package com.peachpasswords.ui.components

import android.content.Context
import android.graphics.Bitmap
import android.graphics.BitmapFactory
import com.peachpasswords.shared.extractDomain
import dagger.hilt.android.qualifiers.ApplicationContext
import java.io.File
import java.net.IDN
import java.util.Collections
import java.util.Locale
import java.util.concurrent.ConcurrentHashMap
import java.util.concurrent.TimeUnit
import javax.inject.Inject
import javax.inject.Singleton
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.SupervisorJob
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.launch
import kotlinx.coroutines.withContext
import okhttp3.OkHttpClient
import okhttp3.Request

/**
 * U1: real site favicons, offline-first with a disk cache.
 *
 * Source: DuckDuckGo's icon API (`icons.duckduckgo.com/ip3/{domain}.ico`) —
 * June's explicit choice (2026-08-03), superseding the v2.10.11
 * direct-from-site strategy. One small request per domain; the domain name is
 * the only thing transmitted. Failures negative-cache for [MISS_RETRY_MS] and
 * fall back to initials.
 */
@Singleton
class Favicons @Inject constructor(@ApplicationContext private val context: Context) {

    private val client: OkHttpClient by lazy {
        OkHttpClient.Builder()
            .connectTimeout(8, TimeUnit.SECONDS)
            .readTimeout(8, TimeUnit.SECONDS)
            .followRedirects(true)
            .build()
    }
    private val dir: File by lazy { File(context.cacheDir, "favicons").apply { mkdirs() } }
    private val fetchDispatcher = Dispatchers.IO.limitedParallelism(2)
    private val scope = CoroutineScope(SupervisorJob() + fetchDispatcher)
    private val inFlight = Collections.newSetFromMap(ConcurrentHashMap<String, Boolean>())

    /** Bumped whenever any favicon lands on disk; composables key recomposition on it. */
    private val _revision = MutableStateFlow(0)
    val revision: StateFlow<Int> = _revision

    private fun fileFor(domain: String): File? = faviconCacheFile(dir, domain, ".png")
    private fun missFileFor(domain: String): File? = faviconCacheFile(dir, domain, ".miss")

    fun bitmap(domain: String, sizePx: Int): Bitmap? = runCatching {
        val file = fileFor(domain) ?: return null
        if (!file.exists()) return null
        val bounds = BitmapFactory.Options().apply { inJustDecodeBounds = true }
        BitmapFactory.decodeFile(file.absolutePath, bounds)
        if (bounds.outWidth <= 0 || bounds.outHeight <= 0) return null
        var sample = 1
        while (bounds.outWidth / sample > sizePx * 2 && bounds.outHeight / sample > sizePx * 2) sample *= 2
        BitmapFactory.decodeFile(file.absolutePath, BitmapFactory.Options().apply { inSampleSize = sample })
    }.getOrNull()

    /** Fire-and-forget fetches for every domain missing from the cache. */
    fun prefetch(domains: List<String>) {
        for (domain in domains.mapNotNull(::canonicalFaviconDomain).distinct()) {
            if (!needsFetch(domain) || !inFlight.add(domain)) continue
            scope.launch {
                try {
                    fetch(domain)
                } finally {
                    inFlight.remove(domain)
                }
            }
        }
    }

    private fun needsFetch(domain: String): Boolean {
        if (fileFor(domain)?.exists() == true) return false
        val miss = missFileFor(domain) ?: return false
        return !miss.exists() || System.currentTimeMillis() - miss.lastModified() >= MISS_RETRY_MS
    }

    internal suspend fun fetch(domain: String) = withContext(Dispatchers.IO) {
        val canonicalDomain = canonicalFaviconDomain(domain) ?: return@withContext
        val bytes = fetchUrl("https://icons.duckduckgo.com/ip3/$canonicalDomain.ico")
            ?.let(::decodeOrUnwrapIco)
        val target = fileFor(canonicalDomain) ?: return@withContext
        val saved = bytes != null && saveScaledPng(bytes, target)
        if (saved) {
            _revision.value++
        } else {
            runCatching { missFileFor(canonicalDomain)?.createNewFile() }
        }
    }

    /** GET with a bounded read; returns null on any failure or oversize body. */
    private fun fetchUrl(url: String, maxBytes: Long = MAX_ICON_BYTES): ByteArray? = runCatching {
        val request = Request.Builder().url(url).header("User-Agent", "Peach/1.0").build()
        client.newCall(request).execute().use { response ->
            if (!response.isSuccessful) return@runCatching null
            val body = response.body ?: return@runCatching null
            val source = body.source()
            source.request(maxBytes + 1)
            if (source.buffer.size > maxBytes) null else source.readByteArray()
        }
    }.getOrNull()

    private fun saveScaledPng(bytes: ByteArray, target: File): Boolean = runCatching {
        val decoded = BitmapFactory.decodeByteArray(bytes, 0, bytes.size) ?: return false
        val scaled = Bitmap.createScaledBitmap(decoded, ICON_PX, ICON_PX, true)
        target.outputStream().use { scaled.compress(Bitmap.CompressFormat.PNG, 100, it) }
        if (scaled !== decoded) scaled.recycle()
        decoded.recycle()
        true
    }.getOrDefault(false)

    companion object {
        const val ICON_PX = 64
        const val MAX_ICON_BYTES = 256L * 1024L
        const val MISS_RETRY_MS = 7L * 24 * 60 * 60 * 1000
    }
}

/** Canonical registrable DNS host accepted by the favicon network/cache boundary. */
internal fun canonicalFaviconDomain(raw: String): String? {
    if (raw.isEmpty() || raw != raw.trim()) return null
    if (raw.any { it <= '\u001F' || it == '\u007F' || it in "/\\@?#:" }) return null
    if (raw.endsWith('.')) return null
    val ascii = runCatching { IDN.toASCII(raw, IDN.USE_STD3_ASCII_RULES) }
        .getOrNull()
        ?.lowercase(Locale.ROOT)
        ?: return null
    if (ascii.length > 253 || ascii.split('.').any { it.isEmpty() || it.length > 63 }) return null
    return ascii.takeIf { extractDomain(it) == it }
}

/** Builds a contained direct-child cache path only after host validation. */
internal fun faviconCacheFile(directory: File, rawDomain: String, suffix: String): File? {
    if (suffix != ".png" && suffix != ".miss") return null
    val domain = canonicalFaviconDomain(rawDomain) ?: return null
    val base = runCatching { directory.canonicalFile }.getOrNull() ?: return null
    val target = runCatching { File(base, "$domain$suffix").canonicalFile }.getOrNull() ?: return null
    return target.takeIf { it.parentFile == base }
}

/**
 * ICO containers usually wrap a PNG; BitmapFactory sniffs magic bytes and
 * rejects the container. Unwrap the first embedded PNG when present.
 */
internal fun decodeOrUnwrapIco(bytes: ByteArray): ByteArray? {
    if (bytes.size >= 8 && bytes[0] == 0.toByte() && bytes[1] == 0.toByte() &&
        bytes[2] == 1.toByte() && bytes[3] == 0.toByte()
    ) {
        if (bytes.size < 22) return null
        val offset = (bytes[18].toInt() and 0xFF) or
            ((bytes[19].toInt() and 0xFF) shl 8) or
            ((bytes[20].toInt() and 0xFF) shl 16) or
            ((bytes[21].toInt() and 0xFF) shl 24)
        if (offset > 0 && offset + 8 <= bytes.size &&
            bytes[offset] == 0x89.toByte() && bytes[offset + 1] == 0x50.toByte()
        ) {
            return bytes.copyOfRange(offset, bytes.size)
        }
        return null
    }
    return bytes
}