1 files changed, 153 insertions, 0 deletions
diff --git a/utils/markdown/blocks.go b/utils/markdown/blocks.go
new file mode 100644
index 000000000..14972f943
--- /dev/null
+++ b/utils/markdown/blocks.go
@@ -0,0 +1,153 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package markdown
+
+import (
+	"strings"
+)
+
+type continuation struct {
+	Indentation int
+	Remaining   Range
+}
+
+type Block interface {
+	Continuation(indentation int, r Range) *continuation
+	AddLine(indentation int, r Range) bool
+	Close()
+	AllowsBlockStarts() bool
+	HasTrailingBlankLine() bool
+}
+
+type blockBase struct{}
+
+func (*blockBase) AddLine(indentation int, r Range) bool { return false }
+func (*blockBase) Close()                                {}
+func (*blockBase) AllowsBlockStarts() bool               { return true }
+func (*blockBase) HasTrailingBlankLine() bool            { return false }
+
+type ContainerBlock interface {
+	Block
+	AddChild(openBlocks []Block) []Block
+}
+
+type Range struct {
+	Position int
+	End      int
+}
+
+func closeBlocks(blocks []Block, referenceDefinitions *[]*ReferenceDefinition) {
+	for _, block := range blocks {
+		block.Close()
+		if p, ok := block.(*Paragraph); ok && len(p.ReferenceDefinitions) > 0 {
+			*referenceDefinitions = append(*referenceDefinitions, p.ReferenceDefinitions...)
+		}
+	}
+}
+
+func ParseBlocks(markdown string, lines []Line) (*Document, []*ReferenceDefinition) {
+	document := &Document{}
+	var referenceDefinitions []*ReferenceDefinition
+
+	openBlocks := []Block{document}
+
+	for _, line := range lines {
+		r := line.Range
+		lastMatchIndex := 0
+
+		indentation, indentationBytes := countIndentation(markdown, r)
+		r = Range{r.Position + indentationBytes, r.End}
+
+		for i, block := range openBlocks {
+			if continuation := block.Continuation(indentation, r); continuation != nil {
+				indentation = continuation.Indentation
+				r = continuation.Remaining
+				additionalIndentation, additionalIndentationBytes := countIndentation(markdown, r)
+				r = Range{r.Position + additionalIndentationBytes, r.End}
+				indentation += additionalIndentation
+				lastMatchIndex = i
+			} else {
+				break
+			}
+		}
+
+		if openBlocks[lastMatchIndex].AllowsBlockStarts() {
+			if newBlocks := blockStart(markdown, indentation, r, openBlocks[:lastMatchIndex+1], openBlocks[lastMatchIndex+1:]); newBlocks != nil {
+				didAdd := false
+				for i := lastMatchIndex; i >= 0; i-- {
+					if container, ok := openBlocks[i].(ContainerBlock); ok {
+						if newBlocks := container.AddChild(newBlocks); newBlocks != nil {
+							closeBlocks(openBlocks[i+1:], &referenceDefinitions)
+							openBlocks = openBlocks[:i+1]
+							openBlocks = append(openBlocks, newBlocks...)
+							didAdd = true
+							break
+						}
+					}
+				}
+				if didAdd {
+					continue
+				}
+			}
+		}
+
+		isBlank := strings.TrimSpace(markdown[r.Position:r.End]) == ""
+		if paragraph, ok := openBlocks[len(openBlocks)-1].(*Paragraph); ok && !isBlank {
+			paragraph.Text = append(paragraph.Text, r)
+			continue
+		}
+
+		closeBlocks(openBlocks[lastMatchIndex+1:], &referenceDefinitions)
+		openBlocks = openBlocks[:lastMatchIndex+1]
+
+		if openBlocks[lastMatchIndex].AddLine(indentation, r) {
+			continue
+		}
+
+		if paragraph := newParagraph(markdown, r); paragraph != nil {
+			for i := lastMatchIndex; i >= 0; i-- {
+				if container, ok := openBlocks[i].(ContainerBlock); ok {
+					if newBlocks := container.AddChild([]Block{paragraph}); newBlocks != nil {
+						closeBlocks(openBlocks[i+1:], &referenceDefinitions)
+						openBlocks = openBlocks[:i+1]
+						openBlocks = append(openBlocks, newBlocks...)
+						break
+					}
+				}
+			}
+		}
+	}
+
+	closeBlocks(openBlocks, &referenceDefinitions)
+
+	return document, referenceDefinitions
+}
+
+func blockStart(markdown string, indentation int, r Range, matchedBlocks, unmatchedBlocks []Block) []Block {
+	if r.Position >= r.End {
+		return nil
+	}
+
+	if start := blockQuoteStart(markdown, indentation, r, matchedBlocks, unmatchedBlocks); start != nil {
+		return start
+	} else if start := listStart(markdown, indentation, r, matchedBlocks, unmatchedBlocks); start != nil {
+		return start
+	} else if start := indentedCodeStart(markdown, indentation, r, matchedBlocks, unmatchedBlocks); start != nil {
+		return start
+	} else if start := fencedCodeStart(markdown, indentation, r, matchedBlocks, unmatchedBlocks); start != nil {
+		return start
+	}
+
+	return nil
+}
+
+func blockStartOrParagraph(markdown string, indentation int, r Range, matchedBlocks, unmatchedBlocks []Block) []Block {
+	if start := blockStart(markdown, indentation, r, matchedBlocks, unmatchedBlocks); start != nil {
+		return start
+	}
+	if paragraph := newParagraph(markdown, r); paragraph != nil {
+		return []Block{paragraph}
+	}
+	return nil
+}