package protocol

import "io"
import "fmt"
import "bytes"
import "errors"
import "strings"
import "github.com/gomarkdown/markdown"
import "github.com/gomarkdown/markdown/ast"
import "github.com/gomarkdown/markdown/parser"

// Protocol describes a protocol.
type Protocol struct {
	Messages []Message
}

// Message describes a protocol message.
type Message struct {
	Doc string
	Name string
	Fields []Field
}

// Field describes a named value within a message.
type Field struct {
	Doc      string
	Name     string
	Optional bool
	Type     string
}

// ParseReader parses a protocol definition from a reader.
func ParseReader (reader io.Reader) (*Protocol, error) {
	data, err := io.ReadAll(reader)
	if err != nil { return nil, err }
	protocol := new(Protocol)
	err = protocol.UnmarshalText(data)
	if err != nil { return nil, err }
	return protocol, nil
}

// UnmarshalText unmarshals markdown-formatted text data into the protocol.
func (this *Protocol) UnmarshalText (text []byte) error {
	var state int; const (
		stateIdle = iota
		stateMessage
		stateMessageDoc
		stateMessageField
	)

	var message *Message
	addMessage := func (name string) {
		this.Messages = append(this.Messages, Message {
			Name: name,
		})
		message = &this.Messages[len(this.Messages) - 1]
	}

	root := markdown.Parse(text, parser.New())
	for _, node := range root.GetChildren() {
		if node, ok := node.(*ast.Heading); ok {
			if node.Level == 2 {
				if removeBreaks(flatten(node)) == "Messages" {
					state = stateMessage
					continue
				}
			}

			if node.Level > 3 {
				state = stateIdle
				continue
			}

			if state != stateIdle && node.Level == 3 {
				addMessage(removeBreaks(flatten(node)))
				state = stateMessageDoc
			}
		}

		if state == stateIdle { continue }
		if message == nil     { continue }

		switch node := node.(type) {
		case *ast.Paragraph:
			if message.Doc != "" { message.Doc += "\n\n" }
			message.Doc += removeBreaks(flatten(node))
		case *ast.BlockQuote:
			if message.Doc != "" { message.Doc += "\n\n> " }
			message.Doc += removeBreaks(flatten(node))
		case *ast.List:
			fields, err := processFieldList(node)
			if err != nil { return err}
			message.Fields = append(message.Fields, fields...)
		case *ast.Table:
			fields, err := processFieldTable(node)
			if err != nil { return err}
			message.Fields = append(message.Fields, fields...)
		}
	}
	
	return nil
}

func (this *Protocol) MarshalText () ([]byte, error) {
	buffer := bytes.NewBuffer(nil)

	fmt.Fprint(buffer, "# Messages\n")
	for index, message := range this.Messages {
		if index > 0 {
			fmt.Fprint(buffer, "\n")
		}
		fmt.Fprintf(buffer, "## %s\n", message.Name)
		if message.Doc != "" {
			fmt.Fprintf(buffer, "%s\n", message.Doc)
		}
		if len(message.Fields) > 0 {
			fmt.Fprint(buffer, "\n")
		}
		for _, field := range message.Fields {
			fmt.Fprintf(buffer, "- %s", field.Name)
			if field.Type != "" {
				fmt.Fprintf(buffer, " %s", field.Type)
			}
			if field.Doc != "" {
				fmt.Fprintf(buffer, ": %s", field.Doc)
			}
			fmt.Fprint(buffer, "\n")
		}
	}
	
	return buffer.Bytes(), nil
}

func processFieldList (node *ast.List) ([]Field, error) {
	fields := []Field { }
	for _, item := range node.GetChildren() {
		if item, ok := item.(*ast.ListItem); ok {
			field, err := processFieldListItem(removeBreaks(flatten(item)))
			if err != nil { return nil, err }
			fields = append(fields, field)
		}
	}
	return fields, nil
}

func processFieldTable (node *ast.Table) ([]Field, error) {
	fields := []Field { }
	children := node.GetChildren()
	if len(children) != 2 {
		return nil, errors.New("malformed field table")
	}

	// get columns
	columns := []string { }
	if header, ok := children[0].(*ast.TableHeader); ok {
		children := header.GetChildren()
		if len(children) != 1 {
			return nil, errors.New("malformed field table header")
		}
		if row, ok := header.Children[0].(*ast.TableRow); ok {
			for _, cell := range row.GetChildren() {
				if cell, ok := cell.(*ast.TableCell); ok {
					columns = append(columns, flatten(cell))
				}
			}
		} else {
			return nil, errors.New("malformed field table header")
		}
		for index, column := range columns {
			columns[index] = strings.ToLower(column)
		}
	} else {
		return nil, errors.New("malformed field table: no header")
	}

	// get data
	if body, ok := children[1].(*ast.TableBody); ok {
		for _, node := range body.GetChildren() {
		if row, ok := node.(*ast.TableRow); ok {
			children := row.GetChildren()
			if len(children) != len(columns) {
				return nil, errors.New (
					"malformed field table row: wrong " +
					"number of columns")
			}

			field := Field { }
		
			for index, node := range children {
			if cell, ok := node.(*ast.TableCell); ok {
				text := flatten(cell)
				switch columns[index] {
				case "name":
					field.Name = text
				case "required":
					field.Optional = !parseBool(text)
				case "optional":
					field.Optional = parseBool(text)
				case "type":
					field.Type = text
				case "comment", "purpose", "documentation":
					field.Doc = text
				}
			}}

			fields = append(fields, field)
		}}
	} else {
		return nil, errors.New("malformed field table: no body")
	}
	return fields, nil
}

type nodeFlattener struct {
	text string
}
func (this *nodeFlattener) String () string { return this.text }
func (this *nodeFlattener) Visit (node ast.Node, entering bool) ast.WalkStatus {
	if entering {
		if node := node.AsLeaf(); node != nil {
			this.text += string(node.Literal)
		}
	}
	return ast.GoToNext
}
func flatten (node ast.Node) string {
	flattener := new(nodeFlattener)
	ast.Walk(node, flattener)
	return flattener.text
}

func processFieldListItem (bullet string) (Field, error) {
	field := Field { }
	nameAndType, doc, hasDoc := strings.Cut(bullet, ":")
	if hasDoc {
		field.Doc = strings.TrimSpace(doc)
	}

	name, ty, hasType := strings.Cut(strings.TrimSpace(nameAndType), " ")
	if !hasType {
		return Field { }, errors.New(fmt.Sprintf("unspecified type near '%s'", bullet))
	}
	field.Name = strings.TrimSpace(name)
	field.Type = strings.TrimSpace(ty)
	return field, nil
}

func removeBreaks (text string) string {
	text = strings.ReplaceAll(text, "\n", " ")
	text = strings.ReplaceAll(text, "\r", "")
	return text
}

func parseBool (text string) bool {
	switch(strings.ToLower(text)) {
	case "yes": return true
	case "no": return false
	case "true": return true
	case "false": return false
	}
	return false
}