")]
    pub progress_handler: Option<Box<dyn FnMut() -> bool + Send>>,
    #[cfg(feature = "hooks")]
    pub authorizer: Option<crate::hooks::BoxedAuthorizer>,
    #[cfg(feature = "preupdate_hook")]
    pub free_preupdate_hook: Option<unsafe fn(*mut std::os::raw::c_void)>,
    owned: bool,
}

unsafe impl Send for InnerConnection {}

impl InnerConnection {
    #[expect(clippy::mutex_atomic, clippy::arc_with_non_send_sync)] // See unsafe impl Send / Sync for InterruptHandle
    #[inline]
    pub unsafe fn new(db: *mut ffi::sqlite3, owned: bool) -> Self {
        Self {
            db,
            interrupt_lock: Arc::new(Mutex::new(if owned { db } else { ptr::null_mut() })),
            #[cfg(feature = "hooks")]
            free_commit_hook: None,
            #[cfg(feature = "hooks")]
            free_rollback_hook: None,
            #[cfg(feature = "hooks")]
            free_update_hook: None,
            #[cfg(feature = "hooks")]
            progress_handler: None,
            #[cfg(feature = "hooks")]
            authorizer: None,
            #[cfg(feature = "preupdate_hook")]
            free_preupdate_hook: None,
            owned,
        }
    }

    pub fn open_with_flags(
        c_path: &CStr,
        mut flags: OpenFlags,
        vfs: Option<&CStr>,
    ) -> Result<Self> {
        ensure_safe_sqlite_threading_mode()?;

        let z_vfs = match vfs {
            Some(c_vfs) => c_vfs.as_ptr(),
            None => ptr::null(),
        };

        // turn on extended results code before opening database to have a better diagnostic if a failure happens
        let exrescode = if version_number() >= 3_037_000 {
            flags |= OpenFlags::SQLITE_OPEN_EXRESCODE;
            true
        } else {
            false // flag SQLITE_OPEN_EXRESCODE is ignored by SQLite version < 3.37.0
        };

        unsafe {
            let mut db: *mut ffi::sqlite3 = ptr::null_mut();
            let r = ffi::sqlite3_open_v2(c_path.as_ptr(), &mut db, flags.bits(), z_vfs);
            if r != ffi::SQLITE_OK {
                let e = if db.is_null() {
                    error_from_sqlite_code(r, Some(c_path.to_string_lossy().to_string()))
                } else {
                    let mut e = error_from_handle(db, r);
                    if let Error::SqliteFailure(
                        ffi::Error {
                            code: ffi::ErrorCode::CannotOpen,
                            ..
                        },
                        Some(msg),
                    ) = e
                    {
                        e = Error::SqliteFailure(
                            ffi::Error::new(r),
                            Some(format!("{msg}: {}", c_path.to_string_lossy())),
                        );
                    }
                    ffi::sqlite3_close(db);
                    e
                };

                return Err(e);
            }

            // attempt to turn on extended results code; don't fail if we can't.
            if !exrescode {
                ffi::sqlite3_extended_result_codes(db, 1);
            }

            let r = ffi::sqlite3_busy_timeout(db, 5000);
            if r != ffi::SQLITE_OK {
                let e = error_from_handle(db, r);
                ffi::sqlite3_close(db);
                return Err(e);
            }

            Ok(Self::new(db, true))
        }
    }

    #[inline]
    pub fn db(&self) -> *mut ffi::sqlite3 {
        self.db
    }

    #[inline]
    pub fn decode_result(&self, code: c_int) -> Result<()> {
        unsafe { decode_result_raw(self.db(), code) }
    }

    pub fn close(&mut self) -> Result<()> {
        if self.db.is_null() {
            return Ok(());
        }
        self.remove_hooks();
        self.remove_preupdate_hook();
        let mut shared_handle = self.interrupt_lock.lock().unwrap();
        assert!(
            !self.owned || !shared_handle.is_null(),
            "Bug: Somehow interrupt_lock was cleared before the DB was closed"
        );
        if !self.owned {
            self.db = ptr::null_mut();
            return Ok(());
        }
        unsafe {
            let r = ffi::sqlite3_close(self.db);
            // Need to use _raw because _guard has a reference out, and
            // decode_result takes &mut self.
            let r = decode_result_raw(self.db, r);
            if r.is_ok() {
                *shared_handle = ptr::null_mut();
                self.db = ptr::null_mut();
            }
            r
        }
    }

    #[inline]
    pub fn get_interrupt_handle(&self) -> InterruptHandle {
        InterruptHandle {
            db_lock: Arc::clone(&self.interrupt_lock),
        }
    }

    #[inline]
    #[cfg(feature = "load_extension")]
    pub unsafe fn enable_load_extension(&mut self, onoff: c_int) -> Result<()> {
        let r = ffi::sqlite3_enable_load_extension(self.db, onoff);
        self.decode_result(r)
    }

    #[cfg(feature = "load_extension")]
    pub unsafe fn load_extension(
        &self,
        dylib_path: &Path,
        entry_point: Option<&str>,
    ) -> Result<()> {
        let dylib_str = super::path_to_cstring(dylib_path)?;
        let mut errmsg: *mut c_char = ptr::null_mut();
        let r = if let Some(entry_point) = entry_point {
            let c_entry = crate::str_to_cstring(entry_point)?;
            ffi::sqlite3_load_extension(self.db, dylib_str.as_ptr(), c_entry.as_ptr(), &mut errmsg)
        } else {
            ffi::sqlite3_load_extension(self.db, dylib_str.as_ptr(), ptr::null(), &mut errmsg)
        };
        if r == ffi::SQLITE_OK {
            Ok(())
        } else {
            let message = super::errmsg_to_string(errmsg);
            ffi::sqlite3_free(errmsg.cast::<std::os::raw::c_void>());
            Err(error_from_sqlite_code(r, Some(message)))
        }
    }

    #[inline]
    pub fn last_insert_rowid(&self) -> i64 {
        unsafe { ffi::sqlite3_last_insert_rowid(self.db()) }
    }

    pub fn prepare<'a>(
        &mut self,
        conn: &'a Connection,
        sql: &str,
        flags: PrepFlags,
    ) -> Result<Statement<'a>> {
        let mut c_stmt: *mut ffi::sqlite3_stmt = ptr::null_mut();
        let (c_sql, len, _) = str_for_sqlite(sql.as_bytes())?;
        let mut c_tail: *const c_char = ptr::null();
        #[cfg(not(feature = "unlock_notify"))]
        let r = unsafe { self.prepare_(c_sql, len, flags, &mut c_stmt, &mut c_tail) };
        #[cfg(feature = "unlock_notify")]
        let r = unsafe {
            use crate::unlock_notify;
            let mut rc;
            loop {
                rc = self.prepare_(c_sql, len, flags, &mut c_stmt, &mut c_tail);
                if !unlock_notify::is_locked(self.db, rc) {
                    break;
                }
                rc = unlock_notify::wait_for_unlock_notify(self.db);
                if rc != ffi::SQLITE_OK {
                    break;
                }
            }
            rc
        };
        // If there is an error, *ppStmt is set to NULL.
        if r != ffi::SQLITE_OK {
            return Err(unsafe { error_with_offset(self.db, r, sql) });
        }
        // If the input text contains no SQL (if the input is an empty string or a
        // comment) then *ppStmt is set to NULL.
        let tail = if c_tail.is_null() {
            0
        } else {
            let n = (c_tail as isize) - (c_sql as isize);
            if n <= 0 || n >= len as isize {
                0
            } else {
                n as usize
            }
        };
        Ok(Statement::new(conn, unsafe {
            RawStatement::new(c_stmt, tail)
        }))
    }

    #[inline]
    #[cfg(not(feature = "modern_sqlite"))]
    unsafe fn prepare_(
        &self,
        z_sql: *const c_char,
        n_byte: c_int,
        _: PrepFlags,
        pp_stmt: *mut *mut ffi::sqlite3_stmt,
        pz_tail: *mut *const c_char,
    ) -> c_int {
        ffi::sqlite3_prepare_v2(self.db(), z_sql, n_byte, pp_stmt, pz_tail)
    }

    #[inline]
    #[cfg(feature = "modern_sqlite")]
    unsafe fn prepare_(
        &self,
        z_sql: *const c_char,
        n_byte: c_int,
        flags: PrepFlags,
        pp_stmt: *mut *mut ffi::sqlite3_stmt,
        pz_tail: *mut *const c_char,
    ) -> c_int {
        ffi::sqlite3_prepare_v3(self.db(), z_sql, n_byte, flags.bits(), pp_stmt, pz_tail)
    }

    #[inline]
    pub fn changes(&self) -> u64 {
        #[cfg(not(feature = "modern_sqlite"))]
        unsafe {
            ffi::sqlite3_changes(self.db()) as u64
        }
        #[cfg(feature = "modern_sqlite")] // 3.37.0
        unsafe {
            ffi::sqlite3_changes64(self.db()) as u64
        }
    }

    #[inline]
    pub fn total_changes(&self) -> u64 {
        #[cfg(not(feature = "modern_sqlite"))]
        unsafe {
            ffi::sqlite3_total_changes(self.db()) as u64
        }
        #[cfg(feature = "modern_sqlite")] // 3.37.0
        unsafe {
            ffi::sqlite3_total_changes64(self.db()) as u64
        }
    }

    #[inline]
    pub fn is_autocommit(&self) -> bool {
        unsafe { ffi::sqlite3_get_autocommit(self.db()) != 0 }
    }

    pub fn is_busy(&self) -> bool {
        let db = self.db();
        unsafe {
            let mut stmt = ffi::sqlite3_next_stmt(db, ptr::null_mut());
            while !stmt.is_null() {
                if ffi::sqlite3_stmt_busy(stmt) != 0 {
                    return true;
                }
                stmt = ffi::sqlite3_next_stmt(db, stmt);
            }
        }
        false
    }

    pub fn cache_flush(&mut self) -> Result<()> {
        crate::error::check(unsafe { ffi::sqlite3_db_cacheflush(self.db()) })
    }

    #[cfg(not(feature = "hooks"))]
    #[inline]
    fn remove_hooks(&mut self) {}

    #[cfg(not(feature = "preupdate_hook"))]
    #[inline]
    fn remove_preupdate_hook(&mut self) {}

    pub fn db_readonly(&self, db_name: super::DatabaseName<'_>) -> Result<bool> {
        let name = db_name.as_cstr()?;
        let r = unsafe { ffi::sqlite3_db_readonly(self.db, name.as_ptr()) };
        match r {
            0 => Ok(false),
            1 => Ok(true),
            -1 => Err(Error::SqliteFailure(
                ffi::Error::new(ffi::SQLITE_MISUSE),
                Some(format!("{db_name:?} is not the name of a database")),
            )),
            _ => Err(error_from_sqlite_code(
                r,
                Some("Unexpected result".to_owned()),
            )),
        }
    }

    #[cfg(feature = "modern_sqlite")] // 3.37.0
    pub fn txn_state(
        &self,
        db_name: Option<super::DatabaseName<'_>>,
    ) -> Result<super::transaction::TransactionState> {
        let r = if let Some(ref name) = db_name {
            let name = name.as_cstr()?;
            unsafe { ffi::sqlite3_txn_state(self.db, name.as_ptr()) }
        } else {
            unsafe { ffi::sqlite3_txn_state(self.db, ptr::null()) }
        };
        match r {
            0 => Ok(super::transaction::TransactionState::None),
            1 => Ok(super::transaction::TransactionState::Read),
            2 => Ok(super::transaction::TransactionState::Write),
            -1 => Err(Error::SqliteFailure(
                ffi::Error::new(ffi::SQLITE_MISUSE),
                Some(format!("{db_name:?} is not the name of a valid schema")),
            )),
            _ => Err(error_from_sqlite_code(
                r,
                Some("Unexpected result".to_owned()),
            )),
        }
    }

    #[inline]
    #[cfg(feature = "release_memory")]
    pub fn release_memory(&self) -> Result<()> {
        self.decode_result(unsafe { ffi::sqlite3_db_release_memory(self.db) })
    }

    #[cfg(feature = "modern_sqlite")] // 3.41.0
    pub fn is_interrupted(&self) -> bool {
        unsafe { ffi::sqlite3_is_interrupted(self.db) == 1 }
    }
}

impl Drop for InnerConnection {
    #[expect(unused_must_use)]
    #[inline]
    fn drop(&mut self) {
        self.close();
    }
}

// threading mode checks are not necessary (and do not work) on target
// platforms that do not have threading (such as webassembly)
#[cfg(target_arch = "wasm32")]
fn ensure_safe_sqlite_threading_mode() -> Result<()> {
    Ok(())
}

#[cfg(not(any(target_arch = "wasm32")))]
fn ensure_safe_sqlite_threading_mode() -> Result<()> {
    // Ensure SQLite was compiled in threadsafe mode.
    if unsafe { ffi::sqlite3_threadsafe() == 0 } {
        return Err(Error::SqliteSingleThreadedMode);
    }

    // Now we know SQLite is _capable_ of being in Multi-thread of Serialized mode,
    // but it's possible someone configured it to be in Single-thread mode
    // before calling into us. That would mean we're exposing an unsafe API via
    // a safe one (in Rust terminology).
    //
    // We can ask SQLite for a mutex and check for
    // the magic value 8. This isn't documented, but it's what SQLite
    // returns for its mutex allocation function in Single-thread mode.
    const SQLITE_SINGLETHREADED_MUTEX_MAGIC: usize = 8;
    let is_singlethreaded = unsafe {
        let mutex_ptr = ffi::sqlite3_mutex_alloc(0);
        let is_singlethreaded = mutex_ptr as usize == SQLITE_SINGLETHREADED_MUTEX_MAGIC;
        ffi::sqlite3_mutex_free(mutex_ptr);
        is_singlethreaded
    };
    if is_singlethreaded {
        Err(Error::SqliteSingleThreadedMode)
    } else {
        Ok(())
    }
}