// fif - a command-line tool for detecting and optionally correcting files with incorrect extensions.
// Copyright (C) 2021 Lynnesbian
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

#![forbid(unsafe_code)]
#![warn(trivial_casts, unused_lifetimes, unused_qualifications)]

use std::ffi::OsStr;
use std::io::{stdout, BufWriter, Write};
use std::path::Path;
use std::process::exit;

use cfg_if::cfg_if;
use clap::Clap;
use env_logger::Env;
use log::{debug, error, info, trace, warn};
use once_cell::sync::OnceCell;
use walkdir::{DirEntry, WalkDir};

use crate::findings::Findings;
use crate::findings::ScanError;
use crate::formats::{Format, PowerShell, Shell};
use crate::mime_db::MimeDb;
use crate::parameters::{OutputFormat, ScanOpts};
use std::collections::BTreeSet;

mod findings;
mod formats;
mod inspectors;
mod mime_db;
mod parameters;
pub(crate) mod string_type;

#[cfg(test)]
mod tests;

cfg_if! {
	if #[cfg(any(all(unix, feature = "infer-backend"), all(not(unix), not(feature = "xdg-mime-backend"))))] {
		/// A [OnceCell] holding an instance of [mime_db::MimeDb].
		static MIMEDB: OnceCell<mime_db::InferDb> = OnceCell::new();
		/// The backend being used; either "Infer" or "XDG-Mime".
		const BACKEND: &str = "Infer";
	} else {
		/// A [OnceCell] holding an instance of [mime_db::MimeDb].
		static MIMEDB: OnceCell<mime_db::XdgDb> = OnceCell::new();
		/// The backend being used; either "Infer" or "XDG-Mime".
		const BACKEND: &str = "XDG-Mime";
	}
}

#[doc(hidden)]
#[allow(clippy::cognitive_complexity)]
fn main() {
	let args: parameters::Parameters = parameters::Parameters::parse();

	let mut builder = env_logger::Builder::from_env(Env::new().filter_or("RUST_LOG", args.default_verbosity()));

	builder
		// .format(|buf, r| writeln!(buf, "{} - {}", r.level(), r.args()))
		.format_module_path(false) // don't include module in logs, as it's not necessary
		.format_timestamp(None) // don't include timestamps (unnecessary, and the feature flag is disabled anyway)
		// .target(env_logger::Target::Stdout) // log to stdout rather than stderr
		.init();

	trace!("Initialise mimetype database");
	init_db();

	debug!("Iterating directory: {:?}", args.dir);

	let extensions = args.extensions();
	let excludes = args.excluded_extensions();

	if let Some(extensions) = &extensions {
		debug!("Checking files with extensions: {:?}", extensions);
	} else if let Some(excludes) = &excludes {
		debug!("Skipping files with extensions: {:?}", excludes);
	} else {
		debug!("Checking files regardless of extensions");
	}

	let entries = scan_directory(&args.dir, extensions.as_ref(), excludes.as_ref(), &args.get_scan_opts());

	if entries.is_none() {
		// no need to log anything for fatal errors - fif will already have printed something obvious like
		// "[ERROR] /fake/path: No such file or directory (os error 2)". we can assume that if this has happened, the dir
		// given as input doesn't exist or is otherwise unreadable.
		exit(exitcode::NOINPUT);
	}

	let entries = entries.unwrap();

	if entries.is_empty() {
		warn!("No files matching requested options found.");
		exit(exitcode::OK);
	}

	trace!("Found {} items to check", entries.len());

	let results: Vec<_> = scan_from_walkdir(&entries)
		.into_iter()
		.filter(
			|result| result.is_err() || !result.as_ref().unwrap().valid,
			// TODO: find a way to trace! the valid files without doing ↓
			// || if result.as_ref().unwrap().valid { trace!("{:?} ok", result.as_ref().unwrap().file); false } else { true }
		)
		.collect();

	trace!("Scanning complete");

	for result in &results {
		match result {
			Ok(r) => {
				debug!(
					"{:?} is of type {}, should have extension \"{}\"",
					r.file,
					r.mime,
					r.recommended_extension().unwrap_or_else(|| "???".into())
				);
			}
			Err(f) => warn!("{}", f),
		}
	}

	if results.is_empty() {
		info!("All files have valid extensions!");
		exit(0);
	}

	let mut buffered_stdout = BufWriter::new(stdout());

	let result = match args.output_format {
		OutputFormat::Sh => Shell::new().write_all(&mut buffered_stdout, &results),
		OutputFormat::PowerShell => PowerShell::new().write_all(&mut buffered_stdout, &results),
		#[cfg(feature = "json")]
		OutputFormat::Json => formats::Json::new().write_all(&mut buffered_stdout, &results),
		OutputFormat::Text => formats::Text::new().write_all(&mut buffered_stdout, &results),
	};

	if result.is_err() {
		error!("Failed to write to stdout.");
		exit(exitcode::IOERR);
	}

	if buffered_stdout.flush().is_err() {
		error!("Failed to flush stdout.");
		exit(exitcode::IOERR);
	}

	debug!("Done");
}

cfg_if! {
	if #[cfg(windows)] {
		/// Determines whether or not a file is hidden by checking its win32 file attributes.
		fn is_hidden(entry: &DirEntry) -> bool {
		use std::os::windows::prelude::*;
		std::fs::metadata(entry.path()) // try to get metadata for file
			.map_or(
				false,                             // if getting metadata/attributes fails, assume it's not hidden
				|f| f.file_attributes() & 0x2 > 0, // flag for hidden - https://docs.microsoft.com/windows/win32/fileio/file-attribute-constants
			)
		}
	} else {
		/// Determines whether or not a file is hidden by checking for a leading full stop.
		fn is_hidden(entry: &DirEntry) -> bool {
		entry
			.file_name()
			.to_str()
			.map_or(false, |f| f.starts_with('.') && f != ".")
		}
	}
}

/// Returns `true` if a file matches the given criteria. This means checking whether the file's extension appears in
/// `exts` (if specified), potentially skipping over hidden files, and so on.
fn wanted_file(
	entry: &DirEntry,
	exts: Option<&BTreeSet<&str>>,
	exclude: Option<&BTreeSet<&str>>,
	scan_opts: &ScanOpts,
) -> bool {
	if entry.depth() == 0 {
		// the root directory should always be scanned.
		return true;
	}

	if !scan_opts.hidden && is_hidden(entry) {
		// skip hidden files and directories. this check is performed first because it's very lightweight.
		return false;
	}

	if entry.file_type().is_dir() {
		// always allow directories - there's no point doing file extension matching on something that isn't a file.
		return true;
	}

	if let Some(ext) = extension_from_path(entry.path()) {
		// file has extension - discard invalid UTF-8 and normalise it to lowercase.
		let ext = ext.to_string_lossy().to_lowercase();
		let ext = ext.as_str();

		if let Some(exts) = exts {
			// only scan if the file has one of the specified extensions.
			exts.contains(&ext)
		} else {
			// no extensions specified - the file should be scanned unless its extension is on the exclude list.
			exclude.map_or(true, |exclude| !exclude.contains(&ext))
		}
	} else {
		// no file extension
		scan_opts.extensionless
	}
}

/// Given a file path, returns its extension, using [`std::path::Path::extension`].
fn extension_from_path(path: &Path) -> Option<&OsStr> { path.extension() }

/// Inspects the given entry, returning a [`Findings`] on success and a [`ScanError`] on failure.
///
/// In the event of an IO error, the returned [`ScanError`] will be of type [`ScanError::File`]. Otherwise, a
/// [`ScanError::Mime`] will be returned, meaning that the file was scanned successfully, but a mimetype could not be
/// determined.
fn scan_file(entry: &DirEntry) -> Result<Findings, ScanError> {
	// try to determine mimetype for this entry
	let result = inspectors::mime_type(MIMEDB.get().unwrap(), entry.path());

	if result.is_err() {
		// an error occurred while trying to read the file
		return Err(ScanError::File(entry.path()));
	}

	let result = result.unwrap();
	if result.is_none() {
		// the file was read successfully, but we were unable to determine its mimetype
		return Err(ScanError::Mime(entry.path()));
	}

	let result = result.unwrap();

	// set of known extensions for the given mimetype
	let known_exts = inspectors::mime_extension_lookup(result.essence_str().into());
	// file extension for this particular file
	let entry_ext = extension_from_path(entry.path());

	let valid = match known_exts {
		// there is a known set of extensions for this mimetype, and the file has an extension
		Some(e) if entry_ext.is_some() => e.contains(&entry_ext.unwrap().to_string_lossy().to_lowercase().into()),
		// either this file has no extension, or there is no known set of extensions for this mimetype :(
		Some(_) | None => false,
	};

	Ok(Findings {
		file: entry.path(),
		valid,
		mime: result,
	})
}

/// Takes a slice of [`DirEntry`]s and calls [`scan_file`] on each one, returning the results in a vector.
fn scan_from_walkdir(entries: &[DirEntry]) -> Vec<Result<Findings, ScanError>> {
	cfg_if! {
		if #[cfg(feature = "multi-threaded")] {
			use rayon::prelude::*;

			// split the entries into chunks of 32, and iterate over each chunk of entries in a separate thread
			entries
				.par_chunks(32)
				.flat_map(|chunk| {
					chunk
						.iter() // iter over the chunk, which is a slice of DirEntry structs
						.map(|entry| scan_file(entry))
						.collect::<Vec<_>>()
				})
				.collect()
		} else {
			entries.iter().map(|entry: &DirEntry| scan_file(entry)).collect()
		}
	}
}

/// Scans a given directory with [`WalkDir`], filters with [`wanted_file`], checks for errors, and returns a vector of
/// [DirEntry]s.
fn scan_directory(
	dirs: &Path,
	exts: Option<&BTreeSet<&str>>,
	exclude: Option<&BTreeSet<&str>>,
	scan_opts: &ScanOpts,
) -> Option<Vec<DirEntry>> {
	let stepper = WalkDir::new(dirs).follow_links(scan_opts.follow_symlinks).into_iter();
	let mut probably_fatal_error = false;
	let entries: Vec<DirEntry> = stepper
		.filter_entry(|e| wanted_file(e, exts, exclude, scan_opts)) // filter out unwanted files
		.filter_map(|e| {
			if let Err(err) = &e {
				debug!("uh oh spaghettio!! {:#?}", e);
				// log errors to stdout, and remove them from the iterator
				let path = err.path().map_or("General error".into(), Path::to_string_lossy);

				if err.depth() == 0 {
					// if something goes wrong while trying to read the root directory, we're probably not going to get much done
					probably_fatal_error = true;
				}

				// TODO: is there a way to just say `map_or(x, |y| y).thing()` instead of `map_or(x.thing(), |y| y.thing())`?
				// i don't care whether i'm returning a walkdir error or an io error, i just care about whether or not it
				// implements ToString (which they both do). map_or doesn't work on trait objects though :(
				error!(
					"{}: {}",
					path,
					err.io_error().map_or(err.to_string(), |e| e.to_string())
				);
				return None;
			}
			e.ok()
		})
		// remove directories from the final list
		.filter(|e| !e.file_type().is_dir())
		// if fif is invoked without `-f` on a symlinked directory, it will recurse into the symlink (as desired) and ignore
		// any symlinks inside the symlinked root directory. however, the root directory will still be added to `entries` as
		// if it were a file to be scanned, and `scan_file` will fail to scan it, adding "Failed to read ~/whatever" to the
		// output. to avoid this, we can remove all symlinks from `entries` if `-f` is not set. i know this is kind of
		// confusing, but it's honestly kind of hard to explain... maybe a screenshot is better:
		// https://i.imgur.com/DYG7jlB.png
		// adding the symlink filter removes the line that's being pointed to in the image. 0u0
		.filter(|e| scan_opts.follow_symlinks || !e.file_type().is_symlink())
		.collect();

	if probably_fatal_error {
		None
	} else {
		Some(entries)
	}
}

/// Initialises [`MIMEDB`] with a value dependent on the current backend.
fn init_db() {
	cfg_if! {
		if #[cfg(any(all(unix, feature = "infer-backend"), all(not(unix), not(feature = "xdg-mime-backend"))))] {
			MIMEDB
				.set(mime_db::InferDb::init())
				.or(Err("Failed to initialise Infer backend!"))
				.unwrap();
		} else {
			MIMEDB
				.set(mime_db::XdgDb::init())
				.or(Err("Failed to initialise XDG Mime backend!"))
				.unwrap();
		}
	}
}