package lib

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"log/slog"
	"os"
	"path/filepath"
	"strconv"
	"time"
)

// Time entity as defined by the specification.
type Time struct {
	ID         string    `json:"id"`
	ProjectID  string    `json:"project"`
	ActivityID string    `json:"activity"`
	Start      time.Time `json:"start"`
	End        time.Time `json:"end"`
}

// SetTime persists a time entry.
func SetTime(entry *Time) error {
	// Traverse range by day (in case is spans multiple days
	for date := entry.Start.Truncate(24 * time.Hour); !date.After(entry.End); date = date.AddDate(0, 0, 1) {
		start := entry.Start
		if date.After(start) {
			start = date
		}
		end := entry.End
		if date.AddDate(0, 0, 1).Add(-1 * time.Second).Before(end) {
			end = date.AddDate(0, 0, 1).Add(-1 * time.Second)
		}

		dayEntry := Time{
			ProjectID:  entry.ProjectID,
			ActivityID: entry.ActivityID,
			Start:      start,
			End:        end,
		}

		uuid, uuidErr := newUUID()
		if uuidErr != nil {
			return uuidErr
		}

		year, month, day := date.UTC().Date()
		file, fileErr := getTimeFile(year, int(month), day, uuid)
		if fileErr != nil {
			return fileErr
		}

		writeErr := writeTime(&dayEntry, file)
		if writeErr != nil {
			return writeErr
		}
	}

	return nil
}

// readTimeRange reads time entries for a given time range.
func readTimeRange(start, end time.Time) ([]*Time, error) {
	entries := []*Time{}

	// Traverse range by day
	for date := start; !date.After(end); date = date.AddDate(0, 0, 1) {
		// Traverse files
		year, month, day := date.UTC().Date()
		folder, folderErr := getTimeFolder(year, int(month), day)
		if folderErr != nil {
			return nil, folderErr
		}

		slog.Debug(fmt.Sprintf("Read time files from folder %s", folder))
		files, filesErr := os.ReadDir(folder)
		if errors.Is(filesErr, fs.ErrNotExist) {
			return entries, nil
		}
		if filesErr != nil {
			return nil, filesErr
		}
		for _, file := range files {
			entry, entryErr := readTime(filepath.Join(folder, file.Name()))
			if entryErr != nil {
				return nil, entryErr
			}
			if (entry.Start.After(start) && entry.Start.Before(end)) || (entry.End.After(start) && entry.End.Before(end)) {
				entries = append(entries, entry)
			}
		}
	}

	return entries, nil
}

// readTime reads a time entry from a file and converts it into an entity instance.
func readTime(filename string) (*Time, error) {
	file, err := os.Open(filename)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, err
	}
	defer file.Close()

	time := Time{}
	if err := json.NewDecoder(file).Decode(&time); err != nil {
		return nil, err
	}

	return &time, nil
}

// writeTime writes a time instance to a file.
func writeTime(time *Time, filename string) error {
	dirErr := os.MkdirAll(filepath.Dir(filename), 0o750)
	if dirErr != nil {
		return dirErr
	}

	file, fileErr := os.Create(filename)
	if fileErr != nil {
		return fileErr
	}
	defer file.Close()

	encoder := json.NewEncoder(file)
	encoder.SetIndent("", "    ")

	jsonErr := encoder.Encode(time)
	if jsonErr != nil {
		return jsonErr
	}

	return nil
}

// getTimeFolder returns the folder to store time entity files in.
func getTimeFolder(year int, month int, day int) (string, error) {
	folder, err := getDataDir("times")
	if err != nil {
		return "", err
	}

	return filepath.Join(folder, strconv.Itoa(year), strconv.Itoa(month), strconv.Itoa(day)), nil
}

// getTimeFile returns the file name for a time entity instance.
func getTimeFile(year int, month int, day int, name string) (string, error) {
	folder, err := getTimeFolder(year, month, day)
	if err != nil {
		return "", err
	}

	return filepath.Join(folder, name+".json"), nil
}