package store

import (
	"context"
	"errors"
	"fmt"
	"time"

	"github.com/jackc/pgx/v5"
)

type RuntimeRecoveryResult struct {
	ReleasedConcurrencyLeases int64 `json:"releasedConcurrencyLeases"`
	ReleasedRateReservations  int64 `json:"releasedRateReservations"`
	FailedAttempts            int64 `json:"failedAttempts"`
	FailedTasks               int64 `json:"failedTasks"`
	RequeuedAsyncTasks        int64 `json:"requeuedAsyncTasks"`
}

func (s *Store) ReserveRateLimits(ctx context.Context, taskID string, attemptID string, reservations []RateLimitReservation) (RateLimitResult, error) {
	tx, err := s.pool.Begin(ctx)
	if err != nil {
		return RateLimitResult{}, err
	}
	defer tx.Rollback(ctx)

	result := RateLimitResult{}
	for _, reservation := range reservations {
		if reservation.Limit <= 0 || reservation.Amount <= 0 {
			continue
		}
		if reservation.Metric == "" || reservation.Amount > reservation.Limit {
			return RateLimitResult{}, &RateLimitExceededError{
				Metric:    reservation.Metric,
				Message:   fmt.Sprintf("rate limit exceeded: %s request amount %.0f is greater than limit %.0f", reservation.Metric, reservation.Amount, reservation.Limit),
				Retryable: false,
			}
		}
		if reservation.WindowSeconds <= 0 {
			reservation.WindowSeconds = 60
		}
		if reservation.Metric == "concurrent" {
			leaseID, err := reserveConcurrencyLease(ctx, tx, taskID, attemptID, reservation)
			if err != nil {
				return RateLimitResult{}, err
			}
			result.LeaseIDs = append(result.LeaseIDs, leaseID)
			continue
		}
		normalized, err := reserveCounterWindow(ctx, tx, taskID, attemptID, reservation)
		if err != nil {
			return RateLimitResult{}, err
		}
		result.Reservations = append(result.Reservations, normalized)
	}
	return result, tx.Commit(ctx)
}

func reserveConcurrencyLease(ctx context.Context, tx pgx.Tx, taskID string, attemptID string, reservation RateLimitReservation) (string, error) {
	if reservation.LeaseTTLSeconds <= 0 {
		reservation.LeaseTTLSeconds = 120
	}
	var active float64
	var nextAvailableAt time.Time
	if err := tx.QueryRow(ctx, `
SELECT COALESCE(SUM(lease_value), 0)::float8,
       COALESCE(MIN(expires_at), now() + ($3::int * interval '1 second'))
FROM gateway_concurrency_leases
WHERE scope_type = $1
  AND scope_key = $2
  AND released_at IS NULL
  AND expires_at > now()`,
		reservation.ScopeType,
		reservation.ScopeKey,
		reservation.LeaseTTLSeconds,
	).Scan(&active, &nextAvailableAt); err != nil {
		return "", err
	}
	if active+reservation.Amount > reservation.Limit {
		return "", &RateLimitExceededError{
			Metric:     reservation.Metric,
			Message:    fmt.Sprintf("rate limit exceeded: concurrent active %.0f plus request %.0f is greater than limit %.0f", active, reservation.Amount, reservation.Limit),
			RetryAfter: concurrencyRetryAfter(nextAvailableAt),
			Retryable:  true,
		}
	}
	var leaseID string
	if err := tx.QueryRow(ctx, `
INSERT INTO gateway_concurrency_leases (task_id, attempt_id, scope_type, scope_key, lease_value, expires_at)
VALUES ($1::uuid, NULLIF($2, '')::uuid, $3, $4, $5, now() + ($6::int * interval '1 second'))
RETURNING id::text`,
		taskID,
		attemptID,
		reservation.ScopeType,
		reservation.ScopeKey,
		reservation.Amount,
		reservation.LeaseTTLSeconds,
	).Scan(&leaseID); err != nil {
		return "", err
	}
	return leaseID, nil
}

func reserveCounterWindow(ctx context.Context, tx pgx.Tx, taskID string, attemptID string, reservation RateLimitReservation) (RateLimitReservation, error) {
	usedAmount := 0.0
	reservedAmount := reservation.Amount
	var windowStart time.Time
	err := tx.QueryRow(ctx, `
WITH bounds AS (
  SELECT
    to_timestamp(floor(extract(epoch FROM now()) / $7::int) * $7::int) AS window_start,
    to_timestamp(floor(extract(epoch FROM now()) / $7::int) * $7::int) + ($7::int * interval '1 second') AS reset_at
)
INSERT INTO gateway_rate_limit_counters (
  scope_type, scope_key, metric, window_start, limit_value, used_value, reserved_value, reset_at
)
SELECT $1, $2, $3, bounds.window_start, $4, $5, $6, bounds.reset_at
FROM bounds
ON CONFLICT (scope_type, scope_key, metric, window_start) DO UPDATE
SET limit_value = EXCLUDED.limit_value,
    used_value = gateway_rate_limit_counters.used_value + EXCLUDED.used_value,
    reserved_value = gateway_rate_limit_counters.reserved_value + EXCLUDED.reserved_value,
    reset_at = EXCLUDED.reset_at,
    updated_at = now()
WHERE gateway_rate_limit_counters.used_value + gateway_rate_limit_counters.reserved_value + EXCLUDED.used_value + EXCLUDED.reserved_value <= EXCLUDED.limit_value
RETURNING window_start`,
		reservation.ScopeType,
		reservation.ScopeKey,
		reservation.Metric,
		reservation.Limit,
		usedAmount,
		reservedAmount,
		reservation.WindowSeconds,
	).Scan(&windowStart)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			resetAt := time.Now().Add(time.Duration(reservation.WindowSeconds) * time.Second)
			_ = tx.QueryRow(ctx, `
WITH bounds AS (
  SELECT to_timestamp(floor(extract(epoch FROM now()) / $4::int) * $4::int) AS window_start
)
SELECT counters.reset_at
FROM gateway_rate_limit_counters counters
JOIN bounds ON counters.window_start = bounds.window_start
WHERE scope_type = $1
  AND scope_key = $2
  AND metric = $3`,
				reservation.ScopeType,
				reservation.ScopeKey,
				reservation.Metric,
				reservation.WindowSeconds,
			).Scan(&resetAt)
			return RateLimitReservation{}, &RateLimitExceededError{
				Metric:     reservation.Metric,
				Message:    fmt.Sprintf("rate limit exceeded: %s window has no remaining capacity", reservation.Metric),
				RetryAfter: retryAfterUntil(resetAt),
				Retryable:  true,
			}
		}
		return RateLimitReservation{}, err
	}
	reservation.WindowStart = windowStart
	if err := tx.QueryRow(ctx, `
INSERT INTO gateway_rate_limit_reservations (
  task_id, attempt_id, scope_type, scope_key, metric, window_start, limit_value, reserved_amount, status
)
VALUES (
  $1::uuid, NULLIF($2, '')::uuid, $3, $4, $5, $6, $7, $8, 'reserved'
)
RETURNING id::text`,
		taskID,
		attemptID,
		reservation.ScopeType,
		reservation.ScopeKey,
		reservation.Metric,
		windowStart,
		reservation.Limit,
		reservedAmount,
	).Scan(&reservation.ReservationID); err != nil {
		return RateLimitReservation{}, err
	}
	return reservation, nil
}

func retryAfterUntil(when time.Time) time.Duration {
	if when.IsZero() {
		return 0
	}
	duration := time.Until(when)
	if duration < time.Second {
		return time.Second
	}
	return duration
}

func concurrencyRetryAfter(leaseExpiresAt time.Time) time.Duration {
	if leaseExpiresAt.IsZero() {
		return time.Second
	}
	duration := time.Until(leaseExpiresAt)
	if duration <= time.Second {
		return time.Second
	}
	return time.Second
}

func (s *Store) CommitRateLimitReservations(ctx context.Context, reservations []RateLimitReservation, actualByMetric map[string]float64) error {
	return s.finishRateLimitReservations(ctx, reservations, actualByMetric, "committed", "success")
}

func (s *Store) ReleaseRateLimitReservations(ctx context.Context, reservations []RateLimitReservation, reason string) error {
	return s.finishRateLimitReservations(ctx, reservations, nil, "released", reason)
}

func (s *Store) ReleaseConcurrencyLeases(ctx context.Context, leaseIDs []string) error {
	if len(leaseIDs) == 0 {
		return nil
	}
	for _, leaseID := range leaseIDs {
		if leaseID == "" {
			continue
		}
		if _, err := s.pool.Exec(ctx, `
UPDATE gateway_concurrency_leases
SET released_at = now()
WHERE id = $1::uuid AND released_at IS NULL`, leaseID); err != nil && !errors.Is(err, ErrRateLimited) {
			return err
		}
	}
	return nil
}

func (s *Store) RecoverInterruptedRuntimeState(ctx context.Context) (RuntimeRecoveryResult, error) {
	tx, err := s.pool.Begin(ctx)
	if err != nil {
		return RuntimeRecoveryResult{}, err
	}
	defer tx.Rollback(ctx)

	result := RuntimeRecoveryResult{}
	rows, err := tx.Query(ctx, `
UPDATE gateway_rate_limit_reservations
SET status = 'released',
    reason = 'server_restarted',
    finalized_at = now(),
    updated_at = now()
WHERE status = 'reserved'
RETURNING scope_type, scope_key, metric, window_start, reserved_amount::float8`)
	if err != nil {
		return RuntimeRecoveryResult{}, err
	}
	reservations := make([]RateLimitReservation, 0)
	for rows.Next() {
		var reservation RateLimitReservation
		if err := rows.Scan(&reservation.ScopeType, &reservation.ScopeKey, &reservation.Metric, &reservation.WindowStart, &reservation.Amount); err != nil {
			rows.Close()
			return RuntimeRecoveryResult{}, err
		}
		reservations = append(reservations, reservation)
	}
	if err := rows.Err(); err != nil {
		rows.Close()
		return RuntimeRecoveryResult{}, err
	}
	rows.Close()
	for _, reservation := range reservations {
		if err := releaseCounterReservation(ctx, tx, reservation.ScopeType, reservation.ScopeKey, reservation.Metric, reservation.WindowStart, reservation.Amount); err != nil {
			return RuntimeRecoveryResult{}, err
		}
	}
	result.ReleasedRateReservations = int64(len(reservations))

	tag, err := tx.Exec(ctx, `
UPDATE gateway_concurrency_leases
SET released_at = now()
WHERE released_at IS NULL
  AND expires_at > now()`)
	if err != nil {
		return RuntimeRecoveryResult{}, err
	}
	result.ReleasedConcurrencyLeases = tag.RowsAffected()

	tag, err = tx.Exec(ctx, `
UPDATE gateway_task_attempts
SET status = 'failed',
    retryable = true,
    error_code = 'server_restarted',
    error_message = 'attempt interrupted by service restart',
    finished_at = now()
WHERE status = 'running'`)
	if err != nil {
		return RuntimeRecoveryResult{}, err
	}
	result.FailedAttempts = tag.RowsAffected()

	asyncTaskRows, err := tx.Query(ctx, `
UPDATE gateway_tasks
SET status = 'queued',
    error = NULL,
    error_code = NULL,
    error_message = NULL,
    locked_by = NULL,
    locked_at = NULL,
    heartbeat_at = NULL,
    next_run_at = now(),
    finished_at = NULL,
    updated_at = now()
WHERE async_mode = true
  AND status = 'running'
RETURNING id::text`)
	if err != nil {
		return RuntimeRecoveryResult{}, err
	}
	asyncTaskIDs := make([]string, 0)
	for asyncTaskRows.Next() {
		var taskID string
		if err := asyncTaskRows.Scan(&taskID); err != nil {
			asyncTaskRows.Close()
			return RuntimeRecoveryResult{}, err
		}
		asyncTaskIDs = append(asyncTaskIDs, taskID)
	}
	if err := asyncTaskRows.Err(); err != nil {
		asyncTaskRows.Close()
		return RuntimeRecoveryResult{}, err
	}
	asyncTaskRows.Close()
	for _, taskID := range asyncTaskIDs {
		if _, err := tx.Exec(ctx, `
INSERT INTO gateway_task_events (task_id, seq, event_type, status, phase, progress, message, payload, simulated)
VALUES (
  $1::uuid,
  COALESCE((SELECT MAX(seq) + 1 FROM gateway_task_events WHERE task_id = $1::uuid), 1),
  'task.recovered',
  'queued',
  'recovered',
  0.2,
  'async task recovered after service restart',
  '{"code":"server_restarted"}'::jsonb,
  false
)`, taskID); err != nil {
			return RuntimeRecoveryResult{}, err
		}
	}
	result.RequeuedAsyncTasks = int64(len(asyncTaskIDs))

	taskRows, err := tx.Query(ctx, `
UPDATE gateway_tasks
SET status = 'failed',
    error = 'task interrupted by service restart',
    error_code = 'server_restarted',
    error_message = 'task interrupted by service restart',
    finished_at = now(),
    updated_at = now()
WHERE async_mode = false
  AND status = 'running'
RETURNING id::text`)
	if err != nil {
		return RuntimeRecoveryResult{}, err
	}
	taskIDs := make([]string, 0)
	for taskRows.Next() {
		var taskID string
		if err := taskRows.Scan(&taskID); err != nil {
			taskRows.Close()
			return RuntimeRecoveryResult{}, err
		}
		taskIDs = append(taskIDs, taskID)
	}
	if err := taskRows.Err(); err != nil {
		taskRows.Close()
		return RuntimeRecoveryResult{}, err
	}
	taskRows.Close()

	for _, taskID := range taskIDs {
		if _, err := tx.Exec(ctx, `
INSERT INTO gateway_task_events (task_id, seq, event_type, status, phase, progress, message, payload, simulated)
VALUES (
  $1::uuid,
  COALESCE((SELECT MAX(seq) + 1 FROM gateway_task_events WHERE task_id = $1::uuid), 1),
  'task.recovered',
  'failed',
  'recovered',
  1,
  'task interrupted by service restart',
  '{"code":"server_restarted"}'::jsonb,
  false
)`, taskID); err != nil {
			return RuntimeRecoveryResult{}, err
		}
	}
	result.FailedTasks = int64(len(taskIDs))

	return result, tx.Commit(ctx)
}

func (s *Store) finishRateLimitReservations(ctx context.Context, reservations []RateLimitReservation, actualByMetric map[string]float64, status string, reason string) error {
	if len(reservations) == 0 {
		return nil
	}
	tx, err := s.pool.Begin(ctx)
	if err != nil {
		return err
	}
	defer tx.Rollback(ctx)

	for _, reservation := range reservations {
		if reservation.ReservationID == "" {
			continue
		}
		actualAmount := actualByMetric[reservation.Metric]
		if status == "committed" && actualAmount <= 0 {
			actualAmount = reservation.Amount
		}
		var stored RateLimitReservation
		err := tx.QueryRow(ctx, `
UPDATE gateway_rate_limit_reservations
SET status = $2::text,
    reason = NULLIF($3::text, ''),
    actual_amount = CASE WHEN $2::text = 'committed' THEN $4 ELSE actual_amount END,
    finalized_at = now(),
    updated_at = now()
WHERE id = $1::uuid
  AND status = 'reserved'
RETURNING scope_type, scope_key, metric, window_start, reserved_amount::float8`,
			reservation.ReservationID,
			status,
			reason,
			actualAmount,
		).Scan(&stored.ScopeType, &stored.ScopeKey, &stored.Metric, &stored.WindowStart, &stored.Amount)
		if err != nil {
			if errors.Is(err, pgx.ErrNoRows) {
				continue
			}
			return err
		}
		if status == "committed" {
			if err := commitCounterReservation(ctx, tx, stored.ScopeType, stored.ScopeKey, stored.Metric, stored.WindowStart, stored.Amount, actualAmount); err != nil {
				return err
			}
			continue
		}
		if err := releaseCounterReservation(ctx, tx, stored.ScopeType, stored.ScopeKey, stored.Metric, stored.WindowStart, stored.Amount); err != nil {
			return err
		}
	}
	return tx.Commit(ctx)
}

func commitCounterReservation(ctx context.Context, tx pgx.Tx, scopeType string, scopeKey string, metric string, windowStart time.Time, reservedAmount float64, actualAmount float64) error {
	_, err := tx.Exec(ctx, `
UPDATE gateway_rate_limit_counters
SET reserved_value = GREATEST(reserved_value - $5, 0),
    used_value = used_value + $6,
    updated_at = now()
WHERE scope_type = $1
  AND scope_key = $2
  AND metric = $3
  AND window_start = $4`,
		scopeType, scopeKey, metric, windowStart, reservedAmount, actualAmount)
	return err
}

func releaseCounterReservation(ctx context.Context, tx pgx.Tx, scopeType string, scopeKey string, metric string, windowStart time.Time, reservedAmount float64) error {
	_, err := tx.Exec(ctx, `
UPDATE gateway_rate_limit_counters
SET reserved_value = GREATEST(reserved_value - $5, 0),
    updated_at = now()
WHERE scope_type = $1
  AND scope_key = $2
  AND metric = $3
  AND window_start = $4`,
		scopeType, scopeKey, metric, windowStart, reservedAmount)
	return err
}