// gomuks - A terminal Matrix client written in Go.
// Copyright (C) 2019 Tulir Asokan
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

package parser

import (
	"fmt"
	"math"
	"regexp"
	"strconv"
	"strings"

	"github.com/lucasb-eyer/go-colorful"
	"golang.org/x/net/html"

	"maunium.net/go/gomuks/ui/messages"
	"maunium.net/go/mautrix"
	"maunium.net/go/tcell"

	"maunium.net/go/gomuks/matrix/rooms"
	"maunium.net/go/gomuks/ui/widget"
)

var matrixToURL = regexp.MustCompile("^(?:https?://)?(?:www\\.)?matrix\\.to/#/([#@!].*)")

type htmlParser struct {
	room *rooms.Room
}

func AdjustStyleBold(style tcell.Style) tcell.Style {
	return style.Bold(true)
}

func AdjustStyleItalic(style tcell.Style) tcell.Style {
	return style.Italic(true)
}

func AdjustStyleUnderline(style tcell.Style) tcell.Style {
	return style.Underline(true)
}

func AdjustStyleStrikethrough(style tcell.Style) tcell.Style {
	return style.Strikethrough(true)
}

func AdjustStyleTextColor(color tcell.Color) func(tcell.Style) tcell.Style {
	return func(style tcell.Style) tcell.Style {
		return style.Foreground(color)
	}
}

func AdjustStyleBackgroundColor(color tcell.Color) func(tcell.Style) tcell.Style {
	return func(style tcell.Style) tcell.Style {
		return style.Background(color)
	}
}

func (parser *htmlParser) getAttribute(node *html.Node, attribute string) string {
	for _, attr := range node.Attr {
		if attr.Key == attribute {
			return attr.Val
		}
	}
	return ""
}

func digits(num int) int {
	if num <= 0 {
		return 0
	}
	return int(math.Floor(math.Log10(float64(num))) + 1)
}

func (parser *htmlParser) listToTString(node *html.Node, stripLinebreak bool) *messages.HTMLEntity {
	ordered := node.Data == "ol"
	listItems := parser.nodeToEntities(node.FirstChild, stripLinebreak)
	counter := 1
	indentLength := 0
	if ordered {
		start := parser.getAttribute(node, "start")
		if len(start) > 0 {
			counter, _ = strconv.Atoi(start)
		}

		longestIndex := (counter - 1) + len(listItems)
		indentLength = digits(longestIndex)
	}
	var children []*messages.HTMLEntity
	for _, child := range listItems {
		if child.Tag != "li" {
			continue
		}
		var prefix string
		if ordered {
			indexPadding := indentLength - digits(counter)
			prefix = fmt.Sprintf("%d. %s", counter, strings.Repeat(" ", indexPadding))
		} else {
			prefix = "● "
		}
		child.Text = prefix + child.Text
		child.Block = true
		child.Indent = indentLength + 2
		children = append(children, child)
		counter++
	}
	return &messages.HTMLEntity{
		Tag:      node.Data,
		Text:     "",
		Style:    tcell.StyleDefault,
		Children: children,
		Block:    true,
		Indent:   0,
	}
}

func (parser *htmlParser) basicFormatToEntity(node *html.Node, stripLinebreak bool) *messages.HTMLEntity {
	entity := &messages.HTMLEntity{
		Tag:      node.Data,
		Children: parser.nodeToEntities(node.FirstChild, stripLinebreak),
	}
	switch node.Data {
	case "b", "strong":
		entity.AdjustStyle(AdjustStyleBold)
	case "i", "em":
		entity.AdjustStyle(AdjustStyleItalic)
	case "s", "del":
		entity.AdjustStyle(AdjustStyleStrikethrough)
	case "u", "ins":
		entity.AdjustStyle(AdjustStyleUnderline)
	case "font":
		fgColor, ok := parser.parseColor(node, "data-mx-color", "color")
		if ok {
			entity.AdjustStyle(AdjustStyleTextColor(fgColor))
		}
		bgColor, ok := parser.parseColor(node, "data-mx-bg-color", "background-color")
		if ok {
			entity.AdjustStyle(AdjustStyleBackgroundColor(bgColor))
		}
	}
	return entity
}

func (parser *htmlParser) parseColor(node *html.Node, mainName, altName string) (color tcell.Color, ok bool) {
	hex := parser.getAttribute(node, mainName)
	if len(hex) == 0 {
		hex = parser.getAttribute(node, altName)
		if len(hex) == 0 {
			return
		}
	}

	cful, err := colorful.Hex(hex)
	if err != nil {
		color2, found := ColorMap[strings.ToLower(hex)]
		if !found {
			return
		}
		cful, _ = colorful.MakeColor(color2)
	}

	r, g, b := cful.RGB255()
	return tcell.NewRGBColor(int32(r), int32(g), int32(b)), true
}

func (parser *htmlParser) headerToEntity(node *html.Node, stripLinebreak bool) *messages.HTMLEntity {
	length := int(node.Data[1] - '0')
	prefix := strings.Repeat("#", length) + " "
	return (&messages.HTMLEntity{
		Tag:      node.Data,
		Text:     prefix,
		Children: parser.nodeToEntities(node.FirstChild, stripLinebreak),
	}).AdjustStyle(AdjustStyleBold)
}

func (parser *htmlParser) blockquoteToEntity(node *html.Node, stripLinebreak bool) *messages.HTMLEntity {
	return &messages.HTMLEntity{
		Tag:      "blockquote",
		Text:     ">",
		Children: parser.nodeToEntities(node.FirstChild, stripLinebreak),
		Block:    true,
		Indent:   2,
	}
}

func (parser *htmlParser) linkToEntity(node *html.Node, stripLinebreak bool) *messages.HTMLEntity {
	entity := &messages.HTMLEntity{
		Tag:      "a",
		Children: parser.nodeToEntities(node.FirstChild, stripLinebreak),
	}
	href := parser.getAttribute(node, "href")
	if len(href) == 0 {
		return entity
	}
	match := matrixToURL.FindStringSubmatch(href)
	if len(match) == 2 {
		entity.Children = nil
		pillTarget := match[1]
		entity.Text = pillTarget
		if pillTarget[0] == '@' {
			if member := parser.room.GetMember(pillTarget); member != nil {
				entity.Text = member.Displayname
				entity.Style = entity.Style.Foreground(widget.GetHashColor(pillTarget))
			}
		}
	}
	// TODO add click action for links
	return entity
}

func (parser *htmlParser) codeblockToEntity(node *html.Node) *messages.HTMLEntity {
	return &messages.HTMLEntity{
		Tag:      "pre",
		Children: parser.nodeToEntities(node.FirstChild, false),
		Block:    true,
	}
}

func (parser *htmlParser) tagNodeToEntity(node *html.Node, stripLinebreak bool) *messages.HTMLEntity {
	switch node.Data {
	case "blockquote":
		return parser.blockquoteToEntity(node, stripLinebreak)
	case "ol", "ul":
		return parser.listToTString(node, stripLinebreak)
	case "h1", "h2", "h3", "h4", "h5", "h6":
		return parser.headerToEntity(node, stripLinebreak)
	case "br":
		return &messages.HTMLEntity{Tag: "br", Block: true}
	case "b", "strong", "i", "em", "s", "del", "u", "ins", "font":
		return parser.basicFormatToEntity(node, stripLinebreak)
	case "a":
		return parser.linkToEntity(node, stripLinebreak)
	case "pre":
		return parser.codeblockToEntity(node)
	default:
		return &messages.HTMLEntity{
			Tag:      node.Data,
			Children: parser.nodeToEntities(node.FirstChild, stripLinebreak),
			Block:    parser.isBlockTag(node.Data),
		}
	}
}

func (parser *htmlParser) singleNodeToEntity(node *html.Node, stripLinebreak bool) *messages.HTMLEntity {
	switch node.Type {
	case html.TextNode:
		if stripLinebreak {
			node.Data = strings.Replace(node.Data, "\n", "", -1)
		}
		return &messages.HTMLEntity{
			Tag:  "text",
			Text: node.Data,
		}
	case html.ElementNode:
		return parser.tagNodeToEntity(node, stripLinebreak)
	case html.DocumentNode:
		return &messages.HTMLEntity{
			Tag:      "html",
			Children: parser.nodeToEntities(node.FirstChild, stripLinebreak),
			Block:    true,
		}
	default:
		return nil
	}
}

func (parser *htmlParser) nodeToEntities(node *html.Node, stripLinebreak bool) (entities []*messages.HTMLEntity) {
	for ; node != nil; node = node.NextSibling {
		if entity := parser.singleNodeToEntity(node, stripLinebreak); entity != nil {
			entities = append(entities, entity)
		}
	}
	return
}

var BlockTags = []string{"p", "h1", "h2", "h3", "h4", "h5", "h6", "ol", "ul", "pre", "blockquote", "div", "hr", "table"}

func (parser *htmlParser) isBlockTag(tag string) bool {
	for _, blockTag := range BlockTags {
		if tag == blockTag {
			return true
		}
	}
	return false
}

func (parser *htmlParser) Parse(htmlData string) *messages.HTMLEntity {
	node, _ := html.Parse(strings.NewReader(htmlData))
	return parser.singleNodeToEntity(node, true)
}

// ParseHTMLMessage parses a HTML-formatted Matrix event into a UIMessage.
func ParseHTMLMessage(room *rooms.Room, evt *mautrix.Event, senderDisplayname string) *messages.HTMLEntity {
	htmlData := evt.Content.FormattedBody
	htmlData = strings.Replace(htmlData, "\t", "    ", -1)

	parser := htmlParser{room}
	root := parser.Parse(htmlData)
	root.Block = false

	if evt.Content.MsgType == mautrix.MsgEmote {
		root = &messages.HTMLEntity{
			Tag: "emote",
			Children: []*messages.HTMLEntity{
				{Text: "* "},
				{Text: senderDisplayname, Style: tcell.StyleDefault.Foreground(widget.GetHashColor(evt.Sender))},
				{Text: " "},
				root,
			},
		}
	}

	return root
}