Huge refactor to a more value based system, doing away with terminals. Also introduces unit testing

1 files changed, 288 insertions, 0 deletions

diff --git a/json/read.go b/json/read.go
new file mode 100644
index 0000000..6a68467
--- /dev/null
+++ b/json/read.go
@@ -0,0 +1,288 @@
+package json
+
+import (
+	"bufio"
+	"main/walk"
+	"strings"
+	"strconv"
+	"errors"
+)
+
+func isWhitespace(r rune) bool {
+	for _, ws := range " \t\r\n" {
+		if r == ws {
+			return true
+		}
+	}
+	return false
+}
+
+func isNumberRune(r rune) bool {
+	return '0' <= r && r <= '9' || r == '.'
+}
+
+type JSONReaderStructure int
+const (
+	JSONReaderStructureArray JSONReaderStructure = iota
+	JSONReaderStructureMap
+)
+
+type JSONReaderState int
+const (
+	JSONReaderStateValue JSONReaderState = iota
+	JSONReaderStateValueEnd
+)
+
+func NewJSONReader(reader *bufio.Reader) *JSONReader {
+	return &JSONReader {
+		path: nil,
+		structure: nil,
+		state: JSONReaderStateValue,
+		reader: reader,
+	}
+}
+
+type JSONReader struct {
+	path []walk.Value
+	structure []JSONReaderStructure
+	state JSONReaderState
+	reader *bufio.Reader
+}
+
+func (reader *JSONReader) Read() (walk.WalkItem, error) {
+	switch reader.state {
+	case JSONReaderStateValue:
+		if len(reader.structure) == 0 {
+			path := reader.clonePath()
+			value, err := reader.readValue()
+			if err != nil {
+				panic("Missing JSON input")
+			}
+			return walk.WalkItem {
+				Path: path,
+				Value: []walk.Value{value},
+			}, nil
+		}
+		switch reader.structure[len(reader.structure) - 1] {
+		case JSONReaderStructureArray:
+			r, err := reader.nextNonWsRune()
+			if err != nil {
+				panic("Missing rest of array")
+			}
+			if r == ']' {
+				reader.structure = reader.structure[:len(reader.structure) - 1]
+				reader.path = reader.path[:len(reader.path) - 1]
+				reader.state = JSONReaderStateValueEnd
+				return reader.Read()
+			}
+			reader.reader.UnreadRune()
+			prevIndex := reader.path[len(reader.path) - 1].(walk.NumberScalar)
+			reader.path[len(reader.path) - 1] = prevIndex + 1
+			path := reader.clonePath()
+			value, err := reader.readValue()
+			if err != nil {
+				panic("Missing value in array")
+			}
+			return walk.WalkItem {
+				Path: path,
+				Value: []walk.Value{value},
+			}, nil
+		case JSONReaderStructureMap:
+			r, err := reader.nextNonWsRune()
+			if err != nil {
+				panic("Reached EOF inside JSON map")
+			}
+			if r == '}' {
+				reader.structure = reader.structure[:len(reader.structure) - 1]
+				reader.path = reader.path[:len(reader.path) - 1]
+				reader.state = JSONReaderStateValueEnd
+				return reader.Read()
+			}
+			if r != '"' {
+				panic("Expected key in map, found something else")
+			}
+			key := reader.readString()
+			reader.path[len(reader.path) - 1] = walk.StringStructure(key)
+			r, err = reader.nextNonWsRune()
+			if err != nil {
+				panic("Reached EOF after map key")
+			}
+			if r != ':' {
+				panic("Expected : after map key, found something else")
+			}
+			path := reader.clonePath()
+			value, err := reader.readValue()
+			if err != nil {
+				panic("Missing value in map")
+			}
+			return walk.WalkItem {
+				Path: path,
+				Value: []walk.Value{value},
+			}, nil
+		default:
+			panic("Invalid JSONReaderStructure")
+		}
+	case JSONReaderStateValueEnd:
+		if len(reader.structure) == 0 {
+			_, err := reader.nextNonWsRune()
+			if err == nil {
+				panic("input continues after JSON value")
+			}
+			return walk.WalkItem{}, errors.New("eof")
+		}
+		switch reader.structure[len(reader.structure) - 1] {
+		case JSONReaderStructureArray:
+			r, err := reader.nextNonWsRune()
+			if err != nil {
+				panic("Missing end of array")
+			}
+			if r == ']' {
+				reader.path = reader.path[:len(reader.path) - 1]
+				reader.structure = reader.structure[:len(reader.structure) - 1]
+				reader.state = JSONReaderStateValueEnd
+				return reader.Read()
+			}
+			if r != ',' {
+				panic("Missing , after array value")
+			}
+			reader.state = JSONReaderStateValue
+			return reader.Read()
+		case JSONReaderStructureMap:
+			r, err := reader.nextNonWsRune()
+			if err != nil {
+				panic("Missing end of map")
+			}
+			if r == '}' {
+				reader.path = reader.path[:len(reader.path) - 1]
+				reader.structure = reader.structure[:len(reader.structure) - 1]
+				reader.state = JSONReaderStateValueEnd
+				return reader.Read()
+			}
+			if r != ',' {
+				panic("Missing , after map value")
+			}
+			reader.state = JSONReaderStateValue
+			return reader.Read()
+		default:
+			panic("Invalid JSONReaderStructure")
+		}
+	default:
+		panic("Invalid JSONReaderState")
+	}
+}
+
+func (reader *JSONReader) readValue() (walk.Value, error) {
+	r, err := reader.nextNonWsRune()
+	if err != nil {
+		panic("Missing value in JSON")
+	}
+	switch r {
+		case 'n':
+			reader.requireString("ull")
+			reader.state = JSONReaderStateValueEnd
+			return walk.NullScalar{}, nil
+		case 'f':
+			reader.requireString("alse")
+			reader.state = JSONReaderStateValueEnd
+			return walk.BoolScalar(false), nil
+		case 't':
+			reader.requireString("rue")
+			reader.state = JSONReaderStateValueEnd
+			return walk.BoolScalar(true), nil
+		case '"':
+			v := reader.readString()
+			reader.state = JSONReaderStateValueEnd
+			return walk.StringStructure(v), nil
+		case '{':
+			reader.state = JSONReaderStateValue
+			reader.structure = append(reader.structure, JSONReaderStructureMap)
+			reader.path = append(reader.path, walk.StringStructure(""))
+			return walk.MapStructure(make(map[string]walk.Value)), nil
+		case '[':
+			reader.state = JSONReaderStateValue
+			reader.structure = append(reader.structure, JSONReaderStructureArray)
+			reader.path = append(reader.path, walk.NumberScalar(-1))
+			return walk.ArrayStructure{}, nil
+	}
+	if isNumberRune(r) {
+		var builder strings.Builder
+		builder.WriteRune(r)
+		for {
+			r, _, err = reader.reader.ReadRune()
+			if err != nil {
+				break
+			}
+			if !isNumberRune(r) {
+				reader.reader.UnreadRune()
+				break
+			}
+			builder.WriteRune(r)
+		}
+		number, parseError := strconv.ParseFloat(builder.String(), 64)
+		if parseError != nil {
+			panic("Invalid number")
+		}
+		reader.state = JSONReaderStateValueEnd
+		return walk.NumberScalar(number), nil
+	}
+	panic("Invalid JSON value starting with: " + string(r))
+}
+
+func (reader *JSONReader) readString() string {
+	var builder strings.Builder
+	for {
+		r, _, err := reader.reader.ReadRune()
+		if err != nil {
+			panic("Missing rest of string")
+		}
+		if r == '"' {
+			break
+		}
+		if r == '\\' {
+			r, _, err = reader.reader.ReadRune()
+			if err != nil {
+				panic("Missing rune after \\")
+			}
+			builder.WriteRune(r)
+			continue
+		}
+		builder.WriteRune(r)
+	}
+	return builder.String()
+}
+
+func (reader *JSONReader) nextNonWsRune() (rune, error) {
+	for {
+		r, _, err := reader.reader.ReadRune()
+		if err != nil {
+			return 0, err
+		}
+		if !isWhitespace(r) {
+			return r, nil
+		}
+	}
+}
+
+func (reader *JSONReader) requireString(criteria string) {
+	for _, r := range criteria {
+		reader.require(r)
+	}
+}
+
+func (reader *JSONReader) require(criterion rune) {
+	r, _, err := reader.reader.ReadRune()
+	if err != nil {
+		panic("Error while reading required rune: " + err.Error())
+	}
+	if r != criterion {
+		panic("Required rune not read")
+	}
+}
+
+func (reader *JSONReader) clonePath() []walk.Value {
+	return append([]walk.Value{}, reader.path...)
+}
+
+func (reader *JSONReader) AssertDone() {
+	// TODO
+}