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iterator.go
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iterator.go
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package query
import (
"errors"
"fmt"
)
var errEndOfIter = errors.New("iterator reached the end")
// Iterator allows traversal of a Bloblang function result in iterations.
type Iterator interface {
// Next provides the next element of the iterator, or an error. When the
// iterator has reached the end ErrEndOfIter is returned.
Next() (any, error)
// Len provides a static length of the iterator when possible.
Len() (int, bool)
}
// Iterable is an interface implemented by Bloblang functions that are able to
// expose their results as an interator, allowing for more efficient chaining of
// array based methods.
type Iterable interface {
// TryIterate attempts to create an iterator that walks the function result.
// Some functions will be unable to provide an iterator due to either the
// context or function arguments provided, therefore it's possible that a
// static value will be returned instead.
TryIterate(ctx FunctionContext) (Iterator, any, error)
}
//------------------------------------------------------------------------------
func execTryIter(iFn Iterable, fn Function, ctx FunctionContext) (iter Iterator, v any, err error) {
if iFn != nil {
if iter, v, err = iFn.TryIterate(ctx); err != nil || iter != nil {
return
}
} else if v, err = fn.Exec(ctx); err != nil {
return
}
if arr, ok := v.([]any); ok {
return arrayIterator(arr), nil, nil
}
return
}
func arrayIterator(arr []any) Iterator {
return closureIterator{
next: func() (any, error) {
if len(arr) == 0 {
return nil, errEndOfIter
}
v := arr[0]
arr = arr[1:]
return v, nil
},
len: func() (int, bool) {
return len(arr), true
},
}
}
func drainIter(iter Iterator) ([]any, error) {
var arr []any
if l, ok := iter.Len(); ok {
arr = make([]any, 0, l)
}
for {
v, err := iter.Next()
if err != nil {
if errors.Is(err, errEndOfIter) {
return arr, nil
}
return nil, err
}
arr = append(arr, v)
}
}
type closureIterator struct {
next func() (any, error)
len func() (int, bool)
}
func (c closureIterator) Next() (any, error) {
return c.next()
}
func (c closureIterator) Len() (int, bool) {
if c.len == nil {
return 0, false
}
return c.len()
}
//------------------------------------------------------------------------------
type filterMethod struct {
target Function
iterTarget Iterable
mapFn Function
}
func newFilterMethod(target Function, args ...any) (Function, error) {
mapFn, ok := args[0].(Function)
if !ok {
return nil, fmt.Errorf("expected query argument, received %T", args[0])
}
iterTarget, _ := target.(Iterable)
return &filterMethod{
target: target,
iterTarget: iterTarget,
mapFn: mapFn,
}, nil
}
func (f *filterMethod) Annotation() string {
return "method filter"
}
func (f *filterMethod) TryIterate(ctx FunctionContext) (Iterator, any, error) {
iter, res, err := execTryIter(f.iterTarget, f.target, ctx)
if err != nil {
return nil, nil, err
}
if iter == nil {
res, err = f.execFallback(ctx, res)
return nil, res, err
}
return closureIterator{
next: func() (any, error) {
for {
v, err := iter.Next()
if err != nil {
if err != errEndOfIter {
err = ErrFrom(err, f.target)
}
return nil, err
}
f, err := f.mapFn.Exec(ctx.WithValue(v))
if err != nil {
return nil, err
}
if b, _ := f.(bool); b {
return v, nil
}
}
},
}, nil, nil
}
// We also support filtering objects, so when we're unable to spawn an iterator
// we attempt to process a map.
func (f *filterMethod) execFallback(ctx FunctionContext, res any) (any, error) {
m, ok := res.(map[string]any)
if !ok {
return nil, ErrFrom(NewTypeError(res, ValueArray, ValueObject), f.target)
}
newMap := make(map[string]any, len(m))
for k, v := range m {
var ctxMap any = map[string]any{
"key": k,
"value": v,
}
f, err := f.mapFn.Exec(ctx.WithValue(ctxMap))
if err != nil {
return nil, err
}
if b, _ := f.(bool); b {
newMap[k] = v
}
}
return newMap, nil
}
func (f *filterMethod) Exec(ctx FunctionContext) (any, error) {
iter, res, err := f.TryIterate(ctx)
if err != nil || res != nil {
return res, err
}
return drainIter(iter)
}
func (f *filterMethod) QueryTargets(ctx TargetsContext) (TargetsContext, []TargetPath) {
return f.target.QueryTargets(ctx)
}
//------------------------------------------------------------------------------
type mapEachMethod struct {
target Function
iterTarget Iterable
mapFn Function
}
func newMapEachMethod(target Function, args ...any) (Function, error) {
mapFn, ok := args[0].(Function)
if !ok {
return nil, fmt.Errorf("expected query argument, received %T", args[0])
}
iterTarget, _ := target.(Iterable)
return &mapEachMethod{
target: target,
iterTarget: iterTarget,
mapFn: mapFn,
}, nil
}
func (m *mapEachMethod) Annotation() string {
return "method map_each"
}
func (m *mapEachMethod) TryIterate(ctx FunctionContext) (Iterator, any, error) {
iter, res, err := execTryIter(m.iterTarget, m.target, ctx)
if err != nil {
return nil, nil, err
}
if iter == nil {
res, err = m.execFallback(ctx, res)
return nil, res, err
}
return closureIterator{
next: func() (any, error) {
for {
v, err := iter.Next()
if err != nil {
if err != errEndOfIter {
err = ErrFrom(err, m.target)
}
return nil, err
}
newV, err := m.mapFn.Exec(ctx.WithValue(v))
if err != nil {
return nil, ErrFrom(err, m.mapFn)
}
switch newV.(type) {
case Delete:
case Nothing:
return v, nil
default:
return newV, nil
}
}
},
}, nil, nil
}
func (m *mapEachMethod) execFallback(ctx FunctionContext, res any) (any, error) {
resMap, ok := res.(map[string]any)
if !ok {
return nil, ErrFrom(NewTypeError(res, ValueArray, ValueObject), m.target)
}
newMap := make(map[string]any, len(resMap))
for k, v := range resMap {
var ctxMap any = map[string]any{
"key": k,
"value": v,
}
newV, mapErr := m.mapFn.Exec(ctx.WithValue(ctxMap))
if mapErr != nil {
return nil, fmt.Errorf("failed to process element %v: %w", k, ErrFrom(mapErr, m.mapFn))
}
switch newV.(type) {
case Delete:
case Nothing:
newMap[k] = v
default:
newMap[k] = newV
}
}
return newMap, nil
}
func (m *mapEachMethod) Exec(ctx FunctionContext) (any, error) {
iter, res, err := m.TryIterate(ctx)
if err != nil || res != nil {
return res, err
}
return drainIter(iter)
}
func (m *mapEachMethod) QueryTargets(ctx TargetsContext) (TargetsContext, []TargetPath) {
return m.target.QueryTargets(ctx)
}