package billing

import (
	"context"
	"errors"
	"fmt"
	"math"
	"strings"

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

func (s *Service) ListAccounts(ctx context.Context, tenantID string) ([]Account, error) {
	query := `
		SELECT t.id::text, t.name, COALESCE(w.currency, $1), COALESCE(w.balance_micros, 0),
		       COALESCE(w.reserved_micros, 0), COALESCE(w.balance_micros - w.reserved_micros, 0),
		       COALESCE(w.updated_at, t.created_at)
		FROM tenants t LEFT JOIN tenant_wallets w ON w.tenant_id = t.id`
	args := []any{s.currency}
	if strings.TrimSpace(tenantID) != "" {
		query += ` WHERE t.id=$2`
		args = append(args, tenantID)
	}
	query += ` ORDER BY t.name`
	rows, err := s.db.Query(ctx, query, args...)
	if err != nil {
		return nil, fmt.Errorf("query billing accounts: %w", err)
	}
	defer rows.Close()
	result := make([]Account, 0)
	for rows.Next() {
		var item Account
		if err := rows.Scan(&item.TenantID, &item.TenantName, &item.Currency, &item.BalanceMicros,
			&item.ReservedMicros, &item.AvailableMicros, &item.UpdatedAt); err != nil {
			return nil, fmt.Errorf("scan billing account: %w", err)
		}
		result = append(result, item)
	}
	return result, rows.Err()
}

func (s *Service) ListLedger(ctx context.Context, tenantID string, limit int) ([]LedgerEntry, error) {
	if limit < 1 || limit > 500 {
		limit = 200
	}
	query := `
		SELECT id::text, tenant_id::text, COALESCE(project_id::text, ''), currency, amount_micros,
		       balance_after_micros, kind, source_type, source_id, description, created_at
		FROM billing_ledger`
	args := []any{}
	if strings.TrimSpace(tenantID) != "" {
		query += ` WHERE tenant_id = $1 ORDER BY created_at DESC LIMIT $2`
		args = append(args, tenantID, limit)
	} else {
		query += ` ORDER BY created_at DESC LIMIT $1`
		args = append(args, limit)
	}
	rows, err := s.db.Query(ctx, query, args...)
	if err != nil {
		return nil, fmt.Errorf("query billing ledger: %w", err)
	}
	defer rows.Close()
	result := make([]LedgerEntry, 0)
	for rows.Next() {
		var item LedgerEntry
		if err := rows.Scan(&item.ID, &item.TenantID, &item.ProjectID, &item.Currency, &item.AmountMicros,
			&item.BalanceAfterMicros, &item.Kind, &item.SourceType, &item.SourceID,
			&item.Description, &item.CreatedAt); err != nil {
			return nil, fmt.Errorf("scan billing ledger: %w", err)
		}
		result = append(result, item)
	}
	return result, rows.Err()
}

func (s *Service) AdjustBalance(ctx context.Context, input AdjustmentInput) (LedgerEntry, error) {
	input.TenantID = strings.TrimSpace(input.TenantID)
	input.Description = normalizeDescription(input.Description)
	if input.TenantID == "" || input.AmountMicros == 0 {
		return LedgerEntry{}, ErrInvalidAmount
	}
	tx, err := s.db.BeginTx(ctx, pgx.TxOptions{IsoLevel: pgx.ReadCommitted})
	if err != nil {
		return LedgerEntry{}, fmt.Errorf("begin balance adjustment: %w", err)
	}
	defer tx.Rollback(ctx)
	if _, err := tx.Exec(ctx, `
		INSERT INTO tenant_wallets (tenant_id, currency) VALUES ($1, $2)
		ON CONFLICT (tenant_id) DO NOTHING`, input.TenantID, s.currency); err != nil {
		return LedgerEntry{}, fmt.Errorf("ensure adjustment wallet: %w", err)
	}
	var currency string
	var balance, held int64
	if err := tx.QueryRow(ctx, `SELECT currency, balance_micros, reserved_micros FROM tenant_wallets WHERE tenant_id = $1 FOR UPDATE`, input.TenantID).Scan(&currency, &balance, &held); err != nil {
		return LedgerEntry{}, fmt.Errorf("lock adjustment wallet: %w", err)
	}
	if currency != s.currency {
		return LedgerEntry{}, fmt.Errorf("tenant wallet currency %s does not match %s", currency, s.currency)
	}
	if input.AmountMicros > 0 && balance > math.MaxInt64-input.AmountMicros {
		return LedgerEntry{}, ErrInvalidAmount
	}
	newBalance := balance + input.AmountMicros
	if newBalance < held || newBalance < 0 {
		return LedgerEntry{}, ErrInsufficientBalance
	}
	if _, err := tx.Exec(ctx, `UPDATE tenant_wallets SET balance_micros = $2, updated_at = now() WHERE tenant_id = $1`, input.TenantID, newBalance); err != nil {
		return LedgerEntry{}, fmt.Errorf("apply balance adjustment: %w", err)
	}
	sourceID := "adj_" + randomHex(16)
	var result LedgerEntry
	err = tx.QueryRow(ctx, `
		INSERT INTO billing_ledger (tenant_id, currency, amount_micros, balance_after_micros, kind, source_type, source_id, description)
		VALUES ($1,$2,$3,$4,'adjustment','admin',$5,$6)
		RETURNING id::text, tenant_id::text, '', currency, amount_micros, balance_after_micros,
		          kind, source_type, source_id, description, created_at`,
		input.TenantID, s.currency, input.AmountMicros, newBalance, sourceID, input.Description,
	).Scan(&result.ID, &result.TenantID, &result.ProjectID, &result.Currency, &result.AmountMicros,
		&result.BalanceAfterMicros, &result.Kind, &result.SourceType, &result.SourceID,
		&result.Description, &result.CreatedAt)
	if err != nil {
		return LedgerEntry{}, fmt.Errorf("write adjustment ledger entry: %w", err)
	}
	if err := tx.Commit(ctx); err != nil {
		return LedgerEntry{}, fmt.Errorf("commit balance adjustment: %w", err)
	}
	return result, nil
}

func (s *Service) createTopUpOrder(ctx context.Context, input CheckoutInput) (string, int64, error) {
	if !s.stripeEnabled {
		return "", 0, ErrStripeDisabled
	}
	if strings.TrimSpace(input.TenantID) == "" || input.AmountMinor < s.minTopUpMinor || input.AmountMinor > s.maxTopUpMinor {
		return "", 0, ErrInvalidAmount
	}
	amountMicros, err := minorToMicros(s.currency, input.AmountMinor)
	if err != nil {
		return "", 0, err
	}
	var orderID string
	err = s.db.QueryRow(ctx, `
		INSERT INTO topup_orders (tenant_id, amount_minor, amount_micros, currency)
		VALUES ($1,$2,$3,$4) RETURNING id::text`, input.TenantID, input.AmountMinor, amountMicros, s.currency,
	).Scan(&orderID)
	if err != nil {
		return "", 0, fmt.Errorf("create top-up order: %w", err)
	}
	return orderID, amountMicros, nil
}

func minorToMicros(currency string, amount int64) (int64, error) {
	if amount <= 0 {
		return 0, ErrInvalidAmount
	}
	factor := int64(10_000)
	switch strings.ToLower(currency) {
	case "bif", "clp", "djf", "gnf", "jpy", "kmf", "krw", "mga", "pyg", "rwf", "ugx", "vnd", "vuv", "xaf", "xof", "xpf":
		factor = 1_000_000
	case "bhd", "jod", "kwd", "omr", "tnd":
		factor = 1_000
	}
	if amount > math.MaxInt64/factor {
		return 0, ErrInvalidAmount
	}
	return amount * factor, nil
}

func isNotFound(err error) bool {
	return errors.Is(err, pgx.ErrNoRows)
}