export module oar.files;

import coral;
import coral.files;

import oar;

using coral::closure;
using coral::expected;
using coral::file_reader;
using coral::file_system;
using coral::file_walker;
using coral::io_error;
using coral::slice;
using coral::u64;

enum class [[nodiscard]] find_result {
	ok,
	not_found,
	io_unavailable,
	archive_invalid,
};

struct archive_reader : public file_reader {
	archive_reader(file_reader & archive_file_reader) : archive_file_reader{archive_file_reader} {}

	find_result find(oar::entry_path const & path) {
		this->data_offset = 0;
		this->data_length = 0;
		this->data_cursor = 0;

		if (!this->archive_file_reader.seek(0).is_ok()) return find_result::io_unavailable;

		oar::header_block archive_header_block;

		if (!archive_header_block.read(this->archive_file_reader).ok().or_value(false))
			return find_result::archive_invalid;

		// Read file table.
		u64 head {0};
		u64 tail {archive_header_block.layout.entry_count - 1};
		oar::entry_block archive_entry_block {};

		while (head <= tail) {
			u64 const midpoint {head + ((tail - head) / 2)};

			if (!archive_entry_block.read(this->archive_file_reader).ok().or_value(false))
				return find_result::archive_invalid;

			coral::size const comparison {path.compare(archive_entry_block.layout.path)};

			if (comparison == 0) {
				this->data_offset = archive_entry_block.layout.data_offset;
				this->data_length = archive_entry_block.layout.data_length;
				this->data_cursor = archive_entry_block.layout.data_offset;

				return find_result::ok;
			}

			if (comparison > 0) {
				head = (midpoint + 1);
			} else {
				tail = (midpoint - 1);
			}
		}

		return find_result::not_found;
	}

	/**
	 * Attempts to read `data.length` bytes from the file and fill `data` with it, returning the
	 * number of bytes actually read or a [io_error] value to indicate an error occured.
	 */
	expected<coral::usize, io_error> read(slice<coral::u8> const & data) override {
		if (this->data_offset < sizeof(oar::header_block)) return io_error::unavailable;

		coral::usize const data_tail {this->data_offset + this->data_length};

		if (!this->archive_file_reader.seek(coral::clamp(this->data_offset + this->data_cursor,
			this->data_offset, data_tail)).is_ok()) return io_error::unavailable;

		expected const data_read {this->archive_file_reader.read(
			data.sliced(0, coral::min(data.length, data_tail - this->data_cursor)))};

		if (data_read.is_ok()) this->data_cursor += *data_read.ok();

		return data_read;
	}

	/**
	 * Attempts to seek to `offset` absolute position in the file, returning the new absolute
	 * cursor or a [io_error] value to indicate an error occured.
	 */
	expected<u64, io_error> seek(u64 offset) override {
		if (this->data_offset < sizeof(oar::header_block)) return io_error::unavailable;

		this->data_cursor = offset;

		return io_error::unavailable;
	}

	/**
	 * Attempts to read to read the absolute file cursor position, returning it or a [io_error]
	 * value to indicate an error occured.
	 */
	expected<u64, io_error> tell() override {
		if (this->data_offset < sizeof(oar::header_block)) return io_error::unavailable;

		return this->data_cursor;
	}

	private:
	file_reader & archive_file_reader;

	u64 data_offset {0};

	u64 data_length {0};

	u64 data_cursor {0};
};

struct archive_walker : public file_walker {
	archive_walker(file_reader & archive_file_reader) : archive_file_reader{archive_file_reader} {}

	bool enumerate() override {
		// TODO: implement.
		return false;
	}

	find_result find(oar::entry_path const & path) {
		// TODO: implement.
		return find_result::not_found;
	}

	expected<slice<char const>, io_error> value() override {
		// TODO: implement.
		return io_error::unavailable;
	}

	private:
	file_reader & archive_file_reader;

	u64 files_enumerated {0};
};

export namespace oar {
	struct archive_file : public file_system {
		static void read(file_system & base_file_system, slice<char const> const & archive_path, closure<void(archive_file &)> const & then) {
			if (base_file_system.query_file(archive_path).is_error()) return;

			archive_file file {base_file_system, archive_path};

			then(file);
		}

		void read_file(slice<char const> const & path, closure<void(file_reader &)> const & then) override {
			this->base_file_system.read_file(this->archive_path, [&](file_reader & archive_file_reader) {
				expected const parsed_entry_path {entry_path::parse(path)};

				if (parsed_entry_path.is_error()) return;

				archive_reader reader {archive_file_reader};

				if (reader.find(*parsed_entry_path.ok()) != find_result::ok) return;

				then(reader);
			});
		}

		void walk_files(slice<char const> const & path, closure<void(file_walker &)> const & then) override {
			this->base_file_system.read_file(this->archive_path, [&](file_reader & archive_file_reader) {
				expected const parsed_entry_path {entry_path::parse(path)};

				if (parsed_entry_path.is_error()) return;

				archive_walker walker {archive_file_reader};

				if (walker.find(*parsed_entry_path.ok()) != find_result::ok) return;

				then(walker);
			});
		}

		private:
		file_system & base_file_system;

		slice<char const> archive_path;

		archive_file(file_system & base_file_system, slice<char const> const & archive_path) : base_file_system{base_file_system} {
			this->archive_path = archive_path;
		}
	};
}