package store

import (
	"database/sql"
	"fmt"
	"time"

	"task-dashboard/internal/config"
	"task-dashboard/internal/models"
)

// defaultChainProjectColor is used for the project a chain auto-creates for
// itself, since the chain-creation API takes no color -- unlike
// HandleWidgetProjectsCreate, where the client always supplies one.
const defaultChainProjectColor = "#8B5CF6"

// CreateChain creates a backing project (per the design's "a chain is
// effectively a project with strict sequential unlocking"), a task_chains
// row, and one native_tasks row per entry in tasks. Position 0 is created
// unlocked with due_date = now; the rest are locked with no due date. All
// in one transaction so a partial chain never exists.
func (s *Store) CreateChain(name string, tasks []models.ChainTaskInput) (*models.Chain, error) {
	if len(tasks) == 0 {
		return nil, fmt.Errorf("chain must have at least one task")
	}

	project, err := s.CreateProject(name, defaultChainProjectColor)
	if err != nil {
		return nil, err
	}

	chainID := newTaskID()
	now := config.Now()

	tx, err := s.db.Begin()
	if err != nil {
		return nil, err
	}
	defer func() { _ = tx.Rollback() }()

	if _, err := tx.Exec(`
		INSERT INTO task_chains (id, project_id, status, created_at) VALUES (?, ?, 'active', ?)
	`, chainID, project.ID, now); err != nil {
		return nil, err
	}

	for i, t := range tasks {
		unlocked := i == 0
		var dueDate *time.Time
		if unlocked {
			dueDate = &now
		}
		priority := t.Priority
		if priority == 0 {
			priority = 1
		}
		if _, err := tx.Exec(`
			INSERT INTO native_tasks (id, content, description, project_name, project_id, priority, due_date, chain_id, chain_position, chain_unlocked, created_at, updated_at)
			VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
		`, newTaskID(), t.Content, t.Description, project.Name, project.ID, priority, dueDate, chainID, i, unlocked, now, now); err != nil {
			return nil, err
		}
	}

	if err := tx.Commit(); err != nil {
		return nil, err
	}

	return &models.Chain{ID: chainID, ProjectID: project.ID, Status: "active", CreatedAt: now}, nil
}

// GetChain returns a single chain by id, or ErrNativeTaskNotFound.
func (s *Store) GetChain(id string) (*models.Chain, error) {
	var c models.Chain
	err := s.db.QueryRow(`
		SELECT id, project_id, status, created_at FROM task_chains WHERE id = ?
	`, id).Scan(&c.ID, &c.ProjectID, &c.Status, &c.CreatedAt)
	if err == sql.ErrNoRows {
		return nil, ErrNativeTaskNotFound
	}
	if err != nil {
		return nil, err
	}
	return &c, nil
}

// GetChains returns every active or paused chain, oldest first. Completed
// and abandoned chains are excluded -- they're done, not part of "current
// work" surfaces like the Tasks tab.
func (s *Store) GetChains() ([]models.Chain, error) {
	rows, err := s.db.Query(`
		SELECT id, project_id, status, created_at FROM task_chains
		WHERE status IN ('active', 'paused')
		ORDER BY created_at ASC
	`)
	if err != nil {
		return nil, err
	}
	defer func() { _ = rows.Close() }()

	var chains []models.Chain
	for rows.Next() {
		var c models.Chain
		if err := rows.Scan(&c.ID, &c.ProjectID, &c.Status, &c.CreatedAt); err != nil {
			return nil, err
		}
		chains = append(chains, c)
	}
	return chains, rows.Err()
}

// GetChainTasks returns every task in the chain, locked and unlocked both,
// ordered by chain_position -- the full checklist view.
func (s *Store) GetChainTasks(chainID string) ([]models.Task, error) {
	rows, err := s.db.Query(`
		SELECT id, content, description, project_name, project_id, due_date, priority, completed, labels, created_at,
		       recurrence_freq, recurrence_interval, recurrence_weekdays, recurrence_series_id, next_occurrence_override, estimated_minutes,
		       chain_id, chain_position, chain_unlocked,
		       bucket_id, bucket_state, bucket_last_active_at
		FROM native_tasks
		WHERE chain_id = ?
		ORDER BY chain_position ASC
	`, chainID)
	if err != nil {
		return nil, err
	}
	defer func() { _ = rows.Close() }()
	return scanNativeTasks(rows)
}

// SetChainStatus updates a chain's status (active/paused/abandoned/completed).
// Resuming a paused chain (status "active" from a current status of
// "paused") catches up any advancement that was deferred while paused --
// per the design, "the chain must be explicitly resumed for the next task
// to unlock," i.e. resuming itself performs the unlock, not merely
// re-arming future completions to do so. Without this, a chain paused
// immediately after a completion (before its successor could unlock) would
// stay stuck forever: no task is ever unlocked, so no future completion
// could trigger advanceChain either. Returns ErrNativeTaskNotFound if id
// doesn't match any row.
func (s *Store) SetChainStatus(id, status string) error {
	if status == "active" {
		current, err := s.GetChain(id)
		if err != nil {
			return err
		}
		if current.Status == "paused" {
			maxCompleted, err := s.maxCompletedChainPosition(id)
			if err != nil {
				return err
			}
			if maxCompleted != nil {
				if err := s.advanceChain(id, *maxCompleted); err != nil {
					return err
				}
			}
		}
	}

	result, err := s.db.Exec(`UPDATE task_chains SET status = ? WHERE id = ?`, status, id)
	if err != nil {
		return err
	}
	return checkRowsAffected(result)
}

// maxCompletedChainPosition returns the highest chain_position among
// completed tasks in the chain, or nil if none are completed yet.
func (s *Store) maxCompletedChainPosition(chainID string) (*int, error) {
	var pos sql.NullInt64
	err := s.db.QueryRow(`
		SELECT MAX(chain_position) FROM native_tasks WHERE chain_id = ? AND completed = 1
	`, chainID).Scan(&pos)
	if err != nil {
		return nil, err
	}
	if !pos.Valid {
		return nil, nil
	}
	p := int(pos.Int64)
	return &p, nil
}

// advanceChain is called from CompleteNativeTask (when the just-completed
// task has a chain_id set and the chain isn't paused) and from
// SetChainStatus's resume catch-up. Idempotent: if the successor position
// is already unlocked, it's left untouched (so a resume catch-up run
// against a chain that was never actually stuck is a no-op, not a
// due_date-resetting re-unlock). Completing/catching-up-to the last
// position marks the chain completed instead of unlocking a successor.
func (s *Store) advanceChain(chainID string, completedPosition int) error {
	var successorID string
	var successorUnlocked bool
	err := s.db.QueryRow(`
		SELECT id, chain_unlocked FROM native_tasks WHERE chain_id = ? AND chain_position = ?
	`, chainID, completedPosition+1).Scan(&successorID, &successorUnlocked)
	if err == sql.ErrNoRows {
		// No next position -- the completed task was the last in the chain.
		return s.SetChainStatus(chainID, "completed")
	}
	if err != nil {
		return err
	}
	if successorUnlocked {
		return nil
	}

	now := config.Now()
	_, err = s.db.Exec(`
		UPDATE native_tasks SET chain_unlocked = 1, due_date = ?, updated_at = ? WHERE id = ?
	`, now, now, successorID)
	return err
}