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

use {
	fossil::store,
	lazy_static::lazy_static,
	libc::{c_int, EINVAL, ENOENT, ENOSYS, EROFS},
	log::debug,
	prost::Message,
	std::{
		io::{self, Read},
		time::{Duration, SystemTime, UNIX_EPOCH},
	},
};

lazy_static! {
	static ref EPOCH_PLUS_ONE: SystemTime = UNIX_EPOCH + Duration::from_secs(1);
}

fn file_attr(ino: u64, node: &memtree::Node) -> fuser::FileAttr {
	let size = match node {
		memtree::Node::Directory(d) => d.len() as u64,
		memtree::Node::File(f) => f.size as u64,
		memtree::Node::Link { target } => target.len() as u64,
	};

	let blksize = 512;
	fuser::FileAttr {
		// Inode number
		ino,
		// Size in bytes
		size,
		// Size in blocks
		// TODO(edef): switch to u64::div_ceil
		blocks: (size + blksize as u64 - 1) / (blksize as u64),
		// Time of last access
		atime: *EPOCH_PLUS_ONE,
		// Time of last modification
		mtime: *EPOCH_PLUS_ONE,
		// Time of last change
		ctime: *EPOCH_PLUS_ONE,
		// Time of creation (macOS only)
		crtime: *EPOCH_PLUS_ONE,
		// Kind of file (directory, file, pipe, etc)
		kind: match node {
			memtree::Node::Directory(_) => fuser::FileType::Directory,
			memtree::Node::File(_) => fuser::FileType::RegularFile,
			memtree::Node::Link { .. } => fuser::FileType::Symlink,
		},
		// Permissions
		perm: match node {
			memtree::Node::Directory(_) => 0o755,
			_ => 0o644,
		},
		// Number of hard links
		nlink: 1,
		// User id
		uid: 1000,
		// Group id
		gid: 100,
		// Rdev
		rdev: 0,
		// Block size
		blksize,
		// Flags (macOS only, see chflags(2))
		flags: 0,
	}
}

fn main() {
	env_logger::init();

	let store = fossil::Store::open("fossil.db").unwrap();
	let root = memtree::load_root(&store, {
		let mut stdin = io::stdin();

		let mut bytes = Vec::new();
		stdin.read_to_end(&mut bytes).unwrap();

		store::Directory::decode(&*bytes).unwrap()
	});

	fuser::mount2(
		Filesystem::open(store, root),
		"mnt",
		&[fuser::MountOption::DefaultPermissions],
	)
	.unwrap();
}

struct Filesystem {
	store: fossil::Store,
	root: memtree::Node,
}

impl Filesystem {
	fn open(store: fossil::Store, root: memtree::Directory) -> Filesystem {
		Filesystem {
			store,
			root: memtree::Node::Directory(root),
		}
	}

	fn find(&self, ino: u64) -> Option<&memtree::Node> {
		self.root.find(ino.checked_sub(1)?.try_into().ok()?)
	}
}

impl fuser::Filesystem for Filesystem {
	fn init(
		&mut self,
		_req: &fuser::Request<'_>,
		_config: &mut fuser::KernelConfig,
	) -> Result<(), c_int> {
		Ok(())
	}

	fn destroy(&mut self) {}

	fn lookup(
		&mut self,
		_req: &fuser::Request<'_>,
		parent: u64,
		name: &std::ffi::OsStr,
		reply: fuser::ReplyEntry,
	) {
		let dir = match self.find(parent) {
			Some(memtree::Node::Directory(d)) => d,
			Some(_) => {
				reply.error(EINVAL);
				return;
			}
			None => {
				reply.error(ENOENT);
				return;
			}
		};

		let entry = name.to_str().and_then(|name| dir.lookup(name));
		match entry {
			None => reply.error(ENOENT),
			Some((idx, node)) => {
				let ino = parent + idx as u64 + 1;
				reply.entry(&Duration::ZERO, &file_attr(ino, node), 0);
			}
		}
	}

	fn forget(&mut self, _req: &fuser::Request<'_>, _ino: u64, _nlookup: u64) {}

	fn getattr(&mut self, _req: &fuser::Request<'_>, ino: u64, reply: fuser::ReplyAttr) {
		if let Some(node) = self.find(ino) {
			reply.attr(&Duration::ZERO, &file_attr(ino, node));
		} else {
			reply.error(ENOENT);
		}
	}

	fn setattr(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_mode: Option<u32>,
		_uid: Option<u32>,
		_gid: Option<u32>,
		_size: Option<u64>,
		_atime: Option<fuser::TimeOrNow>,
		_mtime: Option<fuser::TimeOrNow>,
		_ctime: Option<std::time::SystemTime>,
		_fh: Option<u64>,
		_crtime: Option<std::time::SystemTime>,
		_chgtime: Option<std::time::SystemTime>,
		_bkuptime: Option<std::time::SystemTime>,
		_flags: Option<u32>,
		reply: fuser::ReplyAttr,
	) {
		reply.error(EROFS);
	}

	fn readlink(&mut self, _req: &fuser::Request<'_>, ino: u64, reply: fuser::ReplyData) {
		match self.find(ino) {
			Some(memtree::Node::Link { target }) => reply.data(target.as_bytes()),
			Some(_) => reply.error(EINVAL),
			None => reply.error(ENOENT),
		}
	}

	fn mknod(
		&mut self,
		_req: &fuser::Request<'_>,
		_parent: u64,
		_name: &std::ffi::OsStr,
		_mode: u32,
		_umask: u32,
		_rdev: u32,
		reply: fuser::ReplyEntry,
	) {
		reply.error(EROFS);
	}

	fn mkdir(
		&mut self,
		_req: &fuser::Request<'_>,
		_parent: u64,
		_name: &std::ffi::OsStr,
		_mode: u32,
		_umask: u32,
		reply: fuser::ReplyEntry,
	) {
		reply.error(EROFS);
	}

	fn unlink(
		&mut self,
		_req: &fuser::Request<'_>,
		_parent: u64,
		_name: &std::ffi::OsStr,
		reply: fuser::ReplyEmpty,
	) {
		reply.error(EROFS);
	}

	fn rmdir(
		&mut self,
		_req: &fuser::Request<'_>,
		parent: u64,
		name: &std::ffi::OsStr,
		reply: fuser::ReplyEmpty,
	) {
		debug!(
			"[Not Implemented] rmdir(parent: {:#x?}, name: {:?})",
			parent, name,
		);
		reply.error(ENOSYS);
	}

	fn symlink(
		&mut self,
		_req: &fuser::Request<'_>,
		_parent: u64,
		_name: &std::ffi::OsStr,
		_link: &std::path::Path,
		reply: fuser::ReplyEntry,
	) {
		reply.error(EROFS);
	}

	fn rename(
		&mut self,
		_req: &fuser::Request<'_>,
		_parent: u64,
		_name: &std::ffi::OsStr,
		_newparent: u64,
		_newname: &std::ffi::OsStr,
		_flags: u32,
		reply: fuser::ReplyEmpty,
	) {
		reply.error(EROFS);
	}

	fn link(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_newparent: u64,
		_newname: &std::ffi::OsStr,
		reply: fuser::ReplyEntry,
	) {
		reply.error(EROFS);
	}

	fn open(&mut self, _req: &fuser::Request<'_>, _ino: u64, _flags: i32, reply: fuser::ReplyOpen) {
		reply.opened(0, 0);
	}

	fn read(
		&mut self,
		_req: &fuser::Request<'_>,
		ino: u64,
		_fh: u64,
		offset: i64,
		size: u32,
		_flags: i32,
		_lock_owner: Option<u64>,
		reply: fuser::ReplyData,
	) {
		match self.find(ino) {
			Some(memtree::Node::File(f)) => {
				let offset = offset as usize;
				let size = size as usize;

				let content = self.store.read_blob(f.ident);
				let mut buffer = content.get(offset..).unwrap_or_default();
				if buffer.len() > size {
					buffer = &buffer[..size];
				}
				reply.data(buffer);
			}
			Some(_) => reply.error(EINVAL),
			None => reply.error(ENOENT),
		}
	}

	fn write(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_fh: u64,
		_offset: i64,
		_data: &[u8],
		_write_flags: u32,
		_flags: i32,
		_lock_owner: Option<u64>,
		reply: fuser::ReplyWrite,
	) {
		reply.error(EROFS);
	}

	fn flush(
		&mut self,
		_req: &fuser::Request<'_>,
		ino: u64,
		fh: u64,
		lock_owner: u64,
		reply: fuser::ReplyEmpty,
	) {
		debug!(
			"[Not Implemented] flush(ino: {:#x?}, fh: {}, lock_owner: {:?})",
			ino, fh, lock_owner
		);
		reply.error(ENOSYS);
	}

	fn release(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_fh: u64,
		_flags: i32,
		_lock_owner: Option<u64>,
		_flush: bool,
		reply: fuser::ReplyEmpty,
	) {
		reply.ok();
	}

	fn fsync(
		&mut self,
		_req: &fuser::Request<'_>,
		ino: u64,
		fh: u64,
		datasync: bool,
		reply: fuser::ReplyEmpty,
	) {
		debug!(
			"[Not Implemented] fsync(ino: {:#x?}, fh: {}, datasync: {})",
			ino, fh, datasync
		);
		reply.error(ENOSYS);
	}

	fn opendir(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_flags: i32,
		reply: fuser::ReplyOpen,
	) {
		reply.opened(0, 0);
	}

	fn readdir(
		&mut self,
		_req: &fuser::Request<'_>,
		ino: u64,
		_fh: u64,
		offset: i64,
		mut reply: fuser::ReplyDirectory,
	) {
		let dir = match self.find(ino) {
			Some(memtree::Node::Directory(d)) => d,
			Some(_) => {
				reply.error(EINVAL);
				return;
			}
			None => {
				reply.error(ENOENT);
				return;
			}
		};

		let mut children = vec![
			(ino, fuser::FileType::Directory, "."),
			(ino, fuser::FileType::Directory, ".."),
		];

		for (name, idx, node) in dir.iter() {
			let kind = match node {
				memtree::Node::Directory(_) => fuser::FileType::Directory,
				memtree::Node::File(_) => fuser::FileType::RegularFile,
				memtree::Node::Link { .. } => fuser::FileType::Symlink,
			};
			children.push((ino + idx as u64 + 1, kind, name));
		}

		for (offset, &(ino, kind, name)) in children.iter().enumerate().skip(offset as usize) {
			if reply.add(ino, (offset + 1) as i64, kind, name) {
				break;
			}
		}

		reply.ok();
	}

	fn readdirplus(
		&mut self,
		_req: &fuser::Request<'_>,
		ino: u64,
		fh: u64,
		offset: i64,
		reply: fuser::ReplyDirectoryPlus,
	) {
		debug!(
			"[Not Implemented] readdirplus(ino: {:#x?}, fh: {}, offset: {})",
			ino, fh, offset
		);
		reply.error(ENOSYS);
	}

	fn releasedir(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_fh: u64,
		_flags: i32,
		reply: fuser::ReplyEmpty,
	) {
		reply.ok();
	}

	fn fsyncdir(
		&mut self,
		_req: &fuser::Request<'_>,
		ino: u64,
		fh: u64,
		datasync: bool,
		reply: fuser::ReplyEmpty,
	) {
		debug!(
			"[Not Implemented] fsyncdir(ino: {:#x?}, fh: {}, datasync: {})",
			ino, fh, datasync
		);
		reply.error(ENOSYS);
	}

	fn statfs(&mut self, _req: &fuser::Request<'_>, _ino: u64, reply: fuser::ReplyStatfs) {
		reply.statfs(0, 0, 0, 0, 0, 512, 255, 0);
	}

	fn setxattr(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_name: &std::ffi::OsStr,
		_value: &[u8],
		_flags: i32,
		_position: u32,
		reply: fuser::ReplyEmpty,
	) {
		reply.error(EROFS);
	}

	fn getxattr(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_name: &std::ffi::OsStr,
		_size: u32,
		reply: fuser::ReplyXattr,
	) {
		reply.error(ENOSYS);
	}

	fn listxattr(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_size: u32,
		reply: fuser::ReplyXattr,
	) {
		reply.error(ENOSYS);
	}

	fn removexattr(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_name: &std::ffi::OsStr,
		reply: fuser::ReplyEmpty,
	) {
		reply.error(EROFS);
	}

	fn access(&mut self, _req: &fuser::Request<'_>, ino: u64, mask: i32, reply: fuser::ReplyEmpty) {
		debug!("[Not Implemented] access(ino: {:#x?}, mask: {})", ino, mask);
		reply.error(ENOSYS);
	}

	fn create(
		&mut self,
		_req: &fuser::Request<'_>,
		_parent: u64,
		_name: &std::ffi::OsStr,
		_mode: u32,
		_umask: u32,
		_flags: i32,
		reply: fuser::ReplyCreate,
	) {
		reply.error(EROFS);
	}

	fn getlk(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_fh: u64,
		_lock_owner: u64,
		_start: u64,
		_end: u64,
		_typ: i32,
		_pid: u32,
		reply: fuser::ReplyLock,
	) {
		reply.error(ENOSYS);
	}

	fn setlk(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_fh: u64,
		_lock_owner: u64,
		_start: u64,
		_end: u64,
		_typ: i32,
		_pid: u32,
		_sleep: bool,
		reply: fuser::ReplyEmpty,
	) {
		reply.error(ENOSYS);
	}

	fn bmap(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_blocksize: u32,
		_idx: u64,
		reply: fuser::ReplyBmap,
	) {
		reply.error(ENOSYS);
	}

	fn ioctl(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_fh: u64,
		_flags: u32,
		_cmd: u32,
		_in_data: &[u8],
		_out_size: u32,
		reply: fuser::ReplyIoctl,
	) {
		reply.error(ENOSYS);
	}

	fn fallocate(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino: u64,
		_fh: u64,
		_offset: i64,
		_length: i64,
		_mode: i32,
		reply: fuser::ReplyEmpty,
	) {
		reply.error(EROFS);
	}

	fn lseek(
		&mut self,
		_req: &fuser::Request<'_>,
		ino: u64,
		fh: u64,
		offset: i64,
		whence: i32,
		reply: fuser::ReplyLseek,
	) {
		debug!(
			"[Not Implemented] lseek(ino: {:#x?}, fh: {}, offset: {}, whence: {})",
			ino, fh, offset, whence
		);
		reply.error(ENOSYS);
	}

	fn copy_file_range(
		&mut self,
		_req: &fuser::Request<'_>,
		_ino_in: u64,
		_fh_in: u64,
		_offset_in: i64,
		_ino_out: u64,
		_fh_out: u64,
		_offset_out: i64,
		_len: u64,
		_flags: u32,
		reply: fuser::ReplyWrite,
	) {
		reply.error(EROFS);
	}
}

mod memtree {
	pub use fossil::FileRef;
	use {
		fossil::store,
		prost::Message,
		std::{collections::BTreeMap, fmt},
	};

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

	#[derive(Default)]
	pub struct Directory {
		by_index: BTreeMap<u32, Node>,
		by_name: BTreeMap<String, u32>,
		size: u32,
	}

	impl Directory {
		pub fn iter(&self) -> impl Iterator<Item = (&str, u32, &Node)> {
			let by_name = self.by_name.iter();
			let by_index = self.by_index.iter();

			by_name.zip(by_index).map(|((name, &idx), (&idy, node))| {
				assert_eq!(idx, idy);
				(name.as_str(), idx, node)
			})
		}

		pub fn lookup(&self, name: &str) -> Option<(u32, &Node)> {
			let &idx = self.by_name.get(name)?;
			Some((idx, &self.by_index[&idx]))
		}
	}

	impl fmt::Debug for Directory {
		fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
			f.debug_struct("Directory")
				.field("size", &self.size)
				.field("entries", &DirectoryMembers(self))
				.finish()
		}
	}

	struct DirectoryMembers<'a>(&'a Directory);

	impl fmt::Debug for DirectoryMembers<'_> {
		fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
			f.debug_map()
				.entries(self.0.iter().map(|(name, idx, node)| ((name, idx), node)))
				.finish()
		}
	}

	pub fn load_root(store: &fossil::Store, pb: store::Directory) -> Directory {
		let mut children = BTreeMap::new();

		for store::DirectoryNode {
			name,
			r#ref,
			size: _,
		} in pb.directories
		{
			let bytes = store.read_blob(fossil::digest_from_bytes(&r#ref));
			let pb = store::Directory::decode(&*bytes).unwrap();
			let child = load_root(store, pb);
			children.insert(name, Node::Directory(child));
		}

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

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

		Directory::from_children(children)
	}

	impl Directory {
		fn from_children(children: BTreeMap<String, Node>) -> Directory {
			let mut d = Directory::default();
			for (name, child) in children {
				let index = d.size;
				let size = match child {
					Node::Directory(Directory { size, .. }) => {
						size.checked_add(1).expect("overflow")
					}
					Node::File(_) | Node::Link { .. } => 1,
				};

				d.size = index.checked_add(size).expect("overflow");
				d.by_name.insert(name, index);
				d.by_index.insert(index, child);
			}
			d
		}

		pub fn len(&self) -> usize {
			let len = self.by_index.len();
			let lem = self.by_name.len();
			debug_assert_eq!(len, lem);
			len
		}
	}

	impl Node {
		pub fn find(&self, mut index: u32) -> Option<&Node> {
			let mut root = self;
			loop {
				let d = match (index, root) {
					(0, _) => {
						break Some(root);
					}
					(_, Node::Directory(d)) => {
						index -= 1;
						d
					}
					_ => {
						break None;
					}
				};

				let (&child_index, child) = d.by_index.range(..=index).next_back()?;
				root = child;
				index = index.checked_sub(child_index).unwrap();
			}
		}
	}
}