use std::collections::VecDeque;
use std::io::{Read, Seek};
use std::sync::Arc;

use polars_error::{PolarsResult, polars_bail, polars_err};
use polars_utils::aliases::PlHashMap;
use polars_utils::pl_str::PlSmallStr;

use super::Dictionaries;
use super::deserialize::{read, skip};
use crate::array::*;
use crate::datatypes::{ArrowDataType, ArrowSchema, Field};
use crate::io::ipc::read::OutOfSpecKind;
use crate::io::ipc::{IpcField, IpcSchema};
use crate::record_batch::RecordBatchT;

#[derive(Debug, Eq, PartialEq, Hash)]
enum ProjectionResult<A> {
    Selected(A),
    NotSelected(A),
}

/// An iterator adapter that will return `Some(x)` or `None`
/// # Panics
/// The iterator panics iff the `projection` is not strictly increasing.
struct ProjectionIter<'a, A, I: Iterator<Item = A>> {
    projection: &'a [usize],
    iter: I,
    current_count: usize,
    current_projection: usize,
}

impl<'a, A, I: Iterator<Item = A>> ProjectionIter<'a, A, I> {
    /// # Panics
    /// iff `projection` is empty
    pub fn new(projection: &'a [usize], iter: I) -> Self {
        Self {
            projection: &projection[1..],
            iter,
            current_count: 0,
            current_projection: projection[0],
        }
    }
}

impl<A, I: Iterator<Item = A>> Iterator for ProjectionIter<'_, A, I> {
    type Item = ProjectionResult<A>;

    fn next(&mut self) -> Option<Self::Item> {
        if let Some(item) = self.iter.next() {
            let result = if self.current_count == self.current_projection {
                if !self.projection.is_empty() {
                    assert!(self.projection[0] > self.current_projection);
                    self.current_projection = self.projection[0];
                    self.projection = &self.projection[1..];
                } else {
                    self.current_projection = 0 // a value that most likely already passed
                };
                Some(ProjectionResult::Selected(item))
            } else {
                Some(ProjectionResult::NotSelected(item))
            };
            self.current_count += 1;
            result
        } else {
            None
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

/// Returns a [`RecordBatchT`] from a reader.
/// # Panic
/// Panics iff the projection is not in increasing order (e.g. `[1, 0]` nor `[0, 1, 1]` are valid)
#[allow(clippy::too_many_arguments)]
pub fn read_record_batch<R: Read + Seek>(
    batch: arrow_format::ipc::RecordBatchRef,
    fields: &ArrowSchema,
    ipc_schema: &IpcSchema,
    projection: Option<&[usize]>,
    limit: Option<usize>,
    dictionaries: &Dictionaries,
    version: arrow_format::ipc::MetadataVersion,
    reader: &mut R,
    block_offset: u64,
    scratch: &mut Vec<u8>,
) -> PolarsResult<RecordBatchT<Box<dyn Array>>> {
    assert_eq!(fields.len(), ipc_schema.fields.len());
    let buffers = batch
        .buffers()
        .map_err(|err| polars_err!(oos = OutOfSpecKind::InvalidFlatbufferBuffers(err)))?
        .ok_or_else(|| polars_err!(oos = OutOfSpecKind::MissingMessageBuffers))?;
    let mut variadic_buffer_counts = batch
        .variadic_buffer_counts()
        .map_err(|err| polars_err!(oos = OutOfSpecKind::InvalidFlatbufferRecordBatches(err)))?
        .map(|v| v.iter().map(|v| v as usize).collect::<VecDeque<usize>>())
        .unwrap_or_else(VecDeque::new);
    let mut buffers: VecDeque<arrow_format::ipc::BufferRef> = buffers.iter().collect();

    let field_nodes = batch
        .nodes()
        .map_err(|err| polars_err!(oos = OutOfSpecKind::InvalidFlatbufferNodes(err)))?
        .ok_or_else(|| polars_err!(oos = OutOfSpecKind::MissingMessageNodes))?;
    let mut field_nodes = field_nodes.iter().collect::<VecDeque<_>>();

    let columns = if let Some(projection) = projection {
        let projection = ProjectionIter::new(
            projection,
            fields.iter_values().zip(ipc_schema.fields.iter()),
        );

        projection
            .map(|maybe_field| match maybe_field {
                ProjectionResult::Selected((field, ipc_field)) => Ok(Some(read(
                    &mut field_nodes,
                    &mut variadic_buffer_counts,
                    field,
                    ipc_field,
                    &mut buffers,
                    reader,
                    dictionaries,
                    block_offset,
                    ipc_schema.is_little_endian,
                    batch.compression().map_err(|err| {
                        polars_err!(oos = OutOfSpecKind::InvalidFlatbufferCompression(err))
                    })?,
                    limit,
                    version,
                    scratch,
                )?)),
                ProjectionResult::NotSelected((field, _)) => {
                    skip(
                        &mut field_nodes,
                        &field.dtype,
                        &mut buffers,
                        &mut variadic_buffer_counts,
                    )?;
                    Ok(None)
                },
            })
            .filter_map(|x| x.transpose())
            .collect::<PolarsResult<Vec<_>>>()?
    } else {
        fields
            .iter_values()
            .zip(ipc_schema.fields.iter())
            .map(|(field, ipc_field)| {
                read(
                    &mut field_nodes,
                    &mut variadic_buffer_counts,
                    field,
                    ipc_field,
                    &mut buffers,
                    reader,
                    dictionaries,
                    block_offset,
                    ipc_schema.is_little_endian,
                    batch.compression().map_err(|err| {
                        polars_err!(oos = OutOfSpecKind::InvalidFlatbufferCompression(err))
                    })?,
                    limit,
                    version,
                    scratch,
                )
            })
            .collect::<PolarsResult<Vec<_>>>()?
    };

    let length = batch
        .length()
        .map_err(|_| polars_err!(oos = OutOfSpecKind::MissingData))
        .unwrap()
        .try_into()
        .map_err(|_| polars_err!(oos = OutOfSpecKind::NegativeFooterLength))?;
    let length = limit.map(|limit| limit.min(length)).unwrap_or(length);

    let mut schema: ArrowSchema = fields.iter_values().cloned().collect();
    if let Some(projection) = projection {
        schema = schema.try_project_indices(projection).unwrap();
    }
    RecordBatchT::try_new(length, Arc::new(schema), columns)
}

fn find_first_dict_field_d<'a>(
    id: i64,
    dtype: &'a ArrowDataType,
    ipc_field: &'a IpcField,
) -> Option<(&'a Field, &'a IpcField)> {
    use ArrowDataType::*;
    match dtype.to_storage() {
        Dictionary(_, inner, _) => find_first_dict_field_d(id, inner.as_ref(), ipc_field),
        List(field) | LargeList(field) | FixedSizeList(field, ..) | Map(field, ..) => {
            find_first_dict_field(id, field.as_ref(), &ipc_field.fields[0])
        },
        Struct(fields) => {
            for (field, ipc_field) in fields.iter().zip(ipc_field.fields.iter()) {
                if let Some(f) = find_first_dict_field(id, field, ipc_field) {
                    return Some(f);
                }
            }
            None
        },
        Union(u) => {
            for (field, ipc_field) in u.fields.iter().zip(ipc_field.fields.iter()) {
                if let Some(f) = find_first_dict_field(id, field, ipc_field) {
                    return Some(f);
                }
            }
            None
        },
        _ => None,
    }
}

fn find_first_dict_field<'a>(
    id: i64,
    field: &'a Field,
    ipc_field: &'a IpcField,
) -> Option<(&'a Field, &'a IpcField)> {
    if let Some(field_id) = ipc_field.dictionary_id {
        if id == field_id {
            return Some((field, ipc_field));
        }
    }
    find_first_dict_field_d(id, &field.dtype, ipc_field)
}

pub(crate) fn first_dict_field<'a>(
    id: i64,
    fields: &'a ArrowSchema,
    ipc_fields: &'a [IpcField],
) -> PolarsResult<(&'a Field, &'a IpcField)> {
    assert_eq!(fields.len(), ipc_fields.len());
    for (field, ipc_field) in fields.iter_values().zip(ipc_fields.iter()) {
        if let Some(field) = find_first_dict_field(id, field, ipc_field) {
            return Ok(field);
        }
    }
    Err(polars_err!(
        oos = OutOfSpecKind::InvalidId { requested_id: id }
    ))
}

/// Reads a dictionary from the reader,
/// updating `dictionaries` with the resulting dictionary
#[allow(clippy::too_many_arguments)]
pub fn read_dictionary<R: Read + Seek>(
    batch: arrow_format::ipc::DictionaryBatchRef,
    fields: &ArrowSchema,
    ipc_schema: &IpcSchema,
    dictionaries: &mut Dictionaries,
    reader: &mut R,
    block_offset: u64,
    scratch: &mut Vec<u8>,
) -> PolarsResult<()> {
    if batch
        .is_delta()
        .map_err(|err| polars_err!(oos = OutOfSpecKind::InvalidFlatbufferIsDelta(err)))?
    {
        polars_bail!(ComputeError: "delta dictionary batches not supported")
    }

    let id = batch
        .id()
        .map_err(|err| polars_err!(oos = OutOfSpecKind::InvalidFlatbufferId(err)))?;
    let (first_field, first_ipc_field) = first_dict_field(id, fields, &ipc_schema.fields)?;

    let batch = batch
        .data()
        .map_err(|err| polars_err!(oos = OutOfSpecKind::InvalidFlatbufferData(err)))?
        .ok_or_else(|| polars_err!(oos = OutOfSpecKind::MissingData))?;

    let value_type =
        if let ArrowDataType::Dictionary(_, value_type, _) = first_field.dtype.to_storage() {
            value_type.as_ref()
        } else {
            polars_bail!(oos = OutOfSpecKind::InvalidIdDataType { requested_id: id })
        };

    // Make a fake schema for the dictionary batch.
    let fields = std::iter::once((
        PlSmallStr::EMPTY,
        Field::new(PlSmallStr::EMPTY, value_type.clone(), false),
    ))
    .collect();
    let ipc_schema = IpcSchema {
        fields: vec![first_ipc_field.clone()],
        is_little_endian: ipc_schema.is_little_endian,
    };
    let chunk = read_record_batch(
        batch,
        &fields,
        &ipc_schema,
        None,
        None, // we must read the whole dictionary
        dictionaries,
        arrow_format::ipc::MetadataVersion::V5,
        reader,
        block_offset,
        scratch,
    )?;

    dictionaries.insert(id, chunk.into_arrays().pop().unwrap());

    Ok(())
}

#[derive(Clone)]
pub struct ProjectionInfo {
    pub columns: Vec<usize>,
    pub map: PlHashMap<usize, usize>,
    pub schema: ArrowSchema,
}

pub fn prepare_projection(schema: &ArrowSchema, mut projection: Vec<usize>) -> ProjectionInfo {
    let schema = projection
        .iter()
        .map(|x| {
            let (k, v) = schema.get_at_index(*x).unwrap();
            (k.clone(), v.clone())
        })
        .collect();

    // todo: find way to do this more efficiently
    let mut indices = (0..projection.len()).collect::<Vec<_>>();
    indices.sort_unstable_by_key(|&i| &projection[i]);
    let map = indices.iter().copied().enumerate().fold(
        PlHashMap::default(),
        |mut acc, (index, new_index)| {
            acc.insert(index, new_index);
            acc
        },
    );
    projection.sort_unstable();

    // check unique
    if !projection.is_empty() {
        let mut previous = projection[0];

        for &i in &projection[1..] {
            assert!(
                previous < i,
                "The projection on IPC must not contain duplicates"
            );
            previous = i;
        }
    }

    ProjectionInfo {
        columns: projection,
        map,
        schema,
    }
}

pub fn apply_projection(
    chunk: RecordBatchT<Box<dyn Array>>,
    map: &PlHashMap<usize, usize>,
) -> RecordBatchT<Box<dyn Array>> {
    let length = chunk.len();

    // re-order according to projection
    let (schema, arrays) = chunk.into_schema_and_arrays();
    let mut new_schema = schema.as_ref().clone();
    let mut new_arrays = arrays.clone();

    map.iter().for_each(|(old, new)| {
        let (old_name, old_field) = schema.get_at_index(*old).unwrap();
        let (new_name, new_field) = new_schema.get_at_index_mut(*new).unwrap();

        *new_name = old_name.clone();
        *new_field = old_field.clone();

        new_arrays[*new] = arrays[*old].clone();
    });

    RecordBatchT::new(length, Arc::new(new_schema), new_arrays)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn project_iter() {
        let iter = 1..6;
        let iter = ProjectionIter::new(&[0, 2, 4], iter);
        let result: Vec<_> = iter.collect();
        use ProjectionResult::*;
        assert_eq!(
            result,
            vec![
                Selected(1),
                NotSelected(2),
                Selected(3),
                NotSelected(4),
                Selected(5)
            ]
        )
    }
}
