go/src/infra/fleetconsole/internal/ent/entx/builder.go

// Copyright 2026 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package entx

import (
	"fmt"

	"entgo.io/ent/dialect"
	"entgo.io/ent/dialect/sql"

	ent "go.chromium.org/infra/fleetconsole/internal/ent/generated"
)

// True returns a standard SQL TRUE predicate.
// This is primarily used for constructing custom ON clauses in JOINs (e.g., ON TRUE)
// or for "no-op" filters in complex modification blocks where a predicate is required.
func True() *sql.Predicate {
	return sql.P(func(b *sql.Builder) {
		b.WriteString("TRUE")
	})
}

// CrossJoin adds a CROSS JOIN (implemented as JOIN ON TRUE) to the selector.
//
// Usage:
//
//	entx.CrossJoin(s, t)
func CrossJoin(s *sql.Selector, t sql.TableView) *sql.Selector {
	return s.Join(t).OnP(True())
}

// Lateral creates a table selector for use in LATERAL joins.
func Lateral(name string) *sql.SelectTable {
	return sql.Table(fmt.Sprintf("LATERAL %s", name))
}

// CountIf generates COUNT(*) FILTER (WHERE <predicate>) or
// COUNT(CASE WHEN <predicate> THEN 1 END) depending on the dialect.
func CountIf(p *sql.Predicate) ent.AggregateFunc {
	return func(s *sql.Selector) string {
		// Sync the predicate's internal builder with the main query.
		// We set Total() so the predicate generates placeholders ($5, $6)
		// that continue from where the main query left off.
		p.SetDialect(s.Dialect())
		p.SetTotal(s.Total())

		// Compile the predicate to SQL and arguments.
		condition, args := p.Query()

		// Inject the arguments into the main query.
		// We use sql.Expr("", args...) to trick the builder into appending
		// the arguments to its internal slice WITHOUT writing any new SQL
		// text to the buffer (because the expr string is empty).
		s.Arg(sql.Expr("", args...))

		if s.Dialect() == dialect.Postgres {
			// Return the standard Postgres aggregation SQL.
			return fmt.Sprintf("COUNT(*) FILTER (WHERE %s)", condition)
		}

		return fmt.Sprintf("COUNT(CASE WHEN %s THEN 1 END)", condition)
	}
}