package timeoff

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"time"
)

var ErrNotFound = fmt.Errorf("time off request not found")

type Request struct {
	ID          int64      `json:"id"`
	VolunteerID int64      `json:"volunteer_id"`
	StartsAt    time.Time  `json:"starts_at"`
	EndsAt      time.Time  `json:"ends_at"`
	Reason      string     `json:"reason,omitempty"`
	Status      string     `json:"status"`
	ReviewedBy  *int64     `json:"reviewed_by,omitempty"`
	ReviewedAt  *time.Time `json:"reviewed_at,omitempty"`
	CreatedAt   time.Time  `json:"created_at"`
	UpdatedAt   time.Time  `json:"updated_at"`
}

type CreateInput struct {
	StartsAt         string `json:"starts_at"`
	EndsAt           string `json:"ends_at"`
	Reason           string `json:"reason"`
	VolunteerID      int64  `json:"volunteer_id,omitempty"`       // admin creating for another volunteer
	ConfirmConflicts bool   `json:"confirm_conflicts,omitempty"`  // acknowledge shift conflicts
}

type UpdateInput struct {
	StartsAt string `json:"starts_at"`
	EndsAt   string `json:"ends_at"`
	Reason   string `json:"reason"`
}

type ReviewInput struct {
	Status string `json:"status"` // "approved" | "rejected"
}

// ConflictingShift is a shift instance that overlaps with a time-off period.
type ConflictingShift struct {
	InstanceID int64  `json:"instance_id"`
	Name       string `json:"name"`
	Date       string `json:"date"`
	StartTime  string `json:"start_time"`
	EndTime    string `json:"end_time"`
}

// RemovedShift records that a volunteer was removed from a shift due to time off.
type RemovedShift struct {
	ID          int64 `json:"id"`
	TimeOffID   int64 `json:"time_off_id"`
	InstanceID  int64 `json:"instance_id"`
	VolunteerID int64 `json:"volunteer_id"`
}

type Store struct {
	db *sql.DB
}

func NewStore(db *sql.DB) *Store {
	return &Store{db: db}
}

func (s *Store) Create(ctx context.Context, volunteerID int64, in CreateInput) (*Request, error) {
	res, err := s.db.ExecContext(ctx,
		`INSERT INTO time_off_requests (volunteer_id, starts_at, ends_at, reason) VALUES (?, ?, ?, ?)`,
		volunteerID, in.StartsAt, in.EndsAt, in.Reason,
	)
	if err != nil {
		return nil, fmt.Errorf("insert time off request: %w", err)
	}
	id, _ := res.LastInsertId()
	return s.GetByID(ctx, id)
}

func (s *Store) GetByID(ctx context.Context, id int64) (*Request, error) {
	req := &Request{}
	var startsAt, endsAt, createdAt, updatedAt string
	var reason sql.NullString
	var reviewedBy sql.NullInt64
	var reviewedAt sql.NullString

	err := s.db.QueryRowContext(ctx,
		`SELECT id, volunteer_id, starts_at, ends_at, reason, status, reviewed_by, reviewed_at, created_at, updated_at
		 FROM time_off_requests WHERE id = ?`, id,
	).Scan(&req.ID, &req.VolunteerID, &startsAt, &endsAt, &reason, &req.Status, &reviewedBy, &reviewedAt, &createdAt, &updatedAt)
	if errors.Is(err, sql.ErrNoRows) {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("get time off request: %w", err)
	}
	req.StartsAt, _ = time.Parse("2006-01-02 15:04:05", startsAt)
	req.EndsAt, _ = time.Parse("2006-01-02 15:04:05", endsAt)
	req.CreatedAt, _ = time.Parse("2006-01-02 15:04:05", createdAt)
	req.UpdatedAt, _ = time.Parse("2006-01-02 15:04:05", updatedAt)
	if reason.Valid {
		req.Reason = reason.String
	}
	if reviewedBy.Valid {
		req.ReviewedBy = &reviewedBy.Int64
	}
	if reviewedAt.Valid {
		t, _ := time.Parse("2006-01-02 15:04:05", reviewedAt.String)
		req.ReviewedAt = &t
	}
	return req, nil
}

func (s *Store) List(ctx context.Context, volunteerID int64) ([]Request, error) {
	query := `SELECT id, volunteer_id, starts_at, ends_at, reason, status, reviewed_by, reviewed_at, created_at, updated_at FROM time_off_requests`
	args := []any{}
	if volunteerID > 0 {
		query += ` WHERE volunteer_id = ?`
		args = append(args, volunteerID)
	}
	query += ` ORDER BY starts_at DESC`

	rows, err := s.db.QueryContext(ctx, query, args...)
	if err != nil {
		return nil, fmt.Errorf("list time off requests: %w", err)
	}
	defer rows.Close()

	var requests []Request
	for rows.Next() {
		var req Request
		var startsAt, endsAt, createdAt, updatedAt string
		var reason sql.NullString
		var reviewedBy sql.NullInt64
		var reviewedAt sql.NullString
		if err := rows.Scan(&req.ID, &req.VolunteerID, &startsAt, &endsAt, &reason, &req.Status, &reviewedBy, &reviewedAt, &createdAt, &updatedAt); err != nil {
			return nil, err
		}
		req.StartsAt, _ = time.Parse("2006-01-02 15:04:05", startsAt)
		req.EndsAt, _ = time.Parse("2006-01-02 15:04:05", endsAt)
		req.CreatedAt, _ = time.Parse("2006-01-02 15:04:05", createdAt)
		req.UpdatedAt, _ = time.Parse("2006-01-02 15:04:05", updatedAt)
		if reason.Valid {
			req.Reason = reason.String
		}
		if reviewedBy.Valid {
			req.ReviewedBy = &reviewedBy.Int64
		}
		if reviewedAt.Valid {
			t, _ := time.Parse("2006-01-02 15:04:05", reviewedAt.String)
			req.ReviewedAt = &t
		}
		requests = append(requests, req)
	}
	return requests, rows.Err()
}

func (s *Store) Review(ctx context.Context, id, reviewerID int64, status string) (*Request, error) {
	_, err := s.db.ExecContext(ctx,
		`UPDATE time_off_requests SET status=?, reviewed_by=?, reviewed_at=NOW(), updated_at=NOW() WHERE id=?`,
		status, reviewerID, id,
	)
	if err != nil {
		return nil, fmt.Errorf("review time off request: %w", err)
	}
	return s.GetByID(ctx, id)
}

// Update edits a time-off request's dates and reason.
func (s *Store) Update(ctx context.Context, id int64, in UpdateInput) (*Request, error) {
	_, err := s.db.ExecContext(ctx,
		`UPDATE time_off_requests SET starts_at=?, ends_at=?, reason=?, updated_at=NOW() WHERE id=?`,
		in.StartsAt, in.EndsAt, in.Reason, id,
	)
	if err != nil {
		return nil, fmt.Errorf("update time off request: %w", err)
	}
	return s.GetByID(ctx, id)
}

// Delete removes a time-off request.
func (s *Store) Delete(ctx context.Context, id int64) error {
	result, err := s.db.ExecContext(ctx, `DELETE FROM time_off_requests WHERE id = ?`, id)
	if err != nil {
		return fmt.Errorf("delete time off request: %w", err)
	}
	affected, _ := result.RowsAffected()
	if affected == 0 {
		return ErrNotFound
	}
	return nil
}

// ConflictingShifts returns published shift instances where the volunteer is assigned
// and the shift date falls within the given date range (inclusive).
func (s *Store) ConflictingShifts(ctx context.Context, volunteerID int64, startsAt, endsAt string) ([]ConflictingShift, error) {
	rows, err := s.db.QueryContext(ctx,
		`SELECT si.id, si.name, si.date, si.start_time, si.end_time
		 FROM shift_instances si
		 JOIN shift_instance_volunteers siv ON siv.instance_id = si.id
		 WHERE siv.volunteer_id = ?
		   AND si.date >= ?
		   AND si.date <= ?
		 ORDER BY si.date`, volunteerID, startsAt, endsAt,
	)
	if err != nil {
		return nil, fmt.Errorf("query conflicting shifts: %w", err)
	}
	defer rows.Close()

	var shifts []ConflictingShift
	for rows.Next() {
		var cs ConflictingShift
		if err := rows.Scan(&cs.InstanceID, &cs.Name, &cs.Date, &cs.StartTime, &cs.EndTime); err != nil {
			return nil, err
		}
		shifts = append(shifts, cs)
	}
	return shifts, rows.Err()
}

// RemoveFromConflictingShifts removes the volunteer from shifts that overlap with
// the time-off period and records the removals for later restoration.
func (s *Store) RemoveFromConflictingShifts(ctx context.Context, timeOffID, volunteerID int64, startsAt, endsAt string) ([]ConflictingShift, error) {
	conflicts, err := s.ConflictingShifts(ctx, volunteerID, startsAt, endsAt)
	if err != nil {
		return nil, err
	}
	if len(conflicts) == 0 {
		return nil, nil
	}

	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return nil, fmt.Errorf("begin tx: %w", err)
	}
	defer tx.Rollback()

	for _, c := range conflicts {
		// Record the removal
		if _, err := tx.ExecContext(ctx,
			`INSERT INTO time_off_removed_shifts (time_off_id, instance_id, volunteer_id) VALUES (?, ?, ?)`,
			timeOffID, c.InstanceID, volunteerID,
		); err != nil {
			return nil, fmt.Errorf("record removal: %w", err)
		}
		// Remove volunteer from shift
		if _, err := tx.ExecContext(ctx,
			`DELETE FROM shift_instance_volunteers WHERE instance_id = ? AND volunteer_id = ?`,
			c.InstanceID, volunteerID,
		); err != nil {
			return nil, fmt.Errorf("remove from shift: %w", err)
		}
	}

	if err := tx.Commit(); err != nil {
		return nil, fmt.Errorf("commit: %w", err)
	}
	return conflicts, nil
}

// RemovedShiftsForTimeOff returns shifts from which the volunteer was removed
// due to the given time-off request (for preview before admin deletes time off).
func (s *Store) RemovedShiftsForTimeOff(ctx context.Context, timeOffID int64) ([]ConflictingShift, error) {
	rows, err := s.db.QueryContext(ctx,
		`SELECT si.id, si.name, si.date, si.start_time, si.end_time
		 FROM time_off_removed_shifts tors
		 JOIN shift_instances si ON si.id = tors.instance_id
		 WHERE tors.time_off_id = ?
		 ORDER BY si.date`, timeOffID,
	)
	if err != nil {
		return nil, fmt.Errorf("query removed shifts: %w", err)
	}
	defer rows.Close()

	var shifts []ConflictingShift
	for rows.Next() {
		var cs ConflictingShift
		if err := rows.Scan(&cs.InstanceID, &cs.Name, &cs.Date, &cs.StartTime, &cs.EndTime); err != nil {
			return nil, err
		}
		shifts = append(shifts, cs)
	}
	return shifts, rows.Err()
}

// RestoreRemovedShifts re-adds the volunteer to shifts they were removed from
// when the given time-off request is deleted (FR-T04).
func (s *Store) RestoreRemovedShifts(ctx context.Context, timeOffID int64) ([]ConflictingShift, error) {
	// Get the removals first
	rows, err := s.db.QueryContext(ctx,
		`SELECT tors.instance_id, tors.volunteer_id, si.name, si.date, si.start_time, si.end_time
		 FROM time_off_removed_shifts tors
		 JOIN shift_instances si ON si.id = tors.instance_id
		 WHERE tors.time_off_id = ?`, timeOffID,
	)
	if err != nil {
		return nil, fmt.Errorf("query removals: %w", err)
	}
	defer rows.Close()

	type removal struct {
		instanceID  int64
		volunteerID int64
		shift       ConflictingShift
	}
	var removals []removal
	for rows.Next() {
		var r removal
		if err := rows.Scan(&r.instanceID, &r.volunteerID, &r.shift.Name, &r.shift.Date, &r.shift.StartTime, &r.shift.EndTime); err != nil {
			return nil, err
		}
		r.shift.InstanceID = r.instanceID
		removals = append(removals, r)
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}

	if len(removals) == 0 {
		return nil, nil
	}

	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return nil, fmt.Errorf("begin tx: %w", err)
	}
	defer tx.Rollback()

	var restored []ConflictingShift
	for _, r := range removals {
		// Re-add to shift (ignore duplicate if they were re-added manually)
		_, err := tx.ExecContext(ctx,
			`INSERT IGNORE INTO shift_instance_volunteers (instance_id, volunteer_id) VALUES (?, ?)`,
			r.instanceID, r.volunteerID,
		)
		if err != nil {
			return nil, fmt.Errorf("restore to shift: %w", err)
		}
		restored = append(restored, r.shift)
	}

	// Clean up removal records (CASCADE will handle this on time-off delete,
	// but we clean up explicitly since we're restoring)
	if _, err := tx.ExecContext(ctx,
		`DELETE FROM time_off_removed_shifts WHERE time_off_id = ?`, timeOffID,
	); err != nil {
		return nil, fmt.Errorf("clean removals: %w", err)
	}

	if err := tx.Commit(); err != nil {
		return nil, fmt.Errorf("commit: %w", err)
	}
	return restored, nil
}

// HasApprovedTimeOff checks if a volunteer has approved time off covering the given date.
func (s *Store) HasApprovedTimeOff(ctx context.Context, volunteerID int64, date string) (bool, error) {
	var count int
	err := s.db.QueryRowContext(ctx,
		`SELECT COUNT(*) FROM time_off_requests
		 WHERE volunteer_id = ? AND status = 'approved'
		   AND ? >= DATE(starts_at) AND ? <= DATE(ends_at)`,
		volunteerID, date, date,
	).Scan(&count)
	if err != nil {
		return false, fmt.Errorf("check time off: %w", err)
	}
	return count > 0, nil
}