package com.looker.droidify.database

import android.content.Context
import android.database.Cursor
import android.os.CancellationSignal
import android.os.OperationCanceledException
import androidx.loader.content.AsyncTaskLoader

class QueryLoader(context: Context, private val query: (CancellationSignal) -> Cursor?) :
    AsyncTaskLoader<Cursor>(context) {
    private val observer = ForceLoadContentObserver()
    private var cancellationSignal: CancellationSignal? = null
    private var cursor: Cursor? = null

    override fun loadInBackground(): Cursor? {
        val cancellationSignal = synchronized(this) {
            if (isLoadInBackgroundCanceled) {
                throw OperationCanceledException()
            }
            val cancellationSignal = CancellationSignal()
            this.cancellationSignal = cancellationSignal
            cancellationSignal
        }
        try {
            val cursor = query(cancellationSignal)
            if (cursor != null) {
                try {
                    cursor.count // Ensure the cursor window is filled
                    cursor.registerContentObserver(observer)
                } catch (e: Exception) {
                    cursor.close()
                    throw e
                }
            }
            return cursor
        } finally {
            synchronized(this) {
                this.cancellationSignal = null
            }
        }
    }

    override fun cancelLoadInBackground() {
        super.cancelLoadInBackground()

        synchronized(this) {
            cancellationSignal?.cancel()
        }
    }

    override fun deliverResult(data: Cursor?) {
        if (isReset) {
            data?.close()
        } else {
            val oldCursor = cursor
            cursor = data
            if (isStarted) {
                super.deliverResult(data)
            }
            if (oldCursor != data) {
                oldCursor.closeIfNeeded()
            }
        }
    }

    override fun onStartLoading() {
        cursor?.let(this::deliverResult)
        if (takeContentChanged() || cursor == null) {
            forceLoad()
        }
    }

    override fun onStopLoading() {
        cancelLoad()
    }

    override fun onCanceled(data: Cursor?) {
        data.closeIfNeeded()
    }

    override fun onReset() {
        super.onReset()

        stopLoading()
        cursor.closeIfNeeded()
        cursor = null
    }

    private fun Cursor?.closeIfNeeded() {
        if (this != null && !isClosed) {
            close()
        }
    }
}