use crate::{
    builder::encode_unixfs_pb,
    protobufs,
    types::Block,
    unixfs::{DataType, Node, UnixFsFile},
};
use anyhow::Result;
use async_stream::try_stream;
use bytes::Bytes;
use futures::{Stream, StreamExt};
use libipld::Cid;
use std::collections::VecDeque;
use wnfs_common::{utils::CondSend, BlockStore};

/// Default degree number for balanced tree, taken from unixfs specs
/// <https://github.com/ipfs/specs/blob/main/UNIXFS.md#layout>
pub const DEFAULT_DEGREE: usize = 174;

#[derive(Debug, PartialEq, Eq)]
pub enum TreeBuilder {
    /// TreeBuilder that builds a "balanced tree" with a max degree size of
    /// degree
    Balanced { degree: usize },
}

impl TreeBuilder {
    pub fn balanced_tree() -> Self {
        Self::balanced_tree_with_degree(DEFAULT_DEGREE)
    }

    pub fn balanced_tree_with_degree(degree: usize) -> Self {
        assert!(degree > 1);
        TreeBuilder::Balanced { degree }
    }

    pub fn stream_tree<'a>(
        &self,
        chunks: impl Stream<Item = std::io::Result<Bytes>> + CondSend + 'a,
        store: &'a impl BlockStore,
    ) -> impl Stream<Item = Result<(Cid, Block)>> + 'a {
        match self {
            TreeBuilder::Balanced { degree } => stream_balanced_tree(chunks, *degree, store),
        }
    }
}

#[derive(Clone, Debug, PartialEq)]
struct LinkInfo {
    raw_data_len: u64,
    encoded_len: u64,
}

fn stream_balanced_tree<'a>(
    in_stream: impl Stream<Item = std::io::Result<Bytes>> + CondSend + 'a,
    degree: usize,
    store: &'a impl BlockStore,
) -> impl Stream<Item = Result<(Cid, Block)>> + 'a {
    try_stream! {
        // degree = 8
        // VecDeque![ vec![] ]
        // ..
        // VecDeque![ vec![0, 1, 2, 3, 4, 5, 6, 7] ]
        // VecDeque![ vec![8], vec![p0] ]

        // ..

        // VecDeque![ vec![0, 1, 2, 3, 4, 5, 6, 7] vec![p0] ]
        // VecDeque![ vec![], vec![p0, p1]]

        // ..

        // VecDeque![ vec![0, 1, 2, 3, 4, 5, 6, 7] vec![p0, p1, p2, p3, p4, p5, p6, p7], ]
        // VecDeque![ vec![], vec![p0, p1, p2, p3, p4, p5, p6, p7], vec![] ]
        // VecDeque![ vec![8], vec![p8], vec![pp0] ]
        //
        // A vecdeque of vecs, the first vec representing the lowest layer of stem nodes
        // and the last vec representing the root node
        // Since we emit leaf and stem nodes as we go, we only need to keep track of the
        // most "recent" branch, storing the links to that node's children & yielding them
        // when each node reaches `degree` number of links
        let mut tree: VecDeque<Vec<(Cid, LinkInfo)>> = VecDeque::new();
        tree.push_back(Vec::with_capacity(degree));

        let in_stream = in_stream.map(|chunk| TreeNode::Leaf(chunk?).encode());

        tokio::pin!(in_stream);

        while let Some(chunk) = in_stream.next().await {
            let (block, link_info) = chunk?;
            let tree_len = tree.len();

            // check if the leaf node of the tree is full
            if tree[0].len() == degree {
                // if so, iterate through nodes
                for i in 0..tree_len {
                    // if we encounter any nodes that are not full, break
                    if tree[i].len() < degree {
                        break;
                    }

                    // in this case we have a full set of links & we are
                    // at the top of the tree. Time to make a new layer.
                    if i == tree_len - 1 {
                        tree.push_back(Vec::with_capacity(degree));
                    }

                    // create node, keeping the cid
                    let links = std::mem::replace(&mut tree[i], Vec::with_capacity(degree));
                    let (block, link_info) = TreeNode::Stem(links).encode()?;
                    let cid = block.store(store).await?;
                    yield (cid, block);

                    // add link_info to parent node
                    tree[i+1].push((cid, link_info));
                }
                // at this point the tree will be able to recieve new links
                // without "overflowing", aka the leaf node and stem nodes
                // have fewer than `degree` number of links
            }

            // now that we know the tree is in a "healthy" state to
            // recieve more links, add the link to the tree
            let cid = block.store(store).await?;
            tree[0].push((cid, link_info));
            yield (cid, block);
            // at this point, the leaf node may have `degree` number of
            // links, but no other stem node will
        }

        // our stream had 1 chunk that we have already yielded
        if tree.len() == 1 && tree[0].len() == 1 {
            return
        }

        // clean up, aka yield the rest of the stem nodes
        // since all the stem nodes are able to recieve links
        // we don't have to worry about "overflow"
        while let Some(links) = tree.pop_front() {
            let (block, link_info) = TreeNode::Stem(links).encode()?;
            let cid = block.store(store).await?;
            yield (cid, block);

            if let Some(front) = tree.front_mut() {
                front.push((cid, link_info));
            } else {
                // final root, nothing to do
            }
        }
    }
}

fn create_unixfs_node_from_links(links: Vec<(Cid, LinkInfo)>) -> Result<UnixFsFile> {
    let blocksizes: Vec<u64> = links.iter().map(|l| l.1.raw_data_len).collect();
    let filesize: u64 = blocksizes.iter().sum();
    let links = links
        .into_iter()
        .map(|(cid, l)| protobufs::PbLink {
            hash: Some(cid.to_bytes()),
            // ALL "stem" nodes have `name: None`.
            // In kubo, nodes that have links to `leaf` nodes have `name: Some("".to_string())`
            name: None,
            // tsize has no strict definition
            // Iroh's definiton of `tsize` is "the cumulative size of the encoded tree
            // pointed to by this link", so not just the size of the raw content, but including
            // all encoded dag nodes as well.
            // In the `go-merkledag` package, the `merkledag.proto` file, states that tsize
            // is the "cumulative size of the target object"
            // (https://github.com/ipfs/go-merkledag/blob/8335efd4765ed5a512baa7e522c3552d067cf966/pb/merkledag.proto#L29)
            tsize: Some(l.encoded_len),
        })
        .collect();

    // PBNode.Data
    let inner = protobufs::Data {
        r#type: DataType::File as i32,
        // total size of the raw data this node points to
        filesize: Some(filesize),
        // sizes of the raw data pointed to by each link in this node
        blocksizes,
        ..Default::default()
    };

    // create PBNode
    let outer = encode_unixfs_pb(&inner, links)?;

    // create UnixfsNode
    Ok(UnixFsFile::Node(Node { inner, outer }))
}

// Leaf and Stem nodes are the two types of nodes that can exist in the tree
// Leaf nodes encode to `UnixfsNode::Raw`
// Stem nodes encode to `UnixfsNode::File`
enum TreeNode {
    Leaf(Bytes),
    Stem(Vec<(Cid, LinkInfo)>),
}

impl TreeNode {
    fn encode(self) -> Result<(Block, LinkInfo)> {
        match self {
            TreeNode::Leaf(bytes) => {
                let len = bytes.len();
                let node = UnixFsFile::Raw(bytes);
                let block = node.encode()?;
                let link_info = LinkInfo {
                    // in a leaf the raw data len and encoded len are the same since our leaf
                    // nodes are raw unixfs nodes
                    raw_data_len: len as u64,
                    encoded_len: len as u64,
                };
                Ok((block, link_info))
            }
            TreeNode::Stem(links) => {
                let mut encoded_len: u64 = links.iter().map(|(_, l)| l.encoded_len).sum();
                let node = create_unixfs_node_from_links(links)?;
                let block = node.encode()?;
                encoded_len += block.data().len() as u64;
                let raw_data_len = node
                    .filesize()
                    .expect("UnixfsNode::File will have a filesize");
                Ok((
                    block,
                    LinkInfo {
                        raw_data_len,
                        encoded_len,
                    },
                ))
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use bytes::BytesMut;
    use futures::StreamExt;
    use wnfs_common::MemoryBlockStore;

    // chunks are just a single usize integer
    const CHUNK_SIZE: u64 = std::mem::size_of::<usize>() as u64;

    fn test_chunk_stream(num_chunks: usize) -> impl Stream<Item = std::io::Result<Bytes>> {
        futures::stream::iter((0..num_chunks).map(|n| Ok(n.to_be_bytes().to_vec().into())))
    }

    async fn build_expect_tree(num_chunks: usize, degree: usize) -> Vec<Vec<(Cid, Block)>> {
        let store = &MemoryBlockStore::new();
        let chunks = test_chunk_stream(num_chunks);
        tokio::pin!(chunks);
        let mut tree = vec![vec![]];
        let mut links = vec![vec![]];

        if num_chunks / degree == 0 {
            let chunk = chunks.next().await.unwrap().unwrap();
            let leaf = TreeNode::Leaf(chunk);
            let (block, _) = leaf.encode().unwrap();
            let cid = block.store(store).await.unwrap();
            tree[0].push((cid, block));
            return tree;
        }

        while let Some(chunk) = chunks.next().await {
            let chunk = chunk.unwrap();
            let leaf = TreeNode::Leaf(chunk);
            let (block, link_info) = leaf.encode().unwrap();
            let cid = block.store(store).await.unwrap();
            links[0].push((cid, link_info));
            tree[0].push((cid, block));
        }

        while tree.last().unwrap().len() > 1 {
            let prev_layer = links.last().unwrap();
            let count = prev_layer.len() / degree;
            let mut tree_layer = Vec::with_capacity(count);
            let mut links_layer = Vec::with_capacity(count);
            for links in prev_layer.chunks(degree) {
                let stem = TreeNode::Stem(links.to_vec());
                let (block, link_info) = stem.encode().unwrap();
                let cid = block.store(store).await.unwrap();
                links_layer.push((cid, link_info));
                tree_layer.push((cid, block));
            }
            tree.push(tree_layer);
            links.push(links_layer);
        }
        tree
    }

    async fn build_expect_vec_from_tree(
        tree: Vec<Vec<(Cid, Block)>>,
        num_chunks: usize,
        degree: usize,
    ) -> Vec<(Cid, Block)> {
        let mut out = vec![];

        if num_chunks == 1 {
            out.push(tree[0][0].clone());
            return out;
        }

        let mut counts = vec![0; tree.len()];

        for leaf in tree[0].iter() {
            out.push(leaf.clone());
            counts[0] += 1;
            let mut push = counts[0] % degree == 0;
            for (num_layer, count) in counts.iter_mut().enumerate() {
                if num_layer == 0 {
                    continue;
                }
                if !push {
                    break;
                }
                out.push(tree[num_layer][*count].clone());
                *count += 1;
                if *count % degree != 0 {
                    push = false;
                }
            }
        }

        for (num_layer, count) in counts.into_iter().enumerate() {
            if num_layer == 0 {
                continue;
            }
            let layer = tree[num_layer].clone();
            for node in layer.into_iter().skip(count) {
                out.push(node);
            }
        }

        out
    }

    async fn build_expect(num_chunks: usize, degree: usize) -> Vec<(Cid, Block)> {
        let tree = build_expect_tree(num_chunks, degree).await;
        println!("{tree:?}");
        build_expect_vec_from_tree(tree, num_chunks, degree).await
    }

    async fn make_leaf(data: usize, store: &impl BlockStore) -> (Cid, Block, LinkInfo) {
        let (block, link_info) = TreeNode::Leaf(BytesMut::from(&data.to_be_bytes()[..]).freeze())
            .encode()
            .unwrap();
        let cid = block.store(store).await.unwrap();
        (cid, block, link_info)
    }

    async fn make_stem(
        links: Vec<(Cid, LinkInfo)>,
        store: &impl BlockStore,
    ) -> (Cid, Block, LinkInfo) {
        let (block, link_info) = TreeNode::Stem(links).encode().unwrap();
        let cid = block.store(store).await.unwrap();
        (cid, block, link_info)
    }

    #[tokio::test]
    async fn test_build_expect() {
        let store = &MemoryBlockStore::new();
        // manually build tree made of 7 chunks (11 total nodes)
        let (leaf_0_cid, leaf_0, len_0) = make_leaf(0, store).await;
        let (leaf_1_cid, leaf_1, len_1) = make_leaf(1, store).await;
        let (leaf_2_cid, leaf_2, len_2) = make_leaf(2, store).await;
        let (stem_0_cid, stem_0, stem_len_0) = make_stem(
            vec![
                (leaf_0_cid, len_0),
                (leaf_1_cid, len_1),
                (leaf_2_cid, len_2),
            ],
            store,
        )
        .await;
        let (leaf_3_cid, leaf_3, len_3) = make_leaf(3, store).await;
        let (leaf_4_cid, leaf_4, len_4) = make_leaf(4, store).await;
        let (leaf_5_cid, leaf_5, len_5) = make_leaf(5, store).await;
        let (stem_1_cid, stem_1, stem_len_1) = make_stem(
            vec![
                (leaf_3_cid, len_3),
                (leaf_4_cid, len_4),
                (leaf_5_cid, len_5),
            ],
            store,
        )
        .await;
        let (leaf_6_cid, leaf_6, len_6) = make_leaf(6, store).await;
        let (stem_2_cid, stem_2, stem_len_2) = make_stem(vec![(leaf_6_cid, len_6)], store).await;
        let (root_cid, root, _root_len) = make_stem(
            vec![
                (stem_0_cid, stem_len_0),
                (stem_1_cid, stem_len_1),
                (stem_2_cid, stem_len_2),
            ],
            store,
        )
        .await;

        let expect_tree = vec![
            vec![
                (leaf_0_cid, leaf_0.clone()),
                (leaf_1_cid, leaf_1.clone()),
                (leaf_2_cid, leaf_2.clone()),
                (leaf_3_cid, leaf_3.clone()),
                (leaf_4_cid, leaf_4.clone()),
                (leaf_5_cid, leaf_5.clone()),
                (leaf_6_cid, leaf_6.clone()),
            ],
            vec![
                (stem_0_cid, stem_0.clone()),
                (stem_1_cid, stem_1.clone()),
                (stem_2_cid, stem_2.clone()),
            ],
            vec![(root_cid, root.clone())],
        ];
        let got_tree = build_expect_tree(7, 3).await;
        assert_eq!(expect_tree, got_tree);

        let expect_vec = vec![
            (leaf_0_cid, leaf_0),
            (leaf_1_cid, leaf_1),
            (leaf_2_cid, leaf_2),
            (stem_0_cid, stem_0),
            (leaf_3_cid, leaf_3),
            (leaf_4_cid, leaf_4),
            (leaf_5_cid, leaf_5),
            (stem_1_cid, stem_1),
            (leaf_6_cid, leaf_6),
            (stem_2_cid, stem_2),
            (root_cid, root),
        ];
        let got_vec = build_expect_vec_from_tree(got_tree, 7, 3).await;
        assert_eq!(expect_vec, got_vec);
    }

    async fn ensure_equal(
        expect: Vec<(Cid, Block)>,
        got: impl Stream<Item = Result<(Cid, Block)>>,
        expected_filesize: u64,
    ) {
        let mut i = 0;
        tokio::pin!(got);
        let mut got_filesize = 0;
        let mut expected_tsize = 0;
        let mut got_tsize = 0;
        while let Some(node) = got.next().await {
            let (expect_cid, expect_block) = expect
                .get(i)
                .expect("too many nodes in balanced tree stream")
                .clone();
            let (got_cid, got_block) = node.expect("unexpected error in balanced tree stream");
            let len = got_block.data().len() as u64;
            println!("node index {i}");
            assert_eq!(expect_cid, got_cid);
            assert_eq!(expect_block.data(), got_block.data());
            i += 1;
            let expect_node = UnixFsFile::decode(&expect_cid, expect_block.data().clone()).unwrap();
            let got_node = UnixFsFile::decode(&got_cid, got_block.data().clone()).unwrap();
            if let Some(DataType::File) = got_node.typ() {
                assert_eq!(
                    got_node.filesize().unwrap(),
                    got_node.blocksizes().iter().sum::<u64>()
                );
            }
            assert_eq!(expect_node, got_node);
            if expect.len() == i {
                let node = UnixFsFile::decode(&got_cid, got_block.data().clone()).unwrap();
                got_tsize = node.links().map(|l| l.unwrap().tsize.unwrap()).sum();
                got_filesize = got_node.filesize().unwrap();
            } else {
                expected_tsize += len;
            }
        }
        if expect.len() != i {
            panic!(
                "expected at {} nodes of the stream, got {}",
                expect.len(),
                i
            );
        }
        assert_eq!(expected_filesize, got_filesize);
        assert_eq!(expected_tsize, got_tsize);
    }

    #[tokio::test]
    async fn balanced_tree_test_leaf() {
        let store = &MemoryBlockStore::new();
        let num_chunks = 1;
        let expect = build_expect(num_chunks, 3).await;
        let got = stream_balanced_tree(test_chunk_stream(1), 3, store);
        tokio::pin!(got);
        ensure_equal(expect, got, num_chunks as u64 * CHUNK_SIZE).await;
    }

    #[tokio::test]
    async fn balanced_tree_test_height_one() {
        let store = &MemoryBlockStore::new();
        let num_chunks = 3;
        let degrees = 3;
        let expect = build_expect(num_chunks, degrees).await;
        let got = stream_balanced_tree(test_chunk_stream(num_chunks), degrees, store);
        tokio::pin!(got);
        ensure_equal(expect, got, num_chunks as u64 * CHUNK_SIZE).await;
    }

    #[tokio::test]
    async fn balanced_tree_test_height_two_full() {
        let store = &MemoryBlockStore::new();
        let degrees = 3;
        let num_chunks = 9;
        let expect = build_expect(num_chunks, degrees).await;
        let got = stream_balanced_tree(test_chunk_stream(num_chunks), degrees, store);
        tokio::pin!(got);
        ensure_equal(expect, got, num_chunks as u64 * CHUNK_SIZE).await;
    }

    #[tokio::test]
    async fn balanced_tree_test_height_two_not_full() {
        let store = &MemoryBlockStore::new();
        let degrees = 3;
        let num_chunks = 10;
        let expect = build_expect(num_chunks, degrees).await;
        let got = stream_balanced_tree(test_chunk_stream(num_chunks), degrees, store);
        tokio::pin!(got);
        ensure_equal(expect, got, num_chunks as u64 * CHUNK_SIZE).await;
    }

    #[tokio::test]
    async fn balanced_tree_test_height_three() {
        let store = &MemoryBlockStore::new();
        let num_chunks = 125;
        let degrees = 5;
        let expect = build_expect(num_chunks, degrees).await;
        let got = stream_balanced_tree(test_chunk_stream(num_chunks), degrees, store);
        tokio::pin!(got);
        ensure_equal(expect, got, num_chunks as u64 * CHUNK_SIZE).await;
    }

    #[tokio::test]
    async fn balanced_tree_test_large() {
        let store = &MemoryBlockStore::new();
        let num_chunks = 780;
        let degrees = 11;
        let expect = build_expect(num_chunks, degrees).await;
        let got = stream_balanced_tree(test_chunk_stream(num_chunks), degrees, store);
        tokio::pin!(got);
        ensure_equal(expect, got, num_chunks as u64 * CHUNK_SIZE).await;
    }
}