package main

import (
	"encoding/gob"
	"errors"
	"flag"
	"fmt"
	"os"
	"strings"
	"time"

	ws "git.spacehb.net/ws.git"
)

var (
	// Stack of active tasks
	Tags []ws.Tag
	// Active tasks
	TasksDo []ws.Task
	// Completed tasks
	TasksDone []ws.TaskDone
	// Persistent storage for Tasks
)

func AddTask(tagName string, taskText string) {
	if taskText == "" {
		fmt.Println("Task text is required.")
		os.Exit(1)
	}

	if tagName == "" {
		TasksDo = append(TasksDo, ws.Task{Text: taskText})
		return
	}

	tag := ws.Tag(tagName)

	// Validate tag
	found := false
	for _, v := range Tags {
		if tag == v {
			found = true
			break
		}
	}
	if !found {
		fmt.Printf("No tag '%s' found.\n", tagName)
		os.Exit(1)
	}
	TasksDo = append(TasksDo, ws.Task{Text: taskText, Tag: tag})
}

func DeleteTask(shouldDeleteDone bool, n int) {
	if shouldDeleteDone {
		TasksDone = append(TasksDone[:n-1], TasksDone[n:]...)
	} else {
		TasksDo = append(TasksDo[:n-1], TasksDo[n:]...)
	}
}

// save, delete and append task
func ProcrastinateTask(n int) {
	t := TasksDo[n-1]
	TasksDo = append(TasksDo[:n-1], TasksDo[n:]...)
	TasksDo = append(TasksDo, t)
}

func TopTask(n int) {
	var NewTasks []ws.Task

	NewTasks = append(NewTasks, TasksDo[n-1])
	NewTasks = append(NewTasks, TasksDo[:n-1]...)
	if n < len(TasksDo) {
		NewTasks = append(NewTasks, TasksDo[n:]...)
	}

	TasksDo = NewTasks
}

func DoneTask(n int) {
	TasksDone = append(TasksDone, ws.TaskDone{
		Task: TasksDo[n-1],
		Date: time.Now(),
	})
	TasksDo = append(TasksDo[:n-1], TasksDo[n:]...)
}

func UndoTask(n int) {
	TasksDo = append(TasksDo, TasksDone[n-1].Task)
	TasksDone = append(TasksDone[:n-1], TasksDone[n:]...)
}

func DescribeTask(shouldDescribeDone bool, n int, description string) {
	var task *ws.Task

	if shouldDescribeDone {
		task = &TasksDone[n-1].Task
	} else {
		task = &TasksDo[n-1]
	}

	task.Description = description
}

func EditTask(shouldEditDone bool, n int, newText string, newTag ws.Tag) {
	var task *ws.Task

	if shouldEditDone {
		task = &TasksDone[n-1].Task
	} else {
		task = &TasksDo[n-1]
	}

	if newTag != "" {
		found := false
		for _, v := range Tags {
			if newTag == v {
				found = true
				break
			}
		}

		if !found {
			fmt.Printf("No tag '%s' found.\n", newTag)
			os.Exit(1)
		}

		task.Tag = newTag
	}

	if newText != "" {
		task.Text = newText
	}

}

func ListTasks(showDone bool) {
	if len(TasksDo) == 0 && len(TasksDone) == 0 {
		fmt.Println("No tasks.")
		return
	}

	if showDone && len(TasksDone) <= 0 {
		showDone = false
	}

	if len(TasksDo) > 0 {
		if showDone {
			fmt.Println("Active:")
		}
		for i, t := range TasksDo {
			fmt.Printf("% 2d. %s\n", i+1, t)
		}
	}

	if showDone {
		fmt.Println("Done:")
		for i, t := range TasksDone {
			fmt.Printf("% 2d. %s\n", i+1, t)
		}
	}
}

func AddTag(tagName ws.Tag) {
	for i := 0; i < len(Tags); i++ {
		if tagName == Tags[i] {
			fmt.Printf("Tag '%s' already exists.\n", tagName)
			os.Exit(1)
		}
	}
	Tags = append(Tags, tagName)
}

// Delete tag number n
// Only deletes if the tag is not used by any task
func DeleteTag(n int) {
	// Check if the tag is currently used
	for i, v := range TasksDo {
		if v.Tag == Tags[n-1] {
			fmt.Printf("Tag is used by task: %d. %s\n", i+1, v)
			os.Exit(1)
		}
	}
	for i, v := range TasksDone {
		if v.Task.Tag == Tags[n-1] {
			fmt.Printf("Tag is used by done task: %d. %s\n", i+1, v.Task)
			os.Exit(1)
		}
	}

	Tags = append(Tags[:n-1], Tags[n:]...)
}

func ListTags() {
	if len(Tags) == 0 {
		fmt.Println("No tags.")
	}
	for i := 0; i < len(Tags); i++ {
		fmt.Printf("%2d. %s\n", i+1, Tags[i])
	}
}

func wsTagUsage() {
	fmt.Println(`usage: ws tag <command>
COMMANDS
    add     Add a new tag
    del     Delete a tag
    list    List tags`)
}

func wsUsage() {
	fmt.Println(`usage: ws <command>
COMMANDS
    add     Add a new task
    done    Mark an active task as done
    undo    Undo a done task
    desc    Describe a task with more words
    edit    Edit a task's text or tag
    del     Delete an active task
    pc      Procrastinate an active task
    top     Put a task to the top of the stack
    list    List all active and done tasks
    tag     tag commands`)
}

func main() {
	var (
		dec         *gob.Decoder
		f           *os.File
		err         error
		gobdataPath string = ws.GetGobdataPath()
	)

	// Open/Create gob data file if not exist
	{
		f, err = os.Open(gobdataPath)
		if errors.Is(err, os.ErrNotExist) {
			// Do nothing
		} else if err != nil {
			panic(err)
		} else {
			dec = gob.NewDecoder(f)
			err = dec.Decode(&TasksDo)
			if err != nil {
				panic(err)
			}
			err = dec.Decode(&TasksDone)
			if err != nil {
				panic(err)
			}
			err = dec.Decode(&Tags)
			if err != nil {
				panic(err)
			}
		}
	}

	// When no arguments are provided display the first task.
	if len(os.Args) == 1 {
		ListTasks(false)
		os.Exit(0)
	}

	switch os.Args[1] {
	// Add a new task
	case "add":
		var tagName, taskName string

		flagSet := flag.NewFlagSet("add", flag.ExitOnError)
		flagSet.StringVar(&tagName, "t", "", "Set tag name")
		flagSet.Parse(os.Args[2:])

		taskName = strings.Join(flagSet.Args(), " ")

		AddTask(tagName, taskName)
		ListTasks(false)

	// Delete an active task
	case "del":
		var n int
		var shouldDeleteDone bool

		flagSet := flag.NewFlagSet("del", flag.ExitOnError)
		flagSet.IntVar(&n, "n", 1, "Set task number")
		flagSet.BoolVar(&shouldDeleteDone, "d", false, "Should delete a done task")
		flagSet.Parse(os.Args[2:])

		if !shouldDeleteDone {
			if len(TasksDo) == 0 {
				fmt.Println("No tasks to edit.")
				os.Exit(1)
			}

			if len(TasksDo) < n {
				fmt.Println("Task number out of range.")
				os.Exit(1)
			}
		} else {
			if len(TasksDone) == 0 {
				fmt.Println("No done tasks to edit.")
				os.Exit(1)
			}

			if len(TasksDone) < n {
				fmt.Println("Done task number out of range.")
				os.Exit(1)
			}
		}

		DeleteTask(shouldDeleteDone, n)
		ListTasks(shouldDeleteDone)

	// Mark an active task as done
	case "done":
		var n int

		flagSet := flag.NewFlagSet("done", flag.ExitOnError)
		flagSet.IntVar(&n, "n", 1, "Set task number")
		flagSet.Parse(os.Args[2:])

		if len(TasksDo) <= 0 {
			fmt.Println("No tasks to be done.")
			os.Exit(1)
		}

		if len(TasksDo) < n {
			fmt.Println("Task number out of range")
			os.Exit(1)
		}

		DoneTask(n)
		ListTasks(true)

	case "desc":
		var n int
		var shouldDescribeDone bool

		flagSet := flag.NewFlagSet("desc", flag.ExitOnError)
		flagSet.BoolVar(&shouldDescribeDone, "d", false, "Should describe a done task")
		flagSet.IntVar(&n, "n", 1, "Set task number")
		flagSet.Parse(os.Args[2:])

		description := strings.Join(flagSet.Args(), " ")

		if !shouldDescribeDone {
			if len(TasksDo) == 0 {
				fmt.Println("No tasks to describe.")
				os.Exit(1)
			}

			if len(TasksDo) < n {
				fmt.Println("Task number out of range.")
				os.Exit(1)
			}
		} else {
			if len(TasksDone) == 0 {
				fmt.Println("No done tasks to describe.")
				os.Exit(1)
			}

			if len(TasksDone) < n {
				fmt.Println("Done task number out of range.")
				os.Exit(1)
			}
		}

		DescribeTask(shouldDescribeDone, n, description)

		ListTasks(shouldDescribeDone)

	case "edit":
		var n int
		var shouldEditDone bool
		var newTag, newText string

		flagSet := flag.NewFlagSet("edit", flag.ExitOnError)
		flagSet.IntVar(&n, "n", 1, "Set task number")
		flagSet.StringVar(&newTag, "t", "", "Set tag name")
		flagSet.BoolVar(&shouldEditDone, "d", false, "Should edit a done task")
		flagSet.Parse(os.Args[2:])

		if !shouldEditDone {
			if len(TasksDo) == 0 {
				fmt.Println("No tasks to edit.")
				os.Exit(1)
			}

			if len(TasksDo) < n {
				fmt.Println("Task number out of range.")
				os.Exit(1)
			}
		} else {
			if len(TasksDone) == 0 {
				fmt.Println("No done tasks to edit.")
				os.Exit(1)
			}

			if len(TasksDone) < n {
				fmt.Println("Done task number out of range.")
				os.Exit(1)
			}
		}

		newText = strings.Join(flagSet.Args(), " ")

		EditTask(shouldEditDone, n, newText, ws.Tag(newTag))
		ListTasks(shouldEditDone)

	// Undo a done task
	case "undo":
		var n int

		flagSet := flag.NewFlagSet("undo", flag.ExitOnError)
		flagSet.IntVar(&n, "n", 1, "Set task number")
		flagSet.Parse(os.Args[2:])

		if len(TasksDone) <= 0 {
			fmt.Println("No tasks to be undone.")
			os.Exit(1)
		}

		if len(TasksDone) < n {
			fmt.Println("Task number out of range")
			os.Exit(1)
		}

		UndoTask(n)
		ListTasks(true)

	// Procrastinate an active task
	case "pc":
		var n int

		flagSet := flag.NewFlagSet("procrastinate", flag.ExitOnError)
		flagSet.IntVar(&n, "n", 1, "Set task number")
		flagSet.Parse(os.Args[2:])

		if len(TasksDo) <= 0 {
			fmt.Println("No tasks to procrastinate.")
			os.Exit(1)
		}

		if len(TasksDo) < n {
			fmt.Println("Task number out of range")
			os.Exit(1)
		}

		ProcrastinateTask(n)
		ListTasks(false)

	// Put a task at the top
	case "top":
		var n int

		flagSet := flag.NewFlagSet("top", flag.ExitOnError)
		flagSet.IntVar(&n, "n", 0, "Set task number")
		flagSet.Parse(os.Args[2:])

		if n == 0 {
			fmt.Println("Task number is required.")
			os.Exit(1)
		}

		if len(TasksDo) <= 1 {
			fmt.Println("No tasks to put to the top.")
			os.Exit(1)
		}

		if n == 1 {
			fmt.Println("Task already at the top")
			os.Exit(1)
		}

		if len(TasksDo) < n {
			fmt.Println("Task number out of range")
			os.Exit(1)
		}

		TopTask(n)
		ListTasks(false)

	// List all active and done tasks
	case "list":
		ListTasks(true)

	// tag subcommand
	case "tag":
		if len(os.Args) <= 2 {
			wsTagUsage()
			return
		}

		switch os.Args[2] {

		// create a new tag
		case "add":
			tagName := ws.Tag(strings.Join(os.Args[3:], " "))
			AddTag(tagName)
			ListTags()

		// delete a tag
		case "del":
			var n int

			flagSet := flag.NewFlagSet("del", flag.ExitOnError)
			flagSet.IntVar(&n, "n", 1, "Set task number")
			flagSet.Parse(os.Args[3:])

			if len(Tags) <= 0 {
				fmt.Println("No tags to delete.")
				os.Exit(1)
			}

			if len(Tags) < n {
				fmt.Println("Tag number out of range")
				os.Exit(1)
			}

			DeleteTag(n)
			ListTags()

		/* list tags */
		case "list":
			ListTags()
		default:
			wsTagUsage()
		}

	default:
		wsUsage()
	}

	// Save data to gobdata
	f, err = os.Create(gobdataPath)
	if err != nil {
		panic(err)
	}
	enc := gob.NewEncoder(f)
	err = enc.Encode(TasksDo)
	if err != nil {
		panic(err)
	}
	err = enc.Encode(TasksDone)
	if err != nil {
		panic(err)
	}
	err = enc.Encode(Tags)
	if err != nil {
		panic(err)
	}

}