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 := len(writer.path)
	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 JSONWriterStateInMap:
		goto inMap
	case JSONWriterStateInArray:
		goto inArray
	default:
		panic("Invalid JSONWriterState")
	}

	beforeValue: {
		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 len(writer.path) == 0 {
			writer.writer.WriteRune('\n')
			goto beforeValue
		}
		switch writer.path[len(writer.path) - 1].(type) {
		case walk.NumberScalar:
			// TODO: second part of this condition might be redundant
			if len(writer.path) - 1 <= diversionPoint && len(targetPath) >= len(writer.path) && isNumber(targetPath[len(writer.path) - 1]) {
				writer.writer.WriteString(",\n")
				writer.path = writer.path[:len(writer.path) - 1]
				goto inArray
			} else {
				writer.writer.WriteString("\n")
				writer.indent(len(writer.path) - 1)
				writer.writer.WriteString("]")
				writer.path = writer.path[:len(writer.path) - 1]
				goto afterValue
			}
		case walk.StringStructure:
			if len(writer.path) -1 <= diversionPoint && len(targetPath) >= len(writer.path) && isString(targetPath[len(writer.path) - 1]) {
				writer.writer.WriteString(",\n")
				writer.path = writer.path[:len(writer.path) - 1]
				goto inMap
			} else {
				writer.writer.WriteString("\n")
				writer.indent(len(writer.path) - 1)
				writer.writer.WriteString("}")
				writer.path = writer.path[:len(writer.path) - 1]
				goto afterValue
			}
		default:
			panic("Invalid path segment type")
		}
	}

	inMap: {
		if len(writer.path) <= diversionPoint && len(targetPath) > len(writer.path) && isString(targetPath[len(writer.path)]) {
			writer.indent(len(writer.path) + 1)
			writer.writer.WriteString(fmt.Sprintf("%q: ", targetPath[len(writer.path)].(walk.StringStructure)))
			writer.path = append(writer.path, targetPath[len(writer.path)].(walk.StringStructure))
			goto beforeValue
		} else {
			writer.writer.WriteString("\n}")
			goto afterValue
		}
	}

	inArray: {
		if len(writer.path) <= diversionPoint && len(targetPath) > len(writer.path) && isNumber(targetPath[len(writer.path)]) {
			writer.indent(len(writer.path) + 1)
			writer.path = append(writer.path, walk.NumberScalar(0))
			goto beforeValue
		} else {
			writer.writer.WriteString("\n]")
			goto afterValue
		}
	}
}

func (writer *JSONWriter) AssertDone() {
	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()
}