package codegen

import (
	"bufio"
	"fmt"
	"html"
	"io"
	"regexp"
	"strings"

	xhtml "golang.org/x/net/html"
	"golang.org/x/net/html/atom"
)

var reNewline = regexp.MustCompile(`\r?\n`)
var reMultiSpace = regexp.MustCompile(`\s+`)
var reComments = regexp.MustCompile(`<!--.*?-->`)
var reFullnameBlock = regexp.MustCompile(`<fullname>(.+?)<\/fullname>`)
var reFullname = regexp.MustCompile(`<fullname>(.*?)</fullname>`)
var reExamples = regexp.MustCompile(`<examples?>.+?<\/examples?>`)
var reEndNL = regexp.MustCompile(`\n+$`)

// ToGoDoc rewrites a string to insert godocs formatting.
func ToGoDoc(doc string) string {
	doc = strings.TrimSpace(doc)
	if doc == "" {
		return ""
	}

	doc = reNewline.ReplaceAllString(doc, "")
	doc = reMultiSpace.ReplaceAllString(doc, " ")
	doc = reComments.ReplaceAllString(doc, "")

	var fullname string
	parts := reFullnameBlock.FindStringSubmatch(doc)
	if len(parts) > 1 {
		fullname = parts[1]
	}
	// Remove full name block from doc string
	doc = reFullname.ReplaceAllString(doc, "")

	doc = reExamples.ReplaceAllString(doc, "")
	doc = generateDoc(doc)
	doc = reEndNL.ReplaceAllString(doc, "")
	doc = html.UnescapeString(doc)

	// Replace doc with full name if doc is empty.
	if len(doc) == 0 {
		doc = fullname
	}

	return commentify(doc)
}

const (
	indent = "   "
)

// commentify converts a string to a Go comment
func commentify(doc string) string {
	if len(doc) == 0 {
		return ""
	}

	lines := strings.Split(doc, "\n")
	out := make([]string, 0, len(lines))
	for i := 0; i < len(lines); i++ {
		line := lines[i]

		if i > 0 && line == "" && lines[i-1] == "" {
			continue
		}
		out = append(out, line)
	}

	if len(out) > 0 {
		out[0] = "// " + out[0]
		return strings.Join(out, "\n// ")
	}
	return ""
}

func wrap(text string, length int) string {
	var b strings.Builder

	s := bufio.NewScanner(strings.NewReader(text))
	for s.Scan() {
		line := s.Text()

		// cleanup the line's spaces
		var i int
		for i = 0; i < len(line); i++ {
			c := line[i]
			// Ignore leading spaces, e.g indents.
			if !(c == ' ' || c == '\t') {
				break
			}
		}
		line = line[:i] + strings.Join(strings.Fields(line[i:]), " ")
		splitLine(&b, line, length)
	}

	return strings.TrimRight(b.String(), "\n")
}

func splitLine(w stringWriter, line string, length int) {
	leading := getLeadingWhitespace(line)

	line = line[len(leading):]
	length -= len(leading)

	const splitOn = " "
	for len(line) > length {
		// Find the next whitespace to the length
		idx := strings.Index(line[length:], splitOn)
		if idx == -1 {
			break
		}
		offset := length + idx

		if v := line[offset+len(splitOn):]; len(v) == 1 && strings.ContainsAny(v, `,.!?'"`) {
			// Workaround for long lines with space before the punctuation mark.
			break
		}

		w.WriteString(leading)
		w.WriteString(line[:offset])
		w.WriteByte('\n')
		line = strings.TrimLeft(line[offset+len(splitOn):], " \t")
	}

	if len(line) > 0 {
		w.WriteString(leading)
		w.WriteString(line)
	}
	// Add the newline back in that was stripped out by scanner.
	w.WriteByte('\n')
}

func getLeadingWhitespace(v string) string {
	var o strings.Builder
	for _, c := range v {
		if c == ' ' || c == '\t' {
			o.WriteRune(c)
		} else {
			break
		}
	}

	return o.String()
}

// generateDoc will generate the proper doc string for html encoded or plain text doc entries.
func generateDoc(htmlSrc string) string {
	tokenizer := xhtml.NewTokenizer(strings.NewReader(htmlSrc))
	var builder strings.Builder
	if err := encodeHTMLToText(&builder, tokenizer); err != nil {
		panic(fmt.Sprintf("failed to generated docs, %v", err))
	}

	return wrap(strings.Trim(builder.String(), "\n"), 72)
}

type stringWriter interface {
	Write([]byte) (int, error)
	WriteByte(byte) error
	WriteRune(rune) (int, error)
	WriteString(string) (int, error)
}

func encodeHTMLToText(w stringWriter, z *xhtml.Tokenizer) error {
	encoder := newHTMLTokenEncoder(w)
	defer encoder.Flush()

	for {
		tt := z.Next()
		if tt == xhtml.ErrorToken {
			if err := z.Err(); err == io.EOF {
				return nil
			} else if err != nil {
				return err
			}
		}

		if err := encoder.Encode(z.Token()); err != nil {
			return err
		}
	}
}

type htmlTokenHandler interface {
	OnStartTagToken(xhtml.Token) htmlTokenHandler
	OnEndTagToken(xhtml.Token, bool)
	OnSelfClosingTagToken(xhtml.Token)
	OnTextTagToken(xhtml.Token)
}

type htmlTokenEncoder struct {
	w           stringWriter
	depth       int
	handlers    []tokenHandlerItem
	baseHandler tokenHandlerItem
}

type tokenHandlerItem struct {
	handler htmlTokenHandler
	depth   int
}

func newHTMLTokenEncoder(w stringWriter) *htmlTokenEncoder {
	baseHandler := newBlockTokenHandler(w)
	baseHandler.rootBlock = true

	return &htmlTokenEncoder{
		w: w,
		baseHandler: tokenHandlerItem{
			handler: baseHandler,
		},
	}
}

func (e *htmlTokenEncoder) Flush() error {
	e.baseHandler.handler.OnEndTagToken(xhtml.Token{Type: xhtml.TextToken}, true)
	return nil
}

func (e *htmlTokenEncoder) Encode(token xhtml.Token) error {
	h := e.baseHandler
	if len(e.handlers) != 0 {
		h = e.handlers[len(e.handlers)-1]
	}

	switch token.Type {
	case xhtml.StartTagToken:
		e.depth++

		next := h.handler.OnStartTagToken(token)
		if next != nil {
			e.handlers = append(e.handlers, tokenHandlerItem{
				handler: next,
				depth:   e.depth,
			})
		}

	case xhtml.EndTagToken:
		handlerBlockClosing := e.depth == h.depth

		h.handler.OnEndTagToken(token, handlerBlockClosing)

		// Remove all but the root handler as the handler is no longer needed.
		if handlerBlockClosing {
			e.handlers = e.handlers[:len(e.handlers)-1]
		}
		e.depth--

	case xhtml.SelfClosingTagToken:
		h.handler.OnSelfClosingTagToken(token)

	case xhtml.TextToken:
		h.handler.OnTextTagToken(token)
	}

	return nil
}

type baseTokenHandler struct {
	w stringWriter
}

func (e *baseTokenHandler) OnStartTagToken(token xhtml.Token) htmlTokenHandler { return nil }
func (e *baseTokenHandler) OnEndTagToken(token xhtml.Token, blockClosing bool) {}
func (e *baseTokenHandler) OnSelfClosingTagToken(token xhtml.Token)            {}
func (e *baseTokenHandler) OnTextTagToken(token xhtml.Token) {
	e.w.WriteString(token.Data)
}

type blockTokenHandler struct {
	baseTokenHandler

	rootBlock  bool
	origWriter stringWriter
	strBuilder *strings.Builder

	started                bool
	newlineBeforeNextBlock bool
}

func newBlockTokenHandler(w stringWriter) *blockTokenHandler {
	strBuilder := &strings.Builder{}
	return &blockTokenHandler{
		origWriter: w,
		strBuilder: strBuilder,
		baseTokenHandler: baseTokenHandler{
			w: strBuilder,
		},
	}
}
func (e *blockTokenHandler) OnStartTagToken(token xhtml.Token) htmlTokenHandler {
	e.started = true
	if e.newlineBeforeNextBlock {
		e.w.WriteString("\n")
		e.newlineBeforeNextBlock = false
	}

	switch token.DataAtom {
	case atom.A:
		return newLinkTokenHandler(e.w, token)
	case atom.Ul:
		e.w.WriteString("\n")
		e.newlineBeforeNextBlock = true
		return newListTokenHandler(e.w)

	case atom.Div, atom.Dt, atom.P, atom.H1, atom.H2, atom.H3, atom.H4, atom.H5, atom.H6:
		e.w.WriteString("\n")
		e.newlineBeforeNextBlock = true
		return newBlockTokenHandler(e.w)

	case atom.Pre, atom.Code:
		if e.rootBlock {
			e.w.WriteString("\n")
			e.w.WriteString(indent)
			e.newlineBeforeNextBlock = true
		}
		return newBlockTokenHandler(e.w)
	}

	return nil
}
func (e *blockTokenHandler) OnEndTagToken(token xhtml.Token, blockClosing bool) {
	if !blockClosing {
		return
	}

	e.origWriter.WriteString(e.strBuilder.String())
	if e.newlineBeforeNextBlock {
		e.origWriter.WriteString("\n")
		e.newlineBeforeNextBlock = false
	}

	e.strBuilder.Reset()
}

func (e *blockTokenHandler) OnTextTagToken(token xhtml.Token) {
	if e.newlineBeforeNextBlock {
		e.w.WriteString("\n")
		e.newlineBeforeNextBlock = false
	}
	if !e.started {
		token.Data = strings.TrimLeft(token.Data, " \t\n")
	}
	if len(token.Data) != 0 {
		e.started = true
	}
	e.baseTokenHandler.OnTextTagToken(token)
}

type linkTokenHandler struct {
	baseTokenHandler
	linkToken xhtml.Token
}

func newLinkTokenHandler(w stringWriter, token xhtml.Token) *linkTokenHandler {
	return &linkTokenHandler{
		baseTokenHandler: baseTokenHandler{
			w: w,
		},
		linkToken: token,
	}
}
func (e *linkTokenHandler) OnEndTagToken(token xhtml.Token, blockClosing bool) {
	if !blockClosing {
		return
	}

	if href, ok := getHTMLTokenAttr(e.linkToken.Attr, "href"); ok && len(href) != 0 {
		fmt.Fprintf(e.w, " (%s)", strings.TrimSpace(href))
	}
}

type listTokenHandler struct {
	baseTokenHandler

	items int
}

func newListTokenHandler(w stringWriter) *listTokenHandler {
	return &listTokenHandler{
		baseTokenHandler: baseTokenHandler{
			w: w,
		},
	}
}
func (e *listTokenHandler) OnStartTagToken(token xhtml.Token) htmlTokenHandler {
	switch token.DataAtom {
	case atom.Li:
		if e.items >= 1 {
			e.w.WriteString("\n\n")
		}
		e.items++
		return newListItemTokenHandler(e.w)
	}
	return nil
}

func (e *listTokenHandler) OnTextTagToken(token xhtml.Token) {
	// Squash whitespace between list and items
}

type listItemTokenHandler struct {
	baseTokenHandler

	origWriter stringWriter
	strBuilder *strings.Builder
}

func newListItemTokenHandler(w stringWriter) *listItemTokenHandler {
	strBuilder := &strings.Builder{}
	return &listItemTokenHandler{
		origWriter: w,
		strBuilder: strBuilder,
		baseTokenHandler: baseTokenHandler{
			w: strBuilder,
		},
	}
}
func (e *listItemTokenHandler) OnStartTagToken(token xhtml.Token) htmlTokenHandler {
	switch token.DataAtom {
	case atom.P:
		return newBlockTokenHandler(e.w)
	}
	return nil
}
func (e *listItemTokenHandler) OnEndTagToken(token xhtml.Token, blockClosing bool) {
	if !blockClosing {
		return
	}

	e.origWriter.WriteString(indent + "* ")
	e.origWriter.WriteString(strings.TrimSpace(e.strBuilder.String()))
}

type trimSpaceTokenHandler struct {
	baseTokenHandler

	origWriter stringWriter
	strBuilder *strings.Builder
}

func newTrimSpaceTokenHandler(w stringWriter) *trimSpaceTokenHandler {
	strBuilder := &strings.Builder{}
	return &trimSpaceTokenHandler{
		origWriter: w,
		strBuilder: strBuilder,
		baseTokenHandler: baseTokenHandler{
			w: strBuilder,
		},
	}
}
func (e *trimSpaceTokenHandler) OnEndTagToken(token xhtml.Token, blockClosing bool) {
	if !blockClosing {
		return
	}

	e.origWriter.WriteString(strings.TrimSpace(e.strBuilder.String()))
}

func getHTMLTokenAttr(attr []xhtml.Attribute, name string) (string, bool) {
	for _, a := range attr {
		if strings.EqualFold(a.Key, name) {
			return a.Val, true
		}
	}
	return "", false
}
