/// Windows WeChat 进程内存密钥扫描器
///
/// 使用 Windows API：
/// - CreateToolhelp32Snapshot + Process32Next: 枚举进程找 Weixin.exe
/// - OpenProcess: 获取进程句柄（需要 PROCESS_VM_READ | PROCESS_QUERY_INFORMATION）
/// - VirtualQueryEx: 枚举内存区域
/// - ReadProcessMemory: 读取内存内容
use anyhow::{bail, Context, Result};
use std::path::Path;
use windows::Win32::Foundation::{CloseHandle, HANDLE};
use windows::Win32::System::Diagnostics::ToolHelp::{
    CreateToolhelp32Snapshot, Process32First, Process32Next, PROCESSENTRY32, TH32CS_SNAPPROCESS,
};
use windows::Win32::System::Memory::{
    VirtualQueryEx, MEMORY_BASIC_INFORMATION, MEM_COMMIT, PAGE_READWRITE,
};
use windows::Win32::System::Threading::{
    OpenProcess, PROCESS_QUERY_INFORMATION, PROCESS_VM_READ,
};
use windows::Win32::System::Diagnostics::Debug::ReadProcessMemory;

use super::{collect_db_salts, KeyEntry};

const HEX_PATTERN_LEN: usize = 96;
const CHUNK_SIZE: usize = 2 * 1024 * 1024;

/// 查找 Weixin.exe 进程 PID
fn find_wechat_pid() -> Option<u32> {
    // SAFETY: CreateToolhelp32Snapshot 标准 Windows API
    let snap = unsafe {
        CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0).ok()?
    };

    let mut entry = PROCESSENTRY32 {
        dwSize: std::mem::size_of::<PROCESSENTRY32>() as u32,
        ..Default::default()
    };

    // SAFETY: Process32First/Process32Next 标准快照遍历
    unsafe {
        if Process32First(snap, &mut entry).is_err() {
            let _ = CloseHandle(snap);
            return None;
        }
        loop {
            let name = std::ffi::CStr::from_ptr(entry.szExeFile.as_ptr() as *const i8)
                .to_string_lossy();
            if name.eq_ignore_ascii_case("Weixin.exe") {
                let pid = entry.th32ProcessID;
                let _ = CloseHandle(snap);
                return Some(pid);
            }
            if Process32Next(snap, &mut entry).is_err() {
                break;
            }
        }
        let _ = CloseHandle(snap);
    }
    None
}

pub fn scan_keys(db_dir: &Path) -> Result<Vec<KeyEntry>> {
    let pid = find_wechat_pid()
        .context("找不到 Weixin.exe 进程，请确认微信正在运行")?;
    eprintln!("WeChat PID: {}", pid);

    // SAFETY: OpenProcess 请求读取权限
    let process = unsafe {
        OpenProcess(PROCESS_VM_READ | PROCESS_QUERY_INFORMATION, false, pid)
            .context("OpenProcess 失败，请以管理员权限运行")?
    };

    let db_salts = collect_db_salts(db_dir);
    eprintln!("找到 {} 个加密数据库", db_salts.len());

    eprintln!("扫描进程内存...");
    let raw_keys = scan_memory(process)?;
    eprintln!("找到 {} 个候选密钥", raw_keys.len());

    // SAFETY: 关闭进程句柄
    unsafe { let _ = CloseHandle(process); }

    let mut entries = Vec::new();
    for (key_hex, salt_hex) in &raw_keys {
        for (db_salt, db_name) in &db_salts {
            if salt_hex == db_salt {
                entries.push(KeyEntry {
                    db_name: db_name.clone(),
                    enc_key: key_hex.clone(),
                    salt: salt_hex.clone(),
                });
                break;
            }
        }
    }
    eprintln!("匹配到 {}/{} 个密钥", entries.len(), raw_keys.len());
    Ok(entries)
}

fn scan_memory(process: HANDLE) -> Result<Vec<(String, String)>> {
    let mut results: Vec<(String, String)> = Vec::new();
    let mut addr: usize = 0;

    loop {
        let mut mbi = MEMORY_BASIC_INFORMATION::default();
        // SAFETY: VirtualQueryEx 枚举进程内存区域
        let ret = unsafe {
            VirtualQueryEx(
                process,
                Some(addr as *const _),
                &mut mbi,
                std::mem::size_of::<MEMORY_BASIC_INFORMATION>(),
            )
        };
        if ret == 0 {
            break;
        }

        let region_size = mbi.RegionSize;
        let base = mbi.BaseAddress as usize;

        // 只扫描已提交的可读写页面
        if mbi.State == MEM_COMMIT && mbi.Protect == PAGE_READWRITE {
            scan_region(process, base, region_size, &mut results);
        }

        addr = base.saturating_add(region_size);
        if addr == 0 {
            break; // overflow
        }
    }

    Ok(results)
}

fn scan_region(
    process: HANDLE,
    base: usize,
    size: usize,
    results: &mut Vec<(String, String)>,
) {
    let overlap = HEX_PATTERN_LEN + 3;
    let mut offset = 0usize;

    loop {
        if offset >= size {
            break;
        }
        let chunk_size = std::cmp::min(CHUNK_SIZE, size - offset);
        let addr = base + offset;
        let mut buf = vec![0u8; chunk_size];
        let mut bytes_read: usize = 0;

        // SAFETY: ReadProcessMemory 读取目标进程内存
        let ok = unsafe {
            ReadProcessMemory(
                process,
                addr as *const _,
                buf.as_mut_ptr() as *mut _,
                chunk_size,
                Some(&mut bytes_read),
            ).is_ok()
        };

        if ok && bytes_read > 0 {
            buf.truncate(bytes_read);
            search_pattern(&buf, results);
        }

        if chunk_size > overlap {
            offset += chunk_size - overlap;
        } else {
            offset += chunk_size;
        }
    }
}

#[inline]
fn is_hex_char(c: u8) -> bool {
    c.is_ascii_hexdigit()
}

fn search_pattern(buf: &[u8], results: &mut Vec<(String, String)>) {
    let total = HEX_PATTERN_LEN + 3;
    if buf.len() < total {
        return;
    }
    let mut i = 0;
    while i + total <= buf.len() {
        if buf[i] != b'x' || buf[i + 1] != b'\'' {
            i += 1;
            continue;
        }
        let hex_start = i + 2;
        let all_hex = buf[hex_start..hex_start + HEX_PATTERN_LEN]
            .iter()
            .all(|&c| is_hex_char(c));
        if !all_hex {
            i += 1;
            continue;
        }
        if buf[hex_start + HEX_PATTERN_LEN] != b'\'' {
            i += 1;
            continue;
        }
        let key_hex = String::from_utf8_lossy(&buf[hex_start..hex_start + 64])
            .to_lowercase();
        let salt_hex = String::from_utf8_lossy(&buf[hex_start + 64..hex_start + 96])
            .to_lowercase();
        let is_dup = results.iter().any(|(k, s)| k == &key_hex && s == &salt_hex);
        if !is_dup {
            results.push((key_hex, salt_hex));
        }
        i += total;
    }
}