//! rust-langrpg — RPG IV compiler CLI
//!
//! Parses one or more RPG IV source files using the embedded BNF grammar
//! and optionally writes the resulting parse tree to an output file.
//!
//! ## Usage
//!
//! ```text
//! rust-langrpg [OPTIONS] <SOURCES>...
//!
//! Arguments:
//!   <SOURCES>...  RPG IV source file(s) to parse
//!
//! Options:
//!   -o <OUTPUT>   Write the parse tree to this file
//!   -h, --help    Print help
//!   -V, --version Print version
//! ```
//!
//! ## Example
//!
//! ```text
//! cargo run --release -- -o out.txt hello.rpg
//! ```

use std::{
    fs,
    io::{self, Write},
    path::PathBuf,
    process,
};

use clap::Parser;
use rust_langrpg::{load_grammar, parse_as};

// ─────────────────────────────────────────────────────────────────────────────
// CLI definition
// ─────────────────────────────────────────────────────────────────────────────

/// RPG IV free-format compiler — parses source files and emits parse trees.
#[derive(Parser, Debug)]
#[command(name = "rust-langrpg", version, about, long_about = None)]
struct Cli {
    /// RPG IV source file(s) to parse.
    #[arg(required = true, value_name = "SOURCES")]
    sources: Vec<PathBuf>,

    /// Write the parse tree(s) to this file.
    /// If omitted the tree is not printed.
    #[arg(short = 'o', value_name = "OUTPUT")]
    output: Option<PathBuf>,
}

// ─────────────────────────────────────────────────────────────────────────────
// Entry point
// ─────────────────────────────────────────────────────────────────────────────

fn main() {
    let cli = Cli::parse();

    // ── Load grammar ─────────────────────────────────────────────────────────
    let grammar = match load_grammar() {
        Ok(g) => g,
        Err(e) => {
            eprintln!("error: failed to load RPG IV grammar: {e}");
            process::exit(1);
        }
    };

    // ── Build parser ─────────────────────────────────────────────────────────
    let parser = match grammar.build_parser() {
        Ok(p) => p,
        Err(e) => {
            eprintln!("error: failed to build parser: {e}");
            process::exit(1);
        }
    };

    // ── Open output sink ──────────────────────────────────────────────────────
    // `output` is Box<dyn Write> so we can use either a file or a sink that
    // discards everything when -o was not supplied.
    let mut output: Box<dyn Write> = match &cli.output {
        Some(path) => {
            let file = fs::File::create(path).unwrap_or_else(|e| {
                eprintln!("error: cannot open output file '{}': {e}", path.display());
                process::exit(1);
            });
            Box::new(io::BufWriter::new(file))
        }
        None => Box::new(io::sink()),
    };

    // ── Process each source file ──────────────────────────────────────────────
    let mut any_error = false;

    for path in &cli.sources {
        let source = match fs::read_to_string(path) {
            Ok(s) => s,
            Err(e) => {
                eprintln!("error: cannot read '{}': {e}", path.display());
                any_error = true;
                continue;
            }
        };

        // Try the top-level "program" rule first; fall back to "source-file"
        // so the binary is useful even if only one of those rule names exists
        // in the grammar.
        let tree = parse_as(&parser, source.trim(), "program")
            .or_else(|| parse_as(&parser, source.trim(), "source-file"));

        match tree {
            Some(t) => {
                eprintln!("ok: {}", path.display());
                writeln!(output, "=== {} ===", path.display())
                    .and_then(|_| writeln!(output, "{t}"))
                    .unwrap_or_else(|e| {
                        eprintln!("error: write failed: {e}");
                        any_error = true;
                    });
            }
            None => {
                eprintln!("error: '{}' did not match the RPG IV grammar", path.display());
                any_error = true;
            }
        }
    }

    if any_error {
        process::exit(1);
    }
}