wedb_embed 0.1.0

use crate::error::{Error, Result};
use crate::hll::algo::{HLL_DENSE_SIZE, HLL_REGISTERS, extract_dense_hll_result, rapid_hash};
use crate::hll::dense::{
    hll_dense_estimate, hll_dense_get_register, hll_dense_set_register, hll_merge_bytes,
};
use crate::hll::meta::HllEncodeType;
use crate::hll::sparse::{
    hll_dense_to_sparse, hll_sparse_estimate, hll_sparse_get_register, hll_sparse_is_valid,
    hll_sparse_new, hll_sparse_set_register, hll_sparse_to_dense,
};

/// HyperLogLog 独立核心结构（同时支持 Dense 密集与 Sparse 稀疏编码）
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct HyperLogLog {
    pub registers: Vec<u8>,
    pub encode_type: HllEncodeType,
}

impl Default for HyperLogLog {
    fn default() -> Self {
        Self::new()
    }
}

impl HyperLogLog {
    /// 创建默认密集编码的 HyperLogLog
    #[inline]
    pub fn new() -> Self {
        Self {
            registers: vec![0u8; HLL_DENSE_SIZE],
            encode_type: HllEncodeType::Dense,
        }
    }

    /// 创建初始稀疏编码的 HyperLogLog（仅占 2 字节）
    #[inline]
    pub fn new_sparse() -> Self {
        Self {
            registers: hll_sparse_new(),
            encode_type: HllEncodeType::Sparse,
        }
    }

    /// 从字节切片智能构造（自动识别 Sparse 或 Dense 编码）
    #[inline]
    pub fn from_bytes(bytes: &[u8]) -> Self {
        if bytes.len() >= HLL_DENSE_SIZE {
            let mut registers = vec![0u8; HLL_DENSE_SIZE];
            registers.copy_from_slice(&bytes[..HLL_DENSE_SIZE]);
            Self {
                registers,
                encode_type: HllEncodeType::Dense,
            }
        } else if hll_sparse_is_valid(bytes) {
            Self {
                registers: bytes.to_vec(),
                encode_type: HllEncodeType::Sparse,
            }
        } else {
            let mut registers = vec![0u8; HLL_DENSE_SIZE];
            let copy_len = bytes.len().min(HLL_DENSE_SIZE);
            registers[..copy_len].copy_from_slice(&bytes[..copy_len]);
            Self {
                registers,
                encode_type: HllEncodeType::Dense,
            }
        }
    }

    /// 从已校验的稀疏字节流构造
    #[inline]
    pub fn from_sparse_bytes(bytes: &[u8]) -> Result<Self> {
        if !hll_sparse_is_valid(bytes) {
            return Err(Error::invalid_data("invalid sparse hll payload"));
        }
        Ok(Self {
            registers: bytes.to_vec(),
            encode_type: HllEncodeType::Sparse,
        })
    }

    #[inline]
    pub fn to_bytes(&self) -> &[u8] {
        &self.registers
    }

    #[inline]
    pub fn as_slice(&self) -> &[u8] {
        &self.registers
    }

    #[inline]
    pub fn as_mut_slice(&mut self) -> &mut [u8] {
        &mut self.registers
    }

    #[inline]
    pub fn encode_type(&self) -> HllEncodeType {
        self.encode_type
    }

    /// 将当前稀疏结构晋升为 12288 字节密集编码
    pub fn promote_to_dense(&mut self) -> Result<()> {
        if self.encode_type == HllEncodeType::Dense {
            if self.registers.len() < HLL_DENSE_SIZE {
                self.registers.resize(HLL_DENSE_SIZE, 0);
            }
            return Ok(());
        }
        let mut dense_buf = vec![0u8; HLL_DENSE_SIZE];
        hll_sparse_to_dense(&self.registers, &mut dense_buf)?;
        self.registers = dense_buf;
        self.encode_type = HllEncodeType::Dense;
        Ok(())
    }

    /// 提取指定寄存器的计数值（0..63）
    #[inline]
    pub fn get_register(&self, index: usize) -> u8 {
        match self.encode_type {
            HllEncodeType::Dense => hll_dense_get_register(&self.registers, index),
            HllEncodeType::Sparse => hll_sparse_get_register(&self.registers, index).unwrap_or(0),
        }
    }

    /// 设置指定寄存器的计数值
    #[inline]
    pub fn set_register(&mut self, index: usize, val: u8) {
        if index >= HLL_REGISTERS {
            return;
        }
        match self.encode_type {
            HllEncodeType::Dense => {
                if self.registers.len() < HLL_DENSE_SIZE {
                    self.registers.resize(HLL_DENSE_SIZE, 0);
                }
                hll_dense_set_register(&mut self.registers, index, val);
            }
            HllEncodeType::Sparse => {
                match hll_sparse_set_register(&mut self.registers, index, val) {
                    Ok(_) => {}
                    Err(_) => {
                        if self.promote_to_dense().is_ok() {
                            hll_dense_set_register(&mut self.registers, index, val);
                        }
                    }
                }
            }
        }
    }

    /// 添加元素数据
    #[inline]
    pub fn add(&mut self, data: &[u8]) -> bool {
        let h = rapid_hash(data);
        self.add_hash(h)
    }

    /// 添加已计算好的 64 位哈希值
    #[inline]
    pub fn add_hash(&mut self, hash: u64) -> bool {
        let (idx, count) = extract_dense_hll_result(hash);
        match self.encode_type {
            HllEncodeType::Dense => {
                if self.registers.len() < HLL_DENSE_SIZE {
                    self.registers.resize(HLL_DENSE_SIZE, 0);
                }
                let old = hll_dense_get_register(&self.registers, idx);
                if count > old {
                    hll_dense_set_register(&mut self.registers, idx, count);
                    true
                } else {
                    false
                }
            }
            HllEncodeType::Sparse => {
                match hll_sparse_set_register(&mut self.registers, idx, count) {
                    Ok(updated) => updated,
                    Err(_) => {
                        if self.promote_to_dense().is_ok() {
                            let old = hll_dense_get_register(&self.registers, idx);
                            if count > old {
                                hll_dense_set_register(&mut self.registers, idx, count);
                                true
                            } else {
                                false
                            }
                        } else {
                            false
                        }
                    }
                }
            }
        }
    }

    /// 计算当前近似基数估算值
    #[inline]
    pub fn count(&self) -> u64 {
        match self.encode_type {
            HllEncodeType::Dense => hll_dense_estimate(&self.registers),
            HllEncodeType::Sparse => hll_sparse_estimate(&self.registers)
                .unwrap_or_else(|_| hll_dense_estimate(&self.registers)),
        }
    }

    /// 就地合并另一个 HyperLogLog
    pub fn merge(&mut self, other: &Self) {
        if std::ptr::eq(self, other) || other.is_empty() {
            return;
        }

        if self.encode_type == HllEncodeType::Dense && other.encode_type == HllEncodeType::Dense {
            if self.registers.len() < HLL_DENSE_SIZE {
                self.registers.resize(HLL_DENSE_SIZE, 0);
            }
            hll_merge_bytes(&mut self.registers, &other.registers);
            return;
        }

        // 包含稀疏编码时，统一转换为密集编码合并
        self.promote_to_dense().ok();
        let other_dense = match other.encode_type {
            HllEncodeType::Dense => &other.registers[..],
            HllEncodeType::Sparse => {
                let mut buf = vec![0u8; HLL_DENSE_SIZE];
                if hll_sparse_to_dense(&other.registers, &mut buf).is_ok() {
                    hll_merge_bytes(&mut self.registers, &buf);
                    return;
                }
                &other.registers[..]
            }
        };
        hll_merge_bytes(&mut self.registers, other_dense);
    }

    /// 合并原始字节切片
    pub fn merge_bytes(&mut self, other: &[u8]) {
        if other.is_empty() {
            return;
        }
        self.promote_to_dense().ok();
        if other.len() >= HLL_DENSE_SIZE {
            hll_merge_bytes(&mut self.registers, other);
        } else if hll_sparse_is_valid(other) {
            let mut buf = vec![0u8; HLL_DENSE_SIZE];
            if hll_sparse_to_dense(other, &mut buf).is_ok() {
                hll_merge_bytes(&mut self.registers, &buf);
            }
        } else {
            hll_merge_bytes(&mut self.registers, other);
        }
    }

    /// 判断是否全空（估算为 0）
    #[inline]
    pub fn is_empty(&self) -> bool {
        match self.encode_type {
            HllEncodeType::Dense => self.registers.iter().all(|&b| b == 0),
            HllEncodeType::Sparse => self.count() == 0,
        }
    }

    /// 清空所有寄存器
    #[inline]
    pub fn clear(&mut self) {
        match self.encode_type {
            HllEncodeType::Dense => self.registers.fill(0),
            HllEncodeType::Sparse => self.registers = hll_sparse_new(),
        }
    }

    /// 导出为 Dense 密集切片
    pub fn to_dense(&self) -> Result<Vec<u8>> {
        match self.encode_type {
            HllEncodeType::Dense => Ok(self.registers.clone()),
            HllEncodeType::Sparse => {
                let mut buf = vec![0u8; HLL_DENSE_SIZE];
                hll_sparse_to_dense(&self.registers, &mut buf)?;
                Ok(buf)
            }
        }
    }

    /// 尝试导出为 Sparse 稀疏切片（若不可压缩则返回 None）
    pub fn to_sparse(&self) -> Option<Vec<u8>> {
        match self.encode_type {
            HllEncodeType::Sparse => Some(self.registers.clone()),
            HllEncodeType::Dense => hll_dense_to_sparse(&self.registers),
        }
    }

    /// 自检算法正确性与误差边界
    pub fn selftest() -> bool {
        let mut hll = Self::new();
        for i in 0..1000 {
            hll.add(format!("test_element_{i}").as_bytes());
        }
        let est = hll.count();
        (800..=1200).contains(&est)
    }
}