package todotxt

import (
	"encoding/json"
	"fmt"
	"regexp"
	"sort"
	"strings"
	"time"
)

var (
	// DateLayout is used for formatting time.Time into todo.txt date format and vice-versa.
	DateLayout = "2006-01-02"

	priorityRx = regexp.MustCompile(`^(x|x \d{4}-\d{2}-\d{2}|)\s*\(([A-Z])\)\s+`) // Match priority: '(A) ...' or 'x (A) ...' or 'x 2012-12-12 (A) ...'
	// Match created date: '(A) 2012-12-12 ...' or 'x 2012-12-12 (A) 2012-12-12 ...' or 'x (A) 2012-12-12 ...'or 'x 2012-12-12 2012-12-12 ...' or '2012-12-12 ...'
	createdDateRx   = regexp.MustCompile(`^(\([A-Z]\)|x \d{4}-\d{2}-\d{2} \([A-Z]\)|x \([A-Z]\)|x \d{4}-\d{2}-\d{2}|)\s*(\d{4}-\d{2}-\d{2})\s+`)
	completedRx     = regexp.MustCompile(`^x\s+`)                       // Match completed: 'x ...'
	completedDateRx = regexp.MustCompile(`^x\s*(\d{4}-\d{2}-\d{2})\s+`) // Match completed date: 'x 2012-12-12 ...'
	addonTagRx      = regexp.MustCompile(`(^|\s+)([\w-]+):(\S+)`)       // Match additional tags date: '... due:2012-12-12 ...'
	contextRx       = regexp.MustCompile(`(^|\s+)@(\S+)`)               // Match contexts: '@Context ...' or '... @Context ...'
	projectRx       = regexp.MustCompile(`(^|\s+)\+(\S+)`)              // Match projects: '+Project...' or '... +Project ...')
)

// Todo represents a todo.txt task entry.
type Todo struct {
	Id             int               `json:"id"`       // Internal todo id.
	Original       string            `json:"original"` // Original raw todo text.
	Todo           string            `json:"todo"`     // Todo part of todo text.
	Priority       string            `json:"priority"`
	Projects       []string          `json:"projects"`
	Contexts       []string          `json:"contexts"`
	AdditionalTags map[string]string `json:"additionalTags"` // Addon tags will be available here.
	CreatedDate    time.Time         `json:"createdDate"`
	DueDate        time.Time         `json:"dueDate"`
	CompletedDate  time.Time         `json:"completedDate"`
	Completed      bool              `json:"completed"`
}

func (t Todo) MarshalJSON() ([]byte, error) {
	return json.Marshal(struct {
		Id             int               `json:"id"`       // Internal todo id.
		Original       string            `json:"original"` // Original raw todo text.
		Todo           string            `json:"todo"`     // Todo part of todo text.
		Priority       string            `json:"priority"`
		Projects       []string          `json:"projects"`
		Contexts       []string          `json:"contexts"`
		AdditionalTags map[string]string `json:"additionalTags"` // Addon tags will be available here.
		CreatedDate    string            `json:"createdDate"`
		DueDate        string            `json:"dueDate"`
		CompletedDate  string            `json:"completedDate"`
		Completed      bool              `json:"completed"`
	}{
		Id:             t.Id,
		Original:       t.Original,
		Todo:           t.Todo,
		Priority:       t.Priority,
		Projects:       t.Projects,
		Contexts:       t.Contexts,
		AdditionalTags: t.AdditionalTags,
		CreatedDate:    t.CreatedDate.Format(DateLayout),
		DueDate:        t.DueDate.Format(DateLayout),
		CompletedDate:  t.CompletedDate.Format(DateLayout),
		Completed:      t.Completed,
	})
}

func (t *Todo) UnmarshalJSON(data []byte) error {
	type jsonTodo struct {
		Id             int               `json:"id"`       // Internal todo id.
		Original       string            `json:"original"` // Original raw todo text.
		Todo           string            `json:"todo"`     // Todo part of todo text.
		Priority       string            `json:"priority"`
		Projects       []string          `json:"projects"`
		Contexts       []string          `json:"contexts"`
		AdditionalTags map[string]string `json:"additionalTags"` // Addon tags will be available here.
		CreatedDate    string            `json:"createdDate"`
		DueDate        string            `json:"dueDate"`
		CompletedDate  string            `json:"completedDate"`
		Completed      bool              `json:"completed"`
	}
	j := jsonTodo{}
	if err := json.Unmarshal(data, &j); err != nil {
		return err
	}
	var err error
	t.Id = j.Id
	t.Original = j.Original
	t.Todo = j.Todo
	t.Priority = j.Priority
	t.Projects = j.Projects
	t.Contexts = j.Contexts
	t.AdditionalTags = j.AdditionalTags
	if j.CreatedDate != "" {
		t.CreatedDate, err = time.Parse(DateLayout, j.CreatedDate)
		if err != nil {
			return err
		}
	}
	if j.DueDate != "" {
		t.DueDate, err = time.Parse(DateLayout, j.DueDate)
		if err != nil {
			return err
		}
	}
	if j.CompletedDate != "" {
		t.CompletedDate, err = time.Parse(DateLayout, j.CompletedDate)
		if err != nil {
			return err
		}
	}
	t.Completed = j.Completed
	return nil
}

// String returns a complete todo string in todo.txt format.
//
// Contexts,  Projects and additional tags are alphabetically sorted,
// and appendend at the end in the following order:
// Contexts, Projects, Tags
//
// For example:
//
//	"(A) 2013-07-23 Call Dad @Home @Phone +Family due:2013-07-31 customTag1:Important!"
func (todo Todo) String() string {
	var text string

	if todo.Completed {
		text += "x "
		if todo.HasCompletedDate() {
			text += fmt.Sprintf("%s ", todo.CompletedDate.Format(DateLayout))
		}
	}

	if todo.HasPriority() {
		text += fmt.Sprintf("(%s) ", todo.Priority)
	}

	if todo.HasCreatedDate() {
		text += fmt.Sprintf("%s ", todo.CreatedDate.Format(DateLayout))
	}

	text += todo.Todo

	if len(todo.Contexts) > 0 {
		sort.Strings(todo.Contexts)
		for _, context := range todo.Contexts {
			text += fmt.Sprintf(" @%s", context)
		}
	}

	if len(todo.Projects) > 0 {
		sort.Strings(todo.Projects)
		for _, project := range todo.Projects {
			text += fmt.Sprintf(" +%s", project)
		}
	}

	if len(todo.AdditionalTags) > 0 {
		// Sort map alphabetically by keys
		keys := make([]string, 0, len(todo.AdditionalTags))
		for key := range todo.AdditionalTags {
			keys = append(keys, key)
		}
		sort.Strings(keys)
		for _, key := range keys {
			text += fmt.Sprintf(" %s:%s", key, todo.AdditionalTags[key])
		}
	}

	if todo.HasDueDate() {
		text += fmt.Sprintf(" due:%s", todo.DueDate.Format(DateLayout))
	}

	return text
}

// NewTodo creates a new empty Todo with default values. (CreatedDate is set to Now())
func NewTodo() Todo {
	todo := Todo{}
	todo.CreatedDate = time.Now()
	return todo
}

// ParseTodo parses the input text string into a Todo struct.
func ParseTodo(text string) (*Todo, error) {
	var err error

	todo := Todo{}
	todo.Original = strings.Trim(text, "\t\n\r ")
	todo.Todo = todo.Original

	// Check for completed
	if completedRx.MatchString(todo.Original) {
		todo.Completed = true
		// Check for completed date
		if completedDateRx.MatchString(todo.Original) {
			if date, err := time.Parse(DateLayout, completedDateRx.FindStringSubmatch(todo.Original)[1]); err == nil {
				todo.CompletedDate = date
			} else {
				return nil, err
			}
		}

		// Remove from Todo text
		todo.Todo = completedDateRx.ReplaceAllString(todo.Todo, "") // Strip CompletedDate first, otherwise it wouldn't match anymore (^x date...)
		todo.Todo = completedRx.ReplaceAllString(todo.Todo, "")     // Strip 'x '
	}

	// Check for priority
	if priorityRx.MatchString(todo.Original) {
		todo.Priority = priorityRx.FindStringSubmatch(todo.Original)[2]
		todo.Todo = priorityRx.ReplaceAllString(todo.Todo, "") // Remove from Todo text
	}

	// Check for created date
	if createdDateRx.MatchString(todo.Original) {
		if date, err := time.Parse(DateLayout, createdDateRx.FindStringSubmatch(todo.Original)[2]); err == nil {
			todo.CreatedDate = date
			todo.Todo = createdDateRx.ReplaceAllString(todo.Todo, "") // Remove from Todo text
		} else {
			return nil, err
		}
	}

	// function for collecting projects/contexts as slices from text
	getSlice := func(rx *regexp.Regexp) []string {
		matches := rx.FindAllStringSubmatch(todo.Original, -1)
		slice := make([]string, 0, len(matches))
		seen := make(map[string]bool, len(matches))
		for _, match := range matches {
			word := strings.Trim(match[2], "\t\n\r ")
			if _, found := seen[word]; !found {
				slice = append(slice, word)
				seen[word] = true
			}
		}
		sort.Strings(slice)
		return slice
	}

	// Check for contexts
	if contextRx.MatchString(todo.Original) {
		todo.Contexts = getSlice(contextRx)
		todo.Todo = contextRx.ReplaceAllString(todo.Todo, "") // Remove from Todo text
	}

	// Check for projects
	if projectRx.MatchString(todo.Original) {
		todo.Projects = getSlice(projectRx)
		todo.Todo = projectRx.ReplaceAllString(todo.Todo, "") // Remove from Todo text
	}

	// Check for additional tags
	if addonTagRx.MatchString(todo.Original) {
		matches := addonTagRx.FindAllStringSubmatch(todo.Original, -1)
		tags := make(map[string]string, len(matches))
		for _, match := range matches {
			key, value := match[2], match[3]
			if key == "due" { // due date is a known addon tag, it has its own struct field
				if date, err := time.Parse(DateLayout, value); err == nil {
					todo.DueDate = date
				} else {
					return nil, err
				}
			} else if key != "" && value != "" {
				tags[key] = value
			}
		}
		todo.AdditionalTags = tags
		todo.Todo = addonTagRx.ReplaceAllString(todo.Todo, "") // Remove from Todo text
	}

	// Trim any remaining whitespaces from Todo text
	todo.Todo = strings.Trim(todo.Todo, "\t\n\r\f ")

	return &todo, err
}

// HasPriority returns true if the task has a priority.
func (todo *Todo) HasPriority() bool {
	return todo.Priority != ""
}

// HasCreatedDate returns true if the task has a created date.
func (todo *Todo) HasCreatedDate() bool {
	return !todo.CreatedDate.IsZero()
}

// HasDueDate returns true if the task has a due date.
func (todo *Todo) HasDueDate() bool {
	return !todo.DueDate.IsZero()
}

// HasCompletedDate returns true if the task has a completed date.
func (todo *Todo) HasCompletedDate() bool {
	return !todo.CompletedDate.IsZero() && todo.Completed
}

// Complete sets Task.Completed to 'true' if the task was not already completed.
// Also sets Task.CompletedDate to time.Now()
func (todo *Todo) Complete() {
	if !todo.Completed {
		todo.Completed = true
		todo.CompletedDate = time.Now()
	}
}

// Reopen sets Task.Completed to 'false' if the task was completed.
// Also resets Task.CompletedDate.
func (todo *Todo) Reopen() {
	if todo.Completed {
		todo.Completed = false
		todo.CompletedDate = time.Date(1, 1, 1, 0, 0, 0, 0, time.UTC) // time.IsZero() value
	}
}

// IsOverdue returns true if due date is in the past.
//
// This function does not take the Completed flag into consideration.
// You should check Task.Completed first if needed.
func (todo *Todo) IsOverdue() bool {
	if todo.HasDueDate() {
		return todo.DueDate.Before(time.Now())
	}
	return false
}

// Due returns the duration passed since due date, or until due date from now.
// Check with IsOverdue() if the task is overdue or not.
//
// Just as with IsOverdue(), this function does also not take the Completed flag into consideration.
// You should check Task.Completed first if needed.
func (todo *Todo) Due() time.Duration {
	if todo.IsOverdue() {
		return time.Now().Sub(todo.DueDate)
	}
	return todo.DueDate.Sub(time.Now())
}

func (todo *Todo) HasContext(ctx string) bool {
	for _, c := range todo.Contexts {
		if c == ctx {
			return true
		}
	}
	return false
}

func (todo *Todo) HasProject(proj string) bool {
	for _, p := range todo.Projects {
		if p == proj {
			return true
		}
	}
	return false
}

func (todo *Todo) HasTag(name string) bool {
	_, ok := todo.AdditionalTags[name]
	return ok
}

func (todo *Todo) GetTag(name string) string {
	return todo.AdditionalTags[name]
}