package main

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"time"

	"github.com/cenkalti/backoff/v5"
	"github.com/robfig/cron/v3"
)

type InputLine struct {
	RawSchedule, RawTask string
}

type TaskAddingJob struct {
	Schedule cron.Schedule
	Task     cron.Job
	EntryID  cron.EntryID // this doesn't fit super well, but we'll figure that out soon I guess
	Delete   bool
}

type Task struct {
	Name string
}

func (t Task) Run() {
	_, err := backoff.Retry(context.Background(), func() (bool, error) { return true, createTask(t.Name) }, backoff.WithBackOff(backoff.NewExponentialBackOff()))
	if err != nil {
		log.Printf("Failed to create task '%s': %s", t.Name, err)
	}
}

var jobsFromInput = map[InputLine]TaskAddingJob{}
var todoistToken string
var httpClient = http.Client{
	Timeout: 10 * time.Second,
}

func main() {
	if err := setToken(); err != nil {
		log.Fatalf("setting token: %s", err)
	}

	p, err := inputFilePath()
	if err != nil {
		log.Fatalf("getting input file: %s", err)
	}
	log.Printf("Started watching '%s'", p)

	c := cron.New()
	c.Start()

	for {
		err = readInput(p)
		if err != nil {
			log.Printf("Error reading input: %s", err)
			goto SLEEP
		}

		for inputLine, taskAddingJob := range jobsFromInput {
			if jobsFromInput[inputLine].EntryID == 0 {
				taskAddingJob.EntryID = c.Schedule(
					jobsFromInput[inputLine].Schedule,
					jobsFromInput[inputLine].Task,
				)
				jobsFromInput[inputLine] = taskAddingJob

				log.Printf(
					"Added '%s' with recurrence '%s'",
					inputLine.RawTask,
					inputLine.RawSchedule,
				)
			} else if taskAddingJob.Delete {
				c.Remove(taskAddingJob.EntryID)
				delete(jobsFromInput, inputLine)
				log.Printf("Removed '%s'", inputLine.RawTask)
			}
		}

	SLEEP:
		time.Sleep(time.Minute)
	}

}

func setToken() error {
	token := os.Getenv("TODOIST_TOKEN")
	if token == "" {
		return fmt.Errorf("TODOIST_TOKEN env var must be present and non-empty")
	}
	todoistToken = token

	return nil
}

func inputFilePath() (string, error) {
	args := os.Args
	if len(args) != 2 {
		return "", fmt.Errorf("expected one argument (input file path), got %d", len(args)-1)
	}
	p := filepath.Clean(args[1])

	// While we're here, check that the input path actually exists and
	// is stat-able.
	if _, err := os.Stat(p); err != nil {
		return "", fmt.Errorf("cannot stat input file: %w", err)
	}

	return p, nil
}

var inputFileRe = regexp.MustCompile(`([^\s]+\s+[^\s]+\s+[^\s]+\s+[^\s]+\s+[^\s]+)\s+(.*)`)

func readInput(p string) error {
	f, err := os.Open(p)
	if err != nil {
		return fmt.Errorf("opening '%s': %w", p, err)
	}
	defer f.Close()

	previousInput := map[InputLine]struct{}{}
	for k := range jobsFromInput {
		previousInput[k] = struct{}{}
	}
	currentInput := map[InputLine]struct{}{}

	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}

		matches := inputFileRe.FindStringSubmatch(line)
		if matches == nil || len(matches) != 1+2 {
			log.Printf("failed to parse input line: '%s'", line)
			continue
		}

		inputLine := InputLine{
			RawSchedule: matches[1],
			RawTask:     matches[2],
		}

		currentInput[inputLine] = struct{}{}
		if _, ok := previousInput[inputLine]; ok {
			continue
		}

		schedule, err := cron.ParseStandard(inputLine.RawSchedule)
		if err != nil {
			log.Printf(
				"Failed to add '%s' with recurrence '%s': %s",
				inputLine.RawTask,
				inputLine.RawSchedule,
				err,
			)
			continue
		}

		jobsFromInput[inputLine] = TaskAddingJob{
			Schedule: schedule,
			Task:     Task{Name: inputLine.RawTask},
		}
	}
	if err := scanner.Err(); err != nil {
		return fmt.Errorf("scanning: %w", err)
	}

	// Mark stuff that we previously saw, but is now missing, for pruning.
	for k := range previousInput {
		if _, ok := currentInput[k]; !ok {
			v := jobsFromInput[k]
			v.Delete = true
			jobsFromInput[k] = v
		}
	}

	return nil
}

func createTask(task string) error {
	jsonBody := []byte(fmt.Sprintf(`{"content": %s}`, strconv.Quote(task)))
	req, err := http.NewRequest(
		http.MethodPost,
		"https://api.todoist.com/api/v1/tasks",
		bytes.NewBuffer(jsonBody),
	)
	if err != nil {
		return fmt.Errorf("creating request: %w", err)
	}
	req.Header.Add("Authorization", "Bearer "+todoistToken)
	req.Header.Set("Content-Type", "application/json")

	resp, err := httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("doing request: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		bodyBytes, err := io.ReadAll(resp.Body)
		if err != nil {
			return fmt.Errorf("reading body when preparing error message (HTTP status was %d): %w", resp.StatusCode, err)
		}
		return fmt.Errorf("expected 200, got status code %d: body was %s", resp.StatusCode, strconv.Quote(string(bodyBytes)))
	}

	log.Printf("Created task '%s'", task)
	return nil
}