use std::str::FromStr;
use std::io::Write;

use serde::{Serialize, Deserialize};
use itertools::Itertools;
use chrono::{DateTime, Utc, Offset, TimeZone};

use crate::error;
use crate::models::Entry;

#[derive(Debug, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum Formatter {
    Text,
    Custom(String),
}

impl Formatter {
    /// Prints the given entries to the specified output device.
    ///
    /// the current time is given as the `now` argument and the offset from UTC
    /// to the local timezone is given in `offset` to prevent this function from
    /// using a secondary effect to retrieve the time and conver dates. This
    /// also makes it easier to test.
    pub fn print_formatted<W: Write, O: Offset>(&self, entries: Vec<Entry>, out: &mut W, now: DateTime<Utc>, offset: O) -> error::Result<()> {
        match &self {
            Formatter::Text => self.print_formatted_text(entries, out, now, offset)?,
            Formatter::Custom(name) => {
            }
        }

        Ok(())
    }

    /// Print in the default text format. Assume entries are sorted by sheet and
    /// then by start
    fn print_formatted_text<W: Write, O: Offset>(&self, entries: Vec<Entry>, out: &mut W, now: DateTime<Utc>, offset: O) -> error::Result<()> {
        let grouped_entries = entries.into_iter().group_by(|e| e.sheet.to_string());

        // Build a timezone based on the offset given to this function. This
        // will later be used to properly group the entries by date in the local
        // timezone.
        let fixed_offset = offset.fix();

        for (key, group) in grouped_entries.into_iter() {
            writeln!(out, "Timesheet: {}", key)?;
            writeln!(out, "    Day                Start      End        Duration   Notes")?;

            let by_day = group.group_by(|e| fixed_offset.from_utc_datetime(&e.start.naive_utc()).date());

            for (date, entries) in by_day.into_iter() {
                for (i,entry) in entries.into_iter().enumerate() {
                    let start = fixed_offset.from_utc_datetime(&entry.start.naive_utc()).time().to_string();
                    let end = entry.end.map(|t| fixed_offset.from_utc_datetime(&t.naive_utc()).time().to_string()).unwrap_or("        ".into());
                    let duration = entry.end.unwrap_or(now) - entry.start;
                    let duration = format!("{}:{:02}:{:02}", duration.num_hours(), duration.num_minutes() % 60, duration.num_seconds() & 60);

                    if i == 0 {
                        let date = date.format("%a %b %d, %Y").to_string();

                        writeln!(
                            out,
                            "    {date}   {start} - {end}   {duration}    {note}",
                            date=date, start=start, end=end, duration=duration, note=entry.note,
                        )?;
                    } else {
                        writeln!(
                            out,
                            "                       {start} - {end}   {duration}    {note}",
                            start=start, end=end, duration=duration, note=entry.note,
                        )?;
                    }
                }
            }
        }

        Ok(())
    }
}

impl FromStr for Formatter {
    type Err = error::Error;

    fn from_str(s: &str) -> error::Result<Formatter> {
        let lower = s.to_lowercase();

        Ok(match &*lower {
            "text" => Formatter::Text,
            custom_format => Formatter::Custom(custom_format.into()),
        })
    }
}

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

    use pretty_assertions::assert_eq;
    use chrono::TimeZone;

    #[derive(PartialEq, Eq)]
    pub struct PrettyString<'a>(pub &'a str);

    /// Make diff to display string as multi-line string
    impl<'a> fmt::Debug for PrettyString<'a> {
      fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.write_str(self.0)
      }
    }

    #[test]
    fn test_text_output() {
        let formatter = Formatter::Text;
        let mut output = Vec::new();
        let entries = vec![
            Entry::new_sample(1, Utc.ymd(2008, 10, 3).and_hms(12, 0, 0), Some(Utc.ymd(2008, 10, 3).and_hms(14, 0, 0))),
            Entry::new_sample(2, Utc.ymd(2008, 10, 3).and_hms(12, 0, 0), Some(Utc.ymd(2008, 10, 3).and_hms(14, 0, 0))),
            Entry::new_sample(3, Utc.ymd(2008, 10, 5).and_hms(16, 0, 0), Some(Utc.ymd(2008, 10, 3).and_hms(18, 0, 0))),
            Entry::new_sample(4, Utc.ymd(2008, 10, 5).and_hms(18, 0, 0), None),
        ];

        let now = Utc.ymd(2008, 10, 5).and_hms(20, 0, 0);
        let offset = Utc;

        formatter.print_formatted(entries, &mut output, now, offset).unwrap();

        assert_eq!(PrettyString(&String::from_utf8_lossy(&output)), PrettyString("Timesheet: default
    Day                Start      End        Duration   Notes
    Fri Oct 03, 2008   12:00:00 - 14:00:00   2:00:00    entry 1
                       16:00:00 - 18:00:00   2:00:00    entry 2
                                             4:00:00
    Sun Oct 05, 2008   16:00:00 - 18:00:00   2:00:00    entry 3
                       18:00:00 -            2:00:00    entry 4
                                             4:00:00
    -----------------------------------------------------------
    Total                                    8:00:00
"));
    }
}