// SPDX-FileCopyrightText: edef <edef@unfathomable.blue>
// SPDX-License-Identifier: OSL-3.0

use {
	anyhow::{Context, Result},
	byteorder::{BigEndian, ByteOrder},
	prost::Message,
	sled::{transaction::ConflictableTransactionError, Transactional},
	std::{
		cell::{Cell, RefCell},
		collections::BTreeMap,
		fs,
		io::{self, Read, Write},
		os::unix::{fs::PermissionsExt, prelude::FileExt},
		path::Path,
	},
};

pub mod store {
	include!(concat!(env!("OUT_DIR"), "/fossil.store.rs"));
}

const CHUNK_BYTES: usize = 0x400;
const DIGEST_BYTES: usize = blake3::OUT_LEN;

pub struct Store {
	db: sled::Db,
	meta: sled::Tree,
	chunks: RefCell<fs::File>,
	chunks_tail: Cell<u64>,
}

impl Store {
	pub fn open(path: impl AsRef<Path>) -> Result<Store> {
		let path = path.as_ref();

		let db = sled::open(path)?;
		let meta = db.open_tree("meta")?;

		let chunks = fs::OpenOptions::new()
			.read(true)
			.append(true)
			.create(true)
			.open(path.join("chunks"))?;

		let chunks_tail = meta
			.get("chunks_tail")?
			.map(|v| BigEndian::read_u64(&v))
			.unwrap_or_default();

		chunks.set_len(chunks_tail)?;

		Ok(Store {
			db,
			meta,
			chunks: RefCell::new(chunks),
			chunks_tail: Cell::new(chunks_tail),
		})
	}

	pub fn add_path(&self, path: impl AsRef<Path>) -> Node {
		let path = path.as_ref();
		let meta = fs::symlink_metadata(path).unwrap();

		match meta.file_type() {
			ty if ty.is_dir() => {
				let mut d = Directory::new();
				let mut size: u32 = 0;

				for entry in path.read_dir().unwrap() {
					let entry = entry.unwrap();
					let name = entry.file_name().into_string().unwrap();

					let child = self.add_path(entry.path());
					size = size.checked_add(child.size()).expect("overflow");
					d.children.insert(name, child);
				}

				let blob = d.into_pb().encode_to_vec();

				Node::Directory(DirectoryRef {
					ident: self.write_blob(&blob),
					size,
				})
			}
			ty if ty.is_file() => {
				let executable = (meta.permissions().mode() & 0o100) != 0;

				let blob = fs::read(path).unwrap();
				Node::File(FileRef {
					executable,
					ident: self.write_blob(&blob),
					size: blob.len().try_into().expect("overflow"),
				})
			}
			ty if ty.is_symlink() => {
				let target = path
					.read_link()
					.unwrap()
					.to_str()
					.expect("symlink target is invalid UTF-8")
					.to_owned();

				Node::Link { target }
			}
			_ => panic!("not a symlink or a regular file"),
		}
	}

	fn write_blob(&self, data: &[u8]) -> Digest {
		let ident = {
			let mut h = blake3::Hasher::new();
			h.update_rayon(data);
			h.finalize()
		};

		if self.db.contains_key(&*ident.as_bytes()).unwrap() {
			// key already exists
			return ident;
		}

		let mut chunks_file = self.chunks.borrow_mut();
		let offset = self.chunks_tail.get();

		chunks_file.write_all(data).unwrap();
		let chunks_tail = offset + data.len() as u64;

		// TODO(edef): maybe don't use the default tree?
		// we should probably have a "blob" tree,
		// and reserve the default tree for DB metadata

		let slice = Slice {
			offset,
			length: data.len() as u64,
		};

		let slice_buf = {
			let mut buf = [0u8; 16];
			BigEndian::write_u64_into(&[slice.offset, slice.length], &mut buf);
			buf
		};

		let chunks_tail_buf = {
			let mut buf = [0u8; 8];
			BigEndian::write_u64(&mut buf, chunks_tail);
			buf
		};

		// TODO(edef): figure out fsync for durability
		(&*self.db, &self.meta)
			.transaction(|(db, meta)| {
				db.insert(&*ident.as_bytes(), &slice_buf)?;
				meta.insert("chunks_tail", &chunks_tail_buf)?;
				Ok::<_, ConflictableTransactionError>(())
			})
			.unwrap();
		self.chunks_tail.set(chunks_tail);

		ident.into()
	}

	pub fn read_blob(&self, ident: Digest) -> Vec<u8> {
		let mut buffer = Vec::new();
		self.raw_blob(ident).read_to_end(&mut buffer).unwrap();

		let mut outboard = Vec::new();
		let computed_ident: blake3::Hash = {
			let mut encoder = bao::encode::Encoder::new_outboard(io::Cursor::new(&mut outboard));
			encoder.write_all(&buffer).unwrap();
			encoder.finalize().unwrap()
		};

		if computed_ident != ident {
			panic!("hash mismatch");
		}

		buffer
	}

	fn raw_blob(&self, ident: Digest) -> RawBlob<'_> {
		let slice_buf = self
			.db
			.get(&*ident.as_bytes())
			.unwrap()
			.expect("blob not found");

		let slice = Slice {
			offset: BigEndian::read_u64(&slice_buf[0..]),
			length: BigEndian::read_u64(&slice_buf[8..]),
		};

		RawBlob {
			store: self,
			slice,
			position: 0,
		}
	}
}

/// a slice in the chunks file
#[derive(Debug)]
struct Slice {
	offset: u64,
	length: u64,
}

struct RawBlob<'a> {
	store: &'a Store,
	slice: Slice,
	position: u64,
}

impl io::Read for RawBlob<'_> {
	fn read(&mut self, dst: &mut [u8]) -> io::Result<usize> {
		let prev_pos = self.position;
		let next_pos = Ord::min(
			self.position.saturating_add(dst.len() as u64),
			self.slice.length,
		);

		let len = (next_pos - prev_pos) as usize;
		let dst = &mut dst[..len];

		let offset = self.slice.offset + prev_pos;
		self.store
			.chunks
			.borrow()
			.read_exact_at(dst, offset)
			.context("Couldn't read blob data")
			.map_err(|e| io::Error::new(io::ErrorKind::Other, e))?;

		self.position = next_pos;
		Ok(len)
	}
}

// TODO(edef): use checked_add_signed when mixed_integer_ops stabilises
fn checked_add_signed(lhs: u64, rhs: i64) -> Option<u64> {
	if rhs >= 0 {
		lhs.checked_add(rhs as u64)
	} else {
		lhs.checked_sub(rhs.unsigned_abs())
	}
}

impl io::Seek for RawBlob<'_> {
	fn seek(&mut self, pos: io::SeekFrom) -> io::Result<u64> {
		let pos = match pos {
			io::SeekFrom::Start(n) => Some(n),
			io::SeekFrom::End(n) => checked_add_signed(self.slice.length, n),
			io::SeekFrom::Current(n) => checked_add_signed(self.position, n),
		};

		match pos {
			Some(n) if n <= self.slice.length => {
				self.position = n;
				Ok(self.position)
			}
			_ => Err(io::Error::new(
				io::ErrorKind::InvalidInput,
				"seek out of range",
			)),
		}
	}

	fn rewind(&mut self) -> io::Result<()> {
		self.position = 0;
		Ok(())
	}

	fn stream_position(&mut self) -> io::Result<u64> {
		Ok(self.position)
	}
}

pub type Digest = blake3::Hash;

pub struct Directory {
	pub children: BTreeMap<String, Node>,
}

#[derive(Clone)]
pub enum Node {
	Directory(DirectoryRef),
	File(FileRef),
	Link { target: String },
}

#[derive(Clone)]
pub struct DirectoryRef {
	pub ident: Digest,
	pub size: u32,
}

#[derive(Debug, Clone)]
pub struct FileRef {
	pub ident: Digest,
	pub executable: bool,
	pub size: u32,
}

impl Node {
	fn size(&self) -> u32 {
		match self {
			&Node::Directory(DirectoryRef { size, .. }) => size.checked_add(1).expect("overflow"),
			_ => 1,
		}
	}
}

impl Directory {
	pub fn new() -> Directory {
		Directory {
			children: BTreeMap::new(),
		}
	}

	pub fn into_pb(self) -> store::Directory {
		let mut d = store::Directory::default();

		for (name, node) in self.children.into_iter() {
			match node {
				Node::Directory(DirectoryRef { ident, size }) => {
					d.directories.push(store::DirectoryNode {
						name,
						size,
						r#ref: ident.as_bytes().to_vec(),
					})
				}
				Node::File(FileRef {
					ident,
					executable,
					size,
				}) => d.files.push(store::FileNode {
					name,
					r#ref: ident.as_bytes().to_vec(),
					executable,
					size,
				}),
				Node::Link { target } => d.links.push(store::LinkNode { name, target }),
			}
		}

		d
	}

	pub fn from_pb(pb: store::Directory) -> Directory {
		let mut children = BTreeMap::new();

		for child in pb.directories {
			children.insert(
				child.name,
				Node::Directory(DirectoryRef {
					ident: digest_from_bytes(&child.r#ref),
					size: child.size,
				}),
			);
		}

		for child in pb.files {
			children.insert(
				child.name,
				Node::File(FileRef {
					ident: digest_from_bytes(&child.r#ref),
					executable: child.executable,
					size: child.size,
				}),
			);
		}

		for child in pb.links {
			children.insert(
				child.name,
				Node::Link {
					target: child.target,
				},
			);
		}

		Directory { children }
	}
}

#[track_caller]
pub fn digest_from_bytes(bytes: &[u8]) -> Digest {
	if bytes.len() != DIGEST_BYTES {
		panic!(
			"digest is {} bytes, expecting {} bytes",
			bytes.len(),
			DIGEST_BYTES
		);
	}

	let mut buffer = [0; DIGEST_BYTES];
	buffer.copy_from_slice(bytes);
	buffer.into()
}

#[test]
/// Write a blob, and read it back.
fn read_write() {
	let data = {
		let mut h = blake3::Hasher::new();
		h.update(b"test vector");

		let mut buf = Vec::new();
		h.finalize_xof().take(2468).read_to_end(&mut buf).unwrap();
		buf
	};

	// TODO(edef): use a temporary file
	let store = Store::open("fossil.db").unwrap();
	let ident = store.write_blob(&data);
	assert_eq!(data, store.read_blob(ident));
}