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use std::collections::HashMap;
use std::marker::PhantomData;

use super::stmt::StatementUse;
use deserialize::{FromSqlRow, Queryable, QueryableByName};
use result::Error::DeserializationError;
use result::QueryResult;
use sqlite::Sqlite;

pub struct StatementIterator<'a, ST, T> {
    stmt: StatementUse<'a>,
    _marker: PhantomData<(ST, T)>,
}

impl<'a, ST, T> StatementIterator<'a, ST, T> {
    pub fn new(stmt: StatementUse<'a>) -> Self {
        StatementIterator {
            stmt: stmt,
            _marker: PhantomData,
        }
    }
}

impl<'a, ST, T> Iterator for StatementIterator<'a, ST, T>
where
    T: Queryable<ST, Sqlite>,
{
    type Item = QueryResult<T>;

    fn next(&mut self) -> Option<Self::Item> {
        let row = match self.stmt.step() {
            Ok(row) => row,
            Err(e) => return Some(Err(e)),
        };
        row.map(|mut row| {
            T::Row::build_from_row(&mut row)
                .map(T::build)
                .map_err(DeserializationError)
        })
    }
}

pub struct NamedStatementIterator<'a, T> {
    stmt: StatementUse<'a>,
    // The actual lifetime of the stored column name is
    // not really `'a`, but it's impossible to have a better
    // fitting lifetime here.
    // See the `Statement::field_name` method for details
    // how long the underlying livetime is valid
    column_indices: Option<HashMap<&'a str, usize>>,
    _marker: PhantomData<T>,
}

impl<'a, T> NamedStatementIterator<'a, T> {
    #[allow(clippy::new_ret_no_self)]
    pub fn new(stmt: StatementUse<'a>) -> QueryResult<Self> {
        Ok(NamedStatementIterator {
            stmt,
            column_indices: None,
            _marker: PhantomData,
        })
    }

    fn populate_column_indices(&mut self) -> QueryResult<()> {
        let column_indices = (0..self.stmt.num_fields())
            .filter_map(|i| {
                self.stmt.field_name(i).map(|column| {
                    let column = column
                        .to_str()
                        .map_err(|e| DeserializationError(e.into()))?;
                    Ok((column, i))
                })
            })
            .collect::<QueryResult<_>>()?;

        self.column_indices = Some(column_indices);
        Ok(())
    }
}

impl<'a, T> Iterator for NamedStatementIterator<'a, T>
where
    T: QueryableByName<Sqlite>,
{
    type Item = QueryResult<T>;

    fn next(&mut self) -> Option<Self::Item> {
        let row = match self.stmt.step() {
            Ok(row) => row,
            Err(e) => return Some(Err(e)),
        };
        if self.column_indices.is_none() {
            if let Err(e) = self.populate_column_indices() {
                return Some(Err(e));
            }
        }
        row.map(|row| {
            let row = row.into_named(
                self.column_indices
                    .as_ref()
                    .expect("it's there because we populated it above"),
            );
            T::build(&row).map_err(DeserializationError)
        })
    }
}