use anyhow::bail;
use std::{
	fmt::{self, Display, Write as _},
	ops::{Add, Sub},
	str::FromStr
};

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Date {
	pub year: u16,
	pub month: u8,
	pub day: u8
}

impl FromStr for Date {
	type Err = anyhow::Error;

	fn from_str(s: &str) -> anyhow::Result<Self> {
		parse_date(s)
	}
}

impl Display for Date {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		f.write_str(&format_date(*self))
	}
}

/// Parse a date in YYMMDD format.
pub fn parse_date(s: &str) -> anyhow::Result<Date> {
	let int: u32 = s.parse()?;

	let year = int / 10000 + 2000;
	if year / 10 != 202 {
		bail!("Expected a date in 202X");
	}

	let month = int / 100 % 100;
	if month < 1 || month > 12 {
		bail!("Invalid month: {month}");
	}

	let day = int % 100;
	if day < 1 || day > 31 {
		bail!("Invalid day: {day}");
	}

	Ok(Date {
		year: year as _,
		month: month as _,
		day: day as _
	})
}

/// Format a date in YYMMDD format.
pub fn format_date(d: Date) -> String {
	format!("{:02}{:02}{:02}", d.year % 100, d.month, d.day)
}

/// Format a date in DD. MMMM YYYY format.
pub fn format_date_long(d: Date) -> String {
	let month = match d.month {
		1 => "Januar",
		2 => "Februar",
		3 => "März",
		4 => "April",
		5 => "Mai",
		6 => "Juni",
		7 => "Juli",
		8 => "August",
		9 => "September",
		10 => "Oktober",
		11 => "November",
		12 => "Dezember",
		_ => unreachable!()
	};
	format!("{:02}. {month} {:04}", d.day, d.year)
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Time {
	pub seconds: u32,
	pub micros: u32
}

impl Add for Time {
	type Output = Self;

	fn add(self, rhs: Self) -> Self {
		let mut seconds = self.seconds + rhs.seconds;
		let mut micros = self.micros + rhs.micros;
		if micros >= 1_000_000 {
			seconds += 1;
			micros -= 1_000_000;
		}
		Self { seconds, micros }
	}
}

impl Sub for Time {
	type Output = Self;

	fn sub(mut self, rhs: Self) -> Self {
		if rhs.micros > self.micros {
			self.seconds -= 1;
			self.micros += 1_000_000;
		}
		Self {
			seconds: self.seconds - rhs.seconds,
			micros: self.micros - rhs.micros
		}
	}
}

impl FromStr for Time {
	type Err = anyhow::Error;

	fn from_str(s: &str) -> anyhow::Result<Self> {
		parse_time(s)
	}
}

impl Display for Time {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		f.write_str(&format_time(*self))
	}
}

/// Parse a time in hh:mm:ss:sub or hh:mm:ss.micros format.
pub fn parse_time(s: &str) -> anyhow::Result<Time> {
	let split = s.split(':');
	let mut seconds = 0;
	let mut micros = 0;

	for (i, digits) in split.enumerate() {
		// we cannot have more than 4 splits
		if i > 3 {
			bail!("Expected end of input, found ':'")
		}
		// we cannot process data after we have parsed micros
		if micros != 0 {
			bail!("Unexpected microsecond notation");
		}
		// the 4th split is subseconds, converting to micros
		if i == 3 {
			micros = digits.parse::<u32>()? * 1000000 / 60;
			continue;
		}
		// add to seconds and potentially micros
		seconds *= 60;
		if let Some(idx) = digits.find('.') {
			seconds += digits[0 .. idx].parse::<u32>()?;
			let micros_digits = &digits[idx + 1 ..];
			micros = micros_digits.parse::<u32>()?
				* 10_u32.pow((6 - micros_digits.len()) as _);
		} else {
			seconds += digits.parse::<u32>()?;
		}
	}

	Ok(Time { seconds, micros })
}

/// Format a time in hh:mm:ss.micros format.
pub fn format_time(t: Time) -> String {
	let h = t.seconds / 3600;
	let m = (t.seconds / 60) % 60;
	let s = t.seconds % 60;

	let mut out = String::new();
	if h != 0 {
		write!(out, "{h}:").unwrap();
	}
	if h != 0 || m != 0 {
		write!(out, "{m:02}:{s:02}").unwrap();
	} else {
		write!(out, "{s}").unwrap();
	}
	if t.micros != 0 {
		write!(out, ".{:06}", t.micros).unwrap();
		out.truncate(out.trim_end_matches('0').len());
	}

	out
}

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

	fn test_time_parse_only(s: &str, t: Time) {
		let time = parse_time(s).unwrap();
		assert_eq!(time, t);
	}

	fn test_time(s: &str, t: Time) {
		test_time_parse_only(s, t);
		assert_eq!(format_time(t), s);
	}

	#[test]
	fn test_time_0() {
		test_time("0", Time {
			seconds: 0,
			micros: 0
		});
	}

	#[test]
	fn test_time_2_3() {
		test_time("02:03", Time {
			seconds: 123,
			micros: 0
		});
	}

	#[test]
	fn test_time_1_2_3() {
		test_time("1:02:03", Time {
			seconds: 3723,
			micros: 0
		});
	}

	#[test]
	fn test_time_subsecs() {
		test_time_parse_only("1:02:03:30", Time {
			seconds: 3723,
			micros: 500000
		});
	}

	#[test]
	fn test_time_micros() {
		test_time("1:02:03.5", Time {
			seconds: 3723,
			micros: 500000
		});
	}
}