use std::fs;
use std::fs::File;
use std::path::{Path, PathBuf};
use std::io::{ErrorKind, Write, BufRead, BufReader};
use std::collections::HashMap;
use rand::distributions::{Alphanumeric, DistString};

const LOCK_FILE: &str = ".mvwrap";

enum DirListEntry {
    Path(PathBuf),
    Text(String)
}

impl DirListEntry {
    fn to_string(&self) -> String {
        match self {
            DirListEntry::Text(line) => line.clone(),
            // TODO only strip first to chars if they're `./`
            DirListEntry::Path(path) => {
                let checkstring = path.display().to_string();
                if &checkstring[0..2] == "./" {
                    path.display().to_string()[2..].to_string()
                } else {
                    path.display().to_string()
                }
            },
        }
    }

    fn exists(&self) -> bool {
        match self {
            DirListEntry::Text(filename) => Path::new(filename).exists(),
            DirListEntry::Path(path) => path.exists(),
        }
    }
}

pub struct DirList {
    safe_source: bool,
    noop: bool,
    verbose: bool,
    entries: Vec<DirListEntry>,
}

impl DirList {
    pub fn from_current_dir() -> Self {
        let paths : Vec<PathBuf> = match fs::read_dir(".") {
            Err(e) if e.kind() == ErrorKind::NotFound => Vec::new(),
            Err(e) => panic!("Unexpected Error! {:?}", e),
            Ok(entries) => entries.filter_map(|e| e.ok())
                .map(|e| e.path())
                .collect()
        };


        let mut path_list : Vec<DirListEntry> = vec![];
        for path in paths {
            let path_string = path.display().to_string();
            if path_string != format!("./{}", LOCK_FILE) {
                path_list.push(DirListEntry::Path(path));
            }
        }

        path_list.sort_by_key(|dir| dir.to_string());

        Self {
            safe_source: true,
            noop: false,
            verbose: false,
            entries: path_list,
        }
    }

    pub fn from_file(src_file: &String) -> Self {
        let file = File::open(src_file).expect("no such file");
        let buf = BufReader::new(file);
        let lines = buf.lines()
            .map(|l| DirListEntry::Text(l.expect("Could not parse line")))
            .collect();

        Self {
            safe_source: true,
            noop: false,
            verbose: false,
            entries: lines,
        }
    }

    pub fn from_list(list: &[PathBuf]) -> Self {
        Self {
            safe_source: false,
            noop: false,
            verbose: false,
            entries: list.iter().map(|l| DirListEntry::Path(l.clone())).collect(),
        }
    }

    pub fn set_noop(&mut self) {
        self.noop = true;
    }

    pub fn set_verbose(&mut self) {
        self.verbose = true;
    }

    pub fn to_file(&self, target_file: &String) {
        let mut file = File::create(target_file).expect("no such file");

        for entry in &self.entries {
            writeln!(file, "{}", entry.to_string()).expect("Unable to write to file");
        }
    }

    pub fn move_to(&mut self, target_list: &DirList) -> Result<(), String> {
        let src_len = self.entries.len();
        let mut intermediate_files: HashMap<String, String> = HashMap::new();

        self.run_basic_checks(target_list)?;

        if ! self.safe_source {
            // if target == source => next
            // if target exists and is not in source list => Err
            // if target exists and is in source list => use intermediate files, which is normal functionality below
            let tgt_len = target_list.entries.len();
            for i in 0..tgt_len {
                if self.entries[i].to_string() != target_list.entries[i].to_string() {
                    if target_list.entries[i].exists() {
                        return Err(format!("ERROR: Target '{}' already exists", target_list.entries[i].to_string()).to_string());
                    }
                }

            }
        }

        for i in 0..src_len {
            if self.entries[i].to_string() != target_list.entries[i].to_string() {
                // is the destination already in the source list?
                // if so, an intermediate file is needed
                if self.entries.iter().any(|j| j.to_string() == target_list.entries[i].to_string()) {
                    let unique = Self::get_unique_entry(target_list);
                    intermediate_files.insert(unique.clone(), target_list.entries[i].to_string().clone());
                    if ! self.noop {
                        match &self.entries[i] {
                            DirListEntry::Text(name) => fs::rename(name.to_string(), &unique).expect("failed to rename file (text based, unique)"),
                            DirListEntry::Path(path) => fs::rename(path.as_path(), &unique).expect("failed to rename file (path based, unique)"),
                        }
                    }
                    if self.verbose { println!("Moving {} -> {}", self.entries[i].to_string(), unique); }
                } else {
                    if ! self.noop {
                        match &self.entries[i] {
                            DirListEntry::Text(name) => fs::rename(name.to_string(), &target_list.entries[i].to_string()).expect("failed to rename file (text based)"),
                            DirListEntry::Path(path) => fs::rename(path.as_path(), &target_list.entries[i].to_string()).expect("failed to rename file (path based)"),
                        }
                    }
                    if self.verbose { println!("Moving {} -> {}", self.entries[i].to_string(), target_list.entries[i].to_string()); }
                }
            }
        }
        for (src, dst) in intermediate_files.iter() {
            if ! self.noop { fs::rename(src, dst).expect("failed to rename file (intermediate name)"); }
            if self.verbose { println!("Moving {} -> {}", src, dst); }
        }
        Ok(())
    }

    fn get_unique_entry(target_list: &DirList) -> String {
        let mut string = Alphanumeric.sample_string(&mut rand::thread_rng(), 16);

        // Generate unique name that does not exist in current dir and is not in target_list
        while target_list.entries.iter().any(|j| j.to_string() == string) || Path::new(&string).is_file() {
            string = Alphanumeric.sample_string(&mut rand::thread_rng(), 16);
        }
        string
    }

    fn run_basic_checks(&self, target_list: &DirList) -> Result<(), String> {
        // Make sure there are an equal number of sources and destinations
        if self.entries.len() != target_list.entries.len() {
            return Err("ERROR: Source and target list don't have the same number of lines.".to_string());
        }

        // Make sure destination names are not empty
        if target_list.entries.iter().any(|i| i.to_string().is_empty()) {
            return Err("ERROR: You can't move to empty names.".to_string());
        }

        // Make sure all destination files are unique in target_list
        let unique_entries = target_list.entries.iter().map(|x| (x.to_string(), x.to_string())).collect::<HashMap<_, _>>();
        if target_list.entries.len() != unique_entries.len() {
            let doubles = self.show_doubles(target_list);
            let error = format!("ERROR: You're trying to move multiple files to the same name.\n{}", doubles);
            return Err(error);
        }
        Ok(())
    }

    fn show_doubles(&self, target_list: &DirList) -> String {
        let mut paths = HashMap::new();
        let mut doubles = String::new();

        for (linenr, _) in target_list.entries.iter().enumerate() {
            let path_name = target_list.entries[linenr].to_string().clone();
            paths.entry(target_list.entries[linenr].to_string()).or_insert(Vec::new());
            paths.get_mut(&path_name).unwrap().push(linenr);
        }

        for (path, lines) in paths.iter() {
            if lines.len() > 1 {
                for i in lines.iter() {
                    doubles = format!("{doubles}\n[line: {}] {} -> {}", i+1, self.entries[*i].to_string(), path);
                }
                doubles = format!("{doubles}\n");
            }
        }
        doubles
    }
}