//! ZIP structure validation helpers.

use std::fs::{self, File};
use std::io::{Read, Seek, SeekFrom};
use std::path::Path;

const EOCD_SIGNATURE: u32 = 0x0605_4b50;
const ZIP64_EOCD_SIGNATURE: u32 = 0x0606_4b50;
const ZIP64_EOCD_LOCATOR_SIGNATURE: u32 = 0x0706_4b50;
const CENTRAL_DIRECTORY_SIGNATURE: u32 = 0x0201_4b50;
const LOCAL_FILE_HEADER_SIGNATURE: u32 = 0x0403_4b50;
const EOCD_MIN_LEN: u64 = 22;
const EOCD_SEARCH_WINDOW: u64 = EOCD_MIN_LEN + 65_535;
const ZIP64_EOCD_LOCATOR_LEN: u64 = 20;
const ZIP64_EOCD_FIXED_LEN: usize = 56;
const CENTRAL_DIRECTORY_FIXED_LEN: u64 = 46;
const LOCAL_FILE_HEADER_FIXED_LEN: u64 = 30;
const ZIP64_EXTENDED_INFORMATION_EXTRA_ID: u16 = 0x0001;

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(crate) struct ZipStructureReport {
    pub(crate) entry_count: u64,
    pub(crate) uses_zip64: bool,
}

pub(crate) fn path_has_zip_extension(path: &Path) -> bool {
    path.extension()
        .and_then(|extension| extension.to_str())
        .is_some_and(|extension| extension.eq_ignore_ascii_case("zip"))
}

pub(crate) fn url_or_path_has_zip_extension(value: &str) -> bool {
    let value = value.split(['?', '#']).next().unwrap_or(value);
    value
        .rsplit('/')
        .next()
        .is_some_and(|name| name.to_ascii_lowercase().ends_with(".zip"))
}

pub(crate) fn validate_zip_structure(path: &Path) -> Result<ZipStructureReport, String> {
    let metadata = fs::metadata(path)
        .map_err(|error| format!("读取 ZIP 文件信息失败 {}：{error}", path.display()))?;
    if !metadata.is_file() {
        return Err(format!("ZIP 路径不是文件：{}", path.display()));
    }

    let file_len = metadata.len();
    if file_len < EOCD_MIN_LEN {
        return Err(format!(
            "ZIP 文件过短，找不到 EOCD 记录 {}：{} bytes",
            path.display(),
            file_len
        ));
    }

    let mut file = File::open(path)
        .map_err(|error| format!("打开 ZIP 文件失败 {}：{error}", path.display()))?;
    let eocd = find_eocd(&mut file, file_len, path)?;
    let central_directory = read_central_directory_descriptor(&mut file, &eocd, file_len, path)?;
    validate_central_directory(&mut file, &central_directory, file_len, path)?;

    Ok(ZipStructureReport {
        entry_count: central_directory.entry_count,
        uses_zip64: central_directory.uses_zip64,
    })
}

fn find_eocd(file: &mut File, file_len: u64, path: &Path) -> Result<EocdRecord, String> {
    let tail_len = file_len.min(EOCD_SEARCH_WINDOW);
    let tail_start = file_len - tail_len;
    let mut tail = vec![0u8; tail_len as usize];
    file.seek(SeekFrom::Start(tail_start))
        .map_err(|error| format!("定位 ZIP EOCD 搜索窗口失败 {}：{error}", path.display()))?;
    file.read_exact(&mut tail)
        .map_err(|error| format!("读取 ZIP EOCD 搜索窗口失败 {}：{error}", path.display()))?;

    let min_offset = tail.len().saturating_sub(EOCD_MIN_LEN as usize);
    for offset in (0..=min_offset).rev() {
        if read_u32_le(&tail, offset)? != EOCD_SIGNATURE {
            continue;
        }

        let comment_len = read_u16_le(&tail, offset + 20)? as u64;
        let absolute_offset = tail_start + offset as u64;
        if absolute_offset + EOCD_MIN_LEN + comment_len != file_len {
            continue;
        }

        return Ok(EocdRecord {
            offset: absolute_offset,
            disk_number: read_u16_le(&tail, offset + 4)?,
            central_directory_disk: read_u16_le(&tail, offset + 6)?,
            disk_entry_count: read_u16_le(&tail, offset + 8)?,
            total_entry_count: read_u16_le(&tail, offset + 10)?,
            central_directory_size: read_u32_le(&tail, offset + 12)?,
            central_directory_offset: read_u32_le(&tail, offset + 16)?,
        });
    }

    Err(format!("ZIP 文件缺少有效 EOCD 记录：{}", path.display()))
}

fn read_central_directory_descriptor(
    file: &mut File,
    eocd: &EocdRecord,
    file_len: u64,
    path: &Path,
) -> Result<CentralDirectoryDescriptor, String> {
    if eocd.disk_number != 0 || eocd.central_directory_disk != 0 {
        return Err(format!("不支持多卷 ZIP 文件：{}", path.display()));
    }

    let requires_zip64 = eocd.disk_entry_count == u16::MAX
        || eocd.total_entry_count == u16::MAX
        || eocd.central_directory_size == u32::MAX
        || eocd.central_directory_offset == u32::MAX;

    if !requires_zip64 {
        if eocd.disk_entry_count != eocd.total_entry_count {
            return Err(format!(
                "ZIP EOCD 条目计数不一致 {}：disk={} total={}",
                path.display(),
                eocd.disk_entry_count,
                eocd.total_entry_count
            ));
        }

        return Ok(CentralDirectoryDescriptor {
            entry_count: eocd.total_entry_count as u64,
            size: eocd.central_directory_size as u64,
            offset: eocd.central_directory_offset as u64,
            suffix_offset: eocd.offset,
            uses_zip64: false,
        });
    }

    if eocd.offset < ZIP64_EOCD_LOCATOR_LEN {
        return Err(format!("ZIP64 文件缺少 locator：{}", path.display()));
    }

    let locator_offset = eocd.offset - ZIP64_EOCD_LOCATOR_LEN;
    let locator = read_exact_at(file, locator_offset, ZIP64_EOCD_LOCATOR_LEN as usize, path)?;
    if read_u32_le(&locator, 0)? != ZIP64_EOCD_LOCATOR_SIGNATURE {
        return Err(format!("ZIP64 文件缺少有效 locator：{}", path.display()));
    }

    let eocd_disk = read_u32_le(&locator, 4)?;
    let zip64_eocd_offset = read_u64_le(&locator, 8)?;
    let total_disks = read_u32_le(&locator, 16)?;
    if eocd_disk != 0 || total_disks != 1 {
        return Err(format!("不支持多卷 ZIP64 文件：{}", path.display()));
    }

    if zip64_eocd_offset >= file_len {
        return Err(format!(
            "ZIP64 EOCD 偏移越界 {}：offset={}",
            path.display(),
            zip64_eocd_offset
        ));
    }

    let record = read_exact_at(file, zip64_eocd_offset, ZIP64_EOCD_FIXED_LEN, path)?;
    if read_u32_le(&record, 0)? != ZIP64_EOCD_SIGNATURE {
        return Err(format!("ZIP64 EOCD 签名无效：{}", path.display()));
    }

    let record_size = read_u64_le(&record, 4)?;
    if record_size < 44 {
        return Err(format!(
            "ZIP64 EOCD 长度无效 {}：{}",
            path.display(),
            record_size
        ));
    }

    let disk_number = read_u32_le(&record, 16)?;
    let central_directory_disk = read_u32_le(&record, 20)?;
    let disk_entry_count = read_u64_le(&record, 24)?;
    let total_entry_count = read_u64_le(&record, 32)?;
    if disk_number != 0 || central_directory_disk != 0 || disk_entry_count != total_entry_count {
        return Err(format!("ZIP64 EOCD 多卷或条目计数无效：{}", path.display()));
    }

    let central_directory_size = read_u64_le(&record, 40)?;
    let central_directory_offset = read_u64_le(&record, 48)?;

    Ok(CentralDirectoryDescriptor {
        entry_count: total_entry_count,
        size: central_directory_size,
        offset: central_directory_offset,
        suffix_offset: zip64_eocd_offset,
        uses_zip64: true,
    })
}

fn validate_central_directory(
    file: &mut File,
    central_directory: &CentralDirectoryDescriptor,
    file_len: u64,
    path: &Path,
) -> Result<(), String> {
    let central_end = checked_add(
        central_directory.offset,
        central_directory.size,
        "ZIP central directory 边界溢出",
        path,
    )?;
    if central_end > central_directory.suffix_offset || central_end > file_len {
        return Err(format!(
            "ZIP central directory 越界 {}：offset={} size={} file_size={}",
            path.display(),
            central_directory.offset,
            central_directory.size,
            file_len
        ));
    }

    let mut cursor = central_directory.offset;
    for index in 0..central_directory.entry_count {
        if checked_add(
            cursor,
            CENTRAL_DIRECTORY_FIXED_LEN,
            "ZIP central header 边界溢出",
            path,
        )? > central_end
        {
            return Err(format!(
                "ZIP central directory 条目不足 {}：index={}",
                path.display(),
                index
            ));
        }

        let header = read_exact_at(file, cursor, CENTRAL_DIRECTORY_FIXED_LEN as usize, path)?;
        if read_u32_le(&header, 0)? != CENTRAL_DIRECTORY_SIGNATURE {
            return Err(format!(
                "ZIP central header 签名无效 {}：offset={}",
                path.display(),
                cursor
            ));
        }

        let compressed_size_32 = read_u32_le(&header, 20)?;
        let uncompressed_size_32 = read_u32_le(&header, 24)?;
        let file_name_len = read_u16_le(&header, 28)? as u64;
        let extra_len = read_u16_le(&header, 30)? as u64;
        let comment_len = read_u16_le(&header, 32)? as u64;
        let disk_start_16 = read_u16_le(&header, 34)?;
        let local_header_offset_32 = read_u32_le(&header, 42)?;
        let entry_end = checked_add(
            checked_add(
                checked_add(
                    cursor,
                    CENTRAL_DIRECTORY_FIXED_LEN,
                    "ZIP central header 文件名边界溢出",
                    path,
                )?,
                file_name_len,
                "ZIP central header extra 边界溢出",
                path,
            )?,
            extra_len + comment_len,
            "ZIP central header comment 边界溢出",
            path,
        )?;
        if entry_end > central_end {
            return Err(format!(
                "ZIP central header 条目越界 {}：offset={}",
                path.display(),
                cursor
            ));
        }
        if file_name_len == 0 {
            return Err(format!(
                "ZIP central header 文件名为空 {}：offset={}",
                path.display(),
                cursor
            ));
        }

        let name = read_exact_at(
            file,
            cursor + CENTRAL_DIRECTORY_FIXED_LEN,
            file_name_len as usize,
            path,
        )?;
        let extra = read_exact_at(
            file,
            cursor + CENTRAL_DIRECTORY_FIXED_LEN + file_name_len,
            extra_len as usize,
            path,
        )?;

        let zip64 = parse_zip64_extra(
            &extra,
            uncompressed_size_32 == u32::MAX,
            compressed_size_32 == u32::MAX,
            local_header_offset_32 == u32::MAX,
            disk_start_16 == u16::MAX,
            path,
        )?;
        let compressed_size = zip64.compressed_size.unwrap_or(compressed_size_32 as u64);
        let local_header_offset = zip64
            .local_header_offset
            .unwrap_or(local_header_offset_32 as u64);
        let disk_start = zip64.disk_start.unwrap_or(disk_start_16 as u32);
        if disk_start != 0 {
            return Err(format!("不支持多卷 ZIP 条目：{}", path.display()));
        }

        validate_local_file_header(
            file,
            path,
            &name,
            local_header_offset,
            compressed_size,
            central_directory.offset,
        )?;
        cursor = entry_end;
    }

    if cursor != central_end {
        return Err(format!(
            "ZIP central directory 大小与条目不匹配 {}：parsed_end={} expected_end={}",
            path.display(),
            cursor,
            central_end
        ));
    }

    Ok(())
}

fn validate_local_file_header(
    file: &mut File,
    path: &Path,
    central_name: &[u8],
    local_header_offset: u64,
    compressed_size: u64,
    central_directory_offset: u64,
) -> Result<(), String> {
    if local_header_offset >= central_directory_offset {
        return Err(format!(
            "ZIP local header 偏移越界 {}：offset={}",
            path.display(),
            local_header_offset
        ));
    }

    let header = read_exact_at(
        file,
        local_header_offset,
        LOCAL_FILE_HEADER_FIXED_LEN as usize,
        path,
    )?;
    if read_u32_le(&header, 0)? != LOCAL_FILE_HEADER_SIGNATURE {
        return Err(format!(
            "ZIP local header 签名无效 {}：offset={}",
            path.display(),
            local_header_offset
        ));
    }

    let file_name_len = read_u16_le(&header, 26)? as u64;
    let extra_len = read_u16_le(&header, 28)? as u64;
    let data_start = checked_add(
        checked_add(
            checked_add(
                local_header_offset,
                LOCAL_FILE_HEADER_FIXED_LEN,
                "ZIP local header 文件名边界溢出",
                path,
            )?,
            file_name_len,
            "ZIP local header extra 边界溢出",
            path,
        )?,
        extra_len,
        "ZIP local data 边界溢出",
        path,
    )?;
    let data_end = checked_add(
        data_start,
        compressed_size,
        "ZIP local data 压缩数据边界溢出",
        path,
    )?;
    if data_end > central_directory_offset {
        return Err(format!(
            "ZIP local data 越界 {}：data_end={} central_directory_offset={}",
            path.display(),
            data_end,
            central_directory_offset
        ));
    }

    let local_name = read_exact_at(
        file,
        local_header_offset + LOCAL_FILE_HEADER_FIXED_LEN,
        file_name_len as usize,
        path,
    )?;
    if local_name != central_name {
        return Err(format!(
            "ZIP local header 文件名与 central directory 不一致 {}：offset={}",
            path.display(),
            local_header_offset
        ));
    }

    Ok(())
}

fn parse_zip64_extra(
    extra: &[u8],
    need_uncompressed_size: bool,
    need_compressed_size: bool,
    need_local_header_offset: bool,
    need_disk_start: bool,
    path: &Path,
) -> Result<Zip64ExtraValues, String> {
    let mut cursor = 0usize;
    while cursor + 4 <= extra.len() {
        let header_id = read_u16_le(extra, cursor)?;
        let data_size = read_u16_le(extra, cursor + 2)? as usize;
        cursor += 4;
        if cursor + data_size > extra.len() {
            return Err(format!("ZIP extra field 边界无效：{}", path.display()));
        }

        if header_id == ZIP64_EXTENDED_INFORMATION_EXTRA_ID {
            let data = &extra[cursor..cursor + data_size];
            let values = parse_zip64_extended_information(
                data,
                need_uncompressed_size,
                need_compressed_size,
                need_local_header_offset,
                need_disk_start,
                path,
            )?;
            return Ok(values);
        }

        cursor += data_size;
    }

    if need_uncompressed_size || need_compressed_size || need_local_header_offset || need_disk_start
    {
        return Err(format!(
            "ZIP64 条目缺少 extended information extra：{}",
            path.display()
        ));
    }

    Ok(Zip64ExtraValues::default())
}

fn parse_zip64_extended_information(
    data: &[u8],
    need_uncompressed_size: bool,
    need_compressed_size: bool,
    need_local_header_offset: bool,
    need_disk_start: bool,
    path: &Path,
) -> Result<Zip64ExtraValues, String> {
    let mut cursor = 0usize;
    let mut values = Zip64ExtraValues::default();

    if need_uncompressed_size {
        values.uncompressed_size = Some(read_zip64_u64(data, &mut cursor, path)?);
    }
    if need_compressed_size {
        values.compressed_size = Some(read_zip64_u64(data, &mut cursor, path)?);
    }
    if need_local_header_offset {
        values.local_header_offset = Some(read_zip64_u64(data, &mut cursor, path)?);
    }
    if need_disk_start {
        if cursor + 4 > data.len() {
            return Err(format!("ZIP64 extra 缺少 disk start：{}", path.display()));
        }
        values.disk_start = Some(read_u32_le(data, cursor)?);
    }

    Ok(values)
}

fn read_zip64_u64(data: &[u8], cursor: &mut usize, path: &Path) -> Result<u64, String> {
    if *cursor + 8 > data.len() {
        return Err(format!("ZIP64 extra 字段长度不足：{}", path.display()));
    }
    let value = read_u64_le(data, *cursor)?;
    *cursor += 8;
    Ok(value)
}

fn read_exact_at(file: &mut File, offset: u64, len: usize, path: &Path) -> Result<Vec<u8>, String> {
    file.seek(SeekFrom::Start(offset)).map_err(|error| {
        format!(
            "定位 ZIP 文件失败 {}：offset={offset}：{error}",
            path.display()
        )
    })?;
    let mut data = vec![0u8; len];
    file.read_exact(&mut data).map_err(|error| {
        format!(
            "读取 ZIP 文件失败 {}：offset={offset} len={len}：{error}",
            path.display()
        )
    })?;
    Ok(data)
}

fn checked_add(left: u64, right: u64, label: &str, path: &Path) -> Result<u64, String> {
    left.checked_add(right)
        .ok_or_else(|| format!("{label}：{}", path.display()))
}

fn read_u16_le(bytes: &[u8], offset: usize) -> Result<u16, String> {
    let end = offset
        .checked_add(2)
        .ok_or_else(|| "读取 u16 偏移溢出".to_string())?;
    let slice = bytes
        .get(offset..end)
        .ok_or_else(|| "读取 u16 越界".to_string())?;
    Ok(u16::from_le_bytes([slice[0], slice[1]]))
}

fn read_u32_le(bytes: &[u8], offset: usize) -> Result<u32, String> {
    let end = offset
        .checked_add(4)
        .ok_or_else(|| "读取 u32 偏移溢出".to_string())?;
    let slice = bytes
        .get(offset..end)
        .ok_or_else(|| "读取 u32 越界".to_string())?;
    Ok(u32::from_le_bytes([slice[0], slice[1], slice[2], slice[3]]))
}

fn read_u64_le(bytes: &[u8], offset: usize) -> Result<u64, String> {
    let end = offset
        .checked_add(8)
        .ok_or_else(|| "读取 u64 偏移溢出".to_string())?;
    let slice = bytes
        .get(offset..end)
        .ok_or_else(|| "读取 u64 越界".to_string())?;
    Ok(u64::from_le_bytes([
        slice[0], slice[1], slice[2], slice[3], slice[4], slice[5], slice[6], slice[7],
    ]))
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct EocdRecord {
    offset: u64,
    disk_number: u16,
    central_directory_disk: u16,
    disk_entry_count: u16,
    total_entry_count: u16,
    central_directory_size: u32,
    central_directory_offset: u32,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct CentralDirectoryDescriptor {
    entry_count: u64,
    size: u64,
    offset: u64,
    suffix_offset: u64,
    uses_zip64: bool,
}

#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
struct Zip64ExtraValues {
    uncompressed_size: Option<u64>,
    compressed_size: Option<u64>,
    local_header_offset: Option<u64>,
    disk_start: Option<u32>,
}

#[cfg(test)]
mod tests {
    use super::*;
    use tempfile::TempDir;

    fn empty_zip() -> Vec<u8> {
        vec![
            0x50, 0x4b, 0x05, 0x06, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        ]
    }

    fn one_file_zip(name: &[u8], data: &[u8]) -> Vec<u8> {
        let mut bytes = Vec::new();
        bytes.extend_from_slice(&LOCAL_FILE_HEADER_SIGNATURE.to_le_bytes());
        bytes.extend_from_slice(&20u16.to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(&0u32.to_le_bytes());
        bytes.extend_from_slice(&(data.len() as u32).to_le_bytes());
        bytes.extend_from_slice(&(data.len() as u32).to_le_bytes());
        bytes.extend_from_slice(&(name.len() as u16).to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(name);
        bytes.extend_from_slice(data);

        let central_offset = bytes.len() as u32;
        bytes.extend_from_slice(&CENTRAL_DIRECTORY_SIGNATURE.to_le_bytes());
        bytes.extend_from_slice(&20u16.to_le_bytes());
        bytes.extend_from_slice(&20u16.to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(&0u32.to_le_bytes());
        bytes.extend_from_slice(&(data.len() as u32).to_le_bytes());
        bytes.extend_from_slice(&(data.len() as u32).to_le_bytes());
        bytes.extend_from_slice(&(name.len() as u16).to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(&0u32.to_le_bytes());
        bytes.extend_from_slice(&0u32.to_le_bytes());
        bytes.extend_from_slice(name);
        let central_size = bytes.len() as u32 - central_offset;

        bytes.extend_from_slice(&EOCD_SIGNATURE.to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes.extend_from_slice(&1u16.to_le_bytes());
        bytes.extend_from_slice(&1u16.to_le_bytes());
        bytes.extend_from_slice(&central_size.to_le_bytes());
        bytes.extend_from_slice(&central_offset.to_le_bytes());
        bytes.extend_from_slice(&0u16.to_le_bytes());
        bytes
    }

    #[test]
    fn accepts_empty_zip() {
        let temp = TempDir::new().unwrap();
        let path = temp.path().join("empty.zip");
        fs::write(&path, empty_zip()).unwrap();

        let report = validate_zip_structure(&path).unwrap();

        assert_eq!(report.entry_count, 0);
        assert!(!report.uses_zip64);
    }

    #[test]
    fn accepts_one_file_zip() {
        let temp = TempDir::new().unwrap();
        let path = temp.path().join("one.zip");
        fs::write(&path, one_file_zip(b"nested/file.txt", b"hello")).unwrap();

        let report = validate_zip_structure(&path).unwrap();

        assert_eq!(report.entry_count, 1);
        assert!(!report.uses_zip64);
    }

    #[test]
    fn rejects_truncated_zip() {
        let temp = TempDir::new().unwrap();
        let path = temp.path().join("bad.zip");
        let mut bytes = one_file_zip(b"file.txt", b"hello");
        bytes.truncate(bytes.len() - 8);
        fs::write(&path, bytes).unwrap();

        let error = validate_zip_structure(&path).unwrap_err();

        assert!(error.contains("EOCD") || error.contains("越界"));
    }

    #[test]
    fn rejects_local_name_mismatch() {
        let temp = TempDir::new().unwrap();
        let path = temp.path().join("bad-name.zip");
        let mut bytes = one_file_zip(b"file.txt", b"hello");
        let central_name_offset = 30 + b"file.txt".len() + b"hello".len() + 46;
        bytes[central_name_offset] = b'X';
        fs::write(&path, bytes).unwrap();

        let error = validate_zip_structure(&path).unwrap_err();

        assert!(error.contains("文件名"));
    }
}