From cb7c87b8b23a6b0673c72e6eec7b1415975964e8 Mon Sep 17 00:00:00 2001
From: Joscha <joscha@plugh.de>
Date: Mon, 6 Dec 2021 12:47:19 +0000
Subject: [PATCH] Implement formula evaluation for DATE statement

---
 Cargo.lock                  |   7 ++
 Cargo.toml                  |   1 +
 src/eval/command/formula.rs | 176 ++++++++++++++++++++++++++++++++++--
 src/eval/error.rs           |  12 +++
 src/eval/range.rs           |   5 +
 src/eval/util.rs            |  28 ++++--
 src/files/primitives.rs     |  38 ++++----
 7 files changed, 237 insertions(+), 30 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index f46d9ef..4c891b6 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -101,6 +101,12 @@ dependencies = [
  "vec_map",
 ]
 
+[[package]]
+name = "computus"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9eaa21df489b1e50af464db43c1fc69f60492060ac7baae3996fe8a5f476790"
+
 [[package]]
 name = "digest"
 version = "0.8.1"
@@ -370,6 +376,7 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "chrono",
+ "computus",
  "pest",
  "pest_derive",
  "structopt",
diff --git a/Cargo.toml b/Cargo.toml
index d0f72cb..6138e05 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,6 +6,7 @@ edition = "2018"
 [dependencies]
 anyhow = "1.0.45"
 chrono = "0.4.19"
+computus = "1.0.0"
 pest = "2.1.3"
 pest_derive = "2.1.0"
 structopt = "0.3.25"
diff --git a/src/eval/command/formula.rs b/src/eval/command/formula.rs
index 141f555..509b1fa 100644
--- a/src/eval/command/formula.rs
+++ b/src/eval/command/formula.rs
@@ -1,12 +1,134 @@
-use crate::files::commands::{self, Expr, Var};
-use crate::files::primitives::{Spanned, Time};
+use chrono::{Datelike, NaiveDate};
+
+use crate::files::commands::{self, Command, Expr, Var};
+use crate::files::primitives::{Spanned, Time, Weekday};
 
 use super::super::command::CommandState;
+use super::super::date::Dates;
 use super::super::delta::{Delta, DeltaStep};
-use super::super::Result;
+use super::super::{util, DateRange, Error, Result};
+
+fn b2i(b: bool) -> i64 {
+    if b {
+        1
+    } else {
+        0
+    }
+}
+
+fn i2b(i: i64) -> bool {
+    i != 0
+}
+
+impl Var {
+    fn eval(self, date: NaiveDate) -> Result<i64> {
+        Ok(match self {
+            Var::True => 1,
+            Var::False => 0,
+            Var::Monday => 1,
+            Var::Tuesday => 2,
+            Var::Wednesday => 3,
+            Var::Thursday => 4,
+            Var::Friday => 5,
+            Var::Saturday => 6,
+            Var::Sunday => 7,
+            Var::JulianDay => date.num_days_from_ce().into(),
+            Var::Year => date.year().into(),
+            Var::YearLength => util::year_length(date.year()).into(),
+            Var::YearDay => date.ordinal().into(),
+            Var::YearDayReverse => (util::year_length(date.year()) - date.ordinal0()).into(),
+            Var::YearWeek => (date.ordinal0().div_euclid(7) + 1).into(),
+            Var::YearWeekReverse => {
+                #[allow(non_snake_case)]
+                let yD = util::year_length(date.year()) - date.ordinal();
+                (yD.div_euclid(7) + 1).into()
+            }
+            Var::Month => date.month().into(),
+            Var::MonthLength => util::month_length(date.year(), date.month()).into(),
+            Var::MonthWeek => (date.month0().div_euclid(7) + 1).into(),
+            Var::MonthWeekReverse => {
+                #[allow(non_snake_case)]
+                let mD = util::month_length(date.year(), date.month()) - date.month0();
+                (mD.div_euclid(7) + 1).into()
+            }
+            Var::Day => date.day().into(),
+            Var::DayReverse => {
+                let ml = util::month_length(date.year(), date.month());
+                (ml - date.month0()).into()
+            }
+            Var::IsoYear => date.iso_week().year().into(),
+            Var::IsoYearLength => util::iso_year_length(date.iso_week().year()).into(),
+            Var::IsoWeek => date.iso_week().week().into(),
+            Var::Weekday => {
+                let wd: Weekday = date.weekday().into();
+                wd.num().into()
+            }
+            Var::Easter => {
+                let e = computus::gregorian(date.year()).map_err(|e| Error::Easter {
+                    span: todo!(),
+                    date,
+                    msg: e,
+                })?;
+                NaiveDate::from_ymd(e.year, e.month, e.day).ordinal().into()
+            }
+            Var::IsWeekday => {
+                let wd: Weekday = date.weekday().into();
+                b2i(!wd.is_weekend())
+            }
+            Var::IsWeekend => {
+                let wd: Weekday = date.weekday().into();
+                b2i(wd.is_weekend())
+            }
+            Var::IsLeapYear => b2i(util::is_leap_year(date.year())),
+        })
+    }
+}
+
+impl Expr {
+    fn eval(&self, date: NaiveDate) -> Result<i64> {
+        Ok(match self {
+            Expr::Lit(l) => *l,
+            Expr::Var(v) => v.eval(date)?,
+            Expr::Paren(e) => e.eval(date)?,
+            Expr::Neg(e) => -e.eval(date)?,
+            Expr::Add(a, b) => a.eval(date)? + b.eval(date)?,
+            Expr::Sub(a, b) => a.eval(date)? - b.eval(date)?,
+            Expr::Mul(a, b) => a.eval(date)? * b.eval(date)?,
+            Expr::Div(a, b) => {
+                let b = b.eval(date)?;
+                if b == 0 {
+                    return Err(Error::DivByZero {
+                        span: todo!(),
+                        date,
+                    });
+                }
+                a.eval(date)?.div_euclid(b)
+            }
+            Expr::Mod(a, b) => {
+                let b = b.eval(date)?;
+                if b == 0 {
+                    return Err(Error::ModByZero {
+                        span: todo!(),
+                        date,
+                    });
+                }
+                a.eval(date)?.rem_euclid(b)
+            }
+            Expr::Eq(a, b) => b2i(a.eval(date)? == b.eval(date)?),
+            Expr::Neq(a, b) => b2i(a.eval(date)? != b.eval(date)?),
+            Expr::Lt(a, b) => b2i(a.eval(date)? < b.eval(date)?),
+            Expr::Lte(a, b) => b2i(a.eval(date)? <= b.eval(date)?),
+            Expr::Gt(a, b) => b2i(a.eval(date)? > b.eval(date)?),
+            Expr::Gte(a, b) => b2i(a.eval(date)? >= b.eval(date)?),
+            Expr::Not(e) => b2i(!i2b(e.eval(date)?)),
+            Expr::And(a, b) => b2i(i2b(a.eval(date)?) && i2b(b.eval(date)?)),
+            Expr::Or(a, b) => b2i(i2b(a.eval(date)?) || i2b(b.eval(date)?)),
+            Expr::Xor(a, b) => b2i(i2b(a.eval(date)?) ^ i2b(b.eval(date)?)),
+        })
+    }
+}
 
 pub struct FormulaSpec {
-    // TODO Implement more efficient exprs and expr evaluation
     pub start: Expr,
     pub start_delta: Delta,
     pub start_time: Option<Time>,
@@ -78,8 +200,48 @@ impl From<&commands::WeekdaySpec> for FormulaSpec {
     }
 }
 
-impl<'a> CommandState<'a> {
-    pub fn eval_formula_spec(&mut self, spec: FormulaSpec) -> Result<()> {
-        todo!()
+impl FormulaSpec {
+    fn range(&self, s: &CommandState<'_>) -> Option<DateRange> {
+        let mut range = s
+            .range
+            .expand_by(&self.end_delta)
+            .move_by(&self.start_delta);
+
+        if let Command::Task(_) = s.command.command {
+            if let Some(last_done) = s.last_done() {
+                range = range.with_from(last_done.succ())?;
+            }
+        }
+
+        s.limit_from_until(range)
+    }
+
+    fn dates(&self, start: NaiveDate) -> Result<Dates> {
+        let root = self.start_delta.apply_date(start)?;
+        Ok(if let Some(root_time) = self.start_time {
+            let (other, other_time) = self.end_delta.apply_date_time(root, root_time)?;
+            Dates::new_with_time(root, root_time, other, other_time)
+        } else {
+            let other = self.end_delta.apply_date(root)?;
+            Dates::new(root, other)
+        })
+    }
+
+    fn eval(&self, date: NaiveDate) -> Result<bool> {
+        Ok(i2b(self.start.eval(date)?))
+    }
+}
+
+impl<'a> CommandState<'a> {
+    pub fn eval_formula_spec(&mut self, spec: FormulaSpec) -> Result<()> {
+        if let Some(range) = spec.range(self) {
+            for day in range.days() {
+                if spec.eval(day)? {
+                    let dates = spec.dates(day)?;
+                    self.add(self.kind(), Some(dates));
+                }
+            }
+        }
+        Ok(())
     }
 }
diff --git a/src/eval/error.rs b/src/eval/error.rs
index 5b89ad1..dd94351 100644
--- a/src/eval/error.rs
+++ b/src/eval/error.rs
@@ -6,6 +6,7 @@ use crate::files::primitives::{Span, Time};
 
 #[derive(Debug)]
 pub enum Error {
+    /// A delta step resulted in an invalid date.
     DeltaInvalidStep {
         span: Span,
         start: NaiveDate,
@@ -13,6 +14,7 @@ pub enum Error {
         prev: NaiveDate,
         prev_time: Option<Time>,
     },
+    /// A time-based delta step was applied to a date without time.
     DeltaNoTime {
         span: Span,
         start: NaiveDate,
@@ -29,6 +31,16 @@ pub enum Error {
     /// A `MOVE a TO b` statement was executed, but there was no entry at the
     /// date `a`.
     MoveWithoutSource { span: Span },
+    /// A division by zero has occurred.
+    DivByZero { span: Span, date: NaiveDate },
+    /// A modulo operation by zero has occurred.
+    ModByZero { span: Span, date: NaiveDate },
+    /// Easter calculation failed.
+    Easter {
+        span: Span,
+        date: NaiveDate,
+        msg: &'static str,
+    },
 }
 
 pub type Result<T> = result::Result<T, Error>;
diff --git a/src/eval/range.rs b/src/eval/range.rs
index c23f88d..60cc87d 100644
--- a/src/eval/range.rs
+++ b/src/eval/range.rs
@@ -40,6 +40,11 @@ impl DateRange {
         self.until
     }
 
+    pub fn days(&self) -> impl Iterator<Item = NaiveDate> {
+        (self.from.num_days_from_ce()..=self.until.num_days_from_ce())
+            .map(|n| NaiveDate::from_num_days_from_ce(n))
+    }
+
     pub fn years(&self) -> RangeInclusive<i32> {
         self.from.year()..=self.until.year()
     }
diff --git a/src/eval/util.rs b/src/eval/util.rs
index 5a96bf1..077d2e8 100644
--- a/src/eval/util.rs
+++ b/src/eval/util.rs
@@ -1,14 +1,15 @@
-use chrono::{Datelike, NaiveDate};
+use chrono::{Datelike, NaiveDate, Weekday};
 
 pub fn is_leap_year(year: i32) -> bool {
     NaiveDate::from_ymd_opt(year, 2, 29).is_some()
 }
 
-pub fn add_months(year: i32, month: u32, delta: i32) -> (i32, u32) {
-    let month0 = (month as i32) - 1 + delta;
-    let year = year + month0.div_euclid(12);
-    let month = month0.rem_euclid(12) as u32 + 1;
-    (year, month)
+pub fn is_iso_leap_year(year: i32) -> bool {
+    NaiveDate::from_isoywd_opt(year, 53, Weekday::Sun).is_some()
+}
+
+pub fn year_length(year: i32) -> u32 {
+    NaiveDate::from_ymd(year, 12, 31).ordinal()
 }
 
 pub fn month_length(year: i32, month: u32) -> u32 {
@@ -17,3 +18,18 @@ pub fn month_length(year: i32, month: u32) -> u32 {
         .pred()
         .day()
 }
+
+pub fn iso_year_length(year: i32) -> u32 {
+    if is_iso_leap_year(year) {
+        53 * 7
+    } else {
+        52 * 7
+    }
+}
+
+pub fn add_months(year: i32, month: u32, delta: i32) -> (i32, u32) {
+    let month0 = (month as i32) - 1 + delta;
+    let year = year + month0.div_euclid(12);
+    let month = month0.rem_euclid(12) as u32 + 1;
+    (year, month)
+}
diff --git a/src/files/primitives.rs b/src/files/primitives.rs
index cc93a77..2444e75 100644
--- a/src/files/primitives.rs
+++ b/src/files/primitives.rs
@@ -129,32 +129,36 @@ impl From<chrono::Weekday> for Weekday {
 }
 
 impl Weekday {
-    pub fn name(&self) -> &'static str {
+    pub fn name(self) -> &'static str {
         match self {
-            Weekday::Monday => "mon",
-            Weekday::Tuesday => "tue",
-            Weekday::Wednesday => "wed",
-            Weekday::Thursday => "thu",
-            Weekday::Friday => "fri",
-            Weekday::Saturday => "sat",
-            Weekday::Sunday => "sun",
+            Self::Monday => "mon",
+            Self::Tuesday => "tue",
+            Self::Wednesday => "wed",
+            Self::Thursday => "thu",
+            Self::Friday => "fri",
+            Self::Saturday => "sat",
+            Self::Sunday => "sun",
         }
     }
 
-    pub fn num(&self) -> u8 {
+    pub fn num(self) -> u8 {
         match self {
-            Weekday::Monday => 1,
-            Weekday::Tuesday => 2,
-            Weekday::Wednesday => 3,
-            Weekday::Thursday => 4,
-            Weekday::Friday => 5,
-            Weekday::Saturday => 6,
-            Weekday::Sunday => 7,
+            Self::Monday => 1,
+            Self::Tuesday => 2,
+            Self::Wednesday => 3,
+            Self::Thursday => 4,
+            Self::Friday => 5,
+            Self::Saturday => 6,
+            Self::Sunday => 7,
         }
     }
 
+    pub fn is_weekend(self) -> bool {
+        matches!(self, Self::Saturday | Self::Sunday)
+    }
+
     /// How many days from now until the other weekday.
-    pub fn until(&self, other: Self) -> u8 {
+    pub fn until(self, other: Self) -> u8 {
         let num_self = self.num();
         let num_other = other.num();
         if num_self <= num_other {