package com.rssuper.services

import com.rssuper.parsing.FeedParser
import com.rssuper.parsing.ParseResult
import okhttp3.Call
import okhttp3.EventListener
import okhttp3.OkHttpClient
import okhttp3.Request
import okhttp3.Response
import java.io.IOException
import java.util.concurrent.TimeUnit

class FeedFetcher(
    private val timeoutMs: Long = 15000,
    private val maxRetries: Int = 3,
    private val baseRetryDelayMs: Long = 1000
) {
    private val client: OkHttpClient

    init {
        val builder = OkHttpClient.Builder()
            .connectTimeout(timeoutMs, TimeUnit.MILLISECONDS)
            .readTimeout(timeoutMs, TimeUnit.MILLISECONDS)
            .writeTimeout(timeoutMs, TimeUnit.MILLISECONDS)

        builder.eventListenerFactory { call -> TimeoutEventListener(call) }

        client = builder.build()
    }

    fun fetch(
        url: String,
        httpAuth: HTTPAuthCredentials? = null,
        ifNoneMatch: String? = null,
        ifModifiedSince: String? = null
    ): NetworkResult<FetchResult> {
        var lastError: Throwable? = null

        for (attempt in 1..maxRetries) {
            val result = fetchSingleAttempt(url, httpAuth, ifNoneMatch, ifModifiedSince)

            when (result) {
                is NetworkResult.Success -> return result
                is NetworkResult.Failure -> {
                    lastError = result.error
                    if (attempt < maxRetries) {
                        val delay = calculateBackoffDelay(attempt)
                        Thread.sleep(delay)
                    }
                }
            }
        }

        return NetworkResult.Failure(lastError ?: NetworkError.Unknown())
    }

    fun fetchAndParse(url: String, httpAuth: HTTPAuthCredentials? = null): NetworkResult<ParseResult> {
        val fetchResult = fetch(url, httpAuth)
        
        return fetchResult.flatMap { result ->
            try {
                val parseResult = FeedParser.parse(result.feedXml, url)
                NetworkResult.Success(parseResult)
            } catch (e: Exception) {
                NetworkResult.Failure(NetworkError.Unknown(e))
            }
        }
    }

    private fun fetchSingleAttempt(
        url: String,
        httpAuth: HTTPAuthCredentials? = null,
        ifNoneMatch: String? = null,
        ifModifiedSince: String? = null
    ): NetworkResult<FetchResult> {
        val requestBuilder = Request.Builder()
            .url(url)
            .addHeader("User-Agent", "RSSuper/1.0")

        ifNoneMatch?.let { requestBuilder.addHeader("If-None-Match", it) }
        ifModifiedSince?.let { requestBuilder.addHeader("If-Modified-Since", it) }

        httpAuth?.let {
            requestBuilder.addHeader("Authorization", it.toCredentials())
        }

        val request = requestBuilder.build()

        return try {
            val response = client.newCall(request).execute()
            handleResponse(response, url)
        } catch (e: IOException) {
            NetworkResult.Failure(NetworkError.Unknown(e))
        } catch (e: Exception) {
            NetworkResult.Failure(NetworkError.Unknown(e))
        }
    }

    private fun handleResponse(response: Response, url: String): NetworkResult<FetchResult> {
        try {
            val body = response.body

            return when (response.code) {
                200 -> {
                    if (body != null) {
                        NetworkResult.Success(FetchResult.fromResponse(response, url, response.cacheResponse != null))
                    } else {
                        NetworkResult.Failure(NetworkError.Http(response.code, "Empty response body"))
                    }
                }
                304 -> {
                    if (body != null) {
                        NetworkResult.Success(FetchResult.fromResponse(response, url, true))
                    } else {
                        NetworkResult.Failure(NetworkError.Http(response.code, "Empty response body"))
                    }
                }
                in 400..499 -> {
                    NetworkResult.Failure(NetworkError.Http(response.code, "Client error: ${response.message}"))
                }
                in 500..599 -> {
                    NetworkResult.Failure(NetworkError.Http(response.code, "Server error: ${response.message}"))
                }
                else -> {
                    NetworkResult.Failure(NetworkError.Http(response.code, "Unexpected status code: ${response.code}"))
                }
            }
        } finally {
            response.close()
        }
    }

    private fun calculateBackoffDelay(attempt: Int): Long {
        var delay = baseRetryDelayMs
        for (i in 1 until attempt) {
            delay *= 2
        }
        return delay
    }

    private class TimeoutEventListener(private val call: Call) : EventListener() {
        override fun callStart(call: Call) {
        }

        override fun callEnd(call: Call) {
        }

        override fun callFailed(call: Call, ioe: IOException) {
        }
    }

    sealed class NetworkResult<out T> {
        data class Success<T>(val value: T) : NetworkResult<T>()
        data class Failure<T>(val error: Throwable) : NetworkResult<T>()

        fun isSuccess(): Boolean = this is Success
        fun isFailure(): Boolean = this is Failure

        fun getOrNull(): T? = when (this) {
            is Success -> value
            is Failure -> null
        }

        fun <R> map(transform: (T) -> R): NetworkResult<R> = when (this) {
            is Success -> Success(transform(value))
            is Failure -> Failure(error)
        }

        fun <R> flatMap(transform: (T) -> NetworkResult<R>): NetworkResult<R> = when (this) {
            is Success -> transform(value)
            is Failure -> Failure(error)
        }
    }
}