hugolib: Integrate new page parser

See #5324

9 files changed, 466 insertions, 137 deletions

diff --git a/parser/frontmatter.go b/parser/frontmatter.go
index 3716dc112..284d3f955 100644
--- a/parser/frontmatter.go
+++ b/parser/frontmatter.go
@@ -203,6 +203,7 @@ func removeTOMLIdentifier(datum []byte) []byte {
 
 // HandleYAMLMetaData unmarshals YAML-encoded datum and returns a Go interface
 // representing the encoded data structure.
+// TODO(bep) 2errors remove these handlers (and hopefully package)
 func HandleYAMLMetaData(datum []byte) (map[string]interface{}, error) {
 	m := map[string]interface{}{}
 	err := yaml.Unmarshal(datum, &m)
diff --git a/parser/metadecoders/decoder.go b/parser/metadecoders/decoder.go
new file mode 100644
index 000000000..7527d7a08
--- /dev/null
+++ b/parser/metadecoders/decoder.go
@@ -0,0 +1,95 @@
+// Copyright 2018 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package metadecoders
+
+import (
+	"encoding/json"
+
+	"github.com/BurntSushi/toml"
+	"github.com/chaseadamsio/goorgeous"
+	"github.com/gohugoio/hugo/parser/pageparser"
+	"github.com/pkg/errors"
+	yaml "gopkg.in/yaml.v1"
+)
+
+type Format string
+
+const (
+	// These are the supported metdata  formats in Hugo. Most of these are also
+	// supported as /data formats.
+	ORG  Format = "org"
+	JSON Format = "json"
+	TOML Format = "toml"
+	YAML Format = "yaml"
+)
+
+// FormatFromFrontMatterType will return empty if not supported.
+func FormatFromFrontMatterType(typ pageparser.ItemType) Format {
+	switch typ {
+	case pageparser.TypeFrontMatterJSON:
+		return JSON
+	case pageparser.TypeFrontMatterORG:
+		return ORG
+	case pageparser.TypeFrontMatterTOML:
+		return TOML
+	case pageparser.TypeFrontMatterYAML:
+		return YAML
+	default:
+		return ""
+	}
+}
+
+// UnmarshalToMap will unmarshall data in format f into a new map. This is
+// what's needed for Hugo's front matter decoding.
+func UnmarshalToMap(data []byte, f Format) (map[string]interface{}, error) {
+	m := make(map[string]interface{})
+
+	if data == nil {
+		return m, nil
+	}
+
+	var err error
+
+	switch f {
+	case ORG:
+		m, err = goorgeous.OrgHeaders(data)
+	case JSON:
+		err = json.Unmarshal(data, &m)
+	case TOML:
+		_, err = toml.Decode(string(data), &m)
+	case YAML:
+		err = yaml.Unmarshal(data, &m)
+
+		// To support boolean keys, the `yaml` package unmarshals maps to
+		// map[interface{}]interface{}. Here we recurse through the result
+		// and change all maps to map[string]interface{} like we would've
+		// gotten from `json`.
+		if err == nil {
+			for k, v := range m {
+				if vv, changed := stringifyMapKeys(v); changed {
+					m[k] = vv
+				}
+			}
+		}
+	default:
+		return nil, errors.Errorf("unmarshal of format %q is not supported", f)
+	}
+
+	if err != nil {
+		return nil, errors.Wrapf(err, "unmarshal failed for format %q", f)
+	}
+
+	return m, nil
+
+}
diff --git a/parser/metadecoders/json.go b/parser/metadecoders/json.go
new file mode 100644
index 000000000..21ca8a3b9
--- /dev/null
+++ b/parser/metadecoders/json.go
@@ -0,0 +1,31 @@
+// Copyright 2018 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package metadecoders
+
+import "encoding/json"
+
+// HandleJSONData unmarshals JSON-encoded datum and returns a Go interface
+// representing the encoded data structure.
+func HandleJSONData(datum []byte) (interface{}, error) {
+	if datum == nil {
+		// Package json returns on error on nil input.
+		// Return an empty map to be consistent with our other supported
+		// formats.
+		return make(map[string]interface{}), nil
+	}
+
+	var f interface{}
+	err := json.Unmarshal(datum, &f)
+	return f, err
+}
diff --git a/parser/metadecoders/yaml.go b/parser/metadecoders/yaml.go
new file mode 100644
index 000000000..3a520ac07
--- /dev/null
+++ b/parser/metadecoders/yaml.go
@@ -0,0 +1,84 @@
+// Copyright 2018 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// The metadecoders package contains functions to decode metadata (e.g. page front matter)
+// from different formats: TOML, YAML, JSON.
+package metadecoders
+
+import (
+	"fmt"
+
+	"github.com/spf13/cast"
+	yaml "gopkg.in/yaml.v1"
+)
+
+// HandleYAMLData unmarshals YAML-encoded datum and returns a Go interface
+// representing the encoded data structure.
+func HandleYAMLData(datum []byte) (interface{}, error) {
+	var m interface{}
+	err := yaml.Unmarshal(datum, &m)
+	if err != nil {
+		return nil, err
+	}
+
+	// To support boolean keys, the `yaml` package unmarshals maps to
+	// map[interface{}]interface{}. Here we recurse through the result
+	// and change all maps to map[string]interface{} like we would've
+	// gotten from `json`.
+	if mm, changed := stringifyMapKeys(m); changed {
+		return mm, nil
+	}
+
+	return m, nil
+}
+
+// stringifyMapKeys recurses into in and changes all instances of
+// map[interface{}]interface{} to map[string]interface{}. This is useful to
+// work around the impedence mismatch between JSON and YAML unmarshaling that's
+// described here: https://github.com/go-yaml/yaml/issues/139
+//
+// Inspired by https://github.com/stripe/stripe-mock, MIT licensed
+func stringifyMapKeys(in interface{}) (interface{}, bool) {
+	switch in := in.(type) {
+	case []interface{}:
+		for i, v := range in {
+			if vv, replaced := stringifyMapKeys(v); replaced {
+				in[i] = vv
+			}
+		}
+	case map[interface{}]interface{}:
+		res := make(map[string]interface{})
+		var (
+			ok  bool
+			err error
+		)
+		for k, v := range in {
+			var ks string
+
+			if ks, ok = k.(string); !ok {
+				ks, err = cast.ToStringE(k)
+				if err != nil {
+					ks = fmt.Sprintf("%v", k)
+				}
+			}
+			if vv, replaced := stringifyMapKeys(v); replaced {
+				res[ks] = vv
+			} else {
+				res[ks] = v
+			}
+		}
+		return res, true
+	}
+
+	return nil, false
+}
diff --git a/parser/pageparser/item.go b/parser/pageparser/item.go
index 6e93bb696..d97fed734 100644
--- a/parser/pageparser/item.go
+++ b/parser/pageparser/item.go
@@ -16,87 +16,95 @@ package pageparser
 import "fmt"
 
 type Item struct {
-	typ itemType
+	Typ ItemType
 	pos pos
 	Val []byte
 }
 
+type Items []Item
+
 func (i Item) ValStr() string {
 	return string(i.Val)
 }
 
 func (i Item) IsText() bool {
-	return i.typ == tText
+	return i.Typ == tText
 }
 
 func (i Item) IsShortcodeName() bool {
-	return i.typ == tScName
+	return i.Typ == tScName
 }
 
 func (i Item) IsLeftShortcodeDelim() bool {
-	return i.typ == tLeftDelimScWithMarkup || i.typ == tLeftDelimScNoMarkup
+	return i.Typ == tLeftDelimScWithMarkup || i.Typ == tLeftDelimScNoMarkup
 }
 
 func (i Item) IsRightShortcodeDelim() bool {
-	return i.typ == tRightDelimScWithMarkup || i.typ == tRightDelimScNoMarkup
+	return i.Typ == tRightDelimScWithMarkup || i.Typ == tRightDelimScNoMarkup
 }
 
 func (i Item) IsShortcodeClose() bool {
-	return i.typ == tScClose
+	return i.Typ == tScClose
 }
 
 func (i Item) IsShortcodeParam() bool {
-	return i.typ == tScParam
+	return i.Typ == tScParam
 }
 
 func (i Item) IsShortcodeParamVal() bool {
-	return i.typ == tScParamVal
+	return i.Typ == tScParamVal
 }
 
 func (i Item) IsShortcodeMarkupDelimiter() bool {
-	return i.typ == tLeftDelimScWithMarkup || i.typ == tRightDelimScWithMarkup
+	return i.Typ == tLeftDelimScWithMarkup || i.Typ == tRightDelimScWithMarkup
+}
+
+func (i Item) IsFrontMatter() bool {
+	return i.Typ >= TypeFrontMatterYAML && i.Typ <= TypeFrontMatterORG
 }
 
 func (i Item) IsDone() bool {
-	return i.typ == tError || i.typ == tEOF
+	return i.Typ == tError || i.Typ == tEOF
 }
 
 func (i Item) IsEOF() bool {
-	return i.typ == tEOF
+	return i.Typ == tEOF
 }
 
 func (i Item) IsError() bool {
-	return i.typ == tError
+	return i.Typ == tError
 }
 
 func (i Item) String() string {
 	switch {
-	case i.typ == tEOF:
+	case i.Typ == tEOF:
 		return "EOF"
-	case i.typ == tError:
+	case i.Typ == tError:
 		return string(i.Val)
-	case i.typ > tKeywordMarker:
+	case i.Typ > tKeywordMarker:
 		return fmt.Sprintf("<%s>", i.Val)
 	case len(i.Val) > 50:
-		return fmt.Sprintf("%v:%.20q...", i.typ, i.Val)
+		return fmt.Sprintf("%v:%.20q...", i.Typ, i.Val)
 	}
-	return fmt.Sprintf("%v:[%s]", i.typ, i.Val)
+	return fmt.Sprintf("%v:[%s]", i.Typ, i.Val)
 }
 
-type itemType int
+type ItemType int
 
 const (
-	tError itemType = iota
+	tError ItemType = iota
 	tEOF
 
 	// page items
-	tHTMLLead          // <
-	tSummaryDivider    // <!--more-->
-	tSummaryDividerOrg // # more
-	tFrontMatterYAML
-	tFrontMatterTOML
-	tFrontMatterJSON
-	tFrontMatterORG
+	TypeHTMLDocument       // document starting with < as first non-whitespace
+	TypeHTMLComment        // We ignore leading comments
+	TypeLeadSummaryDivider // <!--more-->
+	TypeSummaryDividerOrg  // # more
+	TypeFrontMatterYAML
+	TypeFrontMatterTOML
+	TypeFrontMatterJSON
+	TypeFrontMatterORG
+	TypeIgnore // // The BOM Unicode byte order marker and possibly others
 
 	// shortcode items
 	tLeftDelimScNoMarkup
diff --git a/parser/pageparser/pagelexer.go b/parser/pageparser/pagelexer.go
index c15e977ca..7768b0b2f 100644
--- a/parser/pageparser/pagelexer.go
+++ b/parser/pageparser/pagelexer.go
@@ -33,8 +33,8 @@ const eof = -1
 type stateFunc func(*pageLexer) stateFunc
 
 type lexerShortcodeState struct {
-	currLeftDelimItem  itemType
-	currRightDelimItem itemType
+	currLeftDelimItem  ItemType
+	currRightDelimItem ItemType
 	currShortcodeName  string          // is only set when a shortcode is in opened state
 	closingState       int             // > 0 = on its way to be closed
 	elementStepNum     int             // step number in element
@@ -50,14 +50,24 @@ type pageLexer struct {
 	pos        pos // input position
 	start      pos // item start position
 	width      pos // width of last element
-	lastPos    pos // position of the last item returned by nextItem
 
-	contentSections int
+	// Set when we have parsed any summary divider
+	summaryDividerChecked bool
 
 	lexerShortcodeState
 
 	// items delivered to client
-	items []Item
+	items Items
+}
+
+// Implement the Result interface
+func (l *pageLexer) Iterator() *Iterator {
+	return l.newIterator()
+}
+
+func (l *pageLexer) Input() []byte {
+	return l.input
+
 }
 
 // note: the input position here is normally 0 (start), but
@@ -79,6 +89,10 @@ func newPageLexer(input []byte, inputPosition pos, stateStart stateFunc) *pageLe
 	return lexer
 }
 
+func (l *pageLexer) newIterator() *Iterator {
+	return &Iterator{l: l, lastPos: -1}
+}
+
 // main loop
 func (l *pageLexer) run() *pageLexer {
 	for l.state = l.stateStart; l.state != nil; {
@@ -89,6 +103,7 @@ func (l *pageLexer) run() *pageLexer {
 
 // Shortcode syntax
 var (
+	leftDelimSc            = []byte("{{")
 	leftDelimScNoMarkup    = []byte("{{<")
 	rightDelimScNoMarkup   = []byte(">}}")
 	leftDelimScWithMarkup  = []byte("{{%")
@@ -99,11 +114,14 @@ var (
 
 // Page syntax
 var (
+	byteOrderMark     = '\ufeff'
 	summaryDivider    = []byte("<!--more-->")
 	summaryDividerOrg = []byte("# more")
 	delimTOML         = []byte("+++")
 	delimYAML         = []byte("---")
 	delimOrg          = []byte("#+")
+	htmlCOmmentStart  = []byte("<!--")
+	htmlCOmmentEnd    = []byte("-->")
 )
 
 func (l *pageLexer) next() rune {
@@ -131,13 +149,13 @@ func (l *pageLexer) backup() {
 }
 
 // sends an item back to the client.
-func (l *pageLexer) emit(t itemType) {
+func (l *pageLexer) emit(t ItemType) {
 	l.items = append(l.items, Item{t, l.start, l.input[l.start:l.pos]})
 	l.start = l.pos
 }
 
 // special case, do not send '\\' back to client
-func (l *pageLexer) ignoreEscapesAndEmit(t itemType) {
+func (l *pageLexer) ignoreEscapesAndEmit(t ItemType) {
 	val := bytes.Map(func(r rune) rune {
 		if r == '\\' {
 			return -1
@@ -160,25 +178,12 @@ func (l *pageLexer) ignore() {
 
 var lf = []byte("\n")
 
-// nice to have in error logs
-func (l *pageLexer) lineNum() int {
-	return bytes.Count(l.input[:l.lastPos], lf) + 1
-}
-
 // nil terminates the parser
 func (l *pageLexer) errorf(format string, args ...interface{}) stateFunc {
 	l.items = append(l.items, Item{tError, l.start, []byte(fmt.Sprintf(format, args...))})
 	return nil
 }
 
-// consumes and returns the next item
-func (l *pageLexer) nextItem() Item {
-	item := l.items[0]
-	l.items = l.items[1:]
-	l.lastPos = item.pos
-	return item
-}
-
 func (l *pageLexer) consumeCRLF() bool {
 	var consumed bool
 	for _, r := range crLf {
@@ -192,12 +197,28 @@ func (l *pageLexer) consumeCRLF() bool {
 }
 
 func lexMainSection(l *pageLexer) stateFunc {
+	// Fast forward as far as possible.
+	var l1, l2, l3 int
+	if !l.summaryDividerChecked {
+		// TODO(bep) 2errors make the summary divider per type
+		l1 = l.index(summaryDivider)
+		l2 = l.index(summaryDividerOrg)
+		if l1 == -1 && l2 == -1 {
+			l.summaryDividerChecked = true
+		}
+	}
+	l3 = l.index(leftDelimSc)
+	skip := minPositiveIndex(l1, l2, l3)
+	if skip > 0 {
+		l.pos += pos(skip)
+	}
+
 	for {
 		if l.isShortCodeStart() {
 			if l.pos > l.start {
 				l.emit(tText)
 			}
-			if bytes.HasPrefix(l.input[l.pos:], leftDelimScWithMarkup) {
+			if l.hasPrefix(leftDelimScWithMarkup) {
 				l.currLeftDelimItem = tLeftDelimScWithMarkup
 				l.currRightDelimItem = tRightDelimScWithMarkup
 			} else {
@@ -207,21 +228,21 @@ func lexMainSection(l *pageLexer) stateFunc {
 			return lexShortcodeLeftDelim
 		}
 
-		if l.contentSections <= 1 {
-			if bytes.HasPrefix(l.input[l.pos:], summaryDivider) {
+		if !l.summaryDividerChecked {
+			if l.hasPrefix(summaryDivider) {
 				if l.pos > l.start {
 					l.emit(tText)
 				}
-				l.contentSections++
+				l.summaryDividerChecked = true
 				l.pos += pos(len(summaryDivider))
-				l.emit(tSummaryDivider)
-			} else if bytes.HasPrefix(l.input[l.pos:], summaryDividerOrg) {
+				l.emit(TypeLeadSummaryDivider)
+			} else if l.hasPrefix(summaryDividerOrg) {
 				if l.pos > l.start {
 					l.emit(tText)
 				}
-				l.contentSections++
+				l.summaryDividerChecked = true
 				l.pos += pos(len(summaryDividerOrg))
-				l.emit(tSummaryDividerOrg)
+				l.emit(TypeSummaryDividerOrg)
 			}
 		}
 
@@ -237,7 +258,7 @@ func lexMainSection(l *pageLexer) stateFunc {
 }
 
 func (l *pageLexer) isShortCodeStart() bool {
-	return bytes.HasPrefix(l.input[l.pos:], leftDelimScWithMarkup) || bytes.HasPrefix(l.input[l.pos:], leftDelimScNoMarkup)
+	return l.hasPrefix(leftDelimScWithMarkup) || l.hasPrefix(leftDelimScNoMarkup)
 }
 
 func lexIntroSection(l *pageLexer) stateFunc {
@@ -250,28 +271,37 @@ LOOP:
 
 		switch {
 		case r == '+':
-			return l.lexFrontMatterSection(tFrontMatterTOML, r, "TOML", delimTOML)
+			return l.lexFrontMatterSection(TypeFrontMatterTOML, r, "TOML", delimTOML)
 		case r == '-':
-			return l.lexFrontMatterSection(tFrontMatterYAML, r, "YAML", delimYAML)
+			return l.lexFrontMatterSection(TypeFrontMatterYAML, r, "YAML", delimYAML)
 		case r == '{':
 			return lexFrontMatterJSON
 		case r == '#':
 			return lexFrontMatterOrgMode
+		case r == byteOrderMark:
+			l.emit(TypeIgnore)
 		case !isSpace(r) && !isEndOfLine(r):
+			// No front matter.
 			if r == '<' {
-				l.emit(tHTMLLead)
-				// Not need to look further. Hugo treats this as plain HTML,
-				// no front matter, no shortcodes, no nothing.
-				l.pos = pos(len(l.input))
-				l.emit(tText)
-				break LOOP
+				l.backup()
+				if l.hasPrefix(htmlCOmmentStart) {
+					right := l.index(htmlCOmmentEnd)
+					if right == -1 {
+						return l.errorf("starting HTML comment with no end")
+					}
+					l.pos += pos(right) + pos(len(htmlCOmmentEnd))
+					l.emit(TypeHTMLComment)
+				} else {
+					// Not need to look further. Hugo treats this as plain HTML,
+					// no front matter, no shortcodes, no nothing.
+					l.pos = pos(len(l.input))
+					l.emit(TypeHTMLDocument)
+				}
 			}
-			return l.errorf("failed to detect front matter type; got unknown identifier %q", r)
+			break LOOP
 		}
 	}
 
-	l.contentSections = 1
-
 	// Now move on to the shortcodes.
 	return lexMainSection
 }
@@ -324,7 +354,7 @@ func lexFrontMatterJSON(l *pageLexer) stateFunc {
 	}
 
 	l.consumeCRLF()
-	l.emit(tFrontMatterJSON)
+	l.emit(TypeFrontMatterJSON)
 
 	return lexMainSection
 }
@@ -338,7 +368,7 @@ func lexFrontMatterOrgMode(l *pageLexer) stateFunc {
 
 	l.backup()
 
-	if !bytes.HasPrefix(l.input[l.pos:], delimOrg) {
+	if !l.hasPrefix(delimOrg) {
 		// TODO(bep) consider error
 		return lexMainSection
 	}
@@ -351,7 +381,7 @@ LOOP:
 
 		switch {
 		case r == '\n':
-			if !bytes.HasPrefix(l.input[l.pos:], delimOrg) {
+			if !l.hasPrefix(delimOrg) {
 				break LOOP
 			}
 		case r == eof:
@@ -360,24 +390,25 @@ LOOP:
 		}
 	}
 
-	l.emit(tFrontMatterORG)
+	l.emit(TypeFrontMatterORG)
 
 	return lexMainSection
 
 }
 
+func (l *pageLexer) printCurrentInput() {
+	fmt.Printf("input[%d:]: %q", l.pos, string(l.input[l.pos:]))
+}
+
 // Handle YAML or TOML front matter.
-func (l *pageLexer) lexFrontMatterSection(tp itemType, delimr rune, name string, delim []byte) stateFunc {
+func (l *pageLexer) lexFrontMatterSection(tp ItemType, delimr rune, name string, delim []byte) stateFunc {
+
 	for i := 0; i < 2; i++ {
 		if r := l.next(); r != delimr {
 			return l.errorf("invalid %s delimiter", name)
 		}
 	}
 
-	if !l.consumeCRLF() {
-		return l.errorf("invalid %s delimiter", name)
-	}
-
 	// We don't care about the delimiters.
 	l.ignore()
 
@@ -387,7 +418,7 @@ func (l *pageLexer) lexFrontMatterSection(tp itemType, delimr rune, name string,
 			return l.errorf("EOF looking for end %s front matter delimiter", name)
 		}
 		if isEndOfLine(r) {
-			if bytes.HasPrefix(l.input[l.pos:], delim) {
+			if l.hasPrefix(delim) {
 				l.emit(tp)
 				l.pos += 3
 				l.consumeCRLF()
@@ -402,7 +433,7 @@ func (l *pageLexer) lexFrontMatterSection(tp itemType, delimr rune, name string,
 
 func lexShortcodeLeftDelim(l *pageLexer) stateFunc {
 	l.pos += pos(len(l.currentLeftShortcodeDelim()))
-	if bytes.HasPrefix(l.input[l.pos:], leftComment) {
+	if l.hasPrefix(leftComment) {
 		return lexShortcodeComment
 	}
 	l.emit(l.currentLeftShortcodeDelimItem())
@@ -412,7 +443,7 @@ func lexShortcodeLeftDelim(l *pageLexer) stateFunc {
 }
 
 func lexShortcodeComment(l *pageLexer) stateFunc {
-	posRightComment := bytes.Index(l.input[l.pos:], append(rightComment, l.currentRightShortcodeDelim()...))
+	posRightComment := l.index(append(rightComment, l.currentRightShortcodeDelim()...))
 	if posRightComment <= 1 {
 		return l.errorf("comment must be closed")
 	}
@@ -493,7 +524,7 @@ func lexShortcodeParam(l *pageLexer, escapedQuoteStart bool) stateFunc {
 
 }
 
-func lexShortcodeQuotedParamVal(l *pageLexer, escapedQuotedValuesAllowed bool, typ itemType) stateFunc {
+func lexShortcodeQuotedParamVal(l *pageLexer, escapedQuotedValuesAllowed bool, typ ItemType) stateFunc {
 	openQuoteFound := false
 	escapedInnerQuoteFound := false
 	escapedQuoteState := 0
@@ -592,7 +623,7 @@ Loop:
 }
 
 func lexEndOfShortcode(l *pageLexer) stateFunc {
-	if bytes.HasPrefix(l.input[l.pos:], l.currentRightShortcodeDelim()) {
+	if l.hasPrefix(l.currentRightShortcodeDelim()) {
 		return lexShortcodeRightDelim
 	}
 	switch r := l.next(); {
@@ -606,7 +637,7 @@ func lexEndOfShortcode(l *pageLexer) stateFunc {
 
 // scans the elements inside shortcode tags
 func lexInsideShortcode(l *pageLexer) stateFunc {
-	if bytes.HasPrefix(l.input[l.pos:], l.currentRightShortcodeDelim()) {
+	if l.hasPrefix(l.currentRightShortcodeDelim()) {
 		return lexShortcodeRightDelim
 	}
 	switch r := l.next(); {
@@ -643,11 +674,19 @@ func lexInsideShortcode(l *pageLexer) stateFunc {
 
 // state helpers
 
-func (l *pageLexer) currentLeftShortcodeDelimItem() itemType {
+func (l *pageLexer) index(sep []byte) int {
+	return bytes.Index(l.input[l.pos:], sep)
+}
+
+func (l *pageLexer) hasPrefix(prefix []byte) bool {
+	return bytes.HasPrefix(l.input[l.pos:], prefix)
+}
+
+func (l *pageLexer) currentLeftShortcodeDelimItem() ItemType {
 	return l.currLeftDelimItem
 }
 
-func (l *pageLexer) currentRightShortcodeDelimItem() itemType {
+func (l *pageLexer) currentRightShortcodeDelimItem() ItemType {
 	return l.currRightDelimItem
 }
 
@@ -668,6 +707,23 @@ func (l *pageLexer) currentRightShortcodeDelim() []byte {
 
 // helper functions
 
+// returns the min index > 0
+func minPositiveIndex(indices ...int) int {
+	min := -1
+
+	for _, j := range indices {
+		if j <= 0 {
+			continue
+		}
+		if min == -1 {
+			min = j
+		} else if j < min {
+			min = j
+		}
+	}
+	return min
+}
+
 func isSpace(r rune) bool {
 	return r == ' ' || r == '\t'
 }
diff --git a/parser/pageparser/pagelexer_test.go b/parser/pageparser/pagelexer_test.go
new file mode 100644
index 000000000..5c85df017
--- /dev/null
+++ b/parser/pageparser/pagelexer_test.go
@@ -0,0 +1,29 @@
+// Copyright 2018 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package pageparser
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestMinPositiveIndex(t *testing.T) {
+	assert := require.New(t)
+	assert.Equal(1, minPositiveIndex(4, 1, 2, 3))
+	assert.Equal(2, minPositiveIndex(4, 0, -2, 2, 5))
+	assert.Equal(-1, minPositiveIndex())
+	assert.Equal(-1, minPositiveIndex(-2, -3))
+
+}
diff --git a/parser/pageparser/pageparser.go b/parser/pageparser/pageparser.go
index 948c05edf..b4cdef75c 100644
--- a/parser/pageparser/pageparser.go
+++ b/parser/pageparser/pageparser.go
@@ -17,72 +17,90 @@
 // See slides here: http://cuddle.googlecode.com/hg/talk/lex.html
 package pageparser
 
-func Parse(input []byte) *Tokens {
-	return ParseFrom(input, 0)
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+
+	"github.com/pkg/errors"
+)
+
+// Result holds the parse result.
+type Result interface {
+	// Iterator returns a new Iterator positioned at the benning of the parse tree.
+	Iterator() *Iterator
+	// Input returns the input to Parse.
+	Input() []byte
 }
 
-func ParseFrom(input []byte, from int) *Tokens {
-	lexer := newPageLexer(input, pos(from), lexMainSection) // TODO(bep) 2errors
+var _ Result = (*pageLexer)(nil)
+
+// Parse parses the page in the given reader.
+func Parse(r io.Reader) (Result, error) {
+	b, err := ioutil.ReadAll(r)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to read page content")
+	}
+	lexer := newPageLexer(b, 0, lexIntroSection)
 	lexer.run()
-	return &Tokens{lexer: lexer}
+	return lexer, nil
+
 }
 
-type Tokens struct {
-	lexer     *pageLexer
-	token     [3]Item // 3-item look-ahead is what we currently need
-	peekCount int
+func parseMainSection(input []byte, from int) Result {
+	lexer := newPageLexer(input, pos(from), lexMainSection) // TODO(bep) 2errors
+	lexer.run()
+	return lexer
 }
 
-func (t *Tokens) Next() Item {
-	if t.peekCount > 0 {
-		t.peekCount--
-	} else {
-		t.token[0] = t.lexer.nextItem()
-	}
-	return t.token[t.peekCount]
+// An Iterator has methods to iterate a parsed page with support going back
+// if needed.
+type Iterator struct {
+	l       *pageLexer
+	lastPos pos // position of the last item returned by nextItem
 }
 
-// backs up one token.
-func (t *Tokens) Backup() {
-	t.peekCount++
+// consumes and returns the next item
+func (t *Iterator) Next() Item {
+	t.lastPos++
+	return t.current()
 }
 
-// backs up two tokens.
-func (t *Tokens) Backup2(t1 Item) {
-	t.token[1] = t1
-	t.peekCount = 2
+var errIndexOutOfBounds = Item{tError, 0, []byte("no more tokens")}
+
+func (t *Iterator) current() Item {
+	if t.lastPos >= pos(len(t.l.items)) {
+		return errIndexOutOfBounds
+	}
+	return t.l.items[t.lastPos]
 }
 
-// backs up three tokens.
-func (t *Tokens) Backup3(t2, t1 Item) {
-	t.token[1] = t1
-	t.token[2] = t2