use std::{env, ffi::OsString, fs};

const ICON_FILE_EXTENSION: &'static str = ".svg";
pub const ICON_FILE_EXTENSION_LEN: usize = ICON_FILE_EXTENSION.len();

pub struct Icons {
    icons_dir_path: String,
    icon_filenames: Vec<OsString>,
}

impl Icons {
    /// Build the Icons (handler) struct
    ///
    /// Returns a result with the Icons struct or an error message
    pub fn build() -> Result<Self, &'static str> {
        let icons_dir_arg = env::args()
            .nth(1)
            .unwrap_or(String::from("vendor/lucide/icons"));

        let icon_dir = match fs::read_dir(&icons_dir_arg) {
            Ok(dir) => dir,
            Err(_) => return Err("Failed to read icon directory"),
        };

        let icon_filenames: Vec<_> = icon_dir
            .map(|entry| entry.unwrap().file_name())
            .filter(|entry| entry.to_str().unwrap_or("").ends_with(".svg"))
            .collect();

        Ok(Icons {
            icons_dir_path: icons_dir_arg,
            icon_filenames,
        })
    }

    /// Check if the icon exists
    /// 
    /// Cheap; does not actually call the fs - instead checks against the cached filenames in the Vec internal to this struct.
    /// Therefore, it is not guaranteed to be up-to-date with the actual filesystem
    /// 
    /// icon: the icon name to check (no .svg extension)
    pub fn has_iconname(&self, icon: &str) -> bool {
        self.icon_filenames
            .iter()
            .find(|&i| match i.to_str() {
                Some(i) => &i[..i.len() - ICON_FILE_EXTENSION_LEN] == icon,
                None => false,
            })
            .is_some()
    }

    /// Get the number of icons
    /// 
    /// Cheap; does not actually call the fs - instead returns the length of the cached filenames in the Vec internal to this struct.
    pub fn icons_len(&self) -> usize {
        self.icon_filenames.len()
    }

    /// Read an .svg icon from disk to a Vec<u8>
    /// 
    /// You may want to check if the icon exists first with has_iconname(), although that method does not guarantee the icon is still present on the disk.
    /// 
    /// icon: the icon name to read (no .svg extension)
    pub fn get_icon(&self, icon: &str) -> Option<Vec<u8>> {
        let icon_path = format!("{}/{}.svg", self.icons_dir_path, icon);
        fs::read(icon_path).ok()
    }

    /// Read an .svg icon from disk to a String, instead of a Vec<u8>
    /// 
    /// You may want to check if the icon exists first with has_iconname(), although that method does not guarantee the icon is still present on the disk.
    /// 
    /// icon: the icon name to read (no .svg extension)
    pub fn get_icon_string(&self, icon: &str) -> Option<String> {
        let icon_path = format!("{}/{}.svg", self.icons_dir_path, icon);
        fs::read_to_string(icon_path).ok()
    }
}