1 files changed, 436 insertions, 0 deletions
diff --git a/bridge/github/import_mediator.go b/bridge/github/import_mediator.go
new file mode 100644
index 00000000..825a0f98
--- /dev/null
+++ b/bridge/github/import_mediator.go
@@ -0,0 +1,436 @@
+package github
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/shurcooL/githubv4"
+)
+
+const (
+	// These values influence how fast the github graphql rate limit is exhausted.
+	NUM_ISSUES         = 40
+	NUM_ISSUE_EDITS    = 100
+	NUM_TIMELINE_ITEMS = 100
+	NUM_COMMENT_EDITS  = 100
+
+	CHAN_CAPACITY = 128
+)
+
+// importMediator provides a convenient interface to retrieve issues from the Github GraphQL API.
+type importMediator struct {
+	// Github graphql client
+	gc *githubv4.Client
+
+	// name of the repository owner on Github
+	owner string
+
+	// name of the Github repository
+	project string
+
+	// since specifies which issues to import. Issues that have been updated at or after the
+	// given date should be imported.
+	since time.Time
+
+	// importEvents holds events representing issues, comments, edits, ...
+	// In this channel issues are immediately followed by their issue edits and comments are
+	// immediately followed by their comment edits.
+	importEvents chan ImportEvent
+
+	// Sticky error
+	err error
+}
+
+type ImportEvent interface {
+	isImportEvent()
+}
+
+type RateLimitingEvent struct {
+	msg string
+}
+
+func (RateLimitingEvent) isImportEvent() {}
+
+type IssueEvent struct {
+	issue
+}
+
+func (IssueEvent) isImportEvent() {}
+
+type IssueEditEvent struct {
+	issueId githubv4.ID
+	userContentEdit
+}
+
+func (IssueEditEvent) isImportEvent() {}
+
+type TimelineEvent struct {
+	issueId githubv4.ID
+	timelineItem
+}
+
+func (TimelineEvent) isImportEvent() {}
+
+type CommentEditEvent struct {
+	commentId githubv4.ID
+	userContentEdit
+}
+
+func (CommentEditEvent) isImportEvent() {}
+
+func (mm *importMediator) NextImportEvent() ImportEvent {
+	return <-mm.importEvents
+}
+
+func NewImportMediator(ctx context.Context, client *githubv4.Client, owner, project string, since time.Time) *importMediator {
+	mm := importMediator{
+		gc:           client,
+		owner:        owner,
+		project:      project,
+		since:        since,
+		importEvents: make(chan ImportEvent, CHAN_CAPACITY),
+		err:          nil,
+	}
+	go func() {
+		mm.fillImportEvents(ctx)
+		close(mm.importEvents)
+	}()
+	return &mm
+}
+
+type varmap map[string]interface{}
+
+func newIssueVars(owner, project string, since time.Time) varmap {
+	return varmap{
+		"owner":             githubv4.String(owner),
+		"name":              githubv4.String(project),
+		"issueSince":        githubv4.DateTime{Time: since},
+		"issueFirst":        githubv4.Int(NUM_ISSUES),
+		"issueEditLast":     githubv4.Int(NUM_ISSUE_EDITS),
+		"issueEditBefore":   (*githubv4.String)(nil),
+		"timelineFirst":     githubv4.Int(NUM_TIMELINE_ITEMS),
+		"timelineAfter":     (*githubv4.String)(nil),
+		"commentEditLast":   githubv4.Int(NUM_COMMENT_EDITS),
+		"commentEditBefore": (*githubv4.String)(nil),
+	}
+}
+
+func newIssueEditVars() varmap {
+	return varmap{
+		"issueEditLast": githubv4.Int(NUM_ISSUE_EDITS),
+	}
+}
+
+func newTimelineVars() varmap {
+	return varmap{
+		"timelineFirst":     githubv4.Int(NUM_TIMELINE_ITEMS),
+		"commentEditLast":   githubv4.Int(NUM_COMMENT_EDITS),
+		"commentEditBefore": (*githubv4.String)(nil),
+	}
+}
+
+func newCommentEditVars() varmap {
+	return varmap{
+		"commentEditLast": githubv4.Int(NUM_COMMENT_EDITS),
+	}
+}
+
+func (mm *importMediator) Error() error {
+	return mm.err
+}
+
+func (mm *importMediator) User(ctx context.Context, loginName string) (*user, error) {
+	query := userQuery{}
+	vars := varmap{"login": githubv4.String(loginName)}
+	if err := mm.mQuery(ctx, &query, vars); err != nil {
+		return nil, err
+	}
+	return &query.User, nil
+}
+
+func (mm *importMediator) fillImportEvents(ctx context.Context) {
+	initialCursor := githubv4.String("")
+	issues, hasIssues := mm.queryIssue(ctx, initialCursor)
+	for hasIssues {
+		for _, node := range issues.Nodes {
+			select {
+			case <-ctx.Done():
+				return
+			case mm.importEvents <- IssueEvent{node.issue}:
+			}
+
+			// issue edit events follow the issue event
+			mm.fillIssueEditEvents(ctx, &node)
+			// last come the timeline events
+			mm.fillTimelineEvents(ctx, &node)
+		}
+		if !issues.PageInfo.HasNextPage {
+			break
+		}
+		issues, hasIssues = mm.queryIssue(ctx, issues.PageInfo.EndCursor)
+	}
+}
+
+func (mm *importMediator) fillIssueEditEvents(ctx context.Context, issueNode *issueNode) {
+	edits := &issueNode.UserContentEdits
+	hasEdits := true
+	for hasEdits {
+		for edit := range reverse(edits.Nodes) {
+			if edit.Diff == nil || string(*edit.Diff) == "" {
+				// issueEdit.Diff == nil happen if the event is older than early
+				// 2018, Github doesn't have the data before that. Best we can do is
+				// to ignore the event.
+				continue
+			}
+			select {
+			case <-ctx.Done():
+				return
+			case mm.importEvents <- IssueEditEvent{issueId: issueNode.issue.Id, userContentEdit: edit}:
+			}
+		}
+		if !edits.PageInfo.HasPreviousPage {
+			break
+		}
+		edits, hasEdits = mm.queryIssueEdits(ctx, issueNode.issue.Id, edits.PageInfo.EndCursor)
+	}
+}
+
+func (mm *importMediator) queryIssueEdits(ctx context.Context, nid githubv4.ID, cursor githubv4.String) (*userContentEditConnection, bool) {
+	vars := newIssueEditVars()
+	vars["gqlNodeId"] = nid
+	if cursor == "" {
+		vars["issueEditBefore"] = (*githubv4.String)(nil)
+	} else {
+		vars["issueEditBefore"] = cursor
+	}
+	query := issueEditQuery{}
+	if err := mm.mQuery(ctx, &query, vars); err != nil {
+		mm.err = err
+		return nil, false
+	}
+	connection := &query.Node.Issue.UserContentEdits
+	if len(connection.Nodes) <= 0 {
+		return nil, false
+	}
+	return connection, true
+}
+
+func (mm *importMediator) fillTimelineEvents(ctx context.Context, issueNode *issueNode) {
+	items := &issueNode.TimelineItems
+	hasItems := true
+	for hasItems {
+		for _, item := range items.Nodes {
+			select {
+			case <-ctx.Done():
+				return
+			case mm.importEvents <- TimelineEvent{issueId: issueNode.issue.Id, timelineItem: item}:
+			}
+			if item.Typename == "IssueComment" {
+				// Issue comments are different than other timeline items in that
+				// they may have associated user content edits.
+				// Right after the comment we send the comment edits.
+				mm.fillCommentEdits(ctx, &item)
+			}
+		}
+		if !items.PageInfo.HasNextPage {
+			break
+		}
+		items, hasItems = mm.queryTimeline(ctx, issueNode.issue.Id, items.PageInfo.EndCursor)
+	}
+}
+
+func (mm *importMediator) queryTimeline(ctx context.Context, nid githubv4.ID, cursor githubv4.String) (*timelineItemsConnection, bool) {
+	vars := newTimelineVars()
+	vars["gqlNodeId"] = nid
+	if cursor == "" {
+		vars["timelineAfter"] = (*githubv4.String)(nil)
+	} else {
+		vars["timelineAfter"] = cursor
+	}
+	query := timelineQuery{}
+	if err := mm.mQuery(ctx, &query, vars); err != nil {
+		mm.err = err
+		return nil, false
+	}
+	connection := &query.Node.Issue.TimelineItems
+	if len(connection.Nodes) <= 0 {
+		return nil, false
+	}
+	return connection, true
+}
+
+func (mm *importMediator) fillCommentEdits(ctx context.Context, item *timelineItem) {
+	// Here we are only concerned with timeline items of type issueComment.
+	if item.Typename != "IssueComment" {
+		return
+	}
+	// First: setup message handling while submitting GraphQL queries.
+	comment := &item.IssueComment
+	edits := &comment.UserContentEdits
+	hasEdits := true
+	for hasEdits {
+		for edit := range reverse(edits.Nodes) {
+			if edit.Diff == nil || string(*edit.Diff) == "" {
+				// issueEdit.Diff == nil happen if the event is older than early
+				// 2018, Github doesn't have the data before that. Best we can do is
+				// to ignore the event.
+				continue
+			}
+			select {
+			case <-ctx.Done():
+				return
+			case mm.importEvents <- CommentEditEvent{commentId: comment.Id, userContentEdit: edit}:
+			}
+		}
+		if !edits.PageInfo.HasPreviousPage {
+			break
+		}
+		edits, hasEdits = mm.queryCommentEdits(ctx, comment.Id, edits.PageInfo.EndCursor)
+	}
+}
+
+func (mm *importMediator) queryCommentEdits(ctx context.Context, nid githubv4.ID, cursor githubv4.String) (*userContentEditConnection, bool) {
+	vars := newCommentEditVars()
+	vars["gqlNodeId"] = nid
+	if cursor == "" {
+		vars["commentEditBefore"] = (*githubv4.String)(nil)
+	} else {
+		vars["commentEditBefore"] = cursor
+	}
+	query := commentEditQuery{}
+	if err := mm.mQuery(ctx, &query, vars); err != nil {
+		mm.err = err
+		return nil, false
+	}
+	connection := &query.Node.IssueComment.UserContentEdits
+	if len(connection.Nodes) <= 0 {
+		return nil, false
+	}
+	return connection, true
+}
+
+func (mm *importMediator) queryIssue(ctx context.Context, cursor githubv4.String) (*issueConnection, bool) {
+	vars := newIssueVars(mm.owner, mm.project, mm.since)
+	if cursor == "" {
+		vars["issueAfter"] = (*githubv4.String)(nil)
+	} else {
+		vars["issueAfter"] = githubv4.String(cursor)
+	}
+	query := issueQuery{}
+	if err := mm.mQuery(ctx, &query, vars); err != nil {
+		mm.err = err
+		return nil, false
+	}
+	connection := &query.Repository.Issues
+	if len(connection.Nodes) <= 0 {
+		return nil, false
+	}
+	return connection, true
+}
+
+func reverse(eds []userContentEdit) chan userContentEdit {
+	ret := make(chan userContentEdit)
+	go func() {
+		for i := range eds {
+			ret <- eds[len(eds)-1-i]
+		}
+		close(ret)
+	}()
+	return ret
+}
+
+// mQuery executes a single GraphQL query. The variable query is used to derive the GraphQL query
+// and it is used to populate the response into it. It should be a pointer to a struct that
+// corresponds to the Github graphql schema and it has to implement the rateLimiter interface. If
+// there is a Github rate limiting error, then the function sleeps and retries after the rate limit
+// is expired. If there is another error, then the method will retry before giving up.
+func (mm *importMediator) mQuery(ctx context.Context, query rateLimiter, vars map[string]interface{}) error {
+	if err := mm.queryOnce(ctx, query, vars); err == nil {
+		// success: done
+		return nil
+	}
+	// failure: we will retry
+	// To retry is important for importing projects with a big number of issues, because
+	// there may be temporary network errors or momentary internal errors of the github servers.
+	retries := 3
+	var err error
+	for i := 0; i < retries; i++ {
+		// wait a few seconds before retry
+		sleepTime := time.Duration(8*(i+1)) * time.Second
+		timer := time.NewTimer(sleepTime)
+		select {
+		case <-ctx.Done():
+			stop(timer)
+			return ctx.Err()
+		case <-timer.C:
+		}
+		err = mm.queryOnce(ctx, query, vars)
+		if err == nil {
+			// success: done
+			return nil
+		}
+	}
+	return err
+}
+
+func (mm *importMediator) queryOnce(ctx context.Context, query rateLimiter, vars map[string]interface{}) error {
+	// first: just send the query to the graphql api
+	vars["dryRun"] = githubv4.Boolean(false)
+	qctx, cancel := context.WithTimeout(ctx, defaultTimeout)
+	defer cancel()
+	err := mm.gc.Query(qctx, query, vars)
+	if err == nil {
+		// no error: done
+		return nil
+	}
+	// matching the error string
+	if !strings.Contains(err.Error(), "API rate limit exceeded") {
+		// an error, but not the API rate limit error: done
+		return err
+	}
+	// a rate limit error
+	// ask the graphql api for rate limiting information
+	vars["dryRun"] = githubv4.Boolean(true)
+	qctx, cancel = context.WithTimeout(ctx, defaultTimeout)
+	defer cancel()
+	if err := mm.gc.Query(qctx, query, vars); err != nil {
+		return err
+	}
+	rateLimit := query.rateLimit()
+	if rateLimit.Cost > rateLimit.Remaining {
+		// sleep
+		resetTime := rateLimit.ResetAt.Time
+		// Add a few seconds (8) for good measure
+		resetTime = resetTime.Add(8 * time.Second)
+		msg := fmt.Sprintf("Github GraphQL API: import will sleep until %s", resetTime.String())
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case mm.importEvents <- RateLimitingEvent{msg}:
+		}
+		timer := time.NewTimer(time.Until(resetTime))
+		select {
+		case <-ctx.Done():
+			stop(timer)
+			return ctx.Err()
+		case <-timer.C:
+		}
+	}
+	// run the original query again
+	vars["dryRun"] = githubv4.Boolean(false)
+	qctx, cancel = context.WithTimeout(ctx, defaultTimeout)
+	defer cancel()
+	err = mm.gc.Query(qctx, query, vars)
+	return err // might be nil
+}
+
+func stop(t *time.Timer) {
+	if !t.Stop() {
+		select {
+		case <-t.C:
+		default:
+		}
+	}
+}