package api

import (
	"errors"
	"time"

	"gardomatic.kleiax.de/internal/daterange"
	"gardomatic.kleiax.de/internal/storage"
)

func (app *application) generateTasks(gardenID, userID int, now time.Time) error {
	plants, err := app.models.Plants.GetAllForGarden(gardenID)
	if err != nil {
		return err
	}
	existing, err := app.models.Tasks.GetAllForGarden(gardenID)
	if err != nil {
		return err
	}
	for _, plant := range plants {
		if plant.SpeciesID == nil || (plant.Status != "alive" && plant.Status != "active") {
			continue
		}
		var species storage.Species
		templates, err := app.models.SpeciesTaskTemplates.GetAllForSpecies(gardenID, *plant.SpeciesID)
		if err != nil {
			return err
		}
		for _, template := range templates {
			if !template.Active {
				continue
			}
			if template.TriggerType == storage.TaskTriggerRelativeToSowing || template.TriggerType == storage.TaskTriggerRelativeToHarvest || template.TriggerType == storage.TaskTriggerRelativeToSpeciesPlanting {
				species, err = app.models.Species.Get(gardenID, *plant.SpeciesID)
				if err != nil {
					return err
				}
			}
			if app.models.TaskTemplateOptOuts != nil {
				optedOut, optErr := app.models.TaskTemplateOptOuts.IsOptedOut(gardenID, plant.ID, template.ID)
				if optErr != nil {
					return optErr
				}
				if optedOut {
					continue
				}
			}
			for _, task := range generatedTasksForTemplate(plant, species, template, existing, gardenID, userID, now) {
				if _, err := app.models.Tasks.Insert(task); err != nil && !errors.Is(err, storage.ErrConflict) {
					return err
				}
			}
		}
	}
	return nil
}

func generatedTasksForTemplate(plant storage.Plant, species storage.Species, template storage.SpeciesTaskTemplate, existing []storage.Task, gardenID, userID int, now time.Time) []storage.Task {
	var start, generatedFor time.Time
	switch template.TriggerType {
	case storage.TaskTriggerMonthOfYear:
		if template.MonthFrom == nil || template.DayFrom == nil {
			return nil
		}
		start = nextAnnualStart(now, *template.MonthFrom, *template.DayFrom)
		generatedFor = daterange.Date(start)
	case storage.TaskTriggerRelativeToPlanting:
		if plant.AcquiredAt == nil {
			return nil
		}
		base := daterange.Date(*plant.AcquiredAt)
		start, generatedFor = addTemplateDuration(base, template.TriggerOffset, template.TriggerOffsetUnit), base
	case storage.TaskTriggerRelativeToLastTask:
		base, ok := latestCompletion(existing, plant.ID, template.ID)
		if !ok {
			return nil
		}
		base = daterange.Date(base)
		start, generatedFor = addTemplateDuration(base, template.TriggerOffset, template.TriggerOffsetUnit), base
	case storage.TaskTriggerRelativeToSowing, storage.TaskTriggerRelativeToHarvest, storage.TaskTriggerRelativeToSpeciesPlanting:
		month, day := species.SowMonthFrom, species.SowDayFrom
		if template.TriggerType == storage.TaskTriggerRelativeToHarvest {
			month, day = species.HarvestMonthFrom, species.HarvestDayFrom
		} else if template.TriggerType == storage.TaskTriggerRelativeToSpeciesPlanting {
			month, day = species.PlantingMonthFrom, species.PlantingDayFrom
		}
		if month == nil {
			return nil
		}
		d := 1
		if day != nil {
			d = *day
		}
		base := nextAnnualStart(now, *month, d)
		start, generatedFor = addTemplateDuration(base, template.TriggerOffset, template.TriggerOffsetUnit), daterange.Date(base)
	default:
		return nil
	}
	makeTask := func(windowStart, windowEnd, slot time.Time) storage.Task {
		plantID, templateID := plant.ID, template.ID
		return storage.Task{GardenID: gardenID, PlantID: &plantID, TemplateID: &templateID, Title: template.Title, Description: template.Description, DueAtStart: &windowStart, DueAtEnd: &windowEnd, GeneratedFor: &slot, Recurrence: template.Recurrence, RecurrenceInterval: template.RecurrenceInterval, Priority: template.Priority, Active: true, CreatedBy: userID}
	}
	end := endOfDay(addTemplateDuration(start, template.Duration, template.DurationUnit))
	return []storage.Task{makeTask(start, end, generatedFor)}
}

func nextAnnualStart(now time.Time, month, day int) time.Time {
	lastDay := time.Date(now.Year(), time.Month(month)+1, 0, 0, 0, 0, 0, now.Location()).Day()
	if day > lastDay {
		day = lastDay
	}
	result := time.Date(now.Year(), time.Month(month), day, 0, 0, 0, 0, now.Location())
	if result.Before(daterange.Date(now)) {
		result = result.AddDate(1, 0, 0)
	}
	return result
}

func addTemplateDuration(value time.Time, amount int, unit storage.TaskDurationUnit) time.Time {
	switch unit {
	case storage.TaskDurationWeek:
		return value.AddDate(0, 0, amount*7)
	case storage.TaskDurationMonth:
		return addClampedDate(value, 0, amount)
	default:
		return value.AddDate(0, 0, amount)
	}
}

func endOfDay(value time.Time) time.Time {
	return daterange.Date(value).AddDate(0, 0, 1).Add(-time.Nanosecond)
}

func latestCompletion(tasks []storage.Task, plantID, templateID int) (time.Time, bool) {
	var latest time.Time
	for _, task := range tasks {
		if task.PlantID != nil && *task.PlantID == plantID && task.TemplateID != nil && *task.TemplateID == templateID && task.CompletedAt != nil && task.CompletedAt.After(latest) {
			latest = *task.CompletedAt
		}
	}
	return latest, !latest.IsZero()
}