chore: import upstream snapshot with attribution

internal/filter/engine.go

@@ -0,0 +1,124 @@
+package filter
+
+import (
+	"context"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/google/cel-go/cel"
+	"github.com/pkg/errors"
+)
+
+// Engine parses CEL filters into a dialect-agnostic condition tree.
+type Engine struct {
+	schema Schema
+	env    *cel.Env
+	// nowFunc resolves the value of the `now` variable. It is frozen once per
+	// Compile so a single filter sees a single instant, and is overridable in
+	// tests for deterministic folding.
+	nowFunc func() time.Time
+}
+
+// NewEngine builds a new Engine for the provided schema.
+func NewEngine(schema Schema) (*Engine, error) {
+	env, err := cel.NewEnv(schema.EnvOptions...)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to create CEL environment")
+	}
+	return &Engine{
+		schema:  schema,
+		env:     env,
+		nowFunc: time.Now,
+	}, nil
+}
+
+// Program stores a compiled filter condition.
+type Program struct {
+	schema    Schema
+	condition Condition
+}
+
+// ConditionTree exposes the underlying condition tree.
+func (p *Program) ConditionTree() Condition {
+	return p.condition
+}
+
+// Compile parses the filter string into an executable program.
+func (e *Engine) Compile(_ context.Context, filter string) (*Program, error) {
+	if strings.TrimSpace(filter) == "" {
+		return nil, errors.New("filter expression is empty")
+	}
+
+	ast, issues := e.env.Compile(filter)
+	if issues != nil && issues.Err() != nil {
+		return nil, errors.Wrap(issues.Err(), "failed to compile filter")
+	}
+	parsed, err := cel.AstToParsedExpr(ast)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to convert AST")
+	}
+
+	cond, err := buildCondition(parsed.GetExpr(), parseContext{schema: e.schema, now: e.nowFunc()})
+	if err != nil {
+		return nil, err
+	}
+
+	return &Program{
+		schema:    e.schema,
+		condition: cond,
+	}, nil
+}
+
+// CompileToStatement compiles and renders the filter in a single step.
+func (e *Engine) CompileToStatement(ctx context.Context, filter string, opts RenderOptions) (Statement, error) {
+	program, err := e.Compile(ctx, filter)
+	if err != nil {
+		return Statement{}, err
+	}
+	return program.Render(opts)
+}
+
+// RenderOptions configure SQL rendering.
+type RenderOptions struct {
+	Dialect           DialectName
+	PlaceholderOffset int
+	DisableNullChecks bool
+}
+
+// Statement contains the rendered SQL fragment and its args.
+type Statement struct {
+	SQL  string
+	Args []any
+}
+
+// Render converts the program into a dialect-specific SQL fragment.
+func (p *Program) Render(opts RenderOptions) (Statement, error) {
+	renderer := newRenderer(p.schema, opts)
+	return renderer.Render(p.condition)
+}
+
+var (
+	defaultOnce           sync.Once
+	defaultInst           *Engine
+	defaultErr            error
+	defaultAttachmentOnce sync.Once
+	defaultAttachmentInst *Engine
+	defaultAttachmentErr  error
+)
+
+// DefaultEngine returns the process-wide memo filter engine.
+func DefaultEngine() (*Engine, error) {
+	defaultOnce.Do(func() {
+		defaultInst, defaultErr = NewEngine(NewSchema())
+	})
+	return defaultInst, defaultErr
+}
+
+// DefaultAttachmentEngine returns the process-wide attachment filter engine.
+func DefaultAttachmentEngine() (*Engine, error) {
+	defaultAttachmentOnce.Do(func() {
+		defaultAttachmentInst, defaultAttachmentErr = NewEngine(NewAttachmentSchema())
+	})
+	return defaultAttachmentInst, defaultAttachmentErr
+}