/*!
An ultra simple no-configuration logger with colored output and zero
dependencies.Just add it to dependencies and initalize it as soon as
possible.

```rust
use log::*;
use SimplestLogger;

fn main
{
	SimplestLogger::initalize(LevelFilter::Info);

	// your code!
}
````

SimplestLogger gives lots of line length for longer messages, and uses
easily-distingusishable but theme respecting (ANSI) terminal colors.

We also have some constants you can use to more easily line things up.

In your Cargo.toml you will need:
```toml
log = { version = "0.4", features = ["max_level_trace", "release_max_level_warn"] }
```

Those feature flags aren't really "features", what they do is allows all logs
in debug, but tells the rust compiler to remove any and all `trace!` and
`debug!` macros invocations at *compile time*, meaning you have exactly zero
overhead or performance loss for those macros: only info, warning, and error
have any processing power required in production.

In fact, if you want you can even do `release_max_level_off` and get no cost
for *any* logs in production! Useful for embedded systems and tight storage
constraints--since you can omit the entire log and SimplestLogger crates.
*/

use log::Record;
use log::Level;
use log::Metadata;
use log::LevelFilter;
use log::info;

pub struct SimplestLogger;

// You probably already know this but a lot of devs don't know `static` v. `const`. Basically.
//
// - Const represents a VALUE and is INLINED whereever used. This leads to a
//   (slightly) bugger binary but faster run times.
// - Static represents a MEMORY ADDRESS and is looked for when its used.
//   this leads to a smaller binary but slower run times.
//
// Here we want values sicne we want them inlined, and so true with every case
// in this file.
//
// source: https://stackoverflow.com/questions/52751597/what-is-the-difference-between-a-constant-and-a-static-variable-and-which-should

pub const INDENT: &str = "        ";

const BOLD: &str = "\x1b[1m";
const RESET: &str = "\x1b[0m";

const DEBUG_COLOR: &str = "\x1b[95m";
const INFO_COLOR: &str = "\x1b[96m";
const ERROR_COLOR: &str = "\x1b[91m";
const WARNING_COLOR: &str = "\x1b[93m";

impl SimplestLogger
{
	// TODO: Make it write to a file too.

	#[inline(always)]
	pub fn initalize() -> ()
	{
		/*!
		Initalize your logger. Note that any log macros used before this is
		called will simply be ignored, and that only one logger may be
		initalized and attempting to initalize a logger when there already
		is one will cause the program to panic.
		
		It is best practice to make this line 1 of your main function, and
		use it nowhere else so it is easy to know which cases need to be
		removed.
		
		Note that this function is always inlined as it must only be called
		once, so this micro-optimisation saves you some clock cycles when
		the rust compiler would have otherwise decided not to inline
		this function.

		Initalizes to info by default. Use `SimpelstLogger::set_level()`
		to change the level.
		*/

		match log::set_logger(&SimplestLogger).map(|()| log::set_max_level(LevelFilter::Info))
		{
			Ok(_) => info!("Logger Initalized"),
			Err(_) =>
			{
				println!("       {BOLD}{ERROR_COLOR}Error{RESET} Cannot initalize: there can only be one logger.");
				panic!("tried to initalize a logger where an instance already existed");
			}
		}
	}

	// The compiler will never inline functions not marked with `#[inline]`*,
	// this does not however make it inline: it lets the compiler decide based
	// on how many times it is called. If its called frequently inlining it is
	// a bad idea as it reduces cache hits, but if its called very few times
	// inlining it is a good idea as the overhead of the call may take longer
	// than the actual function itself (as tiny as that is)
	//
	// * it will if its in the main binary, but not if its a crate!

	// TODO: Performance benchmarks on this, inlining it may not help or may
	// make it slower!

	#[inline]
	pub fn set_level(level: LevelFilter) -> ()
	{
		/*!
		Clean interface to set the log level. You can also fdo this directly
		with `log::set_max_level(LevelFilter::YourLevel)`. This function has
		the inline attribute so it should cause no performance loss as opposed
		to doing it directly.
		*/
		log::set_max_level(level)
	}
}

#[doc(hidden)]
impl log::Log for SimplestLogger
{
	#[cold] #[inline(always)]
	fn enabled(&self, metadata: &Metadata) -> bool
	{
		/*!
		this function is never called. It is just a requirement for the implementation.
		*/
		return metadata.level() <= Level::Trace;
	}

	fn log(&self, record: &Record)
	{
		// we don't need to check if its enabled since that is handled with the
		// LevelFilter system, which is better for performance since it must
		// necesarly go through that anyway.
		match record.level()
		{
			Level::Trace => println!("  {BOLD}Trace{RESET} {name} ({file}:{line})",
				name = record.args(),
				file = record.file().unwrap_or("unknown"),
				line = record.line().unwrap_or(0),
			),
			Level::Debug => println!("  {BOLD}{DEBUG_COLOR}Debug{RESET} {}", record.args()),
			Level::Info => println!("   {BOLD}{INFO_COLOR}Info{RESET} {}", record.args()),
			Level::Warn => println!("{BOLD}{WARNING_COLOR}Warning{RESET} {} ({file}:{line})",
				record.args(),
				file = record.file().unwrap_or("unknown"),
				line = record.line().unwrap_or(0),
			),
			Level::Error => println!("  {BOLD}{ERROR_COLOR}Error{RESET} {} ({file}:{line})",
				record.args(),
				file = record.file().unwrap_or("unknown"),
				line = record.line().unwrap_or(0),
			),
		}

		// I believe everything in this entire function asside from the match
		// is inlined, meaning this is as fast as it can realistically get.
	}

	fn flush(&self) {}
}


#[cfg(test)]
mod tests
{
	use super::*;

	#[test]
	fn change_level_with_set_level()
	{
		SimplestLogger::initalize(LevelFilter::Info);
		SimplestLogger::set_level(LevelFilter::Debug);
		todo!("Assertions!");
	}

	#[test] #[should_panic]
	fn panic_on_logger_exist()
	{
		SimplestLogger::initalize(LevelFilter::Info);
		SimplestLogger::initalize(LevelFilter::Debug)
	}
}