use serde::{Deserialize, Serialize};
use std::path::{Path, PathBuf};
use tauri::Manager;

#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
struct DownloadOwnershipRecord {
    id: String,
    primary_path: String,
}

pub fn canonical_download_filename(filename: &str) -> String {
    let leaf = filename.replace('\\', "/");
    let leaf = Path::new(&leaf)
        .file_name()
        .and_then(|name| name.to_str())
        .unwrap_or("download");
    let sanitized = leaf
        .chars()
        .map(|character| {
            if character.is_control()
                || matches!(
                    character,
                    '<' | '>' | ':' | '"' | '/' | '\\' | '|' | '?' | '*'
                )
            {
                '-'
            } else {
                character
            }
        })
        .collect::<String>();
    let sanitized = sanitized.trim().trim_end_matches(['.', ' ']);
    if sanitized.is_empty() || matches!(sanitized, "." | "..") {
        "download".to_string()
    } else if crate::platform::is_windows_reserved_filename(sanitized) {
        let path = Path::new(sanitized);
        let stem = path
            .file_stem()
            .and_then(|value| value.to_str())
            .unwrap_or("download");
        match path.extension().and_then(|value| value.to_str()) {
            Some(extension) => format!("{stem}-.{extension}"),
            None => format!("{stem}-"),
        }
    } else {
        sanitized.to_string()
    }
}

pub fn expected_primary_path(
    app_handle: &tauri::AppHandle,
    destination: &str,
    filename: &str,
) -> Result<PathBuf, String> {
    let resolved_dest = crate::resolve_path(destination, app_handle);
    if !crate::is_safe_path(&resolved_dest, app_handle) {
        return Err("Path traversal blocked".to_string());
    }

    let safe_filename = canonical_download_filename(filename);
    Ok(resolved_dest.join(safe_filename))
}

pub fn register_expected(
    app_handle: &tauri::AppHandle,
    id: &str,
    destination: &str,
    filename: &str,
) -> Result<(), String> {
    let path = expected_primary_path(app_handle, destination, filename)?;
    set_primary_path(app_handle, id, &path)
}

pub fn set_primary_path(
    app_handle: &tauri::AppHandle,
    id: &str,
    path: &Path,
) -> Result<(), String> {
    if !path.is_absolute() {
        return Err("Download ownership path must be absolute".to_string());
    }
    if path.components().any(|component| {
        matches!(
            component,
            std::path::Component::ParentDir | std::path::Component::CurDir
        )
    }) {
        return Err("Download ownership path traversal is not allowed".to_string());
    }
    if std::fs::symlink_metadata(path).is_ok_and(|metadata| metadata.file_type().is_symlink()) {
        return Err("Download ownership path may not be a symlink".to_string());
    }

    let database = app_handle.state::<crate::db::DbState>();
    let connection = database.lock()?;
    crate::db::set_ownership(&connection, id, &path.to_string_lossy())
}

pub fn remove(app_handle: &tauri::AppHandle, id: &str) -> Result<(), String> {
    let database = app_handle.state::<crate::db::DbState>();
    let connection = database.lock()?;
    crate::db::remove_ownership(&connection, id)
}

pub fn primary_path_for_id<R: tauri::Runtime>(
    app_handle: &tauri::AppHandle<R>,
    id: &str,
) -> Result<Option<PathBuf>, String> {
    Ok(load_records(app_handle)?
        .into_iter()
        .find(|record| record.id == id)
        .map(|record| PathBuf::from(record.primary_path)))
}

pub fn known_primary_paths(app_handle: &tauri::AppHandle) -> Result<Vec<PathBuf>, String> {
    let mut paths: Vec<PathBuf> = load_records(app_handle)?
        .into_iter()
        .map(|record| PathBuf::from(record.primary_path))
        .collect();

    // One-time compatibility for downloads created before the backend-owned
    // registry existed. This imports the exact persisted queue path only.
    for path in legacy_download_queue_paths(app_handle)? {
        if !paths.iter().any(|existing| existing == &path) {
            paths.push(path);
        }
    }

    Ok(paths)
}

fn load_records<R: tauri::Runtime>(app_handle: &tauri::AppHandle<R>) -> Result<Vec<DownloadOwnershipRecord>, String> {
    let database = app_handle.state::<crate::db::DbState>();
    let connection = database.lock()?;
    crate::db::load_ownership(&connection).map(|records| {
        records
            .into_iter()
            .map(|(id, primary_path)| DownloadOwnershipRecord { id, primary_path })
            .collect()
    })
}

fn legacy_download_queue_paths(app_handle: &tauri::AppHandle) -> Result<Vec<PathBuf>, String> {
    let settings = crate::settings::load_settings(app_handle).ok();

    let downloads = {
        let database = app_handle.state::<crate::db::DbState>();
        let connection = database.lock()?;
        crate::db::load_downloads(&connection)?
            .into_iter()
            .map(|value| serde_json::from_str::<crate::ipc::DownloadItem>(&value))
            .collect::<Result<Vec<_>, _>>()
            .map_err(|error| format!("Invalid download queue ownership data: {error}"))?
    };

    let mut paths = Vec::new();
    for download in downloads {
        let category = format!("{:?}", download.category);
        let mut destinations = Vec::new();

        if let Some(destination) = download
            .destination
            .clone()
            .filter(|destination| !destination.trim().is_empty())
        {
            destinations.push(destination);
        }

        let category_destination = settings.as_ref().map(|settings| {
            settings
                .category_directory_overrides
                .get(&category)
                .cloned()
                .unwrap_or_else(|| {
                    let subfolder = settings
                        .category_subfolders
                        .get(&category)
                        .cloned()
                        .unwrap_or_else(|| category.clone());
                    let base = std::path::PathBuf::from(&settings.base_download_folder);
                    let destination = if subfolder.is_empty() {
                        base
                    } else {
                        base.join(subfolder)
                    };
                    destination.to_string_lossy().to_string()
                })
        });
        let default_destination = settings
            .as_ref()
            .map(|settings| settings.base_download_folder.clone());

        if destinations.is_empty() {
            let fallback_destination = category_destination.clone().or(default_destination.clone());
            if let Some(destination) = fallback_destination {
                destinations.push(destination);
            }
        }

        if matches!(download.status, crate::ipc::DownloadStatus::Completed) {
            if let Some(destination) = category_destination {
                destinations.push(destination);
            }
            if let Some(destination) = default_destination {
                destinations.push(destination);
            }
            destinations.push("~/Downloads".to_string());
        }

        for destination in destinations {
            if let Ok(path) = expected_primary_path(app_handle, &destination, &download.file_name) {
                if !paths.iter().any(|existing| existing == &path) {
                    paths.push(path);
                }
            }
        }
    }

    Ok(paths)
}

#[cfg(test)]
mod tests {
    use super::canonical_download_filename;

    #[test]
    fn canonicalizes_untrusted_download_filenames() {
        assert_eq!(
            canonical_download_filename("../folder/video?.mp4"),
            "video-.mp4"
        );
        assert_eq!(canonical_download_filename(" report. "), "report");
        assert_eq!(canonical_download_filename(".."), "download");
        assert_eq!(canonical_download_filename("CON.txt"), "CON-.txt");
        assert_eq!(canonical_download_filename("lpt9"), "lpt9-");
    }
}