use std::collections::HashSet;
use std::fs;
use std::io::{Read, Write};
use std::path::{Path, PathBuf};

use tempfile::{tempdir, TempDir};
use zip::write::SimpleFileOptions;
use zip::DateTime;

use crate::error::AppError;
use crate::services::skill::SkillService;

use super::{io_context_localized, localized, MAX_SYNC_ARTIFACT_BYTES, REMOTE_SKILLS_ZIP};

/// Maximum number of entries allowed in a zip archive.
const MAX_EXTRACT_ENTRIES: usize = 10_000;

pub(super) struct SkillsBackup {
    _tmp: TempDir,
    backup_dir: PathBuf,
    ssot_path: PathBuf,
    existed: bool,
}

pub(super) fn zip_skills_ssot(dest_path: &Path) -> Result<(), AppError> {
    let source = SkillService::get_ssot_dir().map_err(|e| {
        localized(
            "webdav.sync.skills_ssot_dir_failed",
            format!("获取 Skills SSOT 目录失败: {e}"),
            format!("Failed to resolve Skills SSOT directory: {e}"),
        )
    })?;
    if let Some(parent) = dest_path.parent() {
        fs::create_dir_all(parent).map_err(|e| AppError::io(parent, e))?;
    }

    let file = fs::File::create(dest_path).map_err(|e| AppError::io(dest_path, e))?;
    let mut writer = zip::ZipWriter::new(file);
    let options = SimpleFileOptions::default()
        .compression_method(zip::CompressionMethod::Deflated)
        .last_modified_time(DateTime::default());

    if source.exists() {
        let canonical_root = fs::canonicalize(&source).unwrap_or_else(|_| source.clone());
        let mut visited = HashSet::new();
        mark_visited_dir(&canonical_root, &mut visited)?;
        zip_dir_recursive(
            &canonical_root,
            &canonical_root,
            &mut writer,
            options,
            &mut visited,
        )?;
    }

    writer.finish().map_err(|e| {
        localized(
            "webdav.sync.skills_zip_write_failed",
            format!("写入 skills.zip 失败: {e}"),
            format!("Failed to write skills.zip: {e}"),
        )
    })?;
    Ok(())
}

pub(super) fn restore_skills_zip(raw: &[u8]) -> Result<(), AppError> {
    let tmp = tempdir().map_err(|e| {
        io_context_localized(
            "webdav.sync.skills_extract_tmpdir_failed",
            "创建 skills 解压临时目录失败",
            "Failed to create temporary directory for skills extraction",
            e,
        )
    })?;
    let zip_path = tmp.path().join(REMOTE_SKILLS_ZIP);
    fs::write(&zip_path, raw).map_err(|e| AppError::io(&zip_path, e))?;

    let file = fs::File::open(&zip_path).map_err(|e| AppError::io(&zip_path, e))?;
    let mut archive = zip::ZipArchive::new(file).map_err(|e| {
        localized(
            "webdav.sync.skills_zip_parse_failed",
            format!("解析 skills.zip 失败: {e}"),
            format!("Failed to parse skills.zip: {e}"),
        )
    })?;

    let extracted = tmp.path().join("skills-extracted");
    fs::create_dir_all(&extracted).map_err(|e| AppError::io(&extracted, e))?;

    if archive.len() > MAX_EXTRACT_ENTRIES {
        return Err(localized(
            "webdav.sync.skills_zip_too_many_entries",
            format!(
                "skills.zip 条目数过多（{}），上限 {MAX_EXTRACT_ENTRIES}",
                archive.len()
            ),
            format!(
                "skills.zip has too many entries ({}), limit is {MAX_EXTRACT_ENTRIES}",
                archive.len()
            ),
        ));
    }

    let mut total_bytes: u64 = 0;
    for idx in 0..archive.len() {
        let mut entry = archive.by_index(idx).map_err(|e| {
            localized(
                "webdav.sync.skills_zip_entry_read_failed",
                format!("读取 ZIP 项失败: {e}"),
                format!("Failed to read ZIP entry: {e}"),
            )
        })?;
        let Some(safe_name) = entry.enclosed_name() else {
            continue;
        };
        let out_path = extracted.join(safe_name);
        if entry.is_dir() {
            fs::create_dir_all(&out_path).map_err(|e| AppError::io(&out_path, e))?;
            continue;
        }
        if let Some(parent) = out_path.parent() {
            fs::create_dir_all(parent).map_err(|e| AppError::io(parent, e))?;
        }
        let mut out = fs::File::create(&out_path).map_err(|e| AppError::io(&out_path, e))?;
        let _written = copy_entry_with_total_limit(
            &mut entry,
            &mut out,
            &mut total_bytes,
            MAX_SYNC_ARTIFACT_BYTES,
            &out_path,
        )?;
    }

    let ssot = SkillService::get_ssot_dir().map_err(|e| {
        localized(
            "webdav.sync.skills_ssot_dir_failed",
            format!("获取 Skills SSOT 目录失败: {e}"),
            format!("Failed to resolve Skills SSOT directory: {e}"),
        )
    })?;
    let bak = ssot.with_extension("bak");

    if ssot.exists() {
        if bak.exists() {
            let _ = fs::remove_dir_all(&bak);
        }
        fs::rename(&ssot, &bak).map_err(|e| AppError::io(&ssot, e))?;
    }

    if let Err(e) = copy_dir_recursive(&extracted, &ssot) {
        if bak.exists() {
            let _ = fs::remove_dir_all(&ssot);
            let _ = fs::rename(&bak, &ssot);
        }
        return Err(e);
    }

    let _ = fs::remove_dir_all(&bak);
    Ok(())
}

pub(super) fn backup_current_skills() -> Result<SkillsBackup, AppError> {
    let ssot = SkillService::get_ssot_dir().map_err(|e| {
        localized(
            "webdav.sync.skills_ssot_dir_failed",
            format!("获取 Skills SSOT 目录失败: {e}"),
            format!("Failed to resolve Skills SSOT directory: {e}"),
        )
    })?;
    let tmp = tempdir().map_err(|e| {
        io_context_localized(
            "webdav.sync.skills_backup_tmpdir_failed",
            "创建 skills 备份临时目录失败",
            "Failed to create temporary directory for skills backup",
            e,
        )
    })?;
    let backup_dir = tmp.path().join("skills-backup");

    let existed = ssot.exists();
    if existed {
        copy_dir_recursive(&ssot, &backup_dir)?;
    }

    Ok(SkillsBackup {
        _tmp: tmp,
        backup_dir,
        ssot_path: ssot,
        existed,
    })
}

pub(super) fn restore_skills_from_backup(backup: &SkillsBackup) -> Result<(), AppError> {
    if backup.ssot_path.exists() {
        fs::remove_dir_all(&backup.ssot_path).map_err(|e| AppError::io(&backup.ssot_path, e))?;
    }

    if backup.existed {
        copy_dir_recursive(&backup.backup_dir, &backup.ssot_path)?;
    }

    Ok(())
}

fn zip_dir_recursive(
    root: &Path,
    current: &Path,
    writer: &mut zip::ZipWriter<fs::File>,
    options: SimpleFileOptions,
    visited: &mut HashSet<PathBuf>,
) -> Result<(), AppError> {
    let mut entries: Vec<_> = fs::read_dir(current)
        .map_err(|e| AppError::io(current, e))?
        .collect::<Result<Vec<_>, _>>()
        .map_err(|e| AppError::io(current, e))?;
    entries.sort_by_key(|e| e.file_name());

    for entry in entries {
        let path = entry.path();
        let name = entry.file_name();
        let name_str = name.to_string_lossy();

        if name_str.starts_with('.') {
            continue;
        }

        let real_path = match fs::canonicalize(&path) {
            Ok(p) if p.starts_with(root) => p,
            Ok(_) => {
                log::warn!(
                    "[WebDAV] Skipping symlink outside skills root: {}",
                    path.display()
                );
                continue;
            }
            Err(_) => path.clone(),
        };

        let rel = real_path
            .strip_prefix(root)
            .or_else(|_| path.strip_prefix(root))
            .map_err(|e| {
                localized(
                    "webdav.sync.zip_relative_path_failed",
                    format!("生成 ZIP 相对路径失败: {e}"),
                    format!("Failed to build relative ZIP path: {e}"),
                )
            })?;
        let rel_str = rel.to_string_lossy().replace('\\', "/");

        if real_path.is_dir() {
            if !mark_visited_dir(&real_path, visited)? {
                log::warn!(
                    "[WebDAV] Skipping already visited directory: {}",
                    real_path.display()
                );
                continue;
            }
            writer
                .add_directory(format!("{rel_str}/"), options)
                .map_err(|e| {
                    localized(
                        "webdav.sync.zip_add_directory_failed",
                        format!("写入 ZIP 目录失败: {e}"),
                        format!("Failed to write ZIP directory entry: {e}"),
                    )
                })?;
            zip_dir_recursive(root, &real_path, writer, options, visited)?;
        } else {
            writer.start_file(&rel_str, options).map_err(|e| {
                localized(
                    "webdav.sync.zip_start_file_failed",
                    format!("写入 ZIP 文件头失败: {e}"),
                    format!("Failed to start ZIP file entry: {e}"),
                )
            })?;
            let mut file = fs::File::open(&real_path).map_err(|e| AppError::io(&real_path, e))?;
            let mut buf = Vec::new();
            file.read_to_end(&mut buf)
                .map_err(|e| AppError::io(&real_path, e))?;
            writer.write_all(&buf).map_err(|e| {
                localized(
                    "webdav.sync.zip_write_file_failed",
                    format!("写入 ZIP 文件内容失败: {e}"),
                    format!("Failed to write ZIP file content: {e}"),
                )
            })?;
        }
    }
    Ok(())
}

fn copy_dir_recursive(src: &Path, dest: &Path) -> Result<(), AppError> {
    let mut visited = HashSet::new();
    copy_dir_recursive_inner(src, dest, &mut visited)
}

fn copy_dir_recursive_inner(
    src: &Path,
    dest: &Path,
    visited: &mut HashSet<PathBuf>,
) -> Result<(), AppError> {
    if !src.exists() {
        return Ok(());
    }
    if !mark_visited_dir(src, visited)? {
        log::warn!(
            "[WebDAV] Skipping already visited copy path: {}",
            src.display()
        );
        return Ok(());
    }
    fs::create_dir_all(dest).map_err(|e| AppError::io(dest, e))?;
    for entry in fs::read_dir(src).map_err(|e| AppError::io(src, e))? {
        let entry = entry.map_err(|e| AppError::io(src, e))?;
        let path = entry.path();
        let dest_path = dest.join(entry.file_name());
        if path.is_dir() {
            copy_dir_recursive_inner(&path, &dest_path, visited)?;
        } else {
            fs::copy(&path, &dest_path).map_err(|e| AppError::io(&dest_path, e))?;
        }
    }
    Ok(())
}

fn mark_visited_dir(path: &Path, visited: &mut HashSet<PathBuf>) -> Result<bool, AppError> {
    let canonical = fs::canonicalize(path).map_err(|e| AppError::io(path, e))?;
    Ok(visited.insert(canonical))
}

fn copy_entry_with_total_limit<R: Read, W: Write>(
    reader: &mut R,
    writer: &mut W,
    total_bytes: &mut u64,
    max_total_bytes: u64,
    out_path: &Path,
) -> Result<u64, AppError> {
    let mut buffer = [0u8; 16 * 1024];
    let mut written = 0u64;
    loop {
        let n = reader
            .read(&mut buffer)
            .map_err(|e| AppError::io(out_path, e))?;
        if n == 0 {
            break;
        }

        if total_bytes.saturating_add(n as u64) > max_total_bytes {
            let max_mb = max_total_bytes / 1024 / 1024;
            return Err(localized(
                "webdav.sync.skills_zip_too_large",
                format!("skills.zip 解压后体积超过上限（{} MB）", max_mb),
                format!("skills.zip extracted size exceeds limit ({} MB)", max_mb),
            ));
        }

        writer
            .write_all(&buffer[..n])
            .map_err(|e| AppError::io(out_path, e))?;
        *total_bytes += n as u64;
        written += n as u64;
    }
    Ok(written)
}

#[cfg(test)]
mod tests {
    use super::{copy_entry_with_total_limit, mark_visited_dir};
    use std::collections::HashSet;
    use std::io::Cursor;
    use std::path::Path;
    use tempfile::tempdir;

    #[test]
    fn mark_visited_dir_tracks_canonical_duplicates() {
        let temp = tempdir().expect("tempdir");
        let dir = temp.path().join("skills");
        std::fs::create_dir_all(&dir).expect("create dir");

        let mut visited = HashSet::new();
        assert!(mark_visited_dir(&dir, &mut visited).expect("first visit"));
        assert!(!mark_visited_dir(&dir, &mut visited).expect("second visit"));
    }

    #[test]
    fn copy_entry_with_total_limit_rejects_oversized_stream_before_write() {
        let mut reader = Cursor::new(vec![1u8; 16]);
        let mut writer = Vec::new();
        let mut total_bytes = 0u64;

        let err = copy_entry_with_total_limit(
            &mut reader,
            &mut writer,
            &mut total_bytes,
            8,
            Path::new("skills-extracted/file.bin"),
        )
        .expect_err("stream larger than limit should be rejected");
        assert!(
            err.to_string().contains("too large") || err.to_string().contains("超过"),
            "unexpected error: {err}"
        );
        assert_eq!(
            writer.len(),
            0,
            "should not write when the first chunk exceeds limit"
        );
    }
}