//! Value extractor system for raidgrep filters.
//!
//! [`Comparators`][Comparator] are special filters that work by first producing a value from a
//! given log (via the [`Producer`][Producer]) trait and then applying a comparison operator
//! ([`CompOp`][CompOp]) between the results. This type of filter gives a lot of flexibility, as it
//! can reduce the number of hard-coded filters one has to create (for example, `-before` and
//! `-after` can be merged).
//!
//! A [`Comparator`][Comparator] can only compare producers which produce the same type of value,
//! and that value must define a total order (i.e. it must implement [`Ord`][Ord]). Note that the
//! actual comparison is done on filter time, that is a [`Comparator`][Comparator] is basically a
//! filter that first uses the producers to produce a value from the given log, and then compares
//! the two resulting values with the given comparison operator.
use std::{
    cmp::Ordering,
    convert::TryFrom,
    ffi::OsStr,
    fmt::{self, Debug},
};

use chrono::{DateTime, Duration, Local, TimeZone, Utc};
use evtclib::Agent;
use once_cell::sync::Lazy;
use regex::Regex;

use super::{log::LogFilter, player::PlayerFilter, Filter, Inclusion};
use crate::{EarlyLogResult, LogResult};

/// The regular expression used to extract datetimes from filenames.
static DATE_REGEX: Lazy<Regex> = Lazy::new(|| Regex::new(r"\d{8}-\d{6}").unwrap());

/// A producer for a given value.
///
/// A producer is something that produces a value of a certain type from a log, which can then be
/// used by [`Comparators`][Comparator] to do the actual comparison.
pub trait Producer: Send + Sync + Debug {
    /// Type of the value that will be produced.
    type Output;

    /// Early production.
    ///
    /// This function should be implemented if the value can already be produced without the
    /// complete log being parsed. This can speed up filtering if a lot of logs end up being thrown
    /// away.
    ///
    /// If a value cannot be produced early, `None` should be returned.
    fn produce_early(&self, _early_log: &EarlyLogResult) -> Option<Self::Output> {
        None
    }

    /// Produce the value from the given log.
    fn produce(&self, log: &LogResult) -> Self::Output;
}

/// The comparison operator to be used.
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
pub enum CompOp {
    /// The first value must be strictly less than the second value.
    Less,
    /// The first value must be less or equal to the second value.
    LessEqual,
    /// Both values must be equal.
    Equal,
    /// The first value must be greater or equal to the second value.
    GreaterEqual,
    /// The first value must be strictly greater than the second value.
    Greater,
}

impl fmt::Display for CompOp {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let symbol = match self {
            CompOp::Less => "<",
            CompOp::LessEqual => "<=",
            CompOp::Equal => "=",
            CompOp::GreaterEqual => ">=",
            CompOp::Greater => ">",
        };
        f.pad(symbol)
    }
}

impl CompOp {
    /// Check whether the comparison operator matches the given ordering.
    pub fn matches(self, cmp: Ordering) -> bool {
        match cmp {
            Ordering::Less => self == CompOp::Less || self == CompOp::LessEqual,
            Ordering::Equal => {
                self == CompOp::LessEqual || self == CompOp::Equal || self == CompOp::GreaterEqual
            }
            Ordering::Greater => self == CompOp::Greater || self == CompOp::GreaterEqual,
        }
    }
}

struct Comparator<V>(
    Box<dyn Producer<Output = V>>,
    CompOp,
    Box<dyn Producer<Output = V>>,
);

impl<V> Debug for Comparator<V> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "({:?} {} {:?})", self.0, self.1, self.2)
    }
}

impl<V> Filter<EarlyLogResult, LogResult> for Comparator<V>
where
    V: Ord,
{
    fn filter_early(&self, early_log: &EarlyLogResult) -> Inclusion {
        self.0
            .produce_early(early_log)
            .and_then(|lhs| self.2.produce_early(early_log).map(|rhs| lhs.cmp(&rhs)))
            .map(|ordering| self.1.matches(ordering))
            .map(Into::into)
            .unwrap_or(Inclusion::Unknown)
    }

    fn filter(&self, log: &LogResult) -> bool {
        let lhs = self.0.produce(log);
        let rhs = self.2.produce(log);
        self.1.matches(lhs.cmp(&rhs))
    }
}

/// Create a log filter that works by comparing two values.
///
/// The values will be produced by the given producers.
///
/// This function acts as a "bridge" between the value producers and the log filter system by
/// actually evaluating the comparison.
pub fn comparison<V: 'static>(
    lhs: Box<dyn Producer<Output = V>>,
    op: CompOp,
    rhs: Box<dyn Producer<Output = V>>,
) -> Box<dyn LogFilter>
where
    V: Ord,
{
    Box::new(Comparator(lhs, op, rhs))
}

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
struct ConstantProducer<V>(V);

impl<V: Send + Sync + Debug + Clone> Producer for ConstantProducer<V> {
    type Output = V;
    fn produce_early(&self, _: &EarlyLogResult) -> Option<Self::Output> {
        Some(self.0.clone())
    }

    fn produce(&self, _: &LogResult) -> Self::Output {
        self.0.clone()
    }
}

/// A producer that always produces the given constant, regardless of the log.
pub fn constant<V: Send + Sync + Debug + Clone + 'static>(
    value: V,
) -> Box<dyn Producer<Output = V>> {
    Box::new(ConstantProducer(value))
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
struct TimeProducer;

impl Producer for TimeProducer {
    type Output = DateTime<Utc>;

    fn produce_early(&self, early_log: &EarlyLogResult) -> Option<Self::Output> {
        early_log
            .log_file
            .file_name()
            .and_then(datetime_from_filename)
    }

    fn produce(&self, log: &LogResult) -> Self::Output {
        log.time
    }
}

/// Try to extract the log time from the filename.
///
/// This expects the filename to have the datetime in the pattern `YYYYmmdd-HHMMSS` somewhere in
/// it.
fn datetime_from_filename(name: &OsStr) -> Option<DateTime<Utc>> {
    let date_match = DATE_REGEX.find(name.to_str()?)?;
    let local_time = Local
        .datetime_from_str(date_match.as_str(), "%Y%m%d-%H%M%S")
        .ok()?;
    Some(local_time.with_timezone(&Utc))
}

/// A producer that produces the time at which a log was created.
pub fn time() -> Box<dyn Producer<Output = DateTime<Utc>>> {
    Box::new(TimeProducer)
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
struct DurationProducer;

impl Producer for DurationProducer {
    type Output = Duration;

    fn produce(&self, log: &LogResult) -> Self::Output {
        log.duration
    }
}

/// A producer that produces the duration that a fight lasted in the log.
pub fn duration() -> Box<dyn Producer<Output = Duration>> {
    Box::new(DurationProducer)
}

#[derive(Debug)]
struct PlayerCountProducer(Box<dyn PlayerFilter>);

impl Producer for PlayerCountProducer {
    type Output = u8;

    fn produce_early(&self, early_log: &EarlyLogResult) -> Option<Self::Output> {
        let mut count = 0;
        for agent in &early_log.evtc.agents {
            if !agent.is_player() {
                continue;
            }

            let agent = Agent::try_from(agent);
            if let Ok(agent) = agent {
                let result = self.0.filter_early(&agent);
                match result {
                    Inclusion::Include => count += 1,
                    Inclusion::Exclude => (),
                    Inclusion::Unknown => return None,
                }
            } else {
                return None;
            }
        }
        Some(count)
    }

    fn produce(&self, log: &LogResult) -> Self::Output {
        log.players.iter().filter(|p| self.0.filter(p)).count() as u8
    }
}

/// A producer that counts the players matching the given filter.
pub fn player_count(filter: Box<dyn PlayerFilter>) -> Box<dyn Producer<Output = u8>> {
    Box::new(PlayerCountProducer(filter))
}

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

    #[test]
    fn test_compop_matches() {
        assert!(CompOp::Less.matches(Ordering::Less));
        assert!(!CompOp::Less.matches(Ordering::Equal));
        assert!(!CompOp::Less.matches(Ordering::Greater));

        assert!(CompOp::LessEqual.matches(Ordering::Less));
        assert!(CompOp::LessEqual.matches(Ordering::Equal));
        assert!(!CompOp::LessEqual.matches(Ordering::Greater));

        assert!(!CompOp::Equal.matches(Ordering::Less));
        assert!(CompOp::Equal.matches(Ordering::Equal));
        assert!(!CompOp::Equal.matches(Ordering::Greater));

        assert!(!CompOp::GreaterEqual.matches(Ordering::Less));
        assert!(CompOp::GreaterEqual.matches(Ordering::Equal));
        assert!(CompOp::GreaterEqual.matches(Ordering::Greater));

        assert!(!CompOp::Greater.matches(Ordering::Less));
        assert!(!CompOp::Greater.matches(Ordering::Equal));
        assert!(CompOp::Greater.matches(Ordering::Greater));
    }
}