use std::fmt::Display;
use std::process;

use clap::{Arg, ArgAction, ArgMatches, Command};
use clap_builder::parser::ValuesRef;
use clap_complete::Shell;

use crate::error::{MyError, MyResult};

pub enum ShellKind {
    Bash,
    PowerShell,
}

pub struct Config {
    pub paths: Vec<String>,
    pub values: Vec<String>,
    pub completion: Option<ShellKind>,
}

const PATHS_SHORT: &'static str = "Values and operations from text files";
const VALUES_SHORT: &'static str = "Values and operations from command line";
const SHELL_SHORT: &'static str = "Create completion script";

const PATHS_LONG: &'static str = "\
Read values and operations from text files or stdin";
const VALUES_LONG: &'static str = "\
Read values and operations from command line";
const SHELL_LONG: &'static str = "\
Create completion script:
Use \"--completion bash\" to create script for Bash
Use \"--completion ps\" to create script for PowerShell";

impl Config {
    pub fn new(name: String, args: Vec<String>) -> MyResult<Config> {
        let mut command = Self::create_command(name.clone());
        let matches = Self::create_matches(&mut command, args)?;
        let config = Self::create_config(&mut command, matches)?;
        if let Some(completion) = config.completion {
            Self::create_completion(&mut command, name, completion);
            process::exit(1);
        }
        return Ok(config);
    }

    fn create_command(name: String) -> Command {
        let mut index = 0;
        let command = Command::new(name)
            .version(clap::crate_version!())
            .about(clap::crate_description!())
            .author(clap::crate_authors!());
        let command = command.arg(Self::create_arg("paths", &mut index)
            .action(ArgAction::Append)
            .help(PATHS_SHORT)
            .long_help(PATHS_LONG));
        let command = command.arg(Self::create_arg("command", &mut index)
            .long("command")
            .short('c')
            .action(ArgAction::Append)
            .value_name("VALUE")
            .num_args(1..)
            .allow_negative_numbers(true)
            .help(VALUES_SHORT)
            .long_help(VALUES_LONG));
        let command = command.arg(Self::create_arg("completion", &mut index)
            .long("completion")
            .action(ArgAction::Set)
            .value_name("SHELL")
            .value_parser(["bash", "ps"])
            .hide_possible_values(true)
            .help(SHELL_SHORT)
            .long_help(SHELL_LONG));
        return command;
    }

    fn create_arg(name: &'static str, index: &mut usize) -> Arg {
        *index += 1;
        return Arg::new(name).display_order(*index);
    }

    fn create_matches(command: &mut Command, args: Vec<String>) -> clap::error::Result<ArgMatches> {
        match command.try_get_matches_from_mut(args) {
            Ok(found) => Ok(found),
            Err(error) => match error.kind() {
                clap::error::ErrorKind::DisplayHelp | clap::error::ErrorKind::DisplayVersion => {
                    let error = error.to_string();
                    let error = error.trim_end();
                    eprintln!("{error}");
                    process::exit(1);
                },
                _ => Err(error),
            }
        }
    }

    fn create_config(command: &mut Command, matches: ArgMatches) -> MyResult<Config> {
        let paths = Self::parse_values(matches.get_many("paths"));
        let values = Self::parse_values(matches.get_many("command"));
        let completion = Self::parse_completion(command, matches.get_one("completion"))?;
        let config = Self {
            paths,
            values,
            completion,
        };
        return Ok(config);
    }

    fn parse_values(values: Option<ValuesRef<String>>) -> Vec<String> {
        values.unwrap_or_default().map(String::to_string).collect()
    }

    fn parse_completion(command: &mut Command, value: Option<&String>) -> MyResult<Option<ShellKind>> {
        let value = value.map(String::as_ref);
        match value {
            Some("bash") => Ok(Some(ShellKind::Bash)),
            Some("ps") => Ok(Some(ShellKind::PowerShell)),
            Some(value) => Err(Self::make_error(command, "completion", value)),
            None => Ok(None),
        }
    }

    fn create_completion(command: &mut Command, name: String, value: ShellKind) {
        let mut stdout = std::io::stdout();
        let value = match value {
            ShellKind::Bash => Shell::Bash,
            ShellKind::PowerShell => Shell::PowerShell,
        };
        clap_complete::generate(value, command, name, &mut stdout);
    }

    fn make_error<T: Display>(command: &mut Command, option: &str, value: T) -> MyError {
        let message = format!("Invalid {option} option: {value}");
        let error = command.error(clap::error::ErrorKind::ValueValidation, message);
        return MyError::Clap(error);
    }
}

impl Default for Config {
    fn default() -> Self {
        Self {
            paths: Vec::new(),
            values: Vec::new(),
            completion: None,
        }
    }
}

#[cfg(test)]
mod tests {
    use std::fmt::Display;

    use crate::config::Config;

    #[test]
    fn test_paths_are_handled() {
        let expected: Vec<String> = vec![];
        let args = vec!["rpn"];
        let config = create_config(args);
        assert_eq!(expected, config.paths);

        let expected = vec!["file1"];
        let args = vec!["rpn", "file1"];
        let config = create_config(args);
        assert_eq!(expected, config.paths);

        let expected = vec!["file1", "file2"];
        let args = vec!["rpn", "file1", "file2"];
        let config = create_config(args);
        assert_eq!(expected, config.paths);
    }

    #[test]
    fn test_values_are_handled() {
        let expected = vec!["1"];
        let args = vec!["rpn", "-c", "1"];
        let config = create_config(args);
        assert_eq!(expected, config.values);

        let expected = vec!["1", "-2", "add"];
        let args = vec!["rpn", "--command", "1", "-2", "add"];
        let config = create_config(args);
        assert_eq!(expected, config.values);
    }

    fn create_config(args: Vec<&str>) -> Config {
        let mut command = Config::create_command(String::from("rpn"));
        let args = args.into_iter().map(String::from).collect();
        let matches = Config::create_matches(&mut command, args).unwrap_or_else(handle_error);
        let config = Config::create_config(&mut command, matches).unwrap_or_else(handle_error);
        return config;
    }

    fn handle_error<T, E: Display>(err: E)-> T {
        panic!("{}", err);
    }
}