package main

import (
	"errors"
	"time"
)

type Database interface {
	GetTracking() (*Task, error)
	GetTasks() ([]*Task, error)
	QueryTask(id *int) (*Task, error)
	StartNewEntry(now time.Time, task *Task) (*Task, error)
	StopEntry(now time.Time) error
	SaveEntry(task *Task) (*Task, error)
}

type InMemDb struct {
	tasks   []*Task
	current *Task
}

var (
	ErrNotFound = errors.New("Not found")
	ErrNotRunning = errors.New("Not running")
)

func NewInMemDb() Database {
	return &InMemDb {
		tasks: []*Task{},
		current: nil,
	}
}

func (db *InMemDb) GetTracking() (*Task, error) {
	return db.current, nil
}

func (db *InMemDb) GetTasks() ([]*Task, error) {
	res := make([]*Task, 0, len(db.tasks))
	for _, task := range db.tasks {
		res = append(res, task)
	}

	return res, nil
}

func (db *InMemDb) QueryTask(id *int) (*Task, error) {
	for _, task := range db.tasks {
		if id != nil && task.Id == *id {
			return task, nil
		}
	}

	return nil, ErrNotFound
}

func (db *InMemDb) StartNewEntry(now time.Time, task *Task) (*Task, error) {
	newTask := &Task {
		Id: len(db.tasks),
		From: task.From,
		To: nil,
		Tag: task.Tag,
		Comment: task.Comment,
	}

	if newTask.From == nil {
		newTask.From = &now
	}

	db.tasks = append(db.tasks, newTask)
	db.StopEntry(now)
	db.current = newTask
	return newTask, nil
}

func (db *InMemDb) StopEntry(now time.Time) error {
	if db.current != nil {
		db.current.To = &now
		db.current = nil
	} else {
		return ErrNotRunning
	}
	return nil
}

func (db *InMemDb) SaveEntry(task *Task) (*Task, error) {
	if task.Id < 0 || task.Id >= len(db.tasks) {
		copyTask := *task
		copyTask.Id = len(db.tasks)
		db.tasks = append(db.tasks, &copyTask)

		return &copyTask, nil
	}
	
	existent := db.tasks[task.Id]
	existent.Comment = task.Comment
	existent.Tag = task.Tag
	existent.From = task.From
	existent.To = task.To
	return existent, nil
}