Adds the json_array IO format

2 files changed, 274 insertions, 0 deletions

diff --git a/json_array/read.go b/json_array/read.go
new file mode 100644
index 0000000..6334197
--- /dev/null
+++ b/json_array/read.go
@@ -0,0 +1,118 @@
+package json_array
+
+import (
+	"main/walk"
+	"encoding/json"
+	"errors"
+	"bufio"
+)
+
+type state int
+const (
+	stateStart state = iota
+	stateValueStart
+	stateEnd
+	stateDead
+)
+
+func atomiseValue(value interface{}) []walk.Atom {
+	switch v := value.(type) {
+		case nil:
+			return []walk.Atom{walk.NewAtomNull()}
+		case bool:
+			return []walk.Atom{walk.NewAtomBool(v)}
+		case float64:
+			return []walk.Atom{walk.NewAtomNumber(v)}
+		case string:
+			atoms := []walk.Atom{walk.NewAtomStringTerminal()}
+			for _, r := range v {
+				atoms = append(atoms, walk.NewAtomStringRune(r))
+			}
+			atoms = append(atoms, walk.NewAtomStringTerminal())
+			return atoms
+		case []interface{}:
+			atoms := []walk.Atom{walk.NewAtomTerminal(walk.ArrayBegin)}
+			for _, element := range v {
+				atoms = append(atoms, atomiseValue(element)...)
+			}
+			atoms = append(atoms, walk.NewAtomTerminal(walk.ArrayEnd))
+			return atoms
+		case map[string]interface{}:
+			atoms := []walk.Atom{walk.NewAtomTerminal(walk.MapBegin)}
+			for key, element := range v {
+				atoms = append(atoms, atomiseValue(key)...)
+				atoms = append(atoms, atomiseValue(element)...)
+			}
+			atoms = append(atoms, walk.NewAtomTerminal(walk.MapEnd))
+			return atoms
+		default:
+			panic("Invalid JSON value type")
+	}
+}
+
+func NewJSONArrayReader(reader *bufio.Reader) *JSONArrayReader {
+	return &JSONArrayReader {
+		decoder: json.NewDecoder(reader),
+		state: stateStart,
+		index: 0,
+	}
+}
+
+type JSONArrayReader struct {
+	decoder *json.Decoder
+	state state
+	index int
+}
+
+func (in *JSONArrayReader) Read() (walk.WalkItem, error) {
+	restart:
+	switch in.state {
+		case stateStart:
+			arrayStart, err := in.decoder.Token()
+			if err != nil {
+				panic("Error reading start of JSON array")
+			}
+			delim, isDelim := arrayStart.(json.Delim)
+			if !isDelim || delim != '[' {
+				panic("JSON input is not an array!")
+			}
+			in.state = stateValueStart
+			goto restart
+		case stateValueStart:
+			if !in.decoder.More() {
+				in.state = stateEnd
+				goto restart
+			}
+			var m interface{}
+			err := in.decoder.Decode(&m)
+			if err != nil {
+				panic("Error decoding array value")
+			}
+			in.index += 1
+			return walk.WalkItem {
+				Path: []walk.Atom{walk.NewAtomNumber(float64(in.index - 1))},
+				Value: atomiseValue(m),
+			}, nil
+		case stateEnd:
+			arrayEnd, err := in.decoder.Token()
+			if err != nil {
+				panic("Error reading end of JSON array")
+			}
+			delim, isDelim := arrayEnd.(json.Delim)
+			if !isDelim || delim != ']' {
+				panic("JSON array wasn't ended")
+			}
+			in.state = stateDead
+			return walk.WalkItem{}, errors.New("eof")
+		case stateDead:
+			return walk.WalkItem{}, errors.New("eof")
+		default:
+			panic("Unreachable!!!")
+	}
+}
+
+func (in *JSONArrayReader) AssertDone() {
+	if in.state != stateDead || in.decoder.More() {
+		panic("More JSON after array value")
+	}
+}
diff --git a/json_array/write.go b/json_array/write.go
new file mode 100644
index 0000000..4d202c4
--- /dev/null
+++ b/json_array/write.go
@@ -0,0 +1,156 @@
+package json_array
+
+import (
+	"bufio"
+	"strings"
+	"main/walk"
+	"encoding/json"
+)
+
+func assembleValue(atoms []walk.Atom) (interface{}, []walk.Atom) {
+	if len(atoms) == 0 {
+		panic("Missing JSON value in output")
+	}
+	switch atoms[0].Typ {
+		case walk.AtomNull:
+			return nil, atoms[1:]
+		case walk.AtomBool:
+			return atoms[0].Bool(), atoms[1:]
+		case walk.AtomNumber:
+			return atoms[0].Number(), atoms[1:]
+		case walk.AtomStringTerminal:
+			var builder strings.Builder
+			atoms = atoms[1:]
+			for {
+				if len(atoms) == 0 {
+					panic("Missing closing string terminal")
+				}
+				if atoms[0].Typ == walk.AtomStringTerminal {
+					break
+				}
+				if atoms[0].Typ != walk.AtomStringRune {
+					panic("Non string rune atom inside string")
+				}
+				builder.WriteRune(atoms[0].StringRune())
+				atoms = atoms[1:]
+			}
+			atoms = atoms[1:]
+			return builder.String(), atoms
+		case walk.AtomStringRune:
+			panic("String rune used outside of string terminals")
+		case walk.AtomTerminal:
+			terminal := atoms[0].Terminal()
+			switch terminal {
+				case walk.ArrayEnd, walk.MapEnd:
+					panic("Tried to extract value from end terminal")
+				case walk.ArrayBegin:
+					var arr []interface{}
+					var element interface{}
+					atoms = atoms[1:]
+					for {
+						if len(atoms) == 0 {
+							panic("Missing array end terminal")
+						}
+						if atoms[0].Typ == walk.AtomTerminal && atoms[0].Terminal() == walk.ArrayEnd {
+							atoms = atoms[1:]
+							break
+						}
+						element, atoms = assembleValue(atoms)
+						arr = append(arr, element)
+					}
+					return arr, atoms
+				case walk.MapBegin:
+					obj := make(map[string]interface{})
+					var key interface{}
+					var element interface{}
+					atoms = atoms[1:]
+					for {
+						if len(atoms) == 0 {
+							panic("Missing map end terminal")
+						}
+						if atoms[0].Typ == walk.AtomTerminal && atoms[0].Terminal() == walk.MapEnd {
+							atoms = atoms[1:]
+							break
+						}
+						key, atoms = assembleValue(atoms)
+						element, atoms = assembleValue(atoms)
+						keyString, keyIsString := key.(string)
+						if !keyIsString {
+							panic("Key is not string")
+						}
+						obj[keyString] = element
+					}
+					return obj, atoms
+				default:
+					panic("Invalid terminal")
+			}
+		default:
+			panic("Invalid atom")
+	}
+}
+
+func outputValue(atoms []walk.Atom, writer *bufio.Writer) {
+	if len(atoms) == 0 {
+		return
+	}
+	value, atoms := assembleValue(atoms)
+	if len(atoms) != 0 {
+		panic("Tried to output more than one JSON value")
+	}
+	bytes, err := json.MarshalIndent(value, "\t", "\t")
+	if err != nil {
+		panic("Error marshalling json into bytes")
+	}
+	_, err = writer.Write(bytes)
+	if err != nil {
+		panic("Error writing value")
+	}
+}
+
+type writerState int
+const (
+	writerStateStart writerState = iota
+	writerStateValue
+)
+
+func NewJSONArrayWriter(writer *bufio.Writer) *JSONArrayWriter {
+	return &JSONArrayWriter {
+		writer: writer,
+		state: writerStateStart,
+	}
+}
+
+type JSONArrayWriter struct {
+	writer *bufio.Writer
+	state writerState
+}
+
+func (out *JSONArrayWriter) Write(item walk.WalkItem) error {
+	switch out.state {
+		case writerStateStart:
+			_, err := out.writer.WriteString("[\n\t")
+			if err != nil {
+				panic("Error outputting [ at beginning of array")
+			}
+			outputValue(item.Value, out.writer)
+			out.state = writerStateValue
+			return nil
+		case writerStateValue:
+			_, err := out.writer.WriteString(",\n\t")
+			if err != nil {
+				panic("Error outputting comma at the end of a value")
+			}
+			outputValue(item.Value, out.writer)
+			return nil
+		default:
+			panic("Invalid writer state")
+	}
+}
+
+func (out *JSONArrayWriter) AssertDone() {
+	if out.state == writerStateStart {
+		out.writer.WriteString("[")
+	}
+	out.writer.WriteString("\n]")
+	out.writer.Flush()
+}