package zoptions

import "time"

type NotifyParameters struct {
	// AlwaysSend makes sure this message
	// is always sent no matter the condition.
	//
	// It will cause `zen` to ignore every other
	// parameters and just send the message.
	AlwaysSend bool

	// InitialBackoff is the starting backoff.
	//
	// If not specified, the default duration is time.Minute.
	InitialBackoff time.Duration
	// MaxBackoff is the maximum backoff. If unset, the default value
	// is time.Hour * 24.
	MaxBackoff time.Duration

	// BackoffFormula is a string that represents the formula to calculate the backoff time
	// when multiple message with the same key is fired off repeatedly.
	//
	// It uses CEL (Common Expression Language) syntax. See: https://github.com/google/cel-go
	// for the language spec.
	//
	// Expression must return a duration type.
	//
	// If invalid cel expression, empty string, or wrong return value, default formula will be used.
	//
	// Available variables:
	//
	//  - `repeat`: the number of times the notification has been sent. type: int.
	//  - `last`: the last time the notification was sent. type: timestamp.
	//  - `prev_backoff`: the backoff value from previous evaluation. 0 if first seen. Type: duration.
	//  - `initial_backoff`: the initial_backoff value. Type: duration
	//  - `max_backoff`: the maximum backoff value. Type: duration
	//
	// Available Non-Standard functions:
	//
	//  // pow multiplies the base with the exponent
	//  pow(base: double, exp: double) -> double
	//
	//  // mult_dur_double multiplies the duration with the double value
	//  mult_dur_double(dur: duration, mult: double) -> duration
	//
	//
	// Example (and also default formula):
	//
	//     mult_dur_double(initial_backoff, pow(1.5, double(repeat))) > max_backoff
	//     	? max_backoff
	//     	: mult_dur_double(initial_backoff, pow(1.5, double(repeat)))
	BackoffFormula string
}

type NotifyOption interface {
	Apply(parameters *NotifyParameters)
}

type NotifyOptionFunc func(parameters *NotifyParameters)

func (f NotifyOptionFunc) Apply(parameters *NotifyParameters) {
	f(parameters)
}

type NotifiyOptionBuilder []NotifyOption

func (no NotifiyOptionBuilder) Apply(parameters *NotifyParameters) {
	for _, opt := range no {
		opt.Apply(parameters)
	}
}

func (no NotifiyOptionBuilder) AlwaysSend(alwaysSend bool) NotifiyOptionBuilder {
	return append(no, NotifyOptionFunc(func(parameters *NotifyParameters) {
		parameters.AlwaysSend = alwaysSend
	}))
}

func (no NotifiyOptionBuilder) InitialBackoff(backoff time.Duration) NotifiyOptionBuilder {
	return append(no, NotifyOptionFunc(func(parameters *NotifyParameters) {
		parameters.InitialBackoff = backoff
	}))
}

func (no NotifiyOptionBuilder) MaxBackoff(maxBackoff time.Duration) NotifiyOptionBuilder {
	return append(no, NotifyOptionFunc(func(parameters *NotifyParameters) {
		parameters.MaxBackoff = maxBackoff
	}))
}

// BackoffFormula is a string that represents the formula to calculate the backoff time
// when multiple message with the same key is fired off repeatedly.
//
// It uses CEL (Common Expression Language) syntax. See: https://github.com/google/cel-go
// for the language spec.
//
// Expression must return a duration type.
//
// If invalid cel expression, empty string, or wrong return value, default formula will be used.
//
// Available variables:
//
//   - `repeat`: the number of times the notification has been sent. type: int.
//   - `last`: the last time the notification was sent. type: timestamp.
//   - `prev_backoff`: the backoff value from previous evaluation. 0 if this message is first seen. Type: duration.
//   - `initial_backoff`: the initial_backoff value. Type: duration
//   - `max_backoff`: the maximum backoff value. Type: duration
//
// Available Non-Standard functions:
//
//	// pow multiplies the base with the exponent
//	pow(base: double, exp: double) -> double
//
//	// mult_dur_double multiplies the duration with the double value
//	mult_dur_double(dur: duration, mult: double) -> duration
//
// Example (and also default formula):
//
//	mult_dur_double(initial_backoff, pow(1.5, double(repeat))) > max_backoff
//		? max_backoff
//		: mult_dur_double(initial_backoff, pow(1.5, double(repeat)))
func (no NotifiyOptionBuilder) BackoffFormula(formula string) NotifiyOptionBuilder {
	return append(no, NotifyOptionFunc(func(parameters *NotifyParameters) {
		parameters.BackoffFormula = formula
	}))
}

func Notify() NotifiyOptionBuilder {
	return NotifiyOptionBuilder{}
}