#![allow(clippy::needless_doctest_main)]

//! A convenient trait for quickly writing binaries in a consistent pattern.
//!
//! # Examples
//! ```rust
//! use anyhow::anyhow;
//! use keyfork_bin::Bin;
//!
//! struct Main;
//!
//! impl Bin for Main {
//!     type Args = (String, String);
//!
//!     fn usage_hint(&self) -> Option<String> {
//!         Some(String::from("<param1> <param2>"))
//!     }
//!
//!     fn validate_args(&self, mut args: impl Iterator<Item = String>) -> keyfork_bin::ProcessResult<Self::Args> {
//!         let arg1 = args.next().ok_or(anyhow!("missing argument 1"))?;
//!         let arg2 = args.next().ok_or(anyhow!("missing argument 2"))?;
//!         Ok((arg1, arg2))
//!     }
//!
//!     fn run(&self, (arg1, arg2): Self::Args) -> keyfork_bin::ProcessResult {
//!         println!("First argument: {arg1}");
//!         println!("Second argument: {arg2}");
//!         Ok(())
//!     }
//!#
//!#    fn main(&self) -> std::process::ExitCode {
//!#        self.main_inner([String::from("hello"), String::from("world")].into_iter())
//!#    }
//! }
//!
//! fn main() {
//!     // Assume the program was called with something like "hello world"...
//!     let bin = Main;
//!     bin.main();
//! }
//! ```

use std::process::ExitCode;

/// A result that may contain any error.
pub type ProcessResult<T = ()> = Result<T, Box<dyn std::error::Error>>;

fn report_err(e: Box<dyn std::error::Error>) {
    eprintln!("Unable to run command: {e}");
    let mut source = e.source();
    while let Some(new_error) = source.take() {
        eprintln!("- Caused by: {new_error}");
        source = new_error.source();
    }
}

/// A trait for implementing the flow of a binary's execution.
pub trait Bin {
    /// The type for command-line arguments required by the function.
    type Args;

    /// A usage hint for how the arguments should be provided to the program.
    fn usage_hint(&self) -> Option<String> {
        None
    }

    /// Validate the arguments provided by the user into types required by the binary.
    #[allow(clippy::missing_errors_doc)]
    fn validate_args(&self, args: impl Iterator<Item = String>) -> ProcessResult<Self::Args>;

    /// Run the binary 
    #[allow(clippy::missing_errors_doc)]
    fn run(&self, args: Self::Args) -> ProcessResult;

    /// The default handler for running the binary and reporting any errors.
    fn main(&self) -> ExitCode {
        self.main_inner(std::env::args())
    }

    #[doc(hidden)]
    fn main_inner(&self, mut args: impl Iterator<Item = String>) -> ExitCode {
        let command = args.next();
        let args = match self.validate_args(args) {
            Ok(args) => args,
            Err(e) => {
                if let (Some(command), Some(hint)) = (command, self.usage_hint()) {
                    eprintln!("Usage: {command} {hint}");
                }
                report_err(e);
                return ExitCode::FAILURE;
            }
        };

        if let Err(e) = self.run(args) {
            report_err(e);
            return ExitCode::FAILURE;
        }

        ExitCode::SUCCESS
    }
}

/// A Bin that doesn't take any arguments.
pub struct ClosureBin<F: Fn() -> ProcessResult> {
    closure: F
}

impl<F> ClosureBin<F> where F: Fn() -> ProcessResult {
    /// Create a new Bin from a closure.
    ///
    /// # Examples
    /// ```rust
    /// use keyfork_bin::{Bin, ClosureBin};
    ///
    /// let bin = ClosureBin::new(|| {
    ///     println!("Hello, world!");
    ///     Ok(())
    /// });
    ///
    /// bin.main();
    /// ```
    pub fn new(closure: F) -> Self {
        Self {
            closure
        }
    }
}

impl<F> Bin for ClosureBin<F> where F: Fn() -> ProcessResult {
    type Args = ();

    fn validate_args(&self, _args: impl Iterator<Item = String>) -> ProcessResult<Self::Args> {
        Ok(())
    }

    fn run(&self, _args: Self::Args) -> ProcessResult {
        let c = &self.closure;
        c()
    }
}