// Package postgres provides PostgreSQL-based implementations of port interfaces.
package postgres

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"strings"

	"github.com/lib/pq"

	"github.com/orchard9/rdev/internal/domain"
	"github.com/orchard9/rdev/internal/port"
)

// SagaRepository implements port.SagaRepository using PostgreSQL.
type SagaRepository struct {
	db *sql.DB
}

// NewSagaRepository creates a new PostgreSQL saga repository.
func NewSagaRepository(db *sql.DB) *SagaRepository {
	return &SagaRepository{db: db}
}

// Ensure SagaRepository implements port.SagaRepository at compile time.
var _ port.SagaRepository = (*SagaRepository)(nil)

// ErrSagaNotFound is returned when a saga is not found.
var ErrSagaNotFound = errors.New("saga not found")

// Create creates a new saga with its steps.
func (r *SagaRepository) Create(ctx context.Context, saga *domain.Saga) error {
	tx, err := r.db.BeginTx(ctx, nil)
	if err != nil {
		return fmt.Errorf("begin transaction: %w", err)
	}
	defer func() { _ = tx.Rollback() }()

	varsJSON, err := json.Marshal(saga.Vars)
	if err != nil {
		return fmt.Errorf("marshal vars: %w", err)
	}

	outputsJSON, err := json.Marshal(saga.Outputs)
	if err != nil {
		return fmt.Errorf("marshal outputs: %w", err)
	}

	// Insert saga
	err = tx.QueryRowContext(ctx, `
		INSERT INTO sagas (
			name, status, definition, vars, outputs, current_step,
			retry_count, max_retries, error
		) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)
		RETURNING id, created_at, updated_at
	`,
		saga.Name,
		string(saga.Status),
		nullString(saga.Definition),
		varsJSON,
		outputsJSON,
		nullString(saga.CurrentStep),
		saga.RetryCount,
		saga.MaxRetries,
		nullString(saga.Error),
	).Scan(&saga.ID, &saga.CreatedAt, &saga.UpdatedAt)
	if err != nil {
		return fmt.Errorf("insert saga: %w", err)
	}

	// Insert steps
	for i := range saga.Steps {
		step := &saga.Steps[i]
		step.SagaID = saga.ID

		retryPolicyJSON, err := json.Marshal(step.RetryPolicy)
		if err != nil {
			return fmt.Errorf("marshal retry policy: %w", err)
		}

		configJSON, err := json.Marshal(step.Config)
		if err != nil {
			return fmt.Errorf("marshal config: %w", err)
		}

		err = tx.QueryRowContext(ctx, `
			INSERT INTO saga_steps (
				saga_id, name, status, action, depends_on, retry_policy,
				compensate, config, retry_count
			) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)
			RETURNING id
		`,
			saga.ID,
			step.Name,
			string(step.Status),
			step.Action,
			pq.Array(step.DependsOn),
			retryPolicyJSON,
			nullString(step.Compensate),
			configJSON,
			step.RetryCount,
		).Scan(&step.ID)
		if err != nil {
			return fmt.Errorf("insert step %s: %w", step.Name, err)
		}
	}

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

	return nil
}

// Get returns a saga by ID, including all steps.
func (r *SagaRepository) Get(ctx context.Context, id string) (*domain.Saga, error) {
	saga, err := r.getSaga(ctx, id)
	if err != nil {
		return nil, err
	}

	steps, err := r.getSteps(ctx, id)
	if err != nil {
		return nil, err
	}
	saga.Steps = steps

	return saga, nil
}

// getSaga retrieves just the saga record (no steps).
func (r *SagaRepository) getSaga(ctx context.Context, id string) (*domain.Saga, error) {
	row := r.db.QueryRowContext(ctx, `
		SELECT id, name, status, definition, vars, outputs, current_step,
			retry_count, max_retries, error, created_at, updated_at, completed_at
		FROM sagas
		WHERE id = $1
	`, id)

	return r.scanSaga(row)
}

// getSteps retrieves all steps for a saga.
func (r *SagaRepository) getSteps(ctx context.Context, sagaID string) ([]domain.SagaStep, error) {
	rows, err := r.db.QueryContext(ctx, `
		SELECT id, saga_id, name, status, action, depends_on, retry_policy,
			compensate, config, output, error, retry_count, started_at, completed_at
		FROM saga_steps
		WHERE saga_id = $1
		ORDER BY id
	`, sagaID)
	if err != nil {
		return nil, fmt.Errorf("query steps: %w", err)
	}
	defer func() { _ = rows.Close() }()

	var steps []domain.SagaStep
	for rows.Next() {
		step, err := r.scanStep(rows)
		if err != nil {
			return nil, err
		}
		steps = append(steps, *step)
	}

	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("iterate steps: %w", err)
	}

	return steps, nil
}

// Update updates a saga's status and metadata (not steps).
func (r *SagaRepository) Update(ctx context.Context, saga *domain.Saga) error {
	varsJSON, err := json.Marshal(saga.Vars)
	if err != nil {
		return fmt.Errorf("marshal vars: %w", err)
	}

	outputsJSON, err := json.Marshal(saga.Outputs)
	if err != nil {
		return fmt.Errorf("marshal outputs: %w", err)
	}

	res, err := r.db.ExecContext(ctx, `
		UPDATE sagas SET
			status = $2,
			vars = $3,
			outputs = $4,
			current_step = $5,
			retry_count = $6,
			error = $7,
			completed_at = $8
		WHERE id = $1
	`,
		saga.ID,
		string(saga.Status),
		varsJSON,
		outputsJSON,
		nullString(saga.CurrentStep),
		saga.RetryCount,
		nullString(saga.Error),
		nullTime(saga.CompletedAt),
	)
	if err != nil {
		return fmt.Errorf("update saga: %w", err)
	}

	rows, err := res.RowsAffected()
	if err != nil {
		return fmt.Errorf("rows affected: %w", err)
	}
	if rows == 0 {
		return ErrSagaNotFound
	}

	return nil
}

// UpdateStep updates a single step's status and output.
func (r *SagaRepository) UpdateStep(ctx context.Context, step *domain.SagaStep) error {
	var outputJSON []byte
	var err error
	if step.Output != nil {
		outputJSON, err = json.Marshal(step.Output)
		if err != nil {
			return fmt.Errorf("marshal output: %w", err)
		}
	}

	res, err := r.db.ExecContext(ctx, `
		UPDATE saga_steps SET
			status = $2,
			output = $3,
			error = $4,
			retry_count = $5,
			started_at = $6,
			completed_at = $7
		WHERE id = $1
	`,
		step.ID,
		string(step.Status),
		outputJSON,
		nullString(step.Error),
		step.RetryCount,
		nullTime(step.StartedAt),
		nullTime(step.CompletedAt),
	)
	if err != nil {
		return fmt.Errorf("update step: %w", err)
	}

	rows, err := res.RowsAffected()
	if err != nil {
		return fmt.Errorf("rows affected: %w", err)
	}
	if rows == 0 {
		return fmt.Errorf("step %s not found", step.ID)
	}

	return nil
}

// List returns sagas matching the given filters.
func (r *SagaRepository) List(ctx context.Context, filters domain.SagaFilters) ([]*domain.Saga, error) {
	filters.Normalize()

	query := strings.Builder{}
	query.WriteString(`
		SELECT id, name, status, definition, vars, outputs, current_step,
			retry_count, max_retries, error, created_at, updated_at, completed_at
		FROM sagas
		WHERE 1=1
	`)

	args := []any{}
	argNum := 1

	if filters.Name != "" {
		fmt.Fprintf(&query, " AND name = $%d", argNum)
		args = append(args, filters.Name)
		argNum++
	}

	if filters.Status != "" {
		fmt.Fprintf(&query, " AND status = $%d", argNum)
		args = append(args, string(filters.Status))
		argNum++
	}

	if !filters.Since.IsZero() {
		fmt.Fprintf(&query, " AND created_at >= $%d", argNum)
		args = append(args, filters.Since)
		argNum++
	}

	query.WriteString(" ORDER BY created_at DESC")

	fmt.Fprintf(&query, " LIMIT $%d", argNum)
	args = append(args, filters.Limit)

	rows, err := r.db.QueryContext(ctx, query.String(), args...)
	if err != nil {
		return nil, fmt.Errorf("query sagas: %w", err)
	}
	defer func() { _ = rows.Close() }()

	var sagas []*domain.Saga
	for rows.Next() {
		saga, err := r.scanSagaRows(rows)
		if err != nil {
			return nil, err
		}
		sagas = append(sagas, saga)
	}

	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("iterate sagas: %w", err)
	}

	return sagas, nil
}

// Delete removes a saga and its steps (cascade).
func (r *SagaRepository) Delete(ctx context.Context, id string) error {
	res, err := r.db.ExecContext(ctx, `DELETE FROM sagas WHERE id = $1`, id)
	if err != nil {
		return fmt.Errorf("delete saga: %w", err)
	}

	rows, err := res.RowsAffected()
	if err != nil {
		return fmt.Errorf("rows affected: %w", err)
	}
	if rows == 0 {
		return ErrSagaNotFound
	}

	return nil
}

// GetPendingSteps returns steps ready to execute (no unmet dependencies).
func (r *SagaRepository) GetPendingSteps(ctx context.Context, sagaID string) ([]domain.SagaStep, error) {
	// Get all steps
	steps, err := r.getSteps(ctx, sagaID)
	if err != nil {
		return nil, err
	}

	// Build completed steps map (includes skipped steps for dependency resolution)
	completed := make(map[string]bool)
	for _, step := range steps {
		if step.Status == domain.StepStatusCompleted || step.Status == domain.StepStatusSkipped {
			completed[step.Name] = true
		}
	}

	// Find runnable steps
	var runnable []domain.SagaStep
	for _, step := range steps {
		if step.CanRun(completed) {
			runnable = append(runnable, step)
		}
	}

	return runnable, nil
}

// sagaScanner interface abstracts sql.Row and sql.Rows for scanning.
type sagaScanner interface {
	Scan(dest ...any) error
}

// scanSaga scans a saga from a QueryRow result.
func (r *SagaRepository) scanSaga(row *sql.Row) (*domain.Saga, error) {
	saga, err := r.scanSagaFrom(row)
	if errors.Is(err, sql.ErrNoRows) {
		return nil, ErrSagaNotFound
	}
	return saga, err
}

// scanSagaRows scans a saga from a Rows result.
func (r *SagaRepository) scanSagaRows(rows *sql.Rows) (*domain.Saga, error) {
	return r.scanSagaFrom(rows)
}

// scanSagaFrom scans a saga from any scanner (Row or Rows).
func (r *SagaRepository) scanSagaFrom(scanner sagaScanner) (*domain.Saga, error) {
	var saga domain.Saga
	var status string
	var definition, currentStep, sagaError sql.NullString
	var completedAt sql.NullTime
	var varsJSON, outputsJSON []byte

	err := scanner.Scan(
		&saga.ID, &saga.Name, &status, &definition, &varsJSON, &outputsJSON,
		&currentStep, &saga.RetryCount, &saga.MaxRetries, &sagaError,
		&saga.CreatedAt, &saga.UpdatedAt, &completedAt,
	)
	if err != nil {
		return nil, fmt.Errorf("scan saga: %w", err)
	}

	saga.Status = domain.SagaStatus(status)
	if definition.Valid {
		saga.Definition = definition.String
	}
	if currentStep.Valid {
		saga.CurrentStep = currentStep.String
	}
	if sagaError.Valid {
		saga.Error = sagaError.String
	}
	if completedAt.Valid {
		saga.CompletedAt = &completedAt.Time
	}
	if len(varsJSON) > 0 {
		if err := json.Unmarshal(varsJSON, &saga.Vars); err != nil {
			return nil, fmt.Errorf("unmarshal vars: %w", err)
		}
	}
	if len(outputsJSON) > 0 {
		if err := json.Unmarshal(outputsJSON, &saga.Outputs); err != nil {
			return nil, fmt.Errorf("unmarshal outputs: %w", err)
		}
	}
	return &saga, nil
}

// scanStep scans a step from a Rows result.
func (r *SagaRepository) scanStep(rows *sql.Rows) (*domain.SagaStep, error) {
	var step domain.SagaStep
	var status string
	var compensate, stepError sql.NullString
	var startedAt, completedAt sql.NullTime
	var retryPolicyJSON, configJSON, outputJSON []byte
	var dependsOn pq.StringArray

	err := rows.Scan(
		&step.ID,
		&step.SagaID,
		&step.Name,
		&status,
		&step.Action,
		&dependsOn,
		&retryPolicyJSON,
		&compensate,
		&configJSON,
		&outputJSON,
		&stepError,
		&step.RetryCount,
		&startedAt,
		&completedAt,
	)
	if err != nil {
		return nil, fmt.Errorf("scan step: %w", err)
	}

	step.Status = domain.StepStatus(status)
	step.DependsOn = []string(dependsOn)
	if compensate.Valid {
		step.Compensate = compensate.String
	}
	if stepError.Valid {
		step.Error = stepError.String
	}
	if startedAt.Valid {
		step.StartedAt = &startedAt.Time
	}
	if completedAt.Valid {
		step.CompletedAt = &completedAt.Time
	}

	if len(retryPolicyJSON) > 0 {
		if err := json.Unmarshal(retryPolicyJSON, &step.RetryPolicy); err != nil {
			return nil, fmt.Errorf("unmarshal retry policy: %w", err)
		}
	}
	if len(configJSON) > 0 {
		if err := json.Unmarshal(configJSON, &step.Config); err != nil {
			return nil, fmt.Errorf("unmarshal config: %w", err)
		}
	}
	if len(outputJSON) > 0 {
		if err := json.Unmarshal(outputJSON, &step.Output); err != nil {
			return nil, fmt.Errorf("unmarshal output: %w", err)
		}
	}

	return &step, nil
}