Merge pull request #173 from yuankunzhang/date-time-builder

refactor: introduce a builder and simplify the date time composition

Author: cakebaker

src/items/builder.rs

@@ -0,0 +1,303 @@
+// For the full copyright and license information, please view the LICENSE
+// file that was distributed with this source code.
+
+use chrono::{DateTime, Datelike, FixedOffset, NaiveDate, TimeZone, Timelike};
+
+use super::{date, relative, time, weekday};
+
+/// The builder is used to construct a DateTime object from various components.
+/// The parser creates a `DateTimeBuilder` object with the parsed components,
+/// but without the baseline date and time. So you normally need to set the base
+/// date and time using the `set_base()` method before calling `build()`, or
+/// leave it unset to use the current date and time as the base.
+#[derive(Debug, Default)]
+pub struct DateTimeBuilder {
+    base: Option<DateTime<FixedOffset>>,
+    timestamp: Option<i32>,
+    date: Option<date::Date>,
+    time: Option<time::Time>,
+    weekday: Option<weekday::Weekday>,
+    timezone: Option<time::Offset>,
+    relative: Vec<relative::Relative>,
+}
+
+impl DateTimeBuilder {
+    pub(super) fn new() -> Self {
+        Self::default()
+    }
+
+    /// Sets the base date and time for the builder. If not set, the current
+    /// date and time will be used.
+    pub(super) fn set_base(mut self, base: DateTime<FixedOffset>) -> Self {
+        self.base = Some(base);
+        self
+    }
+
+    pub(super) fn set_timestamp(mut self, ts: i32) -> Result<Self, &'static str> {
+        if self.timestamp.is_some() {
+            Err("timestamp cannot appear more than once")
+        } else {
+            self.timestamp = Some(ts);
+            Ok(self)
+        }
+    }
+
+    pub(super) fn set_year(mut self, year: u32) -> Result<Self, &'static str> {
+        if let Some(date) = self.date.as_mut() {
+            if date.year.is_some() {
+                Err("year cannot appear more than once")
+            } else {
+                date.year = Some(year);
+                Ok(self)
+            }
+        } else {
+            self.date = Some(date::Date {
+                day: 1,
+                month: 1,
+                year: Some(year),
+            });
+            Ok(self)
+        }
+    }
+
+    pub(super) fn set_date(mut self, date: date::Date) -> Result<Self, &'static str> {
+        if self.date.is_some() || self.timestamp.is_some() {
+            Err("date cannot appear more than once")
+        } else {
+            self.date = Some(date);
+            Ok(self)
+        }
+    }
+
+    pub(super) fn set_time(mut self, time: time::Time) -> Result<Self, &'static str> {
+        if self.time.is_some() || self.timestamp.is_some() {
+            Err("time cannot appear more than once")
+        } else if self.timezone.is_some() && time.offset.is_some() {
+            Err("time offset and timezone are mutually exclusive")
+        } else {
+            self.time = Some(time);
+            Ok(self)
+        }
+    }
+
+    pub(super) fn set_weekday(mut self, weekday: weekday::Weekday) -> Result<Self, &'static str> {
+        if self.weekday.is_some() {
+            Err("weekday cannot appear more than once")
+        } else {
+            self.weekday = Some(weekday);
+            Ok(self)
+        }
+    }
+
+    pub(super) fn set_timezone(mut self, timezone: time::Offset) -> Result<Self, &'static str> {
+        if self.timezone.is_some() {
+            Err("timezone cannot appear more than once")
+        } else if self.time.as_ref().and_then(|t| t.offset.as_ref()).is_some() {
+            Err("time offset and timezone are mutually exclusive")
+        } else {
+            self.timezone = Some(timezone);
+            Ok(self)
+        }
+    }
+
+    pub(super) fn push_relative(mut self, relative: relative::Relative) -> Self {
+        self.relative.push(relative);
+        self
+    }
+
+    pub(super) fn build(self) -> Option<DateTime<FixedOffset>> {
+        let base = self.base.unwrap_or_else(|| chrono::Local::now().into());
+        let mut dt = new_date(
+            base.year(),
+            base.month(),
+            base.day(),
+            0,
+            0,
+            0,
+            0,
+            *base.offset(),
+        )?;
+
+        if let Some(ts) = self.timestamp {
+            dt = chrono::Utc
+                .timestamp_opt(ts.into(), 0)
+                .unwrap()
+                .with_timezone(&dt.timezone());
+        }
+
+        if let Some(date::Date { year, month, day }) = self.date {
+            dt = new_date(
+                year.map(|x| x as i32).unwrap_or(dt.year()),
+                month,
+                day,
+                dt.hour(),
+                dt.minute(),
+                dt.second(),
+                dt.nanosecond(),
+                *dt.offset(),
+            )?;
+        }
+
+        if let Some(time::Time {
+            hour,
+            minute,
+            second,
+            ref offset,
+        }) = self.time
+        {
+            let offset = offset
+                .clone()
+                .and_then(|o| chrono::FixedOffset::try_from(o).ok())
+                .unwrap_or(*dt.offset());
+
+            dt = new_date(
+                dt.year(),
+                dt.month(),
+                dt.day(),
+                hour,
+                minute,
+                second as u32,
+                (second.fract() * 10f64.powi(9)).round() as u32,
+                offset,
+            )?;
+        }
+
+        if let Some(weekday::Weekday { offset, day }) = self.weekday {
+            if self.time.is_none() {
+                dt = new_date(dt.year(), dt.month(), dt.day(), 0, 0, 0, 0, *dt.offset())?;
+            }
+
+            let mut offset = offset;
+            let day = day.into();
+
+            // If the current day is not the target day, we need to adjust
+            // the x value to ensure we find the correct day.
+            //
+            // Consider this:
+            // Assuming today is Monday, next Friday is actually THIS Friday;
+            // but next Monday is indeed NEXT Monday.
+            if dt.weekday() != day && offset > 0 {
+                offset -= 1;
+            }
+
+            // Calculate the delta to the target day.
+            //
+            // Assuming today is Thursday, here are some examples:
+            //
+            // Example 1: last Thursday (x = -1, day = Thursday)
+            //            delta = (3 - 3) % 7 + (-1) * 7 = -7
+            //
+            // Example 2: last Monday (x = -1, day = Monday)
+            //            delta = (0 - 3) % 7 + (-1) * 7 = -3
+            //
+            // Example 3: next Monday (x = 1, day = Monday)
+            //            delta = (0 - 3) % 7 + (0) * 7 = 4
+            // (Note that we have adjusted the x value above)
+            //
+            // Example 4: next Thursday (x = 1, day = Thursday)
+            //            delta = (3 - 3) % 7 + (1) * 7 = 7
+            let delta = (day.num_days_from_monday() as i32
+                - dt.weekday().num_days_from_monday() as i32)
+                .rem_euclid(7)
+                + offset.checked_mul(7)?;
+
+            dt = if delta < 0 {
+                dt.checked_sub_days(chrono::Days::new((-delta) as u64))?
+            } else {
+                dt.checked_add_days(chrono::Days::new(delta as u64))?
+            }
+        }
+
+        for rel in self.relative {
+            if self.timestamp.is_none()
+                && self.date.is_none()
+                && self.time.is_none()
+                && self.weekday.is_none()
+            {
+                dt = base;
+            }
+
+            match rel {
+                relative::Relative::Years(x) => {
+                    dt = dt.with_year(dt.year() + x)?;
+                }
+                relative::Relative::Months(x) => {
+                    // *NOTE* This is done in this way to conform to
+                    // GNU behavior.
+                    let days = last_day_of_month(dt.year(), dt.month());
+                    if x >= 0 {
+                        dt += dt
+                            .date_naive()
+                            .checked_add_days(chrono::Days::new((days * x as u32) as u64))?
+                            .signed_duration_since(dt.date_naive());
+                    } else {
+                        dt += dt
+                            .date_naive()
+                            .checked_sub_days(chrono::Days::new((days * -x as u32) as u64))?
+                            .signed_duration_since(dt.date_naive());
+                    }
+                }
+                relative::Relative::Days(x) => dt += chrono::Duration::days(x.into()),
+                relative::Relative::Hours(x) => dt += chrono::Duration::hours(x.into()),
+                relative::Relative::Minutes(x) => {
+                    dt += chrono::Duration::try_minutes(x.into())?;
+                }
+                // Seconds are special because they can be given as a float
+                relative::Relative::Seconds(x) => {
+                    dt += chrono::Duration::try_seconds(x as i64)?;
+                }
+            }
+        }
+
+        if let Some(offset) = self.timezone {
+            dt = with_timezone_restore(offset, dt)?;
+        }
+
+        Some(dt)
+    }
+}
+
+#[allow(clippy::too_many_arguments)]
+fn new_date(
+    year: i32,
+    month: u32,
+    day: u32,
+    hour: u32,
+    minute: u32,
+    second: u32,
+    nano: u32,
+    offset: FixedOffset,
+) -> Option<DateTime<FixedOffset>> {
+    let newdate = NaiveDate::from_ymd_opt(year, month, day)
+        .and_then(|naive| naive.and_hms_nano_opt(hour, minute, second, nano))?;
+
+    Some(DateTime::<FixedOffset>::from_local(newdate, offset))
+}
+
+/// Restores year, month, day, etc after applying the timezone
+/// returns None if timezone overflows the date
+fn with_timezone_restore(
+    offset: time::Offset,
+    at: DateTime<FixedOffset>,
+) -> Option<DateTime<FixedOffset>> {
+    let offset: FixedOffset = chrono::FixedOffset::try_from(offset).ok()?;
+    let copy = at;
+    let x = at
+        .with_timezone(&offset)
+        .with_day(copy.day())?
+        .with_month(copy.month())?
+        .with_year(copy.year())?
+        .with_hour(copy.hour())?
+        .with_minute(copy.minute())?
+        .with_second(copy.second())?
+        .with_nanosecond(copy.nanosecond())?;
+    Some(x)
+}
+
+fn last_day_of_month(year: i32, month: u32) -> u32 {
+    NaiveDate::from_ymd_opt(year, month + 1, 1)
+        .unwrap_or(NaiveDate::from_ymd_opt(year + 1, 1, 1).unwrap())
+        .pred_opt()
+        .unwrap()
+        .day()
+}