use crate::haskell::{run_haskell_demo, DemoArgs};
use std::ffi::OsString;
use tracing::error;

pub fn run(args: impl IntoIterator<Item = OsString>) -> Result<(), i32> {
    let args: Vec<String> = args
        .into_iter()
        .map(|arg| arg.to_string_lossy().into_owned())
        .collect();

    match parse_command(&args) {
        Ok(Command::Help) => {
            print_usage(args.first().map(String::as_str).unwrap_or("integrations"));
            Ok(())
        }
        Ok(Command::RustCallsHaskell(demo_args)) => match run_haskell_demo(&demo_args) {
            Ok(output) => {
                println!("{output}");
                Ok(())
            }
            Err(message) => {
                error!("{message}");
                Err(1)
            }
        },
        Err(message) => {
            error!("{message}");
            print_usage(args.first().map(String::as_str).unwrap_or("integrations"));
            Err(1)
        }
    }
}

#[derive(Debug, PartialEq, Eq)]
enum Command {
    Help,
    RustCallsHaskell(DemoArgs),
}

fn parse_command(args: &[String]) -> Result<Command, String> {
    match args {
        [_program] => Ok(Command::Help),
        [_program, command] if command == "help" || command == "--help" || command == "-h" => {
            Ok(Command::Help)
        }
        [_program, command, rest @ ..] if command == "rust-calls-haskell" => {
            parse_demo_args(rest).map(Command::RustCallsHaskell)
        }
        [_program, command, ..] => Err(format!("unknown command: {command}")),
        [] => Ok(Command::Help),
    }
}

fn parse_demo_args(args: &[String]) -> Result<DemoArgs, String> {
    let name = args
        .first()
        .cloned()
        .unwrap_or_else(|| "Ada".to_string());
    let left = parse_i32_arg(args.get(1), "left operand", 7)?;
    let right = parse_i32_arg(args.get(2), "right operand", 5)?;
    let library_path = args.get(3).cloned();

    Ok(DemoArgs {
        name,
        left,
        right,
        library_path,
    })
}

fn parse_i32_arg(raw: Option<&String>, label: &str, default: i32) -> Result<i32, String> {
    match raw {
        Some(value) => value
            .parse::<i32>()
            .map_err(|_| format!("invalid {label}: {value}")),
        None => Ok(default),
    }
}

fn print_usage(program: &str) {
    println!("Usage:");
    println!("  {program} rust-calls-haskell [name] [left] [right] [haskell-lib-path]");
    println!();
    println!("Examples:");
    println!("  {program} rust-calls-haskell");
    println!("  {program} rust-calls-haskell Grace 8 3");
}

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

    #[test]
    fn parse_demo_args_uses_defaults() {
        let args: Vec<String> = Vec::new();
        let parsed = parse_demo_args(&args).expect("defaults should parse");

        assert_eq!(
            parsed,
            DemoArgs {
                name: "Ada".to_string(),
                left: 7,
                right: 5,
                library_path: None,
            }
        );
    }

    #[test]
    fn parse_demo_args_accepts_explicit_values() {
        let args = vec![
            "Linus".to_string(),
            "9".to_string(),
            "4".to_string(),
            "haskell/dist-newstyle/demo/libinterop_hs.so".to_string(),
        ];
        let parsed = parse_demo_args(&args).expect("explicit args should parse");

        assert_eq!(
            parsed,
            DemoArgs {
                name: "Linus".to_string(),
                left: 9,
                right: 4,
                library_path: Some("haskell/dist-newstyle/demo/libinterop_hs.so".to_string()),
            }
        );
    }

    #[test]
    fn parse_command_rejects_unknown_commands() {
        let args = vec!["integrations".to_string(), "wat".to_string()];
        let parsed = parse_command(&args);

        assert!(parsed.is_err());
    }
}