use super::{
    as_handle::AsHandle,
    bind::{CDataMut, HasDataType},
    buffer::{buf_ptr, clamp_small_int, mut_buf_ptr},
    column_description::{ColumnDescription, Nullability},
    data_type::DataType,
    drop_handle,
    error::{Error, IntoResult},
};
use odbc_sys::{
    Desc, FreeStmtOption, HDbc, HStmt, Handle, HandleType, Len, ParamType, Pointer, SQLBindCol,
    SQLBindParameter, SQLCloseCursor, SQLColAttributeW, SQLDescribeColW, SQLDescribeParam,
    SQLExecDirectW, SQLExecute, SQLFetch, SQLFreeStmt, SQLGetData, SQLNumResultCols, SQLPrepareW,
    SQLSetStmtAttrW, SqlDataType, SqlReturn, StatementAttribute, ULen,
};
use std::{convert::TryInto, ffi::c_void, marker::PhantomData, ptr::null_mut};
use widestring::U16Str;

/// Wraps a valid (i.e. successfully allocated) ODBC statement handle.
pub struct StatementImpl<'s> {
    parent: PhantomData<&'s HDbc>,
    handle: HStmt,
}

unsafe impl<'c> AsHandle for StatementImpl<'c> {
    fn as_handle(&self) -> Handle {
        self.handle as Handle
    }

    fn handle_type(&self) -> HandleType {
        HandleType::Stmt
    }
}

impl<'s> Drop for StatementImpl<'s> {
    fn drop(&mut self) {
        unsafe {
            drop_handle(self.handle as Handle, HandleType::Stmt);
        }
    }
}

impl<'s> StatementImpl<'s> {
    /// # Safety
    ///
    /// `handle` must be a valid (successfully allocated) statement handle.
    pub unsafe fn new(handle: HStmt) -> Self {
        Self {
            handle,
            parent: PhantomData,
        }
    }
}

/// An ODBC statement handle. In this crate it is implemented by [`self::StatementImpl`]. In ODBC
/// Statements are used to execute statements and retrieve results. Both paramater and result
/// buffers are bound to the statemend and dereferenced during statement execution and fetching
/// results.
///
/// The trait allows us to reason about statements without taking the lifetime of their connection
/// into account. It also allows for the trait to be implemented by a handle taking ownership of
/// both, the statement and the connection.
pub trait Statement {
    /// Binds application data buffers to columns in the result set.
    ///
    /// * `column_number`: `0` is the bookmark column. It is not included in some result sets. All
    /// other columns are numbered starting with `1`. It is an error to bind a higher-numbered
    /// column than there are columns in the result set. This error cannot be detected until the
    /// result set has been created, so it is returned by `fetch`, not `bind_col`.
    /// * `target_type`: The identifier of the C data type of the `value` buffer. When it is
    /// retrieving data from the data source with `fetch`, the driver converts the data to this
    /// type. When it sends data to the source, the driver converts the data from this type.
    /// * `target_value`: Pointer to the data buffer to bind to the column.
    /// * `target_length`: Length of target value in bytes. (Or for a single element in case of bulk
    /// aka. block fetching data).
    /// * `indicator`: Buffer is going to hold length or indicator values.
    ///
    /// # Safety
    ///
    /// It is the callers responsibility to make sure the bound columns live until they are no
    /// longer bound.
    unsafe fn bind_col(
        &mut self,
        column_number: u16,
        target: &mut impl CDataMut,
    ) -> Result<(), Error>;

    /// Returns the next row set in the result set.
    ///
    /// It can be called only while a result set exists: I.e., after a call that creates a result
    /// set and before the cursor over that result set is closed. If any columns are bound, it
    /// returns the data in those columns. If the application has specified a pointer to a row
    /// status array or a buffer in which to return the number of rows fetched, `fetch` also returns
    /// this information. Calls to `fetch` can be mixed with calls to `fetch_scroll`.
    ///
    /// # Safety
    ///
    /// Fetch dereferences bound column pointers.
    unsafe fn fetch(&mut self) -> Result<bool, Error>;

    /// Retrieves data for a single column in the result set or for a single parameter.
    fn get_data(&mut self, col_or_param_num: u16, target: &mut impl CDataMut) -> Result<(), Error>;

    /// Release all column buffers bound by `bind_col`. Except bookmark column.
    fn unbind_cols(&mut self) -> Result<(), Error>;

    /// Bind an integer to hold the number of rows retrieved with fetch in the current row set.
    /// Passing `None` for `num_rows` is going to unbind the value from the statement.
    ///
    /// # Safety
    ///
    /// `num_rows` must not be moved and remain valid, as long as it remains bound to the cursor.
    unsafe fn set_num_rows_fetched(&mut self, num_rows: Option<&mut ULen>) -> Result<(), Error>;

    /// Fetch a column description using the column index.
    ///
    /// # Parameters
    ///
    /// * `column_number`: Column index. `0` is the bookmark column. The other column indices start
    /// with `1`.
    /// * `column_description`: Holds the description of the column after the call. This method does
    /// not provide strong exception safety as the value of this argument is undefined in case of an
    /// error.
    fn describe_col(
        &self,
        column_number: u16,
        column_description: &mut ColumnDescription,
    ) -> Result<(), Error>;

    /// Executes a statement, using the current values of the parameter marker variables if any
    /// parameters exist in the statement. SQLExecDirect is the fastest way to submit an SQL
    /// statement for one-time execution.
    ///
    /// # Safety
    ///
    /// While `self` as always guaranteed to be a valid allocated handle, this function may
    /// dereference bound parameters. It is the callers responsibility to ensure these are still
    /// valid. One strategy is to reset potentially invalid parameters right before the call using
    /// `reset_parameters`.
    ///
    /// # Return
    ///
    /// If an update, insert, or delete statement did not affect any rows at the data source `false`
    /// is returned.
    unsafe fn exec_direct(&mut self, statement_text: &U16Str) -> Result<bool, Error>;

    /// Close an open cursor.
    fn close_cursor(&mut self) -> Result<(), Error>;

    /// Send an SQL statement to the data source for preparation. The application can include one or
    /// more parameter markers in the SQL statement. To include a parameter marker, the application
    /// embeds a question mark (?) into the SQL string at the appropriate position.
    fn prepare(&mut self, statement_text: &U16Str) -> Result<(), Error>;

    /// Executes a statement prepared by `prepare`. After the application processes or discards the
    /// results from a call to `execute`, the application can call SQLExecute again with new
    /// parameter values.
    ///
    /// # Safety
    ///
    /// While `self` as always guaranteed to be a valid allocated handle, this function may
    /// dereference bound parameters. It is the callers responsibility to ensure these are still
    /// valid. One strategy is to reset potentially invalid parameters right before the call using
    /// `reset_parameters`.
    ///
    /// # Return
    ///
    /// If an update, insert, or delete statement did not affect any rows at the data source `false`
    /// is returned.
    unsafe fn execute(&mut self) -> Result<bool, Error>;

    /// Number of columns in result set.
    ///
    /// Can also be used to check, whether or not a result set has been created at all.
    fn num_result_cols(&self) -> Result<i16, Error>;

    /// Sets the batch size for bulk cursors, if retrieving many rows at once.
    ///
    /// # Safety
    ///
    /// It is the callers responsibility to ensure that buffers bound using `bind_col` can hold the
    /// specified amount of rows.
    unsafe fn set_row_array_size(&mut self, size: u32) -> Result<(), Error>;

    /// Specifies the number of values for each parameter. If it is greater than 1, the data and
    /// indicator buffers of the statement point to arrays. The cardinality of each array is equal
    /// to the value of this field.
    ///
    /// # Safety
    ///
    /// The bound buffers must at least hold the number of elements specified in this call then the
    /// statement is executed.
    unsafe fn set_paramset_size(&mut self, size: u32) -> Result<(), Error>;

    /// Sets the binding type to columnar binding for batch cursors.
    ///
    /// Any Positive number indicates a row wise binding with that row length. `0` indicates a
    /// columnar binding.
    ///
    /// # Safety
    ///
    /// It is the callers responsibility to ensure that the bound buffers match the memory layout
    /// specified by this function.
    unsafe fn set_row_bind_type(&mut self, row_size: u32) -> Result<(), Error>;

    /// Binds a buffer holding an input parameter to a parameter marker in an SQL statement. This
    /// specialized version takes a constant reference to parameter, but is therefore limited to
    /// binding input parameters. See [`Statement::bind_parameter`] for the version which can bind
    /// input and output parameters.
    ///
    /// See <https://docs.microsoft.com/en-us/sql/odbc/reference/syntax/sqlbindparameter-function>.
    ///
    /// # Safety
    ///
    /// * It is up to the caller to ensure the lifetimes of the bound parameters.
    /// * Calling this function may influence other statements that share the APD.
    unsafe fn bind_input_parameter(
        &mut self,
        parameter_number: u16,
        parameter: &impl HasDataType,
    ) -> Result<(), Error>;

    /// Binds a buffer holding a single parameter to a parameter marker in an SQL statement. To bind
    /// input parameters using constant references see [`Statement::bind_input_parameter`].
    ///
    /// See <https://docs.microsoft.com/en-us/sql/odbc/reference/syntax/sqlbindparameter-function>.
    ///
    /// # Safety
    ///
    /// * It is up to the caller to ensure the lifetimes of the bound parameters.
    /// * Calling this function may influence other statements that share the APD.
    unsafe fn bind_parameter(
        &mut self,
        parameter_number: u16,
        input_output_type: ParamType,
        parameter: &mut (impl CDataMut + HasDataType),
    ) -> Result<(), Error>;

    /// `true` if a given column in a result set is unsigned or not a numeric type, `false`
    /// otherwise.
    ///
    /// `column_number`: Index of the column, starting at 1.
    fn is_unsigned_column(&self, column_number: u16) -> Result<bool, Error>;

    /// Returns a number identifying the SQL type of the column in the result set.
    ///
    /// `column_number`: Index of the column, starting at 1.
    fn col_type(&self, column_number: u16) -> Result<SqlDataType, Error>;

    /// The concise data type. For the datetime and interval data types, this field returns the
    /// concise data type; for example, `TIME` or `INTERVAL_YEAR`.
    ///
    /// `column_number`: Index of the column, starting at 1.
    fn col_concise_type(&self, column_number: u16) -> Result<SqlDataType, Error>;

    /// Data type of the specified column.
    ///
    /// `column_number`: Index of the column, starting at 1.
    fn col_data_type(&self, column_number: u16) -> Result<DataType, Error>;

    /// Returns the size in bytes of the columns. For variable sized types the maximum size is
    /// returned, excluding a terminating zero.
    ///
    /// `column_number`: Index of the column, starting at 1.
    fn col_octet_length(&self, column_number: u16) -> Result<Len, Error>;

    /// Maximum number of characters required to display data from the column.
    ///
    /// `column_number`: Index of the column, starting at 1.
    fn col_display_size(&self, column_number: u16) -> Result<Len, Error>;

    /// Precision of the column.
    ///
    /// Denotes the applicable precision. For data types SQL_TYPE_TIME, SQL_TYPE_TIMESTAMP, and all
    /// the interval data types that represent a time interval, its value is the applicable
    /// precision of the fractional seconds component.
    fn col_precision(&self, column_number: u16) -> Result<Len, Error>;

    /// The applicable scale for a numeric data type. For DECIMAL and NUMERIC data types, this is
    /// the defined scale. It is undefined for all other data types.
    fn col_scale(&self, column_number: u16) -> Result<Len, Error>;

    /// The column alias, if it applies. If the column alias does not apply, the column name is
    /// returned. If there is no column name or a column alias, an empty string is returned.
    fn col_name(&self, column_number: u16, buf: &mut Vec<u16>) -> Result<(), Error>;

    /// # Safety
    ///
    /// It is the callers responsibility to ensure that `attribute` refers to a numeric attribute.
    unsafe fn numeric_col_attribute(
        &self,
        attribute: Desc,
        column_number: u16,
    ) -> Result<Len, Error>;

    /// Sets the SQL_DESC_COUNT field of the APD to 0, releasing all parameter buffers set for the
    /// given StatementHandle.
    fn reset_parameters(&mut self) -> Result<(), Error>;

    /// Describes parameter marker associated with a prepared SQL statement.
    ///
    /// # Parameters
    ///
    /// * `parameter_number`: Parameter marker number ordered sequentially in increasing parameter
    ///   order, starting at 1.
    fn describe_param(&self, parameter_number: u16) -> Result<ParameterDescription, Error>;
}

impl<'o> Statement for StatementImpl<'o> {
    unsafe fn bind_col(
        &mut self,
        column_number: u16,
        target: &mut impl CDataMut,
    ) -> Result<(), Error> {
        SQLBindCol(
            self.handle,
            column_number,
            target.cdata_type(),
            target.mut_value_ptr(),
            target.buffer_length(),
            target.mut_indicator_ptr(),
        )
        .into_result(self)
    }

    unsafe fn fetch(&mut self) -> Result<bool, Error> {
        match SQLFetch(self.handle) {
            SqlReturn::NO_DATA => Ok(false),
            other => other.into_result(self).map(|()| true),
        }
    }

    fn get_data(&mut self, col_or_param_num: u16, target: &mut impl CDataMut) -> Result<(), Error> {
        unsafe {
            SQLGetData(
                self.handle,
                col_or_param_num,
                target.cdata_type(),
                target.mut_value_ptr(),
                target.buffer_length(),
                target.mut_indicator_ptr(),
            )
        }
        .into_result(self)
    }

    fn unbind_cols(&mut self) -> Result<(), Error> {
        unsafe { SQLFreeStmt(self.handle, FreeStmtOption::Unbind) }.into_result(self)
    }

    unsafe fn set_num_rows_fetched(&mut self, num_rows: Option<&mut ULen>) -> Result<(), Error> {
        let value = num_rows
            .map(|r| r as *mut ULen as Pointer)
            .unwrap_or_else(null_mut);
        SQLSetStmtAttrW(self.handle, StatementAttribute::RowsFetchedPtr, value, 0).into_result(self)
    }

    fn describe_col(
        &self,
        column_number: u16,
        column_description: &mut ColumnDescription,
    ) -> Result<(), Error> {
        let name = &mut column_description.name;
        // Use maximum available capacity.
        name.resize(name.capacity(), 0);
        let mut name_length: i16 = 0;
        let mut data_type = SqlDataType::UNKNOWN_TYPE;
        let mut column_size = 0;
        let mut decimal_digits = 0;
        let mut nullable = odbc_sys::Nullability::UNKNOWN;

        unsafe {
            SQLDescribeColW(
                self.handle,
                column_number,
                mut_buf_ptr(name),
                clamp_small_int(name.len()),
                &mut name_length,
                &mut data_type,
                &mut column_size,
                &mut decimal_digits,
                &mut nullable,
            )
            .into_result(self)?;
        }

        column_description.nullability = Nullability::new(nullable);

        if name_length + 1 > clamp_small_int(name.len()) {
            // Buffer is to small to hold name, retry with larger buffer
            name.resize(name_length as usize + 1, 0);
            self.describe_col(column_number, column_description)
        } else {
            name.resize(name_length as usize, 0);
            column_description.data_type = DataType::new(data_type, column_size, decimal_digits);
            Ok(())
        }
    }

    unsafe fn exec_direct(&mut self, statement_text: &U16Str) -> Result<bool, Error> {
        match SQLExecDirectW(
            self.handle,
            buf_ptr(statement_text.as_slice()),
            statement_text.len().try_into().unwrap(),
        ) {
            SqlReturn::NO_DATA => Ok(false),
            other => other.into_result(self).map(|()| true),
        }
    }

    fn close_cursor(&mut self) -> Result<(), Error> {
        unsafe { SQLCloseCursor(self.handle) }.into_result(self)
    }

    fn prepare(&mut self, statement_text: &U16Str) -> Result<(), Error> {
        unsafe {
            SQLPrepareW(
                self.handle,
                buf_ptr(statement_text.as_slice()),
                statement_text.len().try_into().unwrap(),
            )
        }
        .into_result(self)
    }

    /// Executes a statement prepared by `prepare`. After the application processes or discards the
    /// results from a call to `execute`, the application can call SQLExecute again with new
    /// parameter values.
    ///
    /// # Safety
    ///
    /// While `self` as always guaranteed to be a valid allocated handle, this function may
    /// dereference bound parameters. It is the callers responsibility to ensure these are still
    /// valid. One strategy is to reset potentially invalid parameters right before the call using
    /// `reset_parameters`.
    ///
    /// # Return
    ///
    /// If an update, insert, or delete statement did not affect any rows at the data source `false`
    /// is returned.
    unsafe fn execute(&mut self) -> Result<bool, Error> {
        match SQLExecute(self.handle) {
            SqlReturn::NO_DATA => Ok(false),
            other => other.into_result(self).map(|()| true),
        }
    }

    /// Number of columns in result set.
    ///
    /// Can also be used to check, whether or not a result set has been created at all.
    fn num_result_cols(&self) -> Result<i16, Error> {
        let mut out: i16 = 0;
        unsafe { SQLNumResultCols(self.handle, &mut out) }.into_result(self)?;
        Ok(out)
    }

    /// Sets the batch size for bulk cursors, if retrieving many rows at once.
    ///
    /// # Safety
    ///
    /// It is the callers responsibility to ensure that buffers bound using `bind_col` can hold the
    /// specified amount of rows.
    unsafe fn set_row_array_size(&mut self, size: u32) -> Result<(), Error> {
        assert!(size > 0);
        SQLSetStmtAttrW(
            self.handle,
            StatementAttribute::RowArraySize,
            size as Pointer,
            0,
        )
        .into_result(self)
    }

    /// Specifies the number of values for each parameter. If it is greater than 1, the data and
    /// indicator buffers of the statement point to arrays. The cardinality of each array is equal
    /// to the value of this field.
    ///
    /// # Safety
    ///
    /// The bound buffers must at least hold the number of elements specified in this call then the
    /// statement is executed.
    unsafe fn set_paramset_size(&mut self, size: u32) -> Result<(), Error> {
        assert!(size > 0);
        SQLSetStmtAttrW(
            self.handle,
            StatementAttribute::ParamsetSize,
            size as Pointer,
            0,
        )
        .into_result(self)
    }

    /// Sets the binding type to columnar binding for batch cursors.
    ///
    /// Any Positive number indicates a row wise binding with that row length. `0` indicates a
    /// columnar binding.
    ///
    /// # Safety
    ///
    /// It is the callers responsibility to ensure that the bound buffers match the memory layout
    /// specified by this function.
    unsafe fn set_row_bind_type(&mut self, row_size: u32) -> Result<(), Error> {
        SQLSetStmtAttrW(
            self.handle,
            StatementAttribute::RowBindType,
            row_size as Pointer,
            0,
        )
        .into_result(self)
    }

    /// Binds a buffer holding an input parameter to a parameter marker in an SQL statement. This
    /// specialized version takes a constant reference to parameter, but is therefore limited to
    /// binding input parameters. See [`Statement::bind_parameter`] for the version which can bind
    /// input and output parameters.
    ///
    /// See <https://docs.microsoft.com/en-us/sql/odbc/reference/syntax/sqlbindparameter-function>.
    ///
    /// # Safety
    ///
    /// * It is up to the caller to ensure the lifetimes of the bound parameters.
    /// * Calling this function may influence other statements that share the APD.
    unsafe fn bind_input_parameter(
        &mut self,
        parameter_number: u16,
        parameter: &impl HasDataType,
    ) -> Result<(), Error> {
        let parameter_type = parameter.data_type();
        SQLBindParameter(
            self.handle,
            parameter_number,
            ParamType::Input,
            parameter.cdata_type(),
            parameter_type.data_type(),
            parameter_type.column_size(),
            parameter_type.decimal_digits(),
            // We cast const to mut here, but we specify the input_output_type as input.
            parameter.value_ptr() as *mut c_void,
            parameter.buffer_length(),
            // We cast const to mut here, but we specify the input_output_type as input.
            parameter.indicator_ptr() as *mut Len,
        )
        .into_result(self)
    }

    /// Binds a buffer holding a single parameter to a parameter marker in an SQL statement. To bind
    /// input parameters using constant references see [`Statement::bind_input_parameter`].
    ///
    /// See <https://docs.microsoft.com/en-us/sql/odbc/reference/syntax/sqlbindparameter-function>.
    ///
    /// # Safety
    ///
    /// * It is up to the caller to ensure the lifetimes of the bound parameters.
    /// * Calling this function may influence other statements that share the APD.
    unsafe fn bind_parameter(
        &mut self,
        parameter_number: u16,
        input_output_type: ParamType,
        parameter: &mut (impl CDataMut + HasDataType),
    ) -> Result<(), Error> {
        let parameter_type = parameter.data_type();
        SQLBindParameter(
            self.handle,
            parameter_number,
            input_output_type,
            parameter.cdata_type(),
            parameter_type.data_type(),
            parameter_type.column_size(),
            parameter_type.decimal_digits(),
            parameter.value_ptr() as *mut c_void,
            parameter.buffer_length(),
            parameter.indicator_ptr() as *mut Len,
        )
        .into_result(self)
    }

    /// `true` if a given column in a result set is unsigned or not a numeric type, `false`
    /// otherwise.
    ///
    /// `column_number`: Index of the column, starting at 1.
    fn is_unsigned_column(&self, column_number: u16) -> Result<bool, Error> {
        let out = unsafe { self.numeric_col_attribute(Desc::Unsigned, column_number)? };
        match out {
            0 => Ok(false),
            1 => Ok(true),
            _ => panic!("Unsigned column attribute must be either 0 or 1."),
        }
    }

    /// Returns a number identifying the SQL type of the column in the result set.
    ///
    /// `column_number`: Index of the column, starting at 1.
    fn col_type(&self, column_number: u16) -> Result<SqlDataType, Error> {
        let out = unsafe { self.numeric_col_attribute(Desc::Type, column_number)? };
        Ok(SqlDataType(out.try_into().unwrap()))
    }

    /// The concise data type. For the datetime and interval data types, this field returns the
    /// concise data type; for example, `TIME` or `INTERVAL_YEAR`.
    ///
    /// `column_number`: Index of the column, starting at 1.
    fn col_concise_type(&self, column_number: u16) -> Result<SqlDataType, Error> {
        let out = unsafe { self.numeric_col_attribute(Desc::ConciseType, column_number)? };
        Ok(SqlDataType(out.try_into().unwrap()))
    }

    /// Data type of the specified column.
    ///
    /// `column_number`: Index of the column, starting at 1.
    fn col_data_type(&self, column_number: u16) -> Result<DataType, Error> {
        let kind = self.col_concise_type(column_number)?;
        let dt = match kind {
            SqlDataType::UNKNOWN_TYPE => DataType::Unknown,
            SqlDataType::EXT_VAR_BINARY => DataType::Varbinary {
                length: self.col_octet_length(column_number)?.try_into().unwrap(),
            },
            SqlDataType::EXT_BINARY => DataType::Binary {
                length: self.col_octet_length(column_number)?.try_into().unwrap(),
            },
            SqlDataType::EXT_W_VARCHAR => DataType::WVarchar {
                length: self.col_display_size(column_number)?.try_into().unwrap(),
            },
            SqlDataType::CHAR => DataType::Char {
                length: self.col_display_size(column_number)?.try_into().unwrap(),
            },
            SqlDataType::VARCHAR => DataType::Varchar {
                length: self.col_display_size(column_number)?.try_into().unwrap(),
            },
            SqlDataType::NUMERIC => DataType::Numeric {
                precision: self.col_precision(column_number)?.try_into().unwrap(),
                scale: self.col_scale(column_number)?.try_into().unwrap(),
            },
            SqlDataType::DECIMAL => DataType::Decimal {
                precision: self.col_precision(column_number)?.try_into().unwrap(),
                scale: self.col_scale(column_number)?.try_into().unwrap(),
            },
            SqlDataType::INTEGER => DataType::Integer,
            SqlDataType::SMALLINT => DataType::SmallInt,
            SqlDataType::FLOAT => DataType::Float,
            SqlDataType::REAL => DataType::Real,
            SqlDataType::DOUBLE => DataType::Double,
            SqlDataType::DATE => DataType::Date,
            SqlDataType::TIME => DataType::Time {
                precision: self.col_precision(column_number)?.try_into().unwrap(),
            },
            SqlDataType::TIMESTAMP => DataType::Timestamp {
                precision: self.col_precision(column_number)?.try_into().unwrap(),
            },
            SqlDataType::EXT_BIG_INT => DataType::BigInt,
            SqlDataType::EXT_TINY_INT => DataType::TinyInt,
            SqlDataType::EXT_BIT => DataType::Bit,
            other => {
                let mut column_size = 0;
                let mut decimal_digits = 0;
                let mut name_length = 0;
                let mut data_type = SqlDataType::UNKNOWN_TYPE;
                let mut nullable = odbc_sys::Nullability::UNKNOWN;

                unsafe {
                    SQLDescribeColW(
                        self.handle,
                        column_number,
                        null_mut(),
                        0,
                        &mut name_length,
                        &mut data_type,
                        &mut column_size,
                        &mut decimal_digits,
                        &mut nullable,
                    )
                    .into_result(self)?;
                }
                DataType::Other {
                    data_type: other,
                    column_size,
                    decimal_digits,
                }
            }
        };
        Ok(dt)
    }

    /// Returns the size in bytes of the columns. For variable sized types the maximum size is
    /// returned, excluding a terminating zero.
    ///
    /// `column_number`: Index of the column, starting at 1.
    fn col_octet_length(&self, column_number: u16) -> Result<Len, Error> {
        unsafe { self.numeric_col_attribute(Desc::OctetLength, column_number) }
    }

    /// Maximum number of characters required to display data from the column.
    ///
    /// `column_number`: Index of the column, starting at 1.
    fn col_display_size(&self, column_number: u16) -> Result<Len, Error> {
        unsafe { self.numeric_col_attribute(Desc::DisplaySize, column_number) }
    }

    /// Precision of the column.
    ///
    /// Denotes the applicable precision. For data types SQL_TYPE_TIME, SQL_TYPE_TIMESTAMP, and all
    /// the interval data types that represent a time interval, its value is the applicable
    /// precision of the fractional seconds component.
    fn col_precision(&self, column_number: u16) -> Result<Len, Error> {
        unsafe { self.numeric_col_attribute(Desc::Precision, column_number) }
    }

    /// The applicable scale for a numeric data type. For DECIMAL and NUMERIC data types, this is
    /// the defined scale. It is undefined for all other data types.
    fn col_scale(&self, column_number: u16) -> Result<Len, Error> {
        unsafe { self.numeric_col_attribute(Desc::Scale, column_number) }
    }

    /// The column alias, if it applies. If the column alias does not apply, the column name is
    /// returned. If there is no column name or a column alias, an empty string is returned.
    fn col_name(&self, column_number: u16, buf: &mut Vec<u16>) -> Result<(), Error> {
        // String length in bytes, not characters. Terminating zero is excluded.
        let mut string_length_in_bytes: i16 = 0;
        // Let's utilize all of `buf`s capacity.
        buf.resize(buf.capacity(), 0);
        unsafe {
            SQLColAttributeW(
                self.handle,
                column_number,
                Desc::Name,
                mut_buf_ptr(buf) as Pointer,
                (buf.len() * 2).try_into().unwrap(),
                &mut string_length_in_bytes as *mut i16,
                null_mut(),
            )
            .into_result(self)?;
            if clamp_small_int(buf.len() * 2) < string_length_in_bytes + 2 {
                buf.resize((string_length_in_bytes / 2 + 1).try_into().unwrap(), 0);
                SQLColAttributeW(
                    self.handle,
                    column_number,
                    Desc::Name,
                    mut_buf_ptr(buf) as Pointer,
                    (buf.len() * 2).try_into().unwrap(),
                    &mut string_length_in_bytes as *mut i16,
                    null_mut(),
                )
                .into_result(self)?;
            }
            // Resize buffer to exact string length without terminal zero
            buf.resize(((string_length_in_bytes + 1) / 2).try_into().unwrap(), 0);
        }
        Ok(())
    }

    /// # Safety
    ///
    /// It is the callers responsibility to ensure that `attribute` refers to a numeric attribute.
    unsafe fn numeric_col_attribute(
        &self,
        attribute: Desc,
        column_number: u16,
    ) -> Result<Len, Error> {
        let mut out: Len = 0;
        SQLColAttributeW(
            self.handle,
            column_number,
            attribute,
            null_mut(),
            0,
            null_mut(),
            &mut out as *mut Len,
        )
        .into_result(self)?;
        Ok(out)
    }

    /// Sets the SQL_DESC_COUNT field of the APD to 0, releasing all parameter buffers set for the
    /// given StatementHandle.
    fn reset_parameters(&mut self) -> Result<(), Error> {
        unsafe { SQLFreeStmt(self.handle, FreeStmtOption::ResetParams).into_result(self) }
    }

    /// Describes parameter marker associated with a prepared SQL statement.
    ///
    /// # Parameters
    ///
    /// * `parameter_number`: Parameter marker number ordered sequentially in increasing parameter
    ///   order, starting at 1.
    fn describe_param(&self, parameter_number: u16) -> Result<ParameterDescription, Error> {
        let mut data_type = SqlDataType::UNKNOWN_TYPE;
        let mut parameter_size = 0;
        let mut decimal_digits = 0;
        let mut nullable = odbc_sys::Nullability::UNKNOWN;
        unsafe {
            SQLDescribeParam(
                self.handle,
                parameter_number,
                &mut data_type,
                &mut parameter_size,
                &mut decimal_digits,
                &mut nullable,
            )
        }
        .into_result(self)?;

        Ok(ParameterDescription {
            data_type: DataType::new(data_type, parameter_size, decimal_digits),
            nullable: Nullability::new(nullable),
        })
    }
}

/// Description of a parameter associated with a parameter marker in a prepared statement. Returned
/// by [`crate::Prepared::describe_param`].
#[derive(Debug)]
pub struct ParameterDescription {
    // Todo: rename to nullability.
    /// Indicates wether the parameter may be NULL not.
    pub nullable: Nullability,
    /// The SQL Type associated with that parameter.
    pub data_type: DataType,
}