use std::{
    env, fs,
    path::{Path, PathBuf},
    process::ExitCode,
};

use decodal_core::{Data, Diagnostic, DiagnosticKind, Engine, LoadedSource, SourceLoader, Span};

fn main() -> ExitCode {
    match run() {
        Ok(()) => ExitCode::SUCCESS,
        Err(error) => {
            print_diagnostic(&error);
            ExitCode::FAILURE
        }
    }
}

fn run() -> Result<(), Diagnostic> {
    let mut args = env::args().skip(1);
    let first = args.next().unwrap_or_else(|| String::from("--help"));
    match first.as_str() {
        "--help" | "-h" => {
            print_help();
            Ok(())
        }
        "--version" | "-V" => {
            println!("Decodal {}", decodal_core::version());
            Ok(())
        }
        "check" => {
            let path = args.next().unwrap_or_else(|| String::from("-"));
            let data = materialize_path(&path)?;
            drop(data);
            println!("ok");
            Ok(())
        }
        "eval" | "materialize" => {
            let path = args.next().unwrap_or_else(|| String::from("-"));
            let data = materialize_path(&path)?;
            print_data(&data, 0);
            println!();
            Ok(())
        }
        path => {
            let data = materialize_path(path)?;
            print_data(&data, 0);
            println!();
            Ok(())
        }
    }
}

fn materialize_path(path: &str) -> Result<Data, Diagnostic> {
    let root = read_root_source(path)?;
    let mut engine = Engine::new(FsLoader);
    let module = engine.add_root_source(root.key, root.name, &root.source)?;
    let value = engine.eval_module(module)?;
    engine.materialize(&value)
}

fn read_root_source(path: &str) -> Result<LoadedSource, Diagnostic> {
    if path == "-" {
        use std::io::Read;
        let mut source = String::new();
        std::io::stdin()
            .read_to_string(&mut source)
            .map_err(|error| {
                Diagnostic::new(
                    DiagnosticKind::Import,
                    Span::default(),
                    format!("failed to read stdin: {error}"),
                )
            })?;
        Ok(LoadedSource {
            key: String::from("<stdin>"),
            name: String::from("<stdin>"),
            source,
        })
    } else {
        load_path(Path::new(path))
    }
}

#[derive(Debug, Clone, Copy)]
struct FsLoader;

impl SourceLoader for FsLoader {
    fn load(
        &mut self,
        current_key: Option<&str>,
        specifier: &str,
    ) -> Result<LoadedSource, Diagnostic> {
        let path = Path::new(specifier);
        let path = if path.is_absolute() {
            PathBuf::from(path)
        } else if let Some(current_key) = current_key.filter(|key| *key != "<stdin>") {
            Path::new(current_key)
                .parent()
                .unwrap_or_else(|| Path::new("."))
                .join(path)
        } else {
            PathBuf::from(path)
        };
        load_path(&path)
    }
}

fn load_path(path: &Path) -> Result<LoadedSource, Diagnostic> {
    let canonical = path.canonicalize().map_err(|error| {
        Diagnostic::new(
            DiagnosticKind::Import,
            Span::default(),
            format!("failed to resolve `{}`: {error}", path.display()),
        )
    })?;
    let source = fs::read_to_string(&canonical).map_err(|error| {
        Diagnostic::new(
            DiagnosticKind::Import,
            Span::default(),
            format!("failed to read `{}`: {error}", canonical.display()),
        )
    })?;
    let key = canonical.to_string_lossy().into_owned();
    Ok(LoadedSource {
        name: key.clone(),
        key,
        source,
    })
}

fn print_help() {
    println!("Decodal - Deferred Constraint Data Language");
    println!();
    println!("Usage:");
    println!("  decodal <file.dcdl>        Materialize a DCDL file");
    println!("  decodal eval <file.dcdl>   Materialize a DCDL file");
    println!("  decodal check <file.dcdl>  Evaluate and materialize without printing data");
    println!("  decodal -                  Read DCDL source from stdin");
}

fn print_diagnostic(error: &Diagnostic) {
    eprintln!(
        "error[{kind:?}] {source}:{start}..{end}: {message}",
        kind = error.kind,
        source = error.span.source.0,
        start = error.span.start,
        end = error.span.end,
        message = error.message,
    );
    for label in &error.labels {
        eprintln!(
            "  note {source}:{start}..{end}: {message}",
            source = label.span.source.0,
            start = label.span.start,
            end = label.span.end,
            message = label.message,
        );
    }
}

fn print_data(data: &Data, indent: usize) {
    match data {
        Data::String(value) => print_string(value),
        Data::Int(value) => print!("{value}"),
        Data::Float(value) => print!("{value}"),
        Data::Bool(value) => print!("{value}"),
        Data::Array(items) => {
            print!("[");
            if !items.is_empty() {
                println!();
                for (index, item) in items.iter().enumerate() {
                    print_indent(indent + 2);
                    print_data(item, indent + 2);
                    if index + 1 != items.len() {
                        print!(",");
                    }
                    println!();
                }
                print_indent(indent);
            }
            print!("]");
        }
        Data::Object(fields) => {
            print!("{{");
            if !fields.is_empty() {
                println!();
                for (index, field) in fields.iter().enumerate() {
                    print_indent(indent + 2);
                    print_string(&field.name);
                    print!(": ");
                    print_data(&field.value, indent + 2);
                    if index + 1 != fields.len() {
                        print!(",");
                    }
                    println!();
                }
                print_indent(indent);
            }
            print!("}}");
        }
    }
}

fn print_indent(indent: usize) {
    for _ in 0..indent {
        print!(" ");
    }
}

fn print_string(value: &str) {
    print!("\"");
    for ch in value.chars() {
        match ch {
            '"' => print!("\\\""),
            '\\' => print!("\\\\"),
            '\n' => print!("\\n"),
            '\r' => print!("\\r"),
            '\t' => print!("\\t"),
            ch => print!("{ch}"),
        }
    }
    print!("\"");
}