path: root/json/write.go

package json

import (
	"bufio"
	"fmt"
	"main/walk"
)

func isNumber(value walk.Value) bool {
	_, isFloat := value.(walk.NumberScalar)
	return isFloat
}

func isString(value walk.Value) bool {
	_, isString := value.(walk.StringStructure)
	return isString
}

func segmentEqual(left walk.Value, right walk.Value) bool {
	switch left := left.(type) {
	case walk.NumberScalar:
		_, isNumber := right.(walk.NumberScalar)
		return isNumber
	case walk.StringStructure:
		right, isString := right.(walk.StringStructure)
		return isString && left == right
	default:
		panic("Invalid path segment type")
	}
}

type JSONWriterState int
const (
	JSONWriterStateBeforeValue JSONWriterState = iota
	JSONWriterStateAfterValue JSONWriterState = iota
	JSONWriterStateInArray
	JSONWriterStateInMap
)

func NewJSONWriter(writer *bufio.Writer) *JSONWriter {
	return &JSONWriter {
		path: nil,
		writer: writer,
		state: JSONWriterStateBeforeValue,
	}
}

type JSONWriter struct {
	path []walk.Value
	writer *bufio.Writer
	state JSONWriterState
}

func (writer *JSONWriter) Write(item walk.WalkItem) error {
	path := item.Path
	for _, value := range item.Value {
		err := writer.write(path, value)
		if err != nil {
			return err
		}
	}
	return nil
}

func (writer *JSONWriter) indent(level int) {
	for i := 0; i < level; i += 1 {
		writer.writer.WriteRune('\t')
	}
}

func (writer *JSONWriter) write(targetPath []walk.Value, value walk.Value) error {
	diversionPoint := 0
	for diversionPoint < len(writer.path) && diversionPoint < len(targetPath) && segmentEqual(writer.path[diversionPoint], targetPath[diversionPoint]) {
		diversionPoint += 1
	}

	switch writer.state {
	case JSONWriterStateBeforeValue:
		goto beforeValue
	case JSONWriterStateAfterValue:
		goto afterValue
	case JSONWriterStateInArray:
		goto inArray
	case JSONWriterStateInMap:
		goto inMap
	}

	beforeValue: {
		if diversionPoint < len(writer.path) {
			panic("Writing a value before doing a necessary leave")
		}
		if diversionPoint < len(targetPath) {
			segment := targetPath[diversionPoint]
			switch segment.(type) {
			case walk.NumberScalar:
				writer.writer.WriteString("[\n")
				goto inArray
			case walk.StringStructure:
				writer.writer.WriteString("{\n")
				goto inMap
			default:
				panic("Invalid path segment")
			}
		}

		switch value := value.(type) {
		case walk.NullScalar:
			writer.writer.WriteString("null")
			writer.state = JSONWriterStateAfterValue
			return nil
		case walk.BoolScalar:
			if value {
				writer.writer.WriteString("true")
			} else {
				writer.writer.WriteString("false")
			}
			writer.state = JSONWriterStateAfterValue
			return nil
		case walk.NumberScalar:
			writer.writer.WriteString(fmt.Sprintf("%v", value))
			writer.state = JSONWriterStateAfterValue
			return nil
		case walk.StringStructure:
			writer.writer.WriteString(fmt.Sprintf("%q", value))
			writer.state = JSONWriterStateAfterValue
			return nil
		case walk.ArrayStructure:
			// TODO: write the contents of the structures
			writer.writer.WriteString("[\n")
			writer.state = JSONWriterStateInArray
			return nil
		case walk.MapStructure:
			writer.writer.WriteString("{\n")
			writer.state = JSONWriterStateInMap
			return nil
		default:
			panic("Invalid value type")
		}
	}

	afterValue: {
		if diversionPoint < len(writer.path) {
			if diversionPoint == len(writer.path) - 1 && diversionPoint < len(targetPath) {
				segment := writer.path[diversionPoint]
				switch segment.(type) {
				case walk.NumberScalar:
					_, isNumber := targetPath[diversionPoint].(walk.NumberScalar)
					if isNumber {
						writer.writer.WriteString(",\n")
						writer.path = writer.path[:diversionPoint]
						goto inArray
					}
				case walk.StringStructure:
					_, isString := targetPath[diversionPoint].(walk.StringStructure)
					if isString {
						writer.writer.WriteString(",\n")
						writer.path = writer.path[:diversionPoint]
						goto inMap
					}
				default:
					panic("Invalid segment type")
				}
			}

			writer.writer.WriteString("\n")
			switch writer.path[len(writer.path) - 1].(type) {
			case walk.NumberScalar:
				writer.path = writer.path[:len(writer.path) - 1]
				goto inArray
			case walk.StringStructure:
				writer.path = writer.path[:len(writer.path) - 1]
				goto inMap
			default:
				panic("Invalid segment type")
			}
		}

		// TODO: handle len(writer.path) == 0
		if diversionPoint < len(targetPath) {
			if len(writer.path) == 0 {
				writer.writer.WriteString("\n")
				goto beforeValue
			}
			segment := writer.path[diversionPoint - 1]
			writer.writer.WriteString(",")
			diversionPoint--
			writer.path = writer.path[:diversionPoint]
			switch segment.(type) {
			case walk.NumberScalar:
				goto inArray
			case walk.StringStructure:
				goto inMap
			default:
				panic("Invalid segment type")
			}
		}

		if len(writer.path) == 0 {
			writer.writer.WriteString("\n")
			goto beforeValue
		}
		segment := writer.path[diversionPoint - 1]
		writer.writer.WriteString(",\n")
		diversionPoint--
		writer.path = writer.path[:diversionPoint]
		switch segment.(type) {
		case walk.NumberScalar:
			goto inArray
		case walk.StringStructure:
			goto inMap
		default:
			panic("Invalid segment type")
		}
	}

	inArray: {
		if diversionPoint < len(writer.path) {
			writer.indent(len(writer.path))
			writer.writer.WriteString("]")
			goto afterValue
		}

		if diversionPoint < len(targetPath) {
			switch s := targetPath[diversionPoint].(type) {
			case walk.NumberScalar:
				writer.path = append(writer.path, s)
				diversionPoint++
				writer.indent(len(writer.path))
				goto beforeValue
			case walk.StringStructure:
				writer.indent(len(writer.path))
				writer.writer.WriteString("]")
				goto afterValue
			default:
				panic("Invalid segment type")
			}
		}

		writer.indent(len(writer.path))
		writer.writer.WriteString("]")
		goto afterValue
	}

	inMap: {
		if diversionPoint < len(writer.path) {
			writer.indent(len(writer.path))
			writer.writer.WriteString("}")
			goto afterValue
		}

		if diversionPoint < len(targetPath) {
			switch s := targetPath[diversionPoint].(type) {
			case walk.NumberScalar:
				writer.indent(len(writer.path))
				writer.writer.WriteString("}")
				goto afterValue
			case walk.StringStructure:
				writer.path = append(writer.path, s)
				diversionPoint++
				writer.indent(len(writer.path))
				writer.writer.WriteString(fmt.Sprintf("%q: ", s))
				goto beforeValue
			}
		}

		writer.indent(len(writer.path))
		writer.writer.WriteString("}")
		goto afterValue
	}
}

func (writer *JSONWriter) AssertDone() {
	switch writer.state {
	case JSONWriterStateInArray:
		writer.writer.WriteString("]")
	case JSONWriterStateInMap:
		writer.writer.WriteString("}")
	}
	for i := len(writer.path) - 1; i >= 0; i -= 1 {
		switch writer.path[i].(type) {
		case walk.NumberScalar:
			writer.writer.WriteString("\n")
			writer.indent(i)
			writer.writer.WriteString("]")
		case walk.StringStructure:
			writer.writer.WriteString("\n")
			writer.indent(i)
			writer.writer.WriteString("}")
		default:
			panic("Invalid path segment type")
		}
	}
	writer.writer.Flush()
}