package domain

import (
	"errors"
	"math"
	"time"
)

type ETAInput struct {
	PeopleAhead       int
	IntervalPerPerson time.Duration
	Running           bool
}

type ETAResult struct {
	Available       bool   `json:"available"`
	EstimateMinutes int    `json:"estimate_minutes"`
	MinMinutes      int    `json:"min_minutes"`
	MaxMinutes      int    `json:"max_minutes"`
	Reason          string `json:"reason,omitempty"`
}

func CalculateETA(input ETAInput) (ETAResult, error) {
	if !input.Running {
		return ETAResult{Available: false, Reason: "queue_not_running"}, nil
	}
	if input.PeopleAhead < 0 {
		return ETAResult{}, errors.New("people ahead cannot be negative")
	}
	if input.IntervalPerPerson <= 0 {
		return ETAResult{Available: false, Reason: "missing_interval_configuration"}, nil
	}
	rawMinutes := float64(input.PeopleAhead) * input.IntervalPerPerson.Minutes()
	estimate := roundUpFive(rawMinutes)
	return ETAResult{
		Available:       true,
		EstimateMinutes: estimate,
		MinMinutes:      estimate,
		MaxMinutes:      estimate,
	}, nil
}

func roundUpFive(value float64) int {
	if value <= 0 {
		return 0
	}
	return int(math.Ceil(value/5) * 5)
}