package engine

import (
	"fmt"
	"time"

	"github.com/google/uuid"
)

type Status byte

const (
	StatusPending   Status = 'P'
	StatusCompleted Status = 'C'
	StatusDeleted   Status = 'D'
	StatusRecurring Status = 'R'
)

type Priority int

const (
	PriorityLow     Priority = 0
	PriorityDefault Priority = 1
	PriorityMedium  Priority = 2
	PriorityHigh    Priority = 3
)

type Task struct {
	// Identity
	UUID uuid.UUID
	ID   int

	// Core fields
	Status      Status
	Description string
	Project     *string
	Priority    Priority

	// Timestamps
	Created   time.Time
	Modified  time.Time
	Start     *time.Time
	End       *time.Time
	Due       *time.Time
	Scheduled *time.Time
	Wait      *time.Time
	Until     *time.Time

	// Recurrence (parent-child approach)
	RecurrenceDuration *time.Duration
	ParentUUID         *uuid.UUID

	// Derived fields (not stored in DB)
	Tags []string
}

// timeNow returns current time (allows mocking in tests)
var timeNow = time.Now

// Helper functions for SQL time conversion

func timeToSQL(t *time.Time) interface{} {
	if t == nil {
		return nil
	}
	return t.Unix()
}

func sqlToTime(v interface{}) *time.Time {
	if v == nil {
		return nil
	}
	unix, ok := v.(int64)
	if !ok {
		return nil
	}
	t := time.Unix(unix, 0)
	return &t
}

func durationToSQL(d *time.Duration) interface{} {
	if d == nil {
		return nil
	}
	return int64(*d)
}

func sqlToDuration(v interface{}) *time.Duration {
	if v == nil {
		return nil
	}
	nanos, ok := v.(int64)
	if !ok {
		return nil
	}
	d := time.Duration(nanos)
	return &d
}

func stringPtrToSQL(s *string) interface{} {
	if s == nil {
		return nil
	}
	return *s
}

func sqlToStringPtr(v interface{}) *string {
	if v == nil {
		return nil
	}
	str, ok := v.(string)
	if !ok {
		return nil
	}
	return &str
}

func uuidPtrToSQL(u *uuid.UUID) interface{} {
	if u == nil {
		return nil
	}
	return u.String()
}

func sqlToUUIDPtr(v interface{}) *uuid.UUID {
	if v == nil {
		return nil
	}
	str, ok := v.(string)
	if !ok {
		return nil
	}
	u, err := uuid.Parse(str)
	if err != nil {
		return nil
	}
	return &u
}

// CreateTask creates a new task with the given description
func CreateTask(description string) (*Task, error) {
	return CreateTaskWithModifier(description, nil)
}

// CreateTaskWithModifier creates a new task with the given description and applies modifiers
func CreateTaskWithModifier(description string, mod *Modifier) (*Task, error) {
	now := timeNow()
	task := &Task{
		UUID:        uuid.New(),
		Status:      StatusPending,
		Description: description,
		Priority:    PriorityDefault,
		Created:     now,
		Modified:    now,
		Tags:        []string{},
	}

	// Apply modifiers before saving (for attributes)
	if mod != nil {
		if err := mod.ApplyToNew(task); err != nil {
			return nil, err
		}
	}

	if err := task.Save(); err != nil {
		return nil, err
	}

	// Apply tags after saving (requires task.ID)
	if mod != nil {
		for _, tag := range mod.AddTags {
			if err := task.AddTag(tag); err != nil {
				return nil, err
			}
		}
	}

	return task, nil
}

// GetTask retrieves a task by UUID
func GetTask(taskUUID uuid.UUID) (*Task, error) {
	db := GetDB()
	if db == nil {
		return nil, fmt.Errorf("database not initialized")
	}

	query := `
		SELECT id, uuid, status, description, project, priority,
		       created, modified, start, end, due, scheduled, wait, until_date,
		       recurrence_duration, parent_uuid
		FROM tasks
		WHERE uuid = ?
	`

	task := &Task{}
	var (
		uuidStr       string
		project       interface{}
		created       int64
		modified      int64
		start         interface{}
		end           interface{}
		due           interface{}
		scheduled     interface{}
		wait          interface{}
		until         interface{}
		recurDuration interface{}
		parentUUIDStr interface{}
	)

	err := db.QueryRow(query, taskUUID.String()).Scan(
		&task.ID,
		&uuidStr,
		&task.Status,
		&task.Description,
		&project,
		&task.Priority,
		&created,
		&modified,
		&start,
		&end,
		&due,
		&scheduled,
		&wait,
		&until,
		&recurDuration,
		&parentUUIDStr,
	)

	if err != nil {
		return nil, fmt.Errorf("failed to get task: %w", err)
	}

	// Parse UUID
	task.UUID, err = uuid.Parse(uuidStr)
	if err != nil {
		return nil, fmt.Errorf("failed to parse UUID: %w", err)
	}

	// Convert timestamps
	task.Created = time.Unix(created, 0)
	task.Modified = time.Unix(modified, 0)

	// Convert nullable fields
	task.Project = sqlToStringPtr(project)
	task.Start = sqlToTime(start)
	task.End = sqlToTime(end)
	task.Due = sqlToTime(due)
	task.Scheduled = sqlToTime(scheduled)
	task.Wait = sqlToTime(wait)
	task.Until = sqlToTime(until)
	task.RecurrenceDuration = sqlToDuration(recurDuration)
	task.ParentUUID = sqlToUUIDPtr(parentUUIDStr)

	// Load tags
	tags, err := task.GetTags()
	if err != nil {
		return nil, fmt.Errorf("failed to load tags: %w", err)
	}
	task.Tags = tags

	return task, nil
}

// GetTasks retrieves all tasks with optional filtering
func GetTasks(filter *Filter) ([]*Task, error) {
	db := GetDB()
	if db == nil {
		return nil, fmt.Errorf("database not initialized")
	}

	// Build WHERE clause from filter
	whereClause := "1=1"
	var args []interface{}
	if filter != nil {
		whereClause, args = filter.ToSQL()
	}

	query := fmt.Sprintf(`
		SELECT id, uuid, status, description, project, priority,
		       created, modified, start, end, due, scheduled, wait, until_date,
		       recurrence_duration, parent_uuid
		FROM tasks
		WHERE %s
		ORDER BY 
			CASE WHEN due IS NULL THEN 1 ELSE 0 END,
			due ASC,
			priority DESC
	`, whereClause)

	rows, err := db.Query(query, args...)
	if err != nil {
		return nil, fmt.Errorf("failed to query tasks: %w", err)
	}
	defer rows.Close()

	tasks := []*Task{}

	for rows.Next() {
		task := &Task{}
		var (
			uuidStr       string
			project       interface{}
			created       int64
			modified      int64
			start         interface{}
			end           interface{}
			due           interface{}
			scheduled     interface{}
			wait          interface{}
			until         interface{}
			recurDuration interface{}
			parentUUIDStr interface{}
		)

		err := rows.Scan(
			&task.ID,
			&uuidStr,
			&task.Status,
			&task.Description,
			&project,
			&task.Priority,
			&created,
			&modified,
			&start,
			&end,
			&due,
			&scheduled,
			&wait,
			&until,
			&recurDuration,
			&parentUUIDStr,
		)

		if err != nil {
			return nil, fmt.Errorf("failed to scan task: %w", err)
		}

		// Parse UUID
		task.UUID, err = uuid.Parse(uuidStr)
		if err != nil {
			return nil, fmt.Errorf("failed to parse UUID: %w", err)
		}

		// Convert timestamps
		task.Created = time.Unix(created, 0)
		task.Modified = time.Unix(modified, 0)

		// Convert nullable fields
		task.Project = sqlToStringPtr(project)
		task.Start = sqlToTime(start)
		task.End = sqlToTime(end)
		task.Due = sqlToTime(due)
		task.Scheduled = sqlToTime(scheduled)
		task.Wait = sqlToTime(wait)
		task.Until = sqlToTime(until)
		task.RecurrenceDuration = sqlToDuration(recurDuration)
		task.ParentUUID = sqlToUUIDPtr(parentUUIDStr)

		// Load tags
		tags, err := task.GetTags()
		if err != nil {
			return nil, fmt.Errorf("failed to load tags: %w", err)
		}
		task.Tags = tags

		tasks = append(tasks, task)
	}

	return tasks, nil
}

// Save inserts or updates the task in the database
func (t *Task) Save() error {
	db := GetDB()
	if db == nil {
		return fmt.Errorf("database not initialized")
	}

	t.Modified = timeNow()

	// Check if task exists
	var exists bool
	err := db.QueryRow("SELECT EXISTS(SELECT 1 FROM tasks WHERE uuid = ?)", t.UUID.String()).Scan(&exists)
	if err != nil {
		return fmt.Errorf("failed to check if task exists: %w", err)
	}

	if exists {
		// Update existing task
		query := `
			UPDATE tasks SET
				status = ?, description = ?, project = ?, priority = ?,
				modified = ?, start = ?, end = ?, due = ?,
				scheduled = ?, wait = ?, until_date = ?,
				recurrence_duration = ?, parent_uuid = ?
			WHERE uuid = ?
		`

		_, err = db.Exec(query,
			t.Status,
			t.Description,
			stringPtrToSQL(t.Project),
			t.Priority,
			t.Modified.Unix(),
			timeToSQL(t.Start),
			timeToSQL(t.End),
			timeToSQL(t.Due),
			timeToSQL(t.Scheduled),
			timeToSQL(t.Wait),
			timeToSQL(t.Until),
			durationToSQL(t.RecurrenceDuration),
			uuidPtrToSQL(t.ParentUUID),
			t.UUID.String(),
		)

		if err != nil {
			return fmt.Errorf("failed to update task: %w", err)
		}
	} else {
		// Insert new task
		query := `
			INSERT INTO tasks (
				uuid, status, description, project, priority,
				created, modified, start, end, due, scheduled, wait, until_date,
				recurrence_duration, parent_uuid
			) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
		`

		result, err := db.Exec(query,
			t.UUID.String(),
			t.Status,
			t.Description,
			stringPtrToSQL(t.Project),
			t.Priority,
			t.Created.Unix(),
			t.Modified.Unix(),
			timeToSQL(t.Start),
			timeToSQL(t.End),
			timeToSQL(t.Due),
			timeToSQL(t.Scheduled),
			timeToSQL(t.Wait),
			timeToSQL(t.Until),
			durationToSQL(t.RecurrenceDuration),
			uuidPtrToSQL(t.ParentUUID),
		)

		if err != nil {
			return fmt.Errorf("failed to insert task: %w", err)
		}

		id, err := result.LastInsertId()
		if err != nil {
			return fmt.Errorf("failed to get last insert id: %w", err)
		}
		t.ID = int(id)
	}

	return nil
}

// AddTag adds a tag to the task
func (t *Task) AddTag(tag string) error {
	db := GetDB()
	if db == nil {
		return fmt.Errorf("database not initialized")
	}

	// Ensure task has been saved and has an ID
	if t.ID == 0 {
		return fmt.Errorf("task must be saved before adding tags")
	}

	_, err := db.Exec("INSERT OR IGNORE INTO tags (task_id, tag) VALUES (?, ?)", t.ID, tag)
	if err != nil {
		return fmt.Errorf("failed to add tag: %w", err)
	}

	// Update in-memory tags
	for _, existingTag := range t.Tags {
		if existingTag == tag {
			return nil // Already exists
		}
	}
	t.Tags = append(t.Tags, tag)

	return nil
}

// RemoveTag removes a tag from the task
func (t *Task) RemoveTag(tag string) error {
	db := GetDB()
	if db == nil {
		return fmt.Errorf("database not initialized")
	}

	if t.ID == 0 {
		return fmt.Errorf("task must be saved before removing tags")
	}

	_, err := db.Exec("DELETE FROM tags WHERE task_id = ? AND tag = ?", t.ID, tag)
	if err != nil {
		return fmt.Errorf("failed to remove tag: %w", err)
	}

	// Update in-memory tags
	newTags := []string{}
	for _, existingTag := range t.Tags {
		if existingTag != tag {
			newTags = append(newTags, existingTag)
		}
	}
	t.Tags = newTags

	return nil
}

// GetTags retrieves all tags for the task
func (t *Task) GetTags() ([]string, error) {
	db := GetDB()
	if db == nil {
		return nil, fmt.Errorf("database not initialized")
	}

	if t.ID == 0 {
		return []string{}, nil
	}

	rows, err := db.Query("SELECT tag FROM tags WHERE task_id = ? ORDER BY tag", t.ID)
	if err != nil {
		return nil, fmt.Errorf("failed to get tags: %w", err)
	}
	defer rows.Close()

	tags := []string{}
	for rows.Next() {
		var tag string
		if err := rows.Scan(&tag); err != nil {
			return nil, fmt.Errorf("failed to scan tag: %w", err)
		}
		tags = append(tags, tag)
	}

	return tags, nil
}

// Complete marks a task as completed
func (t *Task) Complete() error {
	t.Status = StatusCompleted
	now := timeNow()
	t.End = &now

	if err := t.Save(); err != nil {
		return err
	}

	// If this is a recurring instance, spawn next instance
	if t.ParentUUID != nil {
		if err := SpawnNextInstance(t); err != nil {
			// Log error but don't fail the completion
			return fmt.Errorf("completed task but failed to spawn next instance: %w", err)
		}
	}

	return nil
}

// Delete marks a task as deleted (soft delete)
func (t *Task) Delete(permanent bool) error {
	db := GetDB()
	if db == nil {
		return fmt.Errorf("database not initialized")
	}

	if permanent {
		// Hard delete - remove from database
		_, err := db.Exec("DELETE FROM tasks WHERE uuid = ?", t.UUID.String())
		if err != nil {
			return fmt.Errorf("failed to delete task: %w", err)
		}
	} else {
		// Soft delete - mark as deleted
		t.Status = StatusDeleted
		now := timeNow()
		t.End = &now
		if err := t.Save(); err != nil {
			return err
		}
	}

	return nil
}

// StartTask sets the start time for a task
func (t *Task) StartTask() error {
	now := timeNow()
	t.Start = &now
	return t.Save()
}

// StopTask clears the start time for a task
func (t *Task) StopTask() error {
	t.Start = nil
	return t.Save()
}

// IsRecurringTemplate returns true if task is a recurring template
func (t *Task) IsRecurringTemplate() bool {
	return t.Status == StatusRecurring && t.RecurrenceDuration != nil && t.ParentUUID == nil
}

// IsRecurringInstance returns true if task is a recurring instance
func (t *Task) IsRecurringInstance() bool {
	return t.ParentUUID != nil
}