use std::io::BufRead;
use std::marker::PhantomData;

use super::CommonOptions;
use super::CopyFormat;
use super::CopyTarget;
use crate::deserialize::FromSqlRow;
#[cfg(feature = "postgres")]
use crate::pg::value::TypeOidLookup;
use crate::pg::Pg;
use crate::query_builder::QueryFragment;
use crate::query_builder::QueryId;
use crate::row::Row;
#[cfg(feature = "postgres")]
use crate::row::{self, Field, PartialRow, RowIndex, RowSealed};
use crate::AppearsOnTable;
use crate::Connection;
use crate::Expression;
use crate::QueryResult;
use crate::Selectable;

#[derive(Default, Debug)]
pub struct CopyToOptions {
    common: CommonOptions,
    header: Option<bool>,
}

impl CopyToOptions {
    fn any_set(&self) -> bool {
        self.common.any_set() || self.header.is_some()
    }
}

impl QueryFragment<Pg> for CopyToOptions {
    fn walk_ast<'b>(
        &'b self,
        mut pass: crate::query_builder::AstPass<'_, 'b, Pg>,
    ) -> crate::QueryResult<()> {
        if self.any_set() {
            let mut comma = "";
            pass.push_sql(" WITH (");
            self.common.walk_ast(pass.reborrow(), &mut comma);
            if let Some(header_is_set) = self.header {
                pass.push_sql(comma);
                // commented out because rustc complains otherwise
                //comma = ", ";
                pass.push_sql("HEADER ");
                pass.push_sql(if header_is_set { "1" } else { "0" });
            }

            pass.push_sql(")");
        }
        Ok(())
    }
}

#[derive(Debug)]
pub struct CopyToCommand<S> {
    options: CopyToOptions,
    p: PhantomData<S>,
}

impl<S> QueryId for CopyToCommand<S>
where
    S: CopyTarget,
{
    type QueryId = ();

    const HAS_STATIC_QUERY_ID: bool = false;
}

impl<S> QueryFragment<Pg> for CopyToCommand<S>
where
    S: CopyTarget,
{
    fn walk_ast<'b>(
        &'b self,
        mut pass: crate::query_builder::AstPass<'_, 'b, Pg>,
    ) -> crate::QueryResult<()> {
        pass.unsafe_to_cache_prepared();
        pass.push_sql("COPY ");
        S::walk_target(pass.reborrow())?;
        pass.push_sql(" TO STDOUT");
        self.options.walk_ast(pass.reborrow())?;
        Ok(())
    }
}

#[derive(Debug, Clone, Copy)]
pub struct NotSet;

pub trait CopyToMarker: Sized {
    fn setup_options<T>(q: CopyToQuery<T, Self>) -> CopyToQuery<T, CopyToOptions>;
}

impl CopyToMarker for NotSet {
    fn setup_options<T>(q: CopyToQuery<T, Self>) -> CopyToQuery<T, CopyToOptions> {
        CopyToQuery {
            target: q.target,
            options: CopyToOptions::default(),
        }
    }
}
impl CopyToMarker for CopyToOptions {
    fn setup_options<T>(q: CopyToQuery<T, Self>) -> CopyToQuery<T, CopyToOptions> {
        q
    }
}
/// The structure returned by [`copy_to`]
///
/// The [`load`] and the [`load_raw`] methods allow
/// to receive the configured data from the database.
/// If you don't have any special needs you should prefer using
/// the more convenient `load` method.
///
/// The `with_*` methods allow to configure the settings used for the
/// copy statement.
///
/// [`load`]: CopyToQuery::load
/// [`load_raw`]: CopyToQuery::load_raw
#[derive(Debug)]
#[must_use = "`COPY TO` statements are only executed when calling `.load()` or `load_raw()`."]
#[cfg(feature = "postgres_backend")]
pub struct CopyToQuery<T, O> {
    target: T,
    options: O,
}

#[cfg(feature = "postgres")]
struct CopyRow<'a> {
    buffers: Vec<Option<&'a [u8]>>,
    result: &'a crate::pg::connection::PgResult,
}

#[cfg(feature = "postgres")]
struct CopyField<'a> {
    field: &'a Option<&'a [u8]>,
    result: &'a crate::pg::connection::PgResult,
    col_idx: usize,
}

#[cfg(feature = "postgres")]
impl<'f> Field<'f, Pg> for CopyField<'f> {
    fn field_name(&self) -> Option<&str> {
        None
    }

    fn value(&self) -> Option<<Pg as crate::backend::Backend>::RawValue<'_>> {
        let value = self.field.as_deref()?;
        Some(crate::pg::PgValue::new_internal(value, self))
    }
}

#[cfg(feature = "postgres")]
impl<'a> TypeOidLookup for CopyField<'a> {
    fn lookup(&self) -> std::num::NonZeroU32 {
        self.result.column_type(self.col_idx)
    }
}

#[cfg(feature = "postgres")]
impl RowSealed for CopyRow<'_> {}

#[cfg(feature = "postgres")]
impl RowIndex<usize> for CopyRow<'_> {
    fn idx(&self, idx: usize) -> Option<usize> {
        if idx < self.field_count() {
            Some(idx)
        } else {
            None
        }
    }
}

#[cfg(feature = "postgres")]
impl<'a> RowIndex<&'a str> for CopyRow<'_> {
    fn idx(&self, _idx: &'a str) -> Option<usize> {
        None
    }
}

#[cfg(feature = "postgres")]
impl<'a> Row<'a, Pg> for CopyRow<'_> {
    type Field<'f> = CopyField<'f>
    where
        'a: 'f,
        Self: 'f;

    type InnerPartialRow = Self;

    fn field_count(&self) -> usize {
        self.buffers.len()
    }

    fn get<'b, I>(&'b self, idx: I) -> Option<Self::Field<'b>>
    where
        'a: 'b,
        Self: RowIndex<I>,
    {
        let idx = self.idx(idx)?;
        let buffer = self.buffers.get(idx)?;
        Some(CopyField {
            field: buffer,
            result: self.result,
            col_idx: idx,
        })
    }

    fn partial_row(
        &self,
        range: std::ops::Range<usize>,
    ) -> row::PartialRow<'_, Self::InnerPartialRow> {
        PartialRow::new(self, range)
    }
}

pub trait ExecuteCopyToConnection: Connection<Backend = Pg> {
    type CopyToBuffer<'a>: BufRead;

    fn make_row<'a, 'b>(
        out: &'a Self::CopyToBuffer<'_>,
        buffers: Vec<Option<&'a [u8]>>,
    ) -> impl Row<'b, Pg> + 'a;

    fn get_buffer<'a>(out: &'a Self::CopyToBuffer<'_>) -> &'a [u8];

    fn execute<T>(&mut self, command: CopyToCommand<T>) -> QueryResult<Self::CopyToBuffer<'_>>
    where
        T: CopyTarget;
}

#[cfg(feature = "postgres")]
impl ExecuteCopyToConnection for crate::PgConnection {
    type CopyToBuffer<'a> = crate::pg::connection::copy::CopyToBuffer<'a>;

    fn make_row<'a, 'b>(
        out: &'a Self::CopyToBuffer<'_>,
        buffers: Vec<Option<&'a [u8]>>,
    ) -> impl Row<'b, Pg> + 'a {
        CopyRow {
            buffers,
            result: out.get_result(),
        }
    }

    fn get_buffer<'a>(out: &'a Self::CopyToBuffer<'_>) -> &'a [u8] {
        out.data_slice()
    }

    fn execute<T>(&mut self, command: CopyToCommand<T>) -> QueryResult<Self::CopyToBuffer<'_>>
    where
        T: CopyTarget,
    {
        self.copy_to(command)
    }
}

#[cfg(feature = "r2d2")]
impl<C> ExecuteCopyToConnection for crate::r2d2::PooledConnection<crate::r2d2::ConnectionManager<C>>
where
    C: ExecuteCopyToConnection + crate::r2d2::R2D2Connection + 'static,
{
    type CopyToBuffer<'a> = C::CopyToBuffer<'a>;

    fn make_row<'a, 'b>(
        out: &'a Self::CopyToBuffer<'_>,
        buffers: Vec<Option<&'a [u8]>>,
    ) -> impl Row<'b, Pg> + 'a {
        C::make_row(out, buffers)
    }

    fn get_buffer<'a>(out: &'a Self::CopyToBuffer<'_>) -> &'a [u8] {
        C::get_buffer(out)
    }

    fn execute<'conn, T>(
        &'conn mut self,
        command: CopyToCommand<T>,
    ) -> QueryResult<Self::CopyToBuffer<'conn>>
    where
        T: CopyTarget,
    {
        C::execute(&mut **self, command)
    }
}

impl<T> CopyToQuery<T, NotSet>
where
    T: CopyTarget,
{
    /// Copy data from the database by returning an iterator of deserialized data
    ///
    /// This function allows to easily load data from the database via a `COPY TO` statement.
    /// It does **not** allow to configure any settings via the `with_*` method, as it internally
    /// sets the required options itself. It will use the binary format to deserialize the result
    /// into the specified type `U`. Column selection is performed via [`Selectable`].
    pub fn load<U, C>(self, conn: &mut C) -> QueryResult<impl Iterator<Item = QueryResult<U>> + '_>
    where
        U: FromSqlRow<<U::SelectExpression as Expression>::SqlType, Pg> + Selectable<Pg>,
        U::SelectExpression: AppearsOnTable<T::Table> + CopyTarget<Table = T::Table>,
        C: ExecuteCopyToConnection,
    {
        let io_result_mapper = |e| crate::result::Error::DeserializationError(Box::new(e));

        let command = CopyToCommand {
            p: PhantomData::<U::SelectExpression>,
            options: CopyToOptions {
                header: None,
                common: CommonOptions {
                    format: Some(CopyFormat::Binary),
                    ..Default::default()
                },
            },
        };
        // see https://www.postgresql.org/docs/current/sql-copy.html for
        // a description of the binary format
        //
        // We don't write oids

        let mut out = ExecuteCopyToConnection::execute(conn, command)?;
        let buffer = out.fill_buf().map_err(io_result_mapper)?;
        if buffer[..super::COPY_MAGIC_HEADER.len()] != super::COPY_MAGIC_HEADER {
            return Err(crate::result::Error::DeserializationError(
                "Unexpected protocol header".into(),
            ));
        }
        // we care only about bit 16-31 here, so we can just skip the bytes in between
        let flags_backward_incompatible = i16::from_be_bytes(
            (&buffer[super::COPY_MAGIC_HEADER.len() + 2..super::COPY_MAGIC_HEADER.len() + 4])
                .try_into()
                .expect("Exactly 2 byte"),
        );
        if flags_backward_incompatible != 0 {
            return Err(crate::result::Error::DeserializationError(
                format!("Unexpected flag value: {flags_backward_incompatible:x}").into(),
            ));
        }
        let header_size = i32::from_be_bytes(
            (&buffer[super::COPY_MAGIC_HEADER.len() + 4..super::COPY_MAGIC_HEADER.len() + 8])
                .try_into()
                .expect("Exactly 4 byte"),
        );
        out.consume(super::COPY_MAGIC_HEADER.len() + 8 + header_size as usize);
        let mut len = None;
        Ok(std::iter::from_fn(move || {
            if let Some(len) = len {
                out.consume(len);
                if let Err(e) = out.fill_buf().map_err(io_result_mapper) {
                    return Some(Err(e));
                }
            }
            let buffer = C::get_buffer(&out);
            len = Some(buffer.len());
            let tuple_count =
                i16::from_be_bytes((&buffer[..2]).try_into().expect("Exactly 2 bytes"));
            if tuple_count > 0 {
                let mut buffers = Vec::with_capacity(tuple_count as usize);
                let mut offset = 2;
                for _t in 0..tuple_count {
                    let data_size = i32::from_be_bytes(
                        (&buffer[offset..offset + 4])
                            .try_into()
                            .expect("Exactly 4 bytes"),
                    );
                    if data_size < 0 {
                        buffers.push(None);
                    } else {
                        buffers.push(Some(&buffer[offset + 4..offset + 4 + data_size as usize]));
                        offset = offset + 4 + data_size as usize;
                    }
                }

                let row = C::make_row(&out, buffers);
                Some(U::build_from_row(&row).map_err(crate::result::Error::DeserializationError))
            } else {
                None
            }
        }))
    }
}

impl<T, O> CopyToQuery<T, O>
where
    O: CopyToMarker,
    T: CopyTarget,
{
    /// Copy data from the database by directly accessing the provided response
    ///
    /// This function returns a type that implements [`std::io::BufRead`] which allows to directly read
    /// the data as provided by the database. The exact format depends on what options are
    /// set via the various `with_*` methods.
    pub fn load_raw<C>(self, conn: &mut C) -> QueryResult<impl BufRead + '_>
    where
        C: ExecuteCopyToConnection,
    {
        let q = O::setup_options(self);
        let command = CopyToCommand {
            p: PhantomData::<T>,
            options: q.options,
        };
        ExecuteCopyToConnection::execute(conn, command)
    }

    /// The format used for the copy statement
    ///
    /// See the [PostgreSQL documentation](https://www.postgresql.org/docs/current/sql-copy.html)
    /// for more details.
    pub fn with_format(self, format: CopyFormat) -> CopyToQuery<T, CopyToOptions> {
        let mut out = O::setup_options(self);
        out.options.common.format = Some(format);
        out
    }

    /// Whether or not the `freeze` option is set
    ///
    /// See the [PostgreSQL documentation](https://www.postgresql.org/docs/current/sql-copy.html)
    /// for more details.
    pub fn with_freeze(self, freeze: bool) -> CopyToQuery<T, CopyToOptions> {
        let mut out = O::setup_options(self);
        out.options.common.freeze = Some(freeze);
        out
    }

    /// Which delimiter should be used for textual output formats
    ///
    /// See the [PostgreSQL documentation](https://www.postgresql.org/docs/current/sql-copy.html)
    /// for more details.
    pub fn with_delimiter(self, delimiter: char) -> CopyToQuery<T, CopyToOptions> {
        let mut out = O::setup_options(self);
        out.options.common.delimiter = Some(delimiter);
        out
    }

    /// Which string should be used in place of a `NULL` value
    /// for textual output formats
    ///
    /// See the [PostgreSQL documentation](https://www.postgresql.org/docs/current/sql-copy.html)
    /// for more details.
    pub fn with_null(self, null: impl Into<String>) -> CopyToQuery<T, CopyToOptions> {
        let mut out = O::setup_options(self);
        out.options.common.null = Some(null.into());
        out
    }

    /// Which quote character should be used for textual output formats
    ///
    /// See the [PostgreSQL documentation](https://www.postgresql.org/docs/current/sql-copy.html)
    /// for more details.
    pub fn with_quote(self, quote: char) -> CopyToQuery<T, CopyToOptions> {
        let mut out = O::setup_options(self);
        out.options.common.quote = Some(quote);
        out
    }

    /// Which escape character should be used for textual output formats
    ///
    /// See the [PostgreSQL documentation](https://www.postgresql.org/docs/current/sql-copy.html)
    /// for more details.
    pub fn with_escape(self, escape: char) -> CopyToQuery<T, CopyToOptions> {
        let mut out = O::setup_options(self);
        out.options.common.escape = Some(escape);
        out
    }

    /// Is a header provided as part of the textual input or not
    ///
    /// See the [PostgreSQL documentation](https://www.postgresql.org/docs/current/sql-copy.html)
    /// for more details.
    pub fn with_header(self, set: bool) -> CopyToQuery<T, CopyToOptions> {
        let mut out = O::setup_options(self);
        out.options.header = Some(set);
        out
    }
}

/// Creates a `COPY TO` statement
///
/// This function constructs a `COPY TO` statement which copies data
/// from the database **to** a client side target. It's designed to move
/// larger amounts of data out of the database.
///
/// This function accepts a target selection (table name or list of columns) as argument.
///
/// There are two ways to use a `COPY TO` statement with diesel:
///
/// * By using [`CopyToQuery::load`] directly to load the deserialized result
///   directly into a specified type
/// * By using the `with_*` methods to configure the format sent by the database
///   and then by calling [`CopyToQuery::load_raw`] to receive the raw data
///   sent by the database.
///
/// The first variant uses the `BINARY` format internally to receive
/// the selected data efficiently. It automatically sets the right options
/// and does not allow to change them via `with_*` methods.
///
/// The second variant allows you to control the behaviour of the
/// generated `COPY TO` statement in detail. You can use the various
/// `with_*` methods for that before issuing the statement via [`CopyToQuery::load_raw`].
/// That method will return an type that implements [`std::io::BufRead`], which
/// allows you to directly read the response from the database in the configured
/// format.
/// See [the postgresql documentation](https://www.postgresql.org/docs/current/sql-copy.html)
/// for more details about the supported formats.
///
/// If you don't have any specific needs you should prefer using the more
/// convenient first variant.
///
/// This functionality is postgresql specific.
///
/// # Examples
///
/// ## Via [`CopyToQuery::load()`]
///
/// ```rust
/// # include!("../../../doctest_setup.rs");
/// # use crate::schema::users;
///
/// #[derive(Queryable, Selectable, PartialEq, Debug)]
/// #[diesel(table_name = users)]
/// #[diesel(check_for_backend(diesel::pg::Pg))]
/// struct User {
///     name: String,
/// }
///
/// # fn run_test() -> QueryResult<()> {
/// # let connection = &mut establish_connection();
/// let out = diesel::copy_to(users::table)
///     .load::<User, _>(connection)?
///     .collect::<Result<Vec<_>, _>>()?;
///
/// assert_eq!(out, vec![User{ name: "Sean".into() }, User{ name: "Tess".into() }]);
/// # Ok(())
/// # }
/// # fn main() {
/// #    run_test().unwrap();
/// # }
/// ```
///
/// ## Via [`CopyToQuery::load_raw()`]
///
/// ```rust
/// # include!("../../../doctest_setup.rs");
/// # fn run_test() -> QueryResult<()> {
/// # use crate::schema::users;
/// use diesel::pg::CopyFormat;
/// use std::io::Read;
/// # let connection = &mut establish_connection();
///
/// let mut copy = diesel::copy_to(users::table)
///     .with_format(CopyFormat::Csv)
///     .load_raw(connection)?;
///
/// let mut out = String::new();
/// copy.read_to_string(&mut out).unwrap();
/// assert_eq!(out, "1,Sean\n2,Tess\n");
/// # Ok(())
/// # }
/// # fn main() {
/// #    run_test().unwrap();
/// # }
/// ```
#[cfg(feature = "postgres_backend")]
pub fn copy_to<T>(target: T) -> CopyToQuery<T, NotSet>
where
    T: CopyTarget,
{
    CopyToQuery {
        target,
        options: NotSet,
    }
}