//! Types dealing with ranges of values

extern mod extra;

use extra::time::Timespec;

/// A trait that normalizes a range bound for a type
pub trait Normalizable {
    /// Given a range bound, returns the normalized version of that bound. For
    /// discrete types such as i32, the normalized lower bound is always
    /// inclusive and the normalized upper bound is always exclusive. Other
    /// types, such as Timespec, have no normalization process so their
    /// implementation is a no-op.
    ///
    /// The logic here should match the logic performed by the equivalent
    /// Postgres type.
    fn normalize<S: BoundSided>(bound: RangeBound<S, Self>)
            -> RangeBound<S, Self>;
}

macro_rules! bounded_normalizable(
    ($t:ty) => (
        impl Normalizable for $t {
            fn normalize<S: BoundSided>(bound: RangeBound<S, $t>)
                    -> RangeBound<S, $t> {
                match BoundSided::side(None::<S>) {
                    Upper if bound.type_ == Inclusive => {
                        assert!(bound.value != Bounded::max_value());
                        RangeBound::new(bound.value + 1, Exclusive)
                    }
                    Lower if bound.type_ == Exclusive => {
                        assert!(bound.value != Bounded::max_value());
                        RangeBound::new(bound.value + 1, Inclusive)
                    }
                    _ => bound
                }
            }
        }
    )
)

bounded_normalizable!(i32)
bounded_normalizable!(i64)

impl Normalizable for Timespec {
    fn normalize<S: BoundSided>(bound: RangeBound<S, Timespec>)
            -> RangeBound<S, Timespec> {
        bound
    }
}

enum BoundSide {
    Upper,
    Lower
}

trait BoundSided {
    // param is a hack to get around lack of hints for self type
    fn side(_: Option<Self>) -> BoundSide;
}

/// A tag type representing an upper bound
#[deriving(Eq,Clone)]
pub struct UpperBound;

/// A tag type representing a lower bound
#[deriving(Eq,Clone)]
pub struct LowerBound;

impl BoundSided for UpperBound {
    fn side(_: Option<UpperBound>) -> BoundSide {
        Upper
    }
}

impl BoundSided for LowerBound {
    fn side(_: Option<LowerBound>) -> BoundSide {
        Lower
    }
}

/// The type of a range bound
#[deriving(Eq,Clone)]
pub enum BoundType {
    /// The bound includes its value
    Inclusive,
    /// The bound excludes its value
    Exclusive
}

/// Represents a one-sided bound.
///
/// The side is determined by the `S` phantom parameter.
#[deriving(Eq,Clone)]
pub struct RangeBound<S, T> {
    /// The value of the bound
    value: T,
    /// The type of the bound
    type_: BoundType
}

impl<S: BoundSided, T: Ord> Ord for RangeBound<S, T> {
    fn lt(&self, other: &RangeBound<S, T>) -> bool {
        match (BoundSided::side(None::<S>), self.type_, other.type_) {
            (Upper, Exclusive, Inclusive)
            | (Lower, Inclusive, Exclusive) => self.value <= other.value,
            _ => self.value < other.value
        }
    }
}

impl<S: BoundSided, T: Ord> RangeBound<S, T> {
    /// Constructs a new range bound
    pub fn new(value: T, type_: BoundType) -> RangeBound<S, T> {
        RangeBound { value: value, type_: type_ }
    }

    /// Determines if a value lies within the range specified by this bound.
    pub fn in_bounds(&self, value: &T) -> bool {
        match (self.type_, BoundSided::side(None::<S>)) {
            (Inclusive, Upper) if value <= &self.value => true,
            (Exclusive, Upper) if value < &self.value => true,
            (Inclusive, Lower) if value >= &self.value => true,
            (Exclusive, Lower) if value > &self.value => true,
            _ => false
        }
    }
}

/// The relation of a value to a range
#[deriving(Eq)]
pub enum RangeComparison {
    /// The value lies above the range
    Above,
    /// The value lies within the range
    Within,
    /// The value lies below the range
    Below
}

/// Represents a range of values.
#[deriving(Eq,Clone)]
pub struct Range<T> {
    priv lower: Option<RangeBound<LowerBound, T>>,
    priv upper: Option<RangeBound<UpperBound, T>>,
}

impl<T: Ord+Normalizable> Range<T> {
    /// Creates a new range.
    ///
    /// If a bound is `None`, the range is unbounded in that direction.
    pub fn new(lower: Option<RangeBound<LowerBound, T>>,
               upper: Option<RangeBound<UpperBound, T>>) -> Range<T> {
        let lower = lower.map(|bound| { Normalizable::normalize(bound) });
        let upper = upper.map(|bound| { Normalizable::normalize(bound) });

        match (&lower, &upper) {
            (&Some(ref lower), &Some(ref upper)) =>
                assert!(lower.value <= upper.value),
            _ => {}
        }

        Range { lower: lower, upper: upper }
    }

    /// Returns the lower bound if it exists.
    pub fn lower<'a>(&'a self) -> &'a Option<RangeBound<LowerBound, T>> {
        &self.lower
    }

    /// Returns the upper bound if it exists.
    pub fn upper<'a>(&'a self) -> &'a Option<RangeBound<UpperBound, T>> {
        &self.upper
    }

    /// Compares a value to this range.
    pub fn cmp(&self, value: &T) -> RangeComparison {
        let lower = do self.lower.as_ref().map_default(true) |b| {
            b.in_bounds(value)
        };
        let upper = do self.upper.as_ref().map_default(true) |b| {
            b.in_bounds(value)
        };

        match (lower, upper) {
            (true, false) => Above,
            (true, true) => Within,
            (false, true) => Below,
            _ => unreachable!()
        }
    }

    /// Determines if a value lies within this range.
    pub fn contains(&self, value: &T) -> bool {
        self.cmp(value) == Within
    }
}

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

    #[test]
    fn test_range_bound_lower_lt() {
        fn check(val1: int, inc1: BoundType, val2: int, inc2: BoundType, expected: bool) {
            let a: RangeBound<LowerBound, int> = RangeBound::new(val1, inc1);
            let b: RangeBound<LowerBound, int> = RangeBound::new(val2, inc2);
            assert_eq!(expected, a < b);
        }

        check(1, Inclusive, 2, Exclusive, true);
        check(1, Exclusive, 2, Inclusive, true);
        check(1, Inclusive, 1, Exclusive, true);
        check(2, Inclusive, 1, Inclusive, false);
        check(2, Exclusive, 1, Exclusive, false);
        check(1, Exclusive, 1, Inclusive, false);
        check(1, Exclusive, 1, Exclusive, false);
        check(1, Inclusive, 1, Inclusive, false);
    }

    #[test]
    fn test_range_bound_upper_lt() {
        fn check(val1: int, inc1: BoundType, val2: int, inc2: BoundType, expected: bool) {
            let a: RangeBound<UpperBound, int> = RangeBound::new(val1, inc1);
            let b: RangeBound<UpperBound, int> = RangeBound::new(val2, inc2);
            assert_eq!(expected, a < b);
        }

        check(1, Inclusive, 2, Exclusive, true);
        check(1, Exclusive, 2, Exclusive, true);
        check(1, Exclusive, 1, Inclusive, true);
        check(2, Inclusive, 1, Inclusive, false);
        check(2, Exclusive, 1, Exclusive, false);
        check(1, Inclusive, 1, Exclusive, false);
        check(1, Inclusive, 1, Inclusive, false);
        check(1, Exclusive, 1, Exclusive, false);
    }

    #[test]
    fn test_range_bound_lower_in_bounds() {
        fn check(bound: int, inc: BoundType, val: int, expected: bool) {
            let b: RangeBound<LowerBound, int> = RangeBound::new(bound, inc);
            assert_eq!(expected, b.in_bounds(&val));
        }

        check(1, Inclusive, 1, true);
        check(1, Exclusive, 1, false);
        check(1, Inclusive, 2, true);
        check(1, Inclusive, 0, false);
    }

    #[test]
    fn test_range_bound_upper_in_bounds() {
        fn check(bound: int, inc: BoundType, val: int, expected: bool) {
            let b: RangeBound<UpperBound, int> = RangeBound::new(bound, inc);
            assert_eq!(expected, b.in_bounds(&val));
        }

        check(1, Inclusive, 1, true);
        check(1, Exclusive, 1, false);
        check(1, Inclusive, 2, false);
        check(1, Inclusive, 0, true);
    }

    #[test]
    fn test_range_cmp() {
        let r =  Range::new(Some(RangeBound::new(1i32, Inclusive)),
                            Some(RangeBound::new(3i32, Inclusive)));
        assert_eq!(Above, r.cmp(&4));
        assert_eq!(Within, r.cmp(&3));
        assert_eq!(Within, r.cmp(&2));
        assert_eq!(Within, r.cmp(&1));
        assert_eq!(Below, r.cmp(&0));

        let r =  Range::new(Some(RangeBound::new(1i32, Exclusive)),
                            Some(RangeBound::new(3i32, Exclusive)));
        assert_eq!(Above, r.cmp(&4));
        assert_eq!(Above, r.cmp(&3));
        assert_eq!(Within, r.cmp(&2));
        assert_eq!(Below, r.cmp(&1));
        assert_eq!(Below, r.cmp(&0));

        let r = Range::new(None, Some(RangeBound::new(3i32, Inclusive)));
        assert_eq!(Above, r.cmp(&4));
        assert_eq!(Within, r.cmp(&2));
        assert_eq!(Within, r.cmp(&Bounded::min_value()));

        let r = Range::new(Some(RangeBound::new(1i32, Inclusive)), None);
        assert_eq!(Within, r.cmp(&Bounded::max_value()));
        assert_eq!(Within, r.cmp(&4));
        assert_eq!(Below, r.cmp(&0));

        let r = Range::new(None, None);
        assert_eq!(Within, r.cmp(&Bounded::max_value()));
        assert_eq!(Within, r.cmp(&0i32));
        assert_eq!(Within, r.cmp(&Bounded::min_value()));
    }

    #[test]
    fn test_normalize_lower() {
        let r: RangeBound<LowerBound, i32> = RangeBound::new(10i32, Inclusive);
        assert_eq!(RangeBound::new(10i32, Inclusive), Normalizable::normalize(r));

        let r: RangeBound<LowerBound, i32> = RangeBound::new(10i32, Exclusive);
        assert_eq!(RangeBound::new(11i32, Inclusive), Normalizable::normalize(r));
    }

    #[test]
    fn test_normalize_upper() {
        let r: RangeBound<UpperBound, i32> = RangeBound::new(10i32, Inclusive);
        assert_eq!(RangeBound::new(11i32, Exclusive), Normalizable::normalize(r));

        let r: RangeBound<UpperBound, i32> = RangeBound::new(10i32, Exclusive);
        assert_eq!(RangeBound::new(10i32, Exclusive), Normalizable::normalize(r));
    }

    #[test]
    fn test_range_normalizes() {
        let r1 = Range::new(Some(RangeBound::new(10i32, Exclusive)),
                            Some(RangeBound::new(15i32, Inclusive)));
        let r2 = Range::new(Some(RangeBound::new(11i32, Inclusive)),
                            Some(RangeBound::new(16i32, Exclusive)));
        assert_eq!(r1, r2);
    }
}