refactor: Refactor commit nodes (#892)

* Remove headsetScanNode

Node no longer really does anything and only serves to misdirect and confuse

* Make cid an option-type

As well as being clearer IMO in it's own right, this will make life easier shortly

* Use parsed.Cid over duplicate prop

* Dont store iteration state

Is much easier if currentCid stays local.  Had to add a couple of checks for when cid is provided as otherwise it starts to take a different (and incorrect) code-path, will likely be removed/optimized shortly.

* Remove legacy comment

* Use parsed.Depth over duplicate prop

* Use parsed.DocKey over duplicate prop

* Use parsed.Field over duplicate prop

Also fixes an explain bug where it was incorrectly reporting field as 'C'

* Simplify commit node constructor

* Set currentValue only when valid

A bit of a nitpick, but it is also now located next to where it is used/returned

* Replace legacy comment with correct comment

* Add cid related comment

* Remove type-unsafe list with slice magic

* Remove odd comment

* Remove commitSelectNode

Doesnt actually do anything anymore

* Remove commitSelectTopNode

It no longer served a purpose

query/graphql/mapper/commitSelect.go

@@ -29,7 +29,7 @@ type CommitSelect struct {
 	Depth client.Option[uint64]
 
 	// The parent Cid for which commit information has been requested.
-	Cid string
+	Cid client.Option[string]
 }
 
 func (s *CommitSelect) CloneTo(index int) Requestable {

query/graphql/mapper/select.go

@@ -10,7 +10,10 @@
 
 package mapper
 
-import "github.com/sourcenetwork/defradb/core"
+import (
+	"github.com/sourcenetwork/defradb/client"
+	"github.com/sourcenetwork/defradb/core"
+)
 
 // Select represents a request to return data from Defra.
 //
@@ -24,7 +27,7 @@ type Select struct {
 	core.DocumentMapping
 
 	// A commit identifier that can be specified to request data at a given time.
-	Cid string
+	Cid client.Option[string]
 
 	// The name of the collection that this Select selects data from.
 	CollectionName string

query/graphql/parser/commit.go

@@ -30,7 +30,7 @@ type CommitSelect struct {
 
 	DocKey    string
 	FieldName client.Option[string]
-	Cid       string
+	Cid       client.Option[string]
 	Depth     client.Option[uint64]
 
 	Limit   *parserTypes.Limit
@@ -68,7 +68,7 @@ func parseCommitSelect(field *ast.Field) (*CommitSelect, error) {
 			commit.DocKey = raw.Value
 		} else if prop == parserTypes.Cid {
 			raw := argument.Value.(*ast.StringValue)
-			commit.Cid = raw.Value
+			commit.Cid = client.Some(raw.Value)
 		} else if prop == parserTypes.Field {
 			raw := argument.Value.(*ast.StringValue)
 			commit.FieldName = client.Some(raw.Value)

query/graphql/parser/query.go

@@ -15,6 +15,7 @@ import (
 
 	"github.com/graphql-go/graphql/language/ast"
 
+	"github.com/sourcenetwork/defradb/client"
 	"github.com/sourcenetwork/defradb/errors"
 	parserTypes "github.com/sourcenetwork/defradb/query/graphql/parser/types"
 )
@@ -57,7 +58,7 @@ type Select struct {
 	Alias string
 
 	DocKeys parserTypes.OptionalDocKeys
-	CID     string
+	CID     client.Option[string]
 
 	// QueryType indicates what kind of query this is
 	// Currently supports: ScanQuery, VersionedScanQuery
@@ -238,7 +239,7 @@ func parseSelect(rootType parserTypes.SelectionType, field *ast.Field, index int
 			}
 		} else if prop == parserTypes.Cid { // parse single CID query field
 			val := astValue.(*ast.StringValue)
-			slct.CID = val.Value
+			slct.CID = client.Some(val.Value)
 		} else if prop == parserTypes.LimitClause { // parse limit/offset
 			val := astValue.(*ast.IntValue)
 			i, err := strconv.ParseInt(val.Value, 10, 64)
@@ -281,7 +282,7 @@ func parseSelect(rootType parserTypes.SelectionType, field *ast.Field, index int
 			}
 		}
 
-		if len(slct.DocKeys.Value) != 0 && len(slct.CID) != 0 {
+		if len(slct.DocKeys.Value) != 0 && slct.CID.HasValue() {
 			slct.QueryType = parserTypes.VersionedScanQuery
 		} else {
 			slct.QueryType = parserTypes.ScanQuery