basic: introduce basic one-shot INI-style decoder

Signed-off-by: Alejandro Mery <amery@jpi.io>

README.md

@@ -16,6 +16,7 @@ of stricter parsers of similar form.
 
 [godoc-lexer]: https://pkg.go.dev/asciigoat.org/core/lexer
 [godoc-parser-parser]: https://pkg.go.dev/asciigoat.org/ini/parser#Parser
+[godoc-basic-parser]: https://pkg.go.dev/asciigoat.org/ini/basic#Decode
 
 [wikipedia-dosini]: https://en.wikipedia.org/wiki/INI_file
 
@@ -25,6 +26,15 @@ of stricter parsers of similar form.
 [`asciigoat`'s lexer][godoc-lexer] to process an `INI`-style document
 emiting tokens and errors via callbacks.
 
+## Basic Parser
+
+[`basic.Decode()`][godoc-basic-parser] provies a one-shot decoder
+that returns a structured document for you to post-process.
+
+To allow for correct handling of repetition of section and field names downstream,
+it uses arrays instead of maps, and makes almost no judgment
+about what section or field names are acceptable.
+
 ## Other Implementations
 
 Other implementations exist, and they are mature and feature-rich, but they

basic/basic.go

@@ -0,0 +1,24 @@
+// Package basic provides a basic representation of dosini-style documents
+package basic
+
+// Document represents an INI-style document
+type Document struct {
+	Global []Field
+
+	Sections []Section
+}
+
+// Section represents an INI-style section with optional GIT-style IDs
+type Section struct {
+	Key     string
+	ID      string
+	EmptyID bool
+
+	Fields []Field
+}
+
+// Field represents a key = value entry in an INI-style document
+type Field struct {
+	Key   string
+	Value string
+}

basic/decoder.go

@@ -0,0 +1,49 @@
+package basic
+
+import (
+	"bytes"
+	"io"
+	"io/fs"
+	"strings"
+
+	"asciigoat.org/ini/parser"
+)
+
+type decoder struct {
+	p   *parser.Parser
+	out *Document
+
+	queue   []*token
+	current *Section
+}
+
+// Decode attempts to decode an INI-style from an [io.Reader] array into a [Document]
+func Decode(r io.Reader) (*Document, error) {
+	var out Document
+
+	if r == nil {
+		return nil, fs.ErrNotExist
+	}
+
+	// parser
+	p := parser.NewParser(r)
+	// decoder
+	dec := decoder{p: p, out: &out}
+	// glue
+	p.OnToken = dec.OnToken
+	p.OnError = dec.OnError
+
+	// Go!
+	err := p.Run()
+	return &out, err
+}
+
+// DecodeBytes attempts to decode an INI-style bytes array into a [Document]
+func DecodeBytes(b []byte) (*Document, error) {
+	return Decode(bytes.NewReader(b))
+}
+
+// DecodeString attempts to decode an INI-style string into a [Document]
+func DecodeString(s string) (*Document, error) {
+	return Decode(strings.NewReader(s))
+}

basic/error.go

@@ -0,0 +1,33 @@
+package basic
+
+import (
+	"errors"
+
+	"asciigoat.org/core/lexer"
+)
+
+var (
+	errInvalidToken = errors.New("invalid token")
+)
+
+func newErrInvalidToken(t *token) *lexer.Error {
+	err := &lexer.Error{
+		Line:    t.pos.Line,
+		Column:  t.pos.Column,
+		Content: t.value,
+		Err:     errInvalidToken,
+	}
+	return err
+}
+
+func (dec *decoder) OnError(pos lexer.Position, content string, err error) error {
+	err = &lexer.Error{
+		Line:    pos.Line,
+		Column:  pos.Column,
+		Content: content,
+		Err:     err,
+	}
+
+	dec.executeFinal()
+	return err
+}

basic/token.go

@@ -0,0 +1,154 @@
+package basic
+
+import (
+	"fmt"
+
+	"asciigoat.org/core/lexer"
+	"asciigoat.org/ini/parser"
+)
+
+type token struct {
+	pos   lexer.Position
+	typ   parser.TokenType
+	value string
+}
+
+func (t token) String() string {
+	return fmt.Sprintf("%s %s: %q", t.pos, t.typ, t.value)
+}
+
+func (dec *decoder) executeFinal() {
+	if len(dec.queue) > 0 {
+		// we have unfinished businesses
+		switch dec.queue[0].typ {
+		case parser.TokenSectionStart:
+			dec.execute(parser.TokenSectionEnd)
+		case parser.TokenFieldKey:
+			dec.execute(parser.TokenFieldValue)
+		}
+	}
+}
+
+func (dec *decoder) execute(typ parser.TokenType) {
+	switch typ {
+	case parser.TokenSectionEnd:
+		name1, ok1 := dec.getValue(1, parser.TokenSectionName)
+
+		if ok1 {
+			name2, ok2 := dec.getValue(2, parser.TokenSectionSubname)
+
+			dec.addSection(name1, name2, ok2)
+		}
+
+		dec.reset()
+	case parser.TokenFieldValue:
+		key, _ := dec.getValue(0, parser.TokenFieldKey)
+		value, _ := dec.getValue(1, parser.TokenFieldValue)
+
+		dec.addField(key, value)
+		dec.reset()
+	}
+}
+
+func (dec *decoder) addSection(key, id string, allowEmptyID bool) {
+	emptyID := allowEmptyID && id == ""
+
+	// index for dec.current
+	n := len(dec.out.Sections)
+
+	// new section
+	dec.out.Sections = append(dec.out.Sections, Section{
+		Key:     key,
+		ID:      id,
+		EmptyID: emptyID,
+	})
+
+	// pointer to the latest section
+	dec.current = &dec.out.Sections[n]
+}
+
+func (dec *decoder) addField(key, value string) {
+	field := Field{
+		Key:   key,
+		Value: value,
+	}
+
+	if p := dec.current; p != nil {
+		// in section
+		p.Fields = append(p.Fields, field)
+	} else {
+		// global
+		dec.out.Global = append(dec.out.Global, field)
+	}
+}
+
+func (dec *decoder) getValue(idx int, typ parser.TokenType) (string, bool) {
+	switch {
+	case idx < 0 || idx >= len(dec.queue):
+		// out of range
+		return "", false
+	case dec.queue[idx].typ != typ:
+		// wrong type
+		return "", false
+	default:
+		return dec.queue[idx].value, true
+	}
+}
+
+func (dec *decoder) reset() {
+	dec.queue = dec.queue[:0]
+}
+
+func (dec *decoder) depth(depth int) bool {
+	return len(dec.queue) == depth
+}
+
+func (dec *decoder) depthAfter(depth int, typ parser.TokenType) bool {
+	_, ok := dec.getValue(depth-1, typ)
+	if ok {
+		return len(dec.queue) == depth
+	}
+	return false
+}
+
+func (dec *decoder) typeOK(typ parser.TokenType) bool {
+	switch typ {
+	case parser.TokenSectionStart, parser.TokenFieldKey:
+		// first token only
+		return dec.depth(0)
+	case parser.TokenSectionName:
+		// right after TokenSectionStart
+		return dec.depthAfter(1, parser.TokenSectionStart)
+	case parser.TokenSectionSubname:
+		// right after TokenSectionName
+		return dec.depthAfter(2, parser.TokenSectionName)
+	case parser.TokenSectionEnd:
+		// only on a section with name
+		_, ok := dec.getValue(1, parser.TokenSectionName)
+		return ok
+	case parser.TokenFieldValue:
+		// right after a TokenFieldKey
+		return dec.depthAfter(1, parser.TokenFieldKey)
+	default:
+		// never
+		return false
+	}
+}
+
+func (dec *decoder) OnToken(pos lexer.Position, typ parser.TokenType, value string) error {
+	t := &token{pos, typ, value}
+
+	switch {
+	case typ == parser.TokenComment:
+		// ignore comments
+		return nil
+	case dec.typeOK(typ):
+		// acceptable token
+		dec.queue = append(dec.queue, t)
+		dec.execute(typ)
+		return nil
+	default:
+		// unacceptable
+		return newErrInvalidToken(t)
+	}
+}