use async_trait::async_trait;
use rand::Rng;
use rand_pcg::Pcg64;
use rand_seeder::Seeder;
use std::fmt;
use minisql::operation::ColumnSelection;
use minisql::restricted_row::RestrictedRow;
use minisql::schema::{Column, TableSchema};
use proto::message::backend::{BackendMessage, ColumnDescription, CommandCompleteData, DataRowData, ErrorResponseData, ReadyForQueryData, RowDescriptionData};
use proto::message::primitive::pglist::PgList;
use proto::writer::backend::BackendProtoWriter;

pub enum CompleteStatus {
    Insert {
        oid: i32,
        rows: i32,
    },
    Delete(usize),
    Select(usize),
    CreateTable,
    CreateIndex,
}

impl fmt::Display for CompleteStatus {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            CompleteStatus::Insert { oid, rows } => write!(f, "INSERT {} {}", oid, rows),
            CompleteStatus::Delete(rows) => write!(f, "DELETE {}", rows),
            CompleteStatus::Select(rows) => write!(f, "SELECT {}", rows),
            CompleteStatus::CreateTable => write!(f, "CREATE TABLE"),
            CompleteStatus::CreateIndex => write!(f, "CREATE INDEX"),
        }
    }
}

#[async_trait]
pub trait ServerProto {
    async fn write_error_message(&mut self, error_message: &str) -> anyhow::Result<()>;
    async fn write_ready_for_query(&mut self) -> anyhow::Result<()>;
    async fn write_empty_query(&mut self) -> anyhow::Result<()>;
    async fn write_table_header(&mut self, table_schema: &TableSchema, columns: &ColumnSelection) -> anyhow::Result<()>;
    async fn write_table_row(&mut self, row: &RestrictedRow) -> anyhow::Result<()>;
    async fn write_command_complete(&mut self, status: CompleteStatus) -> anyhow::Result<()>;
}

#[async_trait]
impl<W> ServerProto for W where W: BackendProtoWriter + Send {
    async fn write_error_message(&mut self, error_message: &str) -> anyhow::Result<()> {
        self.write_proto(ErrorResponseData {
            code: b'M',
            message: format!("{error_message}\0").into(),
        }.into()).await?;

        Ok(())
    }

    async fn write_ready_for_query(&mut self) -> anyhow::Result<()> {
        self.write_proto(ReadyForQueryData { status: b'I' }.into()).await?;
        Ok(())
    }

    async fn write_empty_query(&mut self) -> anyhow::Result<()> {
        self.write_proto(BackendMessage::EmptyQueryResponse).await?;
        Ok(())
    }

    async fn write_table_header(&mut self, table_schema: &TableSchema, columns: &ColumnSelection) -> anyhow::Result<()> {
        let columns = columns.iter()
            .map(|column| column_to_description(table_schema, *column))
            .collect::<anyhow::Result<Vec<ColumnDescription>>>()?;

        self.write_proto(RowDescriptionData { columns: columns.into() }.into()).await?;
        Ok(())
    }

    async fn write_table_row(&mut self, row: &RestrictedRow) -> anyhow::Result<()> {
        let values = row.iter()
            .map(|(_, value)| value.as_text_bytes().into())
            .collect::<Vec<PgList<u8, i32>>>();

        self.write_proto(BackendMessage::DataRow(DataRowData {
            columns: values.into(),
        })).await?;
        Ok(())
    }

    async fn write_command_complete(&mut self, status: CompleteStatus) -> anyhow::Result<()> {
        self.write_proto(BackendMessage::CommandComplete(CommandCompleteData {
            tag: status.to_string().into(),
        })).await?;
        Ok(())
    }
}

fn column_to_description(schema: &TableSchema, column: Column) -> anyhow::Result<ColumnDescription> {
    let table_name = schema.table_name();
    let table_oid = table_name_to_oid(table_name);

    let column_type = schema.column_type(column);
    let name = schema.column_name_from_column(column);

    let column_index = column.try_into()?;
    let type_oid = column_type.type_oid();
    let type_size = column_type.type_size();

    Ok(ColumnDescription {
        name: name.to_string().into(),
        table_oid,
        column_index,
        type_oid,
        type_size,
        type_modifier: -1,
        format_code: 0, // text format
    })
}

/// Hashes the table name into single i32 used as a substitute for the table OID
/// in the PostgreSQL protocol.
fn table_name_to_oid(table_name: &str) -> i32 {
    let mut rng: Pcg64 = Seeder::from(table_name).make_rng();
    rng.gen::<i32>()
}