From 3c34366bdd5d817a184d6b1c901d03a16b6faa4b Mon Sep 17 00:00:00 2001
From: Charlie Stanton <charlie@shtanton.xyz>
Date: Fri, 12 May 2023 14:25:32 +0100
Subject: Adds the json_array IO format

---
 json_array/read.go | 118 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 118 insertions(+)
 create mode 100644 json_array/read.go

(limited to 'json_array/read.go')

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")
+	}
+}
-- 
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