//! thin wrapper around the bits of sqlite we need. why not just use
//! [rusqlite](https://docs.rs/rusqlite) or similar? i ran into a minor annoyance with their API
//! and decided it would be fun to reinvent the wheel a bit and see how i could do. that said, this
//! implementation owes a great deal to theirs.
#![deny(clippy::undocumented_unsafe_blocks)]
#![deny(clippy::missing_safety_doc)]
#![deny(unsafe_op_in_unsafe_fn)]

use std::{
    cell::RefCell,
    ffi::{CString, c_char, c_int, c_uint},
    marker::PhantomData,
    mem::ManuallyDrop,
    ops::{Deref, DerefMut},
    ptr, slice,
    str::FromStr,
};

use libsqlite3_sys as ffi;

mod error;
mod from_sql;
mod params;

pub use error::{Error, GetError, GetResult, Result};
pub use from_sql::{FromSql, Value};
pub use params::{Param, Params};

fn version_number() -> i32 {
    // SAFETY: trivial wrapper
    unsafe { ffi::sqlite3_libversion_number() }
}

bitflags::bitflags! {
    #[derive(Clone, Copy, Debug)]
    #[repr(C)]
    pub struct OpenFlags: c_int {
        const READONLY = ffi::SQLITE_OPEN_READONLY;
        const READWRITE = ffi::SQLITE_OPEN_READWRITE;
        const CREATE = ffi::SQLITE_OPEN_CREATE;
        const URI = ffi::SQLITE_OPEN_URI;
        const MEMORY = ffi::SQLITE_OPEN_MEMORY;
        const NOMUTEX = ffi::SQLITE_OPEN_NOMUTEX;
        const NOFOLLOW = ffi::SQLITE_OPEN_NOFOLLOW;
        const EXRESCODE = ffi::SQLITE_OPEN_EXRESCODE;
    }
}

bitflags::bitflags! {
    #[derive(Clone, Copy, Debug, Default)]
    #[repr(C)]
    pub struct PrepFlags: c_uint {
        const PERSISTENT = ffi::SQLITE_PREPARE_PERSISTENT;
        const NO_VTAB = ffi::SQLITE_PREPARE_NO_VTAB;
        const DONT_LOG = ffi::SQLITE_PREPARE_DONT_LOG;
    }
}

impl Default for OpenFlags {
    fn default() -> Self {
        if version_number() > 3_037_000 {
            Self::READWRITE | Self::CREATE | Self::NOMUTEX | Self::URI | Self::EXRESCODE
        } else {
            Self::READWRITE | Self::CREATE | Self::NOMUTEX | Self::URI
        }
    }
}

pub struct Connection(RefCell<ConnectionInner>);

impl Connection {
    pub fn open(filename: &str) -> Result<Self> {
        Self::open_with_flags(filename, OpenFlags::default())
    }

    pub fn open_with_flags(filename: &str, flags: OpenFlags) -> Result<Self> {
        ConnectionInner::open(filename, flags)
            .map(RefCell::new)
            .map(Self)
    }

    pub fn prepare(&self, src: &str) -> Result<(Statement<'_>, usize)> {
        self.prepare_with_flags(src, PrepFlags::default())
    }

    pub fn prepare_with_flags(
        &self,
        src: &str,
        flags: PrepFlags,
    ) -> Result<(Statement<'_>, usize)> {
        self.prepare_raw(src, flags)
            .map(|(raw, read)| (Statement { raw, conn: self }, read))
    }

    pub fn prepare_raw(&self, src: &str, flags: PrepFlags) -> Result<(RawStatement, usize)> {
        self.0.borrow_mut().prepare_raw(src, flags)
    }

    fn get_error(&self) -> Error {
        self.0.borrow_mut().get_error()
    }

    fn decode_response(&self, code: c_int) -> Result<()> {
        self.0.borrow_mut().decode_response(code)
    }

    fn changes(&self) -> usize {
        self.0.borrow_mut().changes()
    }

    pub fn execute<P: Params>(&self, src: &str, params: P) -> Result<usize> {
        let (mut stmt, read) = self.prepare(src)?;
        if read != src.len() {
            Err(Error::MultipleStatements)
        } else {
            stmt.execute(params)
        }
    }
}

struct ConnectionInner {
    db: *mut ffi::sqlite3,
}

// SAFETY: ConnectionInner owns the underlying pointer, and all its methods are safe to call from
// different threads, just not more than one at a time.
unsafe impl Send for ConnectionInner {}

impl ConnectionInner {
    // we take &str and not &Path because 1. sqlite specifies that the argument should be
    // valid utf-8 and 2. there are valid inputs that aren't actually paths
    fn open(filename: &str, flags: OpenFlags) -> Result<Self> {
        let c_filename = CString::from_str(filename)?;

        let mut db: *mut ffi::sqlite3 = std::ptr::null_mut();
        let r =
        // SAFETY: we're mutating the pointer db, not dereferencing it, so we're good
            unsafe { ffi::sqlite3_open_v2(c_filename.as_ptr(), &mut db, flags.bits(), std::ptr::null()) };

        if r == ffi::SQLITE_OK {
            Ok(Self { db })
        } else if db.is_null() {
            Err(Error::from_code(r))
        } else {
            let e = Error::from_db(db);
            // SAFETY: db came from sqlite3_open_v2 and it's not null so we're good to close it
            let r = unsafe { ffi::sqlite3_close(db) };
            debug_assert_eq!(r, ffi::SQLITE_OK);
            Err(e)
        }
    }

    fn get_error(&mut self) -> Error {
        Error::from_db(self.db)
    }

    fn decode_response(&mut self, code: c_int) -> Result<()> {
        if code == ffi::SQLITE_OK {
            Ok(())
        } else {
            Err(self.get_error())
        }
    }

    fn changes(&mut self) -> usize {
        // SAFETY: this is only ever called immediately after executing a statement, and we're only
        // using the database connection from a single thread at a time, so the value should always
        // be good.
        (unsafe { ffi::sqlite3_changes(self.db) }) as usize
    }

    fn prepare_raw(&mut self, src: &str, flags: PrepFlags) -> Result<(RawStatement, usize)> {
        let mut stmt: *mut ffi::sqlite3_stmt = ptr::null_mut();
        let mut tail: *const c_char = ptr::null();

        // SAFETY: we know self.db hasn't been closed because we only close when we drop, and we
        // know &mut c_stmt isn't null because it's pointing to a thing we own. this upholds
        // sqlite's requirements
        self.decode_response(unsafe {
            ffi::sqlite3_prepare_v3(
                self.db,
                src.as_ptr().cast(),
                src.len() as c_int,
                flags.bits(),
                &mut stmt,
                &mut tail,
            )
        })?;

        if stmt.is_null() {
            Err(Error::EmptyStatement)
        } else {
            // SAFETY: sqlite guarantees that tail will point into src, so we know its address is >=
            let read = unsafe { tail.offset_from_unsigned(src.as_ptr().cast()) };
            Ok((RawStatement::new(stmt), read))
        }
    }
}

impl Drop for ConnectionInner {
    fn drop(&mut self) {
        // SAFETY: Connection always owns the underlying db, so can close it
        let r = unsafe { ffi::sqlite3_close(self.db) };
        debug_assert_eq!(r, ffi::SQLITE_OK);
    }
}

pub struct RawStatement {
    ptr: *mut ffi::sqlite3_stmt,
}

impl Drop for RawStatement {
    fn drop(&mut self) {
        // SAFETY: RawStatement owns its pointer so this should never double free
        unsafe { ffi::sqlite3_finalize(self.ptr) };
    }
}

impl RawStatement {
    fn new(ptr: *mut ffi::sqlite3_stmt) -> Self {
        Self { ptr }
    }

    /// # Safety
    ///
    /// the caller must ensure that `conn` is the database connection that was used to prepare the
    /// statement. this isn't unsafe in a strict sense, since the outcome of failing to uphold this
    /// invariant is just `MISUSE` errors for sqlite but still, don't do it!
    pub unsafe fn with_conn<'a>(&'a mut self, conn: &'a Connection) -> BorrowedStatement<'a> {
        // copying a type w/ a destructor is bad news, but we're immediately wrapping it to make
        // sure the destructor won't be called twice.
        let inner = ManuallyDrop::new(Statement {
            raw: Self { ptr: self.ptr },
            conn,
        });
        BorrowedStatement {
            marker: PhantomData,
            inner,
        }
    }
}

pub struct Statement<'a> {
    raw: RawStatement,
    conn: &'a Connection,
}

// lot of little wrapper functions that we know are safe because holding a borrow guarantees
// we're on the same thread as our database connection, and they don't have any safety requirements
// beyond that.
#[allow(clippy::undocumented_unsafe_blocks)]
impl<'a> Statement<'a> {
    fn ptr(&self) -> *mut ffi::sqlite3_stmt {
        self.raw.ptr
    }

    fn step(&mut self) -> c_int {
        unsafe { ffi::sqlite3_step(self.ptr()) }
    }

    fn column_type(&mut self, i: c_int) -> Result<c_int> {
        let count = unsafe { ffi::sqlite3_column_count(self.ptr()) };
        if i >= count || i < 0 {
            Err(Error::InvalidColumn(i))
        } else {
            Ok(unsafe { ffi::sqlite3_column_type(self.ptr(), i) })
        }
    }

    fn reset_inner(&mut self) -> c_int {
        unsafe { ffi::sqlite3_reset(self.ptr()) }
    }

    fn reset(&mut self) -> Result<()> {
        self.conn.decode_response(self.reset_inner())
    }

    fn bind_i32(&mut self, i: c_int, n: c_int) -> Result<()> {
        let r = unsafe { ffi::sqlite3_bind_int(self.ptr(), i, n) };
        self.conn.decode_response(r)
    }

    fn bind_i64(&mut self, i: c_int, n: i64) -> Result<()> {
        let r = unsafe { ffi::sqlite3_bind_int64(self.ptr(), i, n) };
        self.conn.decode_response(r)
    }

    fn bind_double(&mut self, i: c_int, f: f64) -> Result<()> {
        let r = unsafe { ffi::sqlite3_bind_double(self.ptr(), i, f) };
        self.conn.decode_response(r)
    }

    fn bind_null(&mut self, i: c_int) -> Result<()> {
        let r = unsafe { ffi::sqlite3_bind_null(self.ptr(), i) };
        self.conn.decode_response(r)
    }

    pub fn query<'q, P: Params>(&'q mut self, params: P) -> Result<Rows<'a, 'q>> {
        params.__bind_in(self)?;
        Ok(Rows::new(self))
    }

    pub fn execute<P: Params>(&mut self, params: P) -> Result<usize> {
        params.__bind_in(self)?;
        match self.step() {
            ffi::SQLITE_DONE => {
                self.reset()?;
                Ok(self.conn.changes())
            }
            ffi::SQLITE_ROW => {
                self.reset_inner();
                Err(Error::ExecReturnedRows)
            }
            _ => Err(self.conn.get_error()),
        }
    }
}

pub struct BorrowedStatement<'conn> {
    marker: PhantomData<&'conn mut RawStatement>,
    // using the raw pointer contained in here as a secret &'a mut RawStatement so we can make Deref
    // happy but that means we REALLY DONT WANNA DROP THIS bc we don't *actually* own the
    // underlying pointer
    inner: ManuallyDrop<Statement<'conn>>,
}

impl<'conn> Deref for BorrowedStatement<'conn> {
    type Target = Statement<'conn>;

    fn deref(&self) -> &Self::Target {
        &self.inner
    }
}

impl DerefMut for BorrowedStatement<'_> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.inner
    }
}

pub struct Rows<'conn, 'stmt> {
    stmt: &'stmt mut Statement<'conn>,
    // hate that this is necessary. should be able to get away with making stmt optional but get
    // stuck in borrow checker hell
    finished: bool,
}

impl<'a, 'q> Rows<'a, 'q> {
    fn new(stmt: &'q mut Statement<'a>) -> Self {
        Self {
            stmt,
            finished: false,
        }
    }

    pub fn try_next_row<'row>(&'row mut self) -> Result<Option<Row<'a, 'row>>> {
        if self.finished {
            return Ok(None);
        }

        match self.stmt.step() {
            ffi::SQLITE_ROW => Ok(Some(Row { stmt: self.stmt })),
            ffi::SQLITE_DONE => {
                self.finished = true;
                self.stmt.reset()?;
                Ok(None)
            }
            _ => {
                self.stmt.reset_inner();
                Err(self.stmt.conn.get_error())
            }
        }
    }
}

pub struct Row<'conn, 'row> {
    stmt: &'row mut Statement<'conn>,
}

impl<'row> Row<'_, 'row> {
    // should potentially add a "raw" variant of this that lets the caller just accept the sqlite
    // dynamic conversions
    fn get_value(&mut self, i: c_int) -> Result<Value<'row>> {
        let ptr = self.stmt.ptr();

        Ok(match self.stmt.column_type(i)? {
            ffi::SQLITE_INTEGER => Value::Int(
                // SAFETY: we've verified the type, ptr is valid, etc.
                unsafe { ffi::sqlite3_column_int64(ptr, i) },
            ),
            ffi::SQLITE_FLOAT => Value::Float(
                // SAFETY: same as above
                unsafe { ffi::sqlite3_column_double(ptr, i) },
            ),
            ffi::SQLITE_TEXT => {
                // SAFETY: same as above
                let data = unsafe { ffi::sqlite3_column_text(ptr, i) };
                if data.is_null() {
                    Value::Null
                } else {
                    // SAFETY: going through the criteria for from_raw_parts we have
                    // 1. we know data is non-null, and sqlite has assured us it's valid for len
                    //    bytes
                    // 2. utf-8 strings have no alignment requirements so that's fine
                    // 3. our lifetime restrictions should prevent the statement from being stepped
                    //    again before this reference goes out of scope, so it shouldn't be mutated
                    Value::Text(str::from_utf8(unsafe {
                        let len = ffi::sqlite3_column_bytes(ptr, i) as usize;
                        slice::from_raw_parts(data, len)
                    })?)
                }
            }
            ffi::SQLITE_BLOB => {
                // SAFETY: same as above
                let data: *const u8 = unsafe { ffi::sqlite3_column_blob(ptr, i) }.cast();
                if data.is_null() {
                    Value::Null
                } else {
                    // SAFETY: same as above
                    Value::Blob(unsafe {
                        let len = ffi::sqlite3_column_bytes(ptr, i) as usize;
                        slice::from_raw_parts(data, len)
                    })
                }
            }
            ffi::SQLITE_NULL => Value::Null,
            _ => unreachable!(),
        })
    }

    pub fn get<T: FromSql>(&mut self, col: c_int) -> GetResult<T> {
        let val = self.get_value(col)?;

        T::try_from_sql(val).map_err(GetError::FromSql)
    }
}