package com.example.myapplication.data

import android.content.Context
import com.example.myapplication.Trie
import java.util.concurrent.atomic.AtomicBoolean
import java.util.PriorityQueue
import kotlin.math.max

class BigramPredictor(
    private val context: Context,
    private val trie: Trie
) {
    @Volatile private var model: BigramModel? = null

    private val loading = AtomicBoolean(false)

    // 词 ↔ id 映射
    @Volatile private var word2id: Map<String, Int> = emptyMap()

    @Volatile private var id2word: List<String> = emptyList()
    @Volatile private var topUnigrams: List<String> = emptyList()

    private val unigramCacheSize = 2000

    //预先加载语言模型，并构建词到ID和ID到词的双向映射。
    fun preload() {
        if (!loading.compareAndSet(false, true)) return

        Thread {
            try {
                val m = LanguageModelLoader.load(context)

                model = m

                // 建索引（vocab 与 bigram 索引对齐，注意不丢前三个符号）
                val map = HashMap<String, Int>(m.vocab.size * 2)

                m.vocab.forEachIndexed { idx, w -> map[w] = idx }

                word2id = map

                id2word = m.vocab
                topUnigrams = buildTopUnigrams(m, unigramCacheSize)
            } catch (_: Throwable) {
                // 保持静默，允许无模型运行（仅 Trie 起作用）
            } finally {
                loading.set(false)
            }
        }.start()
    }

    // 模型是否已准备好
    fun isReady(): Boolean = model != null

    //基于上文 lastWord（可空）与前缀 prefix 联想,优先：bigram 条件概率 → Trie 过滤 → Top-K,兜底：unigram Top-K（同样做 Trie 过滤）
    fun suggest(prefix: String, lastWord: String?, topK: Int = 10): List<String> {
        val m = model

        val pfx = prefix.trim()

        if (m == null) {
            // 模型未载入时，纯 Trie 前缀联想（你的 Trie 应提供类似 startsWith）
            return safeTriePrefix(pfx, topK)
        }

        val candidates = mutableListOf<Pair<String, Float>>()

        val lastId = lastWord?.let { word2id[it] }

        if (lastId != null) {
            // 1) bigram 邻域
            val start = m.biRowptr[lastId]

            val end = m.biRowptr[lastId + 1]

            if (start in 0..end && end <= m.biCols.size) {
                // 先把 bigram 候选过一遍前缀过滤
                for (i in start until end) {
                    val nextId = m.biCols[i]

                    val w = m.vocab[nextId]
                    if (pfx.isEmpty() || w.startsWith(pfx, ignoreCase = true)) {
                        val score = m.biLogp[i]  // logP(next|last)

                        candidates += w to score
                    }
                }
            }
        }

        // 2) 如果有 bigram 过滤后的候选，直接取 topK
        if (candidates.isNotEmpty()) {
            return topKByScore(candidates, topK)
        }

        // 3) 兜底：用预计算的 unigram Top-N + 前缀过滤
        if (topK <= 0) return emptyList()

        val cachedUnigrams = getTopUnigrams(m)
        if (pfx.isEmpty()) {
            return cachedUnigrams.take(topK)
        }

        val results = ArrayList<String>(topK)
        if (cachedUnigrams.isNotEmpty()) {
            for (w in cachedUnigrams) {
                if (w.startsWith(pfx, ignoreCase = true)) {
                    results.add(w)
                    if (results.size >= topK) return results
                }
            }
        }

        if (results.size < topK) {
            val fromTrie = safeTriePrefix(pfx, topK)
            for (w in fromTrie) {
                if (w !in results) {
                    results.add(w)
                    if (results.size >= topK) break
                }
            }
        }
        return results
    }

    //供上层在用户选中词时更新“上文”状态
    fun normalizeWordForContext(word: String): String? {
        // 你可以在这里做大小写/符号处理，或将 OOV 映射为 <unk>
        return if (word2id.containsKey(word)) word else "<unk>"
    }

    //在Trie数据结构中查找与给定前缀匹配的字符串，并返回其中评分最高的topK个结果。
    private fun safeTriePrefix(prefix: String, topK: Int): List<String> {
        if (prefix.isEmpty()) return emptyList()

        return try {
            trie.startsWith(prefix, topK)
        } catch (_: Throwable) {
            emptyList()
        }
    }

    private fun getTopUnigrams(model: BigramModel): List<String> {
        val cached = topUnigrams
        if (cached.isNotEmpty()) return cached

        val built = buildTopUnigrams(model, unigramCacheSize)
        topUnigrams = built
        return built
    }

    private fun buildTopUnigrams(model: BigramModel, limit: Int): List<String> {
        if (limit <= 0) return emptyList()
        val heap = topKHeap(limit)

        for (i in model.vocab.indices) {
            heap.offer(model.vocab[i] to model.uniLogp[i])
            if (heap.size > limit) heap.poll()
        }

        return heap.toSortedListDescending()
    }

    //从给定的候选词对列表中，通过一个小顶堆来过滤出评分最高的前k个词
    private fun topKByScore(pairs: List<Pair<String, Float>>, k: Int): List<String> {
        val heap = topKHeap(k)

        for (p in pairs) {
            heap.offer(p)

            if (heap.size > k) heap.poll()
        }

        return heap.toSortedListDescending()
    }

    //创建一个优先队列，用于在一组候选词对中保持评分最高的 k 个词。
    private fun topKHeap(k: Int): PriorityQueue<Pair<String, Float>> {
        // 小顶堆，比较 Float 分数
        return PriorityQueue(k.coerceAtLeast(1)) { a, b ->
            a.second.compareTo(b.second) // 分数小的优先被弹出
        }
    }
    
    // 排序后的候选词列表
    private fun PriorityQueue<Pair<String, Float>>.toSortedListDescending(): List<String> {
        val list = ArrayList<Pair<String, Float>>(this.size)

        while (this.isNotEmpty()) {
            val p = this.poll() ?: continue   // 防御性判断，避免 null
            list.add(p)
        }

        list.reverse() // 从高分到低分

        return list.map { it.first }
    }
}