/*
 * Copyright © 2014-2020 The Android Password Store Authors. All Rights Reserved.
 * SPDX-License-Identifier: GPL-3.0-only
 */
package com.zeapo.pwdstore

import android.app.Application
import android.content.Context
import android.os.Parcelable
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.lifecycle.AndroidViewModel
import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.asFlow
import androidx.lifecycle.asLiveData
import androidx.preference.PreferenceManager
import androidx.recyclerview.selection.ItemDetailsLookup
import androidx.recyclerview.selection.ItemKeyProvider
import androidx.recyclerview.selection.Selection
import androidx.recyclerview.selection.SelectionPredicates
import androidx.recyclerview.selection.SelectionTracker
import androidx.recyclerview.selection.StorageStrategy
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.ListAdapter
import androidx.recyclerview.widget.RecyclerView
import com.zeapo.pwdstore.autofill.oreo.AutofillPreferences
import com.zeapo.pwdstore.autofill.oreo.DirectoryStructure
import com.zeapo.pwdstore.utils.PasswordItem
import com.zeapo.pwdstore.utils.PasswordRepository
import java.io.File
import java.text.Collator
import java.util.Locale
import java.util.Stack
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.ExperimentalCoroutinesApi
import kotlinx.coroutines.FlowPreview
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.asFlow
import kotlinx.coroutines.flow.distinctUntilChanged
import kotlinx.coroutines.flow.drop
import kotlinx.coroutines.flow.emptyFlow
import kotlinx.coroutines.flow.filter
import kotlinx.coroutines.flow.map
import kotlinx.coroutines.flow.mapLatest
import kotlinx.coroutines.flow.toList
import kotlinx.coroutines.yield
import me.zhanghai.android.fastscroll.PopupTextProvider

private fun File.toPasswordItem(root: File) = if (isFile)
    PasswordItem.newPassword(name, this, root)
else
    PasswordItem.newCategory(name, this, root)

private fun PasswordItem.fuzzyMatch(filter: String): Int {
    var i = 0
    var j = 0
    var score = 0
    var bonus = 0
    var bonusIncrement = 0

    val toMatch = longName

    while (i < filter.length && j < toMatch.length) {
        when {
            filter[i].isWhitespace() -> i++
            filter[i].toLowerCase() == toMatch[j].toLowerCase() -> {
                i++
                bonusIncrement += 1
                bonus += bonusIncrement
                score += bonus
            }
            else -> {
                bonus = 0
                bonusIncrement = 0
            }
        }
        j++
    }
    return if (i == filter.length) score else 0
}

private val CaseInsensitiveComparator = Collator.getInstance().apply {
    strength = Collator.PRIMARY
}

private fun PasswordItem.Companion.makeComparator(
    typeSortOrder: PasswordRepository.PasswordSortOrder,
    directoryStructure: DirectoryStructure
): Comparator<PasswordItem> {
    return when (typeSortOrder) {
        PasswordRepository.PasswordSortOrder.FOLDER_FIRST -> compareBy { it.type }
        PasswordRepository.PasswordSortOrder.INDEPENDENT -> compareBy<PasswordItem>()
        PasswordRepository.PasswordSortOrder.FILE_FIRST -> compareByDescending { it.type }
    }
        .then(compareBy(nullsLast(CaseInsensitiveComparator)) {
            directoryStructure.getIdentifierFor(it.file)
        })
        .then(compareBy(nullsLast(CaseInsensitiveComparator)) {
            directoryStructure.getUsernameFor(it.file)
        })
}

val PasswordItem.stableId: String
    get() = file.absolutePath

enum class FilterMode {
    NoFilter,
    StrictDomain,
    Fuzzy
}

enum class SearchMode {
    RecursivelyInSubdirectories,
    InCurrentDirectoryOnly
}

enum class ListMode {
    FilesOnly,
    DirectoriesOnly,
    AllEntries
}

@ExperimentalCoroutinesApi
@FlowPreview
class SearchableRepositoryViewModel(application: Application) : AndroidViewModel(application) {

    companion object {

        fun generateStrictDomainRegex(domain: String): Regex? {
            // Valid domains do not contain path separators.
            if (domain.contains('/'))
                return null
            // Matches the start of a path component, which is either the start of the
            // string or a path separator.
            val prefix = """(?:^|/)"""
            val escapedFilter = Regex.escape(domain.replace("/", ""))
            // Matches either the filter literally or a strict subdomain of the filter term.
            // We allow a lot of freedom in what a subdomain is, as long as it is not an
            // email address.
            val subdomain = """(?:(?:[^/@]+\.)?$escapedFilter)"""
            // Matches the end of a path component, which is either the literal ".gpg" or a
            // path separator.
            val suffix = """(?:\.gpg|/)"""
            // Match any relative path with a component that is a subdomain of the filter.
            return Regex(prefix + subdomain + suffix)
        }
    }

    private var _updateCounter = 0
    private val updateCounter: Int
        get() = _updateCounter

    private fun forceUpdateOnNextSearchAction() {
        _updateCounter++
    }

    private val root
        get() = PasswordRepository.getRepositoryDirectory(getApplication())
    private val settings = PreferenceManager.getDefaultSharedPreferences(getApplication())
    private val showHiddenDirs
        get() = settings.getBoolean("show_hidden_folders", false)
    private val defaultSearchMode
        get() = if (settings.getBoolean("filter_recursively", true)) {
        SearchMode.RecursivelyInSubdirectories
    } else {
        SearchMode.InCurrentDirectoryOnly
    }

    private val typeSortOrder
        get() = PasswordRepository.PasswordSortOrder.getSortOrder(settings)
    private val directoryStructure
        get() = AutofillPreferences.directoryStructure(getApplication())
    private val itemComparator
        get() = PasswordItem.makeComparator(typeSortOrder, directoryStructure)

    private data class SearchAction(
        val baseDirectory: File,
        val filter: String,
        val filterMode: FilterMode,
        val searchMode: SearchMode,
        val listMode: ListMode,
        // This counter can be increased to force a reexecution of the search action even if all
        // other arguments are left unchanged.
        val updateCounter: Int
    )

    private fun makeSearchAction(
        baseDirectory: File,
        filter: String,
        filterMode: FilterMode,
        searchMode: SearchMode,
        listMode: ListMode
    ): SearchAction {
        return SearchAction(
            baseDirectory = baseDirectory,
            filter = filter,
            filterMode = filterMode,
            searchMode = searchMode,
            listMode = listMode,
            updateCounter = updateCounter
        )
    }

    private fun updateSearchAction(action: SearchAction) =
        action.copy(updateCounter = updateCounter)

    private val searchAction = MutableLiveData(
        makeSearchAction(
            baseDirectory = root,
            filter = "",
            filterMode = FilterMode.NoFilter,
            searchMode = SearchMode.InCurrentDirectoryOnly,
            listMode = ListMode.AllEntries
        )
    )
    private val searchActionFlow = searchAction.asFlow().distinctUntilChanged()

    data class SearchResult(val passwordItems: List<PasswordItem>, val isFiltered: Boolean)

    val searchResult = searchActionFlow
        .mapLatest { searchAction ->
            val listResultFlow = when (searchAction.searchMode) {
                SearchMode.RecursivelyInSubdirectories -> listFilesRecursively(searchAction.baseDirectory)
                SearchMode.InCurrentDirectoryOnly -> listFiles(searchAction.baseDirectory)
            }
            val prefilteredResultFlow = when (searchAction.listMode) {
                ListMode.FilesOnly -> listResultFlow.filter { it.isFile }
                ListMode.DirectoriesOnly -> listResultFlow.filter { it.isDirectory }
                ListMode.AllEntries -> listResultFlow
            }
            val filterModeToUse =
                if (searchAction.filter == "") FilterMode.NoFilter else searchAction.filterMode
            val passwordList = when (filterModeToUse) {
                FilterMode.NoFilter -> {
                    prefilteredResultFlow
                        .map { it.toPasswordItem(root) }
                        .toList()
                        .sortedWith(itemComparator)
                }
                FilterMode.StrictDomain -> {
                    check(searchAction.listMode == ListMode.FilesOnly) { "Searches with StrictDomain search mode can only list files" }
                    val regex = generateStrictDomainRegex(searchAction.filter)
                    if (regex != null) {
                        prefilteredResultFlow
                            .filter { absoluteFile ->
                                regex.containsMatchIn(absoluteFile.relativeTo(root).path)
                            }
                            .map { it.toPasswordItem(root) }
                            .toList()
                            .sortedWith(itemComparator)
                    } else {
                        emptyList()
                    }
                }
                FilterMode.Fuzzy -> {
                    prefilteredResultFlow
                        .map {
                            val item = it.toPasswordItem(root)
                            Pair(item.fuzzyMatch(searchAction.filter), item)
                        }
                        .filter { it.first > 0 }
                        .toList()
                        .sortedWith(
                            compareByDescending<Pair<Int, PasswordItem>> { it.first }.thenBy(
                                itemComparator
                            ) { it.second })
                        .map { it.second }
                }
            }
            SearchResult(passwordList, isFiltered = searchAction.filterMode != FilterMode.NoFilter)
        }.asLiveData(Dispatchers.IO)

    private fun shouldTake(file: File) = with(file) {
        if (isDirectory) {
            !isHidden || showHiddenDirs
        } else {
            !isHidden && file.extension == "gpg"
        }
    }

    private fun listFiles(dir: File): Flow<File> {
        return dir.listFiles { file -> shouldTake(file) }?.asFlow() ?: emptyFlow()
    }

    private fun listFilesRecursively(dir: File): Flow<File> {
        return dir
            .walkTopDown().onEnter { file -> shouldTake(file) }
            .asFlow()
            // Skip the root directory
            .drop(1)
            .map {
                yield()
                it
            }
            .filter { file -> shouldTake(file) }
    }

    private val _currentDir = MutableLiveData(root)
    val currentDir = _currentDir as LiveData<File>

    data class NavigationStackEntry(val dir: File, val recyclerViewState: Parcelable?)

    private val navigationStack = Stack<NavigationStackEntry>()

    fun navigateTo(
        newDirectory: File = root,
        listMode: ListMode = ListMode.AllEntries,
        recyclerViewState: Parcelable? = null,
        pushPreviousLocation: Boolean = true
    ) {
        require(newDirectory.isDirectory) { "Can only navigate to a directory" }
        if (pushPreviousLocation) {
            navigationStack.push(NavigationStackEntry(_currentDir.value!!, recyclerViewState))
        }
        searchAction.postValue(
            makeSearchAction(
                filter = "",
                baseDirectory = newDirectory,
                filterMode = FilterMode.NoFilter,
                searchMode = SearchMode.InCurrentDirectoryOnly,
                listMode = listMode
            )
        )
        _currentDir.postValue(newDirectory)
    }

    val canNavigateBack
        get() = navigationStack.isNotEmpty()

    /**
     * Navigate back to the last location on the [navigationStack] and restore a cached scroll
     * position if possible.
     *
     * Returns the old RecyclerView's LinearLayoutManager state as a [Parcelable] if it was cached.
     */
    fun navigateBack(): Parcelable? {
        if (!canNavigateBack) return null
        val (oldDir, oldRecyclerViewState) = navigationStack.pop()
        navigateTo(oldDir, pushPreviousLocation = false)
        return oldRecyclerViewState
    }

    fun reset() {
        navigationStack.clear()
        forceUpdateOnNextSearchAction()
        navigateTo(pushPreviousLocation = false)
    }

    fun search(
        filter: String,
        baseDirectory: File? = null,
        filterMode: FilterMode = FilterMode.Fuzzy,
        searchMode: SearchMode? = null,
        listMode: ListMode = ListMode.AllEntries
    ) {
        require(baseDirectory?.isDirectory != false) { "Can only search in a directory" }
        searchAction.postValue(
            makeSearchAction(
                filter = filter,
                baseDirectory = baseDirectory ?: _currentDir.value!!,
                filterMode = filterMode,
                searchMode = searchMode ?: defaultSearchMode,
                listMode = listMode
            )
        )
    }

    fun forceRefresh() {
        forceUpdateOnNextSearchAction()
        searchAction.postValue(updateSearchAction(searchAction.value!!))
    }
}

private object PasswordItemDiffCallback : DiffUtil.ItemCallback<PasswordItem>() {
    override fun areItemsTheSame(oldItem: PasswordItem, newItem: PasswordItem) =
        oldItem.file.absolutePath == newItem.file.absolutePath

    override fun areContentsTheSame(oldItem: PasswordItem, newItem: PasswordItem) = oldItem == newItem
}

open class SearchableRepositoryAdapter<T : RecyclerView.ViewHolder>(
    private val layoutRes: Int,
    private val viewHolderCreator: (view: View) -> T,
    private val viewHolderBinder: T.(item: PasswordItem) -> Unit
) : ListAdapter<PasswordItem, T>(PasswordItemDiffCallback), PopupTextProvider {

    fun <T : ItemDetailsLookup<String>> makeSelectable(
        recyclerView: RecyclerView,
        itemDetailsLookupCreator: (recyclerView: RecyclerView) -> T
    ) {
        selectionTracker = SelectionTracker.Builder(
            "SearchableRepositoryAdapter",
            recyclerView,
            itemKeyProvider,
            itemDetailsLookupCreator(recyclerView),
            StorageStrategy.createStringStorage()
        ).withSelectionPredicate(SelectionPredicates.createSelectAnything()).build().apply {
            addObserver(object : SelectionTracker.SelectionObserver<String>() {
                override fun onSelectionChanged() {
                    this@SearchableRepositoryAdapter.onSelectionChangedListener?.invoke(
                        requireSelectionTracker().selection
                    )
                }
            })
        }
    }

    private var onItemClickedListener: ((holder: T, item: PasswordItem) -> Unit)? = null
    open fun onItemClicked(listener: (holder: T, item: PasswordItem) -> Unit): SearchableRepositoryAdapter<T> {
        check(onItemClickedListener == null) { "Only a single listener can be registered for onItemClicked" }
        onItemClickedListener = listener
        return this
    }

    private var onSelectionChangedListener: ((selection: Selection<String>) -> Unit)? = null
    open fun onSelectionChanged(listener: (selection: Selection<String>) -> Unit): SearchableRepositoryAdapter<T> {
        check(onSelectionChangedListener == null) { "Only a single listener can be registered for onSelectionChanged" }
        onSelectionChangedListener = listener
        return this
    }

    private val itemKeyProvider = object : ItemKeyProvider<String>(SCOPE_MAPPED) {
        override fun getKey(position: Int) = getItem(position).stableId

        override fun getPosition(key: String) =
            (0 until itemCount).firstOrNull { getItem(it).stableId == key }
                ?: RecyclerView.NO_POSITION
    }

    private var selectionTracker: SelectionTracker<String>? = null
    fun requireSelectionTracker() = selectionTracker!!

    private val selectedFiles
        get() = requireSelectionTracker().selection.map { File(it) }
    fun getSelectedItems(context: Context): List<PasswordItem> {
        val root = PasswordRepository.getRepositoryDirectory(context)
        return selectedFiles.map { it.toPasswordItem(root) }
    }

    final override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): T {
        val view = LayoutInflater.from(parent.context)
            .inflate(layoutRes, parent, false)
        return viewHolderCreator(view)
    }

    final override fun onBindViewHolder(holder: T, position: Int) {
        val item = getItem(position)
        holder.apply {
            viewHolderBinder.invoke(this, item)
            selectionTracker?.let { itemView.isSelected = it.isSelected(item.stableId) }
            itemView.setOnClickListener {
                // Do not emit custom click events while the user is selecting items.
                if (selectionTracker?.hasSelection() != true)
                    onItemClickedListener?.invoke(holder, item)
            }
        }
    }

    final override fun getPopupText(position: Int): String {
        return getItem(position).name[0].toString().toUpperCase(Locale.getDefault())
    }
}