fedilab-Android-App/app/src/main/java/app/fedilab/android/helper/RecyclerViewThreadLines.kt

package app.fedilab.android.helper
/*
 * This file is a part of Fedilab
 *
 * 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.
 *
 * Fedilab 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 Fedilab; if not,
 * see <http://www.gnu.org/licenses>. */

import android.content.Context
import android.content.res.Resources
import android.graphics.*
import android.view.View
import androidx.core.content.res.ResourcesCompat
import androidx.preference.PreferenceManager
import androidx.recyclerview.widget.DividerItemDecoration
import androidx.recyclerview.widget.RecyclerView
import app.fedilab.android.R
import app.fedilab.android.helper.RecyclerViewThreadLines.LineInfo
import app.fedilab.android.client.entities.api.Context as StatusContext

class RecyclerViewThreadLines(context: Context, private val lineInfoList: List<LineInfo>) : DividerItemDecoration(context, VERTICAL) {
    private val lineColors = threadLineColors.map { ResourcesCompat.getColor(context.resources, it, context.theme) }
    private val dashPathEffect = DashPathEffect(floatArrayOf(3.dpToPx, 3.dpToPx), 0F)
    private val borderColor = lineColors[0]
    private val commonPaint = Paint().apply {
        isDither = false
        strokeWidth = 1.5F.dpToPx
        strokeCap = Paint.Cap.BUTT
        strokeJoin = Paint.Join.MITER
        color = borderColor
    }
    private val maxLevel = lineColors.size
    private val fontScale = PreferenceManager.getDefaultSharedPreferences(context).getFloat(context.getString(R.string.SET_FONT_SCALE), 1.1f).toInt()
    private val baseMargin: Int = 6.dpToPx.toInt()
    private val margin: Int = baseMargin * fontScale

    override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) {
        val position = parent.getChildAdapterPosition(view)
        if (position < 0 || position >= lineInfoList.size) return
        val level = lineInfoList[position].level
        val startMargin = margin * level + margin * fontScale
        if (parent.layoutDirection == View.LAYOUT_DIRECTION_LTR) outRect.left = startMargin else outRect.right = startMargin
    }

    override fun onDraw(c: Canvas, parent: RecyclerView, state: RecyclerView.State) {
        val childCount = parent.childCount
        for (i in 0 until childCount) {
            val view = parent.getChildAt(i)
            val position = parent.getChildAdapterPosition(view)
            if (position < 0 || position >= lineInfoList.size) return
            val lineInfo = lineInfoList[position]
            val level = lineInfo.level

            for (j in 0..level) {
                val lineMargin = margin * j.coerceAtLeast(1) + 3.dpToPx
                val lineStart = if (parent.layoutDirection == View.LAYOUT_DIRECTION_LTR) lineMargin else c.width - lineMargin
                var lineTop: Float = (view.top - baseMargin).toFloat()
                val paint = Paint(commonPaint)
                paint.color = if (j > 0) lineColors[j - 1] else Color.GRAY

                // draw lines for below statuses
                if (j != level && lineInfo.lines.contains(j))
                    c.drawLine(lineStart, lineTop, lineStart, view.bottom.toFloat(), paint)

                // draw vertical line for current statuses
                if (j == level && position != 0) {
                    // top the line starts at the middle of the above status
                    if (i > 0) lineTop -= parent.getChildAt(i - 1).height / 2 - 1 // '- 1' is to prevent overlapping with above horizontal line

                    // bottom of the line ends at the middle of the current status
                    var lineBottom = view.bottom.toFloat() - view.height / 2

                    // if below status has a full line for current level, extend the line to the bottom
                    if (position < lineInfoList.lastIndex && lineInfoList[position + 1].lines.contains(level) && j != maxLevel)
                        lineBottom = view.bottom.toFloat()

                    // if level is max, use a dashed line
                    if (j == maxLevel) paint.pathEffect = dashPathEffect

                    c.drawLine(lineStart, lineTop, lineStart, lineBottom, paint)
                }

                // draw horizontal line for current statuses
                if (j == level) {
                    lineTop = view.bottom.toFloat() - view.height / 2
                    val lineEnd = lineStart + margin * 2
                    c.drawLine(lineStart - 1, lineTop, lineEnd, lineTop, paint) // 'lineStart - 1' is to properly connect with the vertical line
                }
            }
        }
    }

    data class LineInfo(var level: Int, var lines: List<Int>)

    private val Int.dpToPx: Float
        get() = this * Resources.getSystem().displayMetrics.density

    private val Float.dpToPx: Float
        get() = this * Resources.getSystem().displayMetrics.density

    companion object {
        val threadLineColors = listOf(R.color.decoration_1, R.color.decoration_2, R.color.decoration_3, R.color.decoration_4, R.color.decoration_5)
    }
}

fun getThreadDecorationInfo(statusContext: StatusContext): MutableList<LineInfo> {
    val lineInfoList = mutableListOf<LineInfo>()
    repeat(statusContext.ancestors.size) { lineInfoList.add(LineInfo(0, listOf(0))) }
    lineInfoList.add(LineInfo(0, listOf(0)))
    val descendantsLineInfoList = List(statusContext.descendants.size) { LineInfo(0, listOf()) }
    for (i in statusContext.descendants.indices) {
        statusContext.descendants[i].let { status ->
            var level = 0
            if (status.in_reply_to_id != null) {
                var replyToId: String? = status.in_reply_to_id
                while (replyToId != null && level < RecyclerViewThreadLines.threadLineColors.size) {
                    level += 1
                    replyToId = statusContext.descendants.firstOrNull { it.id == replyToId }?.in_reply_to_id
                }
            }
            descendantsLineInfoList[i].level = level
        }
    }
    for (i in descendantsLineInfoList.indices.reversed()) {
        val lines: MutableList<Int> = mutableListOf()
        val lineInfo = descendantsLineInfoList[i]
        lines.add(lineInfo.level)
        if (i < descendantsLineInfoList.lastIndex) {
            val belowLineInfo = descendantsLineInfoList[i + 1]
            lines.addAll(belowLineInfo.lines.filter { it < lineInfo.level })
        }
        descendantsLineInfoList[i].lines = lines
    }

    lineInfoList.addAll(descendantsLineInfoList)
    return lineInfoList
}