export module coral.files;

import coral;

export namespace coral {
	/**
	 * [reader] that has a known range of data and may attempt to traverse it freely.
	 */
	struct file_reader : public reader {
		/**
		 * Attempts to seek to the position in the file defined by `offset`, returning the literal absolute position
		 * that was actually sought to or a [io_error] if the operation failed for whatever reason.
		 */
		virtual expected<u64, io_error> seek(u64 offset) = 0;

		/**
		 * Attempts to get the current cursor position in the file, returning the literal absolute position of it or a
		 * [io_error] if the operation failed for whatever reason.
		 */
		virtual expected<u64, io_error> tell() = 0;
	};

	/**
	 * Enumerates a file tree recursively, returning the absolute path of each file within.
	 *
	 * *Note*: file tree walking order is considered implementation-specific.
	 */
	struct file_walker : public enumerator<expected<slice<char const>, io_error>> {
		virtual ~file_walker() {}

		/**
		 * See [enumerator::enumerate].
		 */
		virtual bool enumerate() = 0;

		/**
		 * Returns the last-enumerated path as a sequence of `char`s or an [io_error] if the last enumeration did not
		 * successfully complete.
		 */
		virtual expected<slice<char const>, io_error> value() = 0;
	};

	/**
	 * [writer] that has a known range of data and may attempt to traverse it freely.
	 */
	struct file_writer : public writer {
		/**
		 * Attempts to seek to the position in the file defined by `offset`, returning the literal absolute position
		 * that was actually sought to or a [io_error] if the operation failed for whatever reason.
		 */
		virtual expected<u64, io_error> seek(u64 offset) = 0;

		/**
		 * Attempts to get the current cursor position in the file, returning the literal absolute position of it or a
		 * [io_error] if the operation failed for whatever reason.
		 */
		virtual expected<u64, io_error> tell() = 0;
	};

	/**
	 * Platform-generalized file system interface.
	 */
	struct file_system {
		/**
		 * Errors that may occur during a file system query operation.
		 *
		 * [query_error::unsupported] occurs when either part or all of the query operation is not supported on the
		 * given file system.
		 *
		 * [query_error::io_unavailable] is a general catch-all to report that an implementation-specific I/O error has
		 * occured and the operation could not proceed as a result.
		 */
		enum class query_error {
			unsupported,
			io_unavailable,
		};

		/**
		 * Various meta-information about a file in a file system.
		 */
		struct file_info {
			u64 size;
		};

		virtual ~file_system() {};

		/**
		 * Attempts to query a file in the file system located at `path`, returning a [file_info] describing it or a
		 * [query_error] if the operation failed.
		 */
		virtual expected<file_info, query_error> query_file(slice<char const> const & path) {
			return query_error::unsupported;
		}

		/**
		 * Attempts to read a file in the file system located at `path`, calling `then` if it was successfully opened
		 * for reading and passing the [file_reader] context along.
		 *
		 * See [file_reader] for more information on how to read from the file.
		 */
		virtual void read_file(slice<char const> const & path, closure<void(file_reader &)> const & then) {}

		/**
		 * Attempts to walk the file tree from `path`, calling `then` if it was successfully opened for walking and
		 * passing the [file_walker] context along.
		 *
		 * See [file_walker] for more information on how to traverse the file tree.
		 */
		virtual void walk_files(slice<char const> const & path, closure<void(file_walker &)> const & then) {}

		/**
		 * Attempts to write a file in the file system located at `path`, calling `then` if it was successfully created
		 * and / or opened for writing and passing the [file_writer] context along.
		 *
		 * See [file_writer] for more information on how to write to the file.
		 *
		 * *Note*: Any file already existing at `path` will be overwritten to create a new file for writing.
		 */
		virtual void write_file(slice<char const> const & path, closure<void(file_writer &)> const & then) {}
	};
}