// gomuks - A terminal Matrix client written in Go.
// Copyright (C) 2018 Tulir Asokan
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU 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 General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package widget

import (
	"fmt"
	"time"

	"github.com/gdamore/tcell"
	"github.com/mattn/go-runewidth"
	"maunium.net/go/gomuks/ui/types"
	"maunium.net/go/tview"
)

type MessageView struct {
	*tview.Box

	ScrollOffset    int
	MaxSenderWidth  int
	DateFormat      string
	TimestampFormat string
	TimestampWidth  int
	Separator       rune
	LoadingMessages bool

	widestSender int
	prevWidth    int
	prevHeight   int

	messageIDs map[string]bool
	messages   []*types.Message

	textBuffer []string
	metaBuffer []types.MessageMeta
}

func NewMessageView() *MessageView {
	return &MessageView{
		Box:             tview.NewBox(),
		MaxSenderWidth:  20,
		DateFormat:      "January _2, 2006",
		TimestampFormat: "15:04:05",
		TimestampWidth:  8,
		Separator:       '|',
		ScrollOffset:    0,

		messages:   make([]*types.Message, 0),
		messageIDs: make(map[string]bool),
		textBuffer: make([]string, 0),
		metaBuffer: make([]types.MessageMeta, 0),

		widestSender: 5,
		prevWidth:    -1,
		prevHeight:   -1,
	}
}

func (view *MessageView) NewMessage(id, sender, text string, timestamp time.Time) *types.Message {
	return types.NewMessage(id, sender, text,
		timestamp.Format(view.TimestampFormat),
		timestamp.Format(view.DateFormat),
		GetHashColor(sender))
}

func (view *MessageView) updateWidestSender(sender string) {
	if len(sender) > view.widestSender {
		view.widestSender = len(sender)
		if view.widestSender > view.MaxSenderWidth {
			view.widestSender = view.MaxSenderWidth
		}
	}
}

const (
	AppendMessage  = iota
	PrependMessage
)

func (view *MessageView) AddMessage(message *types.Message, direction int) {
	_, messageExists := view.messageIDs[message.ID]
	if messageExists {
		return
	}

	view.updateWidestSender(message.Sender)

	_, _, width, _ := view.GetInnerRect()
	width -= view.TimestampWidth + TimestampSenderGap + view.widestSender + SenderMessageGap
	message.CalculateBuffer(width)

	if direction == AppendMessage {
		if view.ScrollOffset > 0 {
			view.ScrollOffset += len(message.Buffer)
		}
		view.messages = append(view.messages, message)
	} else if direction == PrependMessage {
		view.messages = append([]*types.Message{message}, view.messages...)
	}

	view.messageIDs[message.ID] = true
	view.appendBuffer(message)
}

func (view *MessageView) recalculateMessageBuffers() {
	_, _, width, _ := view.GetInnerRect()
	width -= view.TimestampWidth + TimestampSenderGap + view.widestSender + SenderMessageGap
	if width != view.prevWidth {
		for _, message := range view.messages {
			message.CalculateBuffer(width)
		}
		view.prevWidth = width
	}
}

func (view *MessageView) appendBuffer(message *types.Message) {
	if len(view.metaBuffer) > 0 {
		prevMeta := view.metaBuffer[len(view.metaBuffer)-1]
		if prevMeta != nil && prevMeta.GetDate() != message.Date {
			view.textBuffer = append(view.textBuffer, fmt.Sprintf("Date changed to %s", message.Date))
			view.metaBuffer = append(view.metaBuffer, &types.BasicMeta{TextColor: tcell.ColorGreen})
		}
	}

	view.textBuffer = append(view.textBuffer, message.Buffer...)
	for range message.Buffer {
		view.metaBuffer = append(view.metaBuffer, message)
	}
}

func (view *MessageView) recalculateBuffer() {
	_, _, width, height := view.GetInnerRect()
	view.textBuffer = make([]string, 0)
	view.metaBuffer = make([]types.MessageMeta, 0)

	if height != view.prevHeight || width != view.prevWidth {
		for _, message := range view.messages {
			view.appendBuffer(message)
		}
		view.prevHeight = height
	}
}

const PaddingAtTop = 5

func (view *MessageView) MoveUp(page bool) {
	_, _, _, height := view.GetInnerRect()

	totalHeight := len(view.textBuffer)
	if view.ScrollOffset >= totalHeight-height {
		// If the user is at the top and presses page up again, add a bit of blank space.
		if page {
			view.ScrollOffset = totalHeight - height + PaddingAtTop
		} else if view.ScrollOffset < totalHeight-height+PaddingAtTop {
			view.ScrollOffset++
		}
		return
	}

	if page {
		view.ScrollOffset += height / 2
	} else {
		view.ScrollOffset++
	}
	if view.ScrollOffset > totalHeight-height {
		view.ScrollOffset = totalHeight - height
	}
}

func (view *MessageView) IsAtTop() bool {
	_, _, _, height := view.GetInnerRect()
	totalHeight := len(view.textBuffer)
	return view.ScrollOffset >= totalHeight-height+PaddingAtTop
}

func (view *MessageView) MoveDown(page bool) {
	_, _, _, height := view.GetInnerRect()
	if page {
		view.ScrollOffset -= height / 2
	} else {
		view.ScrollOffset--
	}
	if view.ScrollOffset < 0 {
		view.ScrollOffset = 0
	}
}

func (view *MessageView) writeLine(screen tcell.Screen, line string, x, y int, color tcell.Color) {
	offsetX := 0
	for _, ch := range line {
		chWidth := runewidth.RuneWidth(ch)
		if chWidth == 0 {
			continue
		}

		for localOffset := 0; localOffset < chWidth; localOffset++ {
			screen.SetContent(x+offsetX+localOffset, y, ch, nil, tcell.StyleDefault.Foreground(color))
		}
		offsetX += chWidth
	}
}

func (view *MessageView) writeLineRight(screen tcell.Screen, line string, x, y, maxWidth int, color tcell.Color) {
	offsetX := maxWidth - runewidth.StringWidth(line)
	if offsetX < 0 {
		offsetX = 0
	}
	for _, ch := range line {
		chWidth := runewidth.RuneWidth(ch)
		if chWidth == 0 {
			continue
		}

		for localOffset := 0; localOffset < chWidth; localOffset++ {
			screen.SetContent(x+offsetX+localOffset, y, ch, nil, tcell.StyleDefault.Foreground(color))
		}
		offsetX += chWidth
		if offsetX > maxWidth {
			break
		}
	}
}

const (
	TimestampSenderGap = 1
	SenderSeparatorGap = 1
	SenderMessageGap   = 3
)

func (view *MessageView) Draw(screen tcell.Screen) {
	view.Box.Draw(screen)

	x, y, _, height := view.GetInnerRect()
	view.recalculateMessageBuffers()
	view.recalculateBuffer()

	if len(view.textBuffer) == 0 {
		view.writeLine(screen, "It's quite empty in here.", x, y+height, tcell.ColorDefault)
		return
	}

	usernameOffsetX := view.TimestampWidth + TimestampSenderGap
	messageOffsetX := usernameOffsetX + view.widestSender + SenderMessageGap
	separatorX := x + usernameOffsetX + view.widestSender + SenderSeparatorGap
	for separatorY := y; separatorY < y+height; separatorY++ {
		screen.SetContent(separatorX, separatorY, view.Separator, nil, tcell.StyleDefault)
	}

	var prevMeta types.MessageMeta
	indexOffset := len(view.textBuffer) - view.ScrollOffset - height
	if indexOffset <= -PaddingAtTop {
		message := "Scroll up to load more messages."
		if view.LoadingMessages {
			message = "Loading more messages..."
		}
		view.writeLine(screen, message, x+messageOffsetX, y, tcell.ColorGreen)
	}
	for line := 0; line < height; line++ {
		index := indexOffset + line
		if index < 0 {
			continue
		} else if index > len(view.textBuffer) {
			break
		}
		text, meta := view.textBuffer[index], view.metaBuffer[index]
		if meta != prevMeta {
			if len(meta.GetTimestamp()) > 0 {
				view.writeLine(screen, meta.GetTimestamp(), x, y+line, meta.GetTimestampColor())
			}
			if len(meta.GetSender()) > 0 && (prevMeta == nil || meta.GetSender() != prevMeta.GetSender()) {
				view.writeLineRight(
					screen, meta.GetSender(),
					x+usernameOffsetX, y+line,
					view.widestSender, meta.GetSenderColor())
			}
			prevMeta = meta
		}
		view.writeLine(screen, text, x+messageOffsetX, y+line, meta.GetTextColor())
	}
}