use std::env;
use std::ffi::OsString;
use std::path::{Path, PathBuf};

pub struct ParsedArgv {
    pub effective_cwd: PathBuf,
    pub has_git_dir_or_work_tree: bool,
    pub subcommand: Option<String>,
    pub is_version_query: bool,
}

const BOOL_TOP_FLAGS: &[&str] = &[
    "-p",
    "-P",
    "--paginate",
    "--no-pager",
    "--bare",
    "--no-replace-objects",
    "--html-path",
    "--man-path",
    "--info-path",
];

pub fn parse_top_level(argv: &[OsString]) -> ParsedArgv {
    let mut effective_cwd = env::current_dir().unwrap_or_else(|_| PathBuf::from("."));
    let mut has_git_dir_or_work_tree = false;
    let mut subcommand: Option<String> = None;
    let mut is_version_query = false;

    let mut i = 0;
    while i < argv.len() {
        let arg = &argv[i];

        if arg == "-C" {
            if let Some(p) = argv.get(i + 1) {
                effective_cwd = effective_cwd.join(Path::new(p));
                i += 2;
                continue;
            }
            break;
        }

        if arg == "-c" {
            i += 2;
            continue;
        }

        if arg == "--git-dir" || arg == "--work-tree" {
            has_git_dir_or_work_tree = true;
            i += 2;
            continue;
        }

        let Some(s) = arg.to_str() else { break };

        if s.starts_with("--git-dir=") || s.starts_with("--work-tree=") {
            has_git_dir_or_work_tree = true;
            i += 1;
            continue;
        }

        if s.starts_with("--namespace=")
            || s.starts_with("--config-env=")
            || s.starts_with("--exec-path=")
            || s == "--exec-path"
        {
            i += 1;
            continue;
        }

        if BOOL_TOP_FLAGS.contains(&s) {
            i += 1;
            continue;
        }

        if s == "--version" || s == "-v" {
            is_version_query = true;
            i += 1;
            continue;
        }

        if s == "--help" || s == "-h" {
            subcommand = Some("help".to_string());
            break;
        }

        if !s.starts_with('-') {
            subcommand = Some(s.to_string());
            break;
        }

        // Unknown leading flag — bail out; it presumably belongs to a subcommand
        // we couldn't identify.
        break;
    }

    ParsedArgv {
        effective_cwd,
        has_git_dir_or_work_tree,
        subcommand,
        is_version_query,
    }
}

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

    fn parse(args: &[&str]) -> ParsedArgv {
        let owned: Vec<OsString> = args.iter().map(OsString::from).collect();
        parse_top_level(&owned)
    }

    #[test]
    fn bare_subcommand() {
        let p = parse(&["status"]);
        assert_eq!(p.subcommand.as_deref(), Some("status"));
        assert!(!p.is_version_query);
        assert!(!p.has_git_dir_or_work_tree);
    }

    #[test]
    fn version_query() {
        let p = parse(&["--version"]);
        assert!(p.is_version_query);
        let p = parse(&["-v"]);
        assert!(p.is_version_query);
    }

    #[test]
    fn dash_capital_c_changes_cwd() {
        let p = parse(&["-C", "/tmp", "status"]);
        assert_eq!(p.subcommand.as_deref(), Some("status"));
        assert_eq!(p.effective_cwd, PathBuf::from("/tmp"));
    }

    #[test]
    fn git_dir_forces_passthrough_flag() {
        let p = parse(&["--git-dir=/foo", "status"]);
        assert!(p.has_git_dir_or_work_tree);

        let p = parse(&["--work-tree", "/foo", "status"]);
        assert!(p.has_git_dir_or_work_tree);
    }

    #[test]
    fn config_kv_consumes_two_args() {
        let p = parse(&["-c", "user.name=Foo", "log"]);
        assert_eq!(p.subcommand.as_deref(), Some("log"));
    }

    #[test]
    fn paginate_skipped() {
        let p = parse(&["--paginate", "log"]);
        assert_eq!(p.subcommand.as_deref(), Some("log"));
    }

    #[test]
    fn help_short_and_long() {
        assert_eq!(parse(&["--help"]).subcommand.as_deref(), Some("help"));
        assert_eq!(parse(&["-h"]).subcommand.as_deref(), Some("help"));
    }
}