/*
Copyright 2022 The Dapr Authors
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
    http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
This package has been forked from https://github.com/robfig/cron available under the MIT license.
You can check the original license at:
		https://github.com/robfig/cron/blob/master/LICENSE
*/

//nolint
package cron

import "time"

// SpecSchedule specifies a duty cycle (to the second granularity), based on a
// traditional crontab specification. It is computed initially and stored as bit sets.
type SpecSchedule struct {
	Second, Minute, Hour, Dom, Month, Dow uint64

	// Override location for this schedule.
	Location *time.Location
}

// bounds provides a range of acceptable values (plus a map of name to value).
type bounds struct {
	min, max uint
	names    map[string]uint
}

// The bounds for each field.
var (
	seconds = bounds{0, 59, nil}
	minutes = bounds{0, 59, nil}
	hours   = bounds{0, 23, nil}
	dom     = bounds{1, 31, nil}
	months  = bounds{1, 12, map[string]uint{
		"jan": 1,
		"feb": 2,
		"mar": 3,
		"apr": 4,
		"may": 5,
		"jun": 6,
		"jul": 7,
		"aug": 8,
		"sep": 9,
		"oct": 10,
		"nov": 11,
		"dec": 12,
	}}
	dow = bounds{0, 6, map[string]uint{
		"sun": 0,
		"mon": 1,
		"tue": 2,
		"wed": 3,
		"thu": 4,
		"fri": 5,
		"sat": 6,
	}}
)

const (
	// Set the top bit if a star was included in the expression.
	starBit = 1 << 63
)

// Next returns the next time this schedule is activated, greater than the given
// time.  If no time can be found to satisfy the schedule, return the zero time.
func (s *SpecSchedule) Next(t time.Time) time.Time {
	// General approach
	//
	// For Month, Day, Hour, Minute, Second:
	// Check if the time value matches.  If yes, continue to the next field.
	// If the field doesn't match the schedule, then increment the field until it matches.
	// While incrementing the field, a wrap-around brings it back to the beginning
	// of the field list (since it is necessary to re-verify previous field
	// values)

	// Convert the given time into the schedule's timezone, if one is specified.
	// Save the original timezone so we can convert back after we find a time.
	// Note that schedules without a time zone specified (time.Local) are treated
	// as local to the time provided.
	origLocation := t.Location()
	loc := s.Location
	if loc == time.Local {
		loc = t.Location()
	}
	if s.Location != time.Local {
		t = t.In(s.Location)
	}

	// Start at the earliest possible time (the upcoming second).
	t = t.Add(1*time.Second - time.Duration(t.Nanosecond())*time.Nanosecond)

	// This flag indicates whether a field has been incremented.
	added := false

	// If no time is found within five years, return zero.
	yearLimit := t.Year() + 5

WRAP:
	if t.Year() > yearLimit {
		return time.Time{}
	}

	// Find the first applicable month.
	// If it's this month, then do nothing.
	for 1<<uint(t.Month())&s.Month == 0 {
		// If we have to add a month, reset the other parts to 0.
		if !added {
			added = true
			// Otherwise, set the date at the beginning (since the current time is irrelevant).
			t = time.Date(t.Year(), t.Month(), 1, 0, 0, 0, 0, loc)
		}
		t = t.AddDate(0, 1, 0)

		// Wrapped around.
		if t.Month() == time.January {
			goto WRAP
		}
	}

	// Now get a day in that month.
	//
	// NOTE: This causes issues for daylight savings regimes where midnight does
	// not exist.  For example: Sao Paulo has DST that transforms midnight on
	// 11/3 into 1am. Handle that by noticing when the Hour ends up != 0.
	for !dayMatches(s, t) {
		if !added {
			added = true
			t = time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, loc)
		}
		t = t.AddDate(0, 0, 1)
		// Notice if the hour is no longer midnight due to DST.
		// Add an hour if it's 23, subtract an hour if it's 1.
		if t.Hour() != 0 {
			if t.Hour() > 12 {
				t = t.Add(time.Duration(24-t.Hour()) * time.Hour)
			} else {
				t = t.Add(time.Duration(-t.Hour()) * time.Hour)
			}
		}

		if t.Day() == 1 {
			goto WRAP
		}
	}

	for 1<<uint(t.Hour())&s.Hour == 0 {
		if !added {
			added = true
			t = time.Date(t.Year(), t.Month(), t.Day(), t.Hour(), 0, 0, 0, loc)
		}
		t = t.Add(1 * time.Hour)

		if t.Hour() == 0 {
			goto WRAP
		}
	}

	for 1<<uint(t.Minute())&s.Minute == 0 {
		if !added {
			added = true
			t = t.Truncate(time.Minute)
		}
		t = t.Add(1 * time.Minute)

		if t.Minute() == 0 {
			goto WRAP
		}
	}

	for 1<<uint(t.Second())&s.Second == 0 {
		if !added {
			added = true
			t = t.Truncate(time.Second)
		}
		t = t.Add(1 * time.Second)

		if t.Second() == 0 {
			goto WRAP
		}
	}

	return t.In(origLocation)
}

// dayMatches returns true if the schedule's day-of-week and day-of-month
// restrictions are satisfied by the given time.
func dayMatches(s *SpecSchedule, t time.Time) bool {
	var (
		domMatch bool = 1<<uint(t.Day())&s.Dom > 0
		dowMatch bool = 1<<uint(t.Weekday())&s.Dow > 0
	)
	if s.Dom&starBit > 0 || s.Dow&starBit > 0 {
		return domMatch && dowMatch
	}
	return domMatch || dowMatch
}