//! Bot-level command registry for the Matrix bot.
//!
//! Commands registered here are handled directly by the bot without invoking
//! the LLM. The registry is the single source of truth — the `help` command
//! iterates it automatically so new commands appear in the help output as soon
//! as they are added.

/// A bot-level command that is handled without LLM invocation.
pub struct BotCommand {
    /// The command keyword (e.g., `"help"`). Always lowercase.
    pub name: &'static str,
    /// Short description shown in help output.
    pub description: &'static str,
    /// Handler that produces the response text (Markdown).
    pub handler: fn(&CommandContext) -> String,
}

/// Context passed to command handlers.
pub struct CommandContext<'a> {
    /// The bot's display name (e.g., "Timmy").
    pub bot_name: &'a str,
    /// Any text after the command keyword, trimmed.
    #[allow(dead_code)]
    pub args: &'a str,
}

/// Returns the full list of registered bot commands.
///
/// Add new commands here — they will automatically appear in `help` output.
pub fn commands() -> &'static [BotCommand] {
    &[BotCommand {
        name: "help",
        description: "Show this list of available commands",
        handler: handle_help,
    }]
}

/// Try to match a user message against a registered bot command.
///
/// The message is expected to be the raw body text from Matrix (e.g.,
/// `"@timmy help"`). The bot mention prefix is stripped before matching.
///
/// Returns `Some(response)` if a command matched, `None` otherwise (the
/// caller should fall through to the LLM).
pub fn try_handle_command(
    bot_name: &str,
    bot_user_id: &str,
    message: &str,
) -> Option<String> {
    let command_text = strip_bot_mention(message, bot_name, bot_user_id);
    let trimmed = command_text.trim();
    if trimmed.is_empty() {
        return None;
    }

    let (cmd_name, args) = match trimmed.split_once(char::is_whitespace) {
        Some((c, a)) => (c, a.trim()),
        None => (trimmed, ""),
    };
    let cmd_lower = cmd_name.to_ascii_lowercase();

    let ctx = CommandContext {
        bot_name,
        args,
    };

    commands()
        .iter()
        .find(|c| c.name == cmd_lower)
        .map(|c| (c.handler)(&ctx))
}

/// Strip the bot mention prefix from a raw message body.
///
/// Handles these forms (case-insensitive where applicable):
/// - `@bot_localpart:server.com rest` → `rest`
/// - `@bot_localpart rest` → `rest`
/// - `DisplayName rest` → `rest`
fn strip_bot_mention<'a>(message: &'a str, bot_name: &str, bot_user_id: &str) -> &'a str {
    let trimmed = message.trim();

    // Try full Matrix user ID (e.g. "@timmy:homeserver.local")
    if let Some(rest) = strip_prefix_ci(trimmed, bot_user_id) {
        return rest;
    }

    // Try @localpart (e.g. "@timmy")
    if let Some(localpart) = bot_user_id.split(':').next()
        && let Some(rest) = strip_prefix_ci(trimmed, localpart)
    {
        return rest;
    }

    // Try display name (e.g. "Timmy")
    if let Some(rest) = strip_prefix_ci(trimmed, bot_name) {
        return rest;
    }

    trimmed
}

/// Case-insensitive prefix strip that also requires the match to end at a
/// word boundary (whitespace, punctuation, or end-of-string).
fn strip_prefix_ci<'a>(text: &'a str, prefix: &str) -> Option<&'a str> {
    if text.len() < prefix.len() {
        return None;
    }
    if !text[..prefix.len()].eq_ignore_ascii_case(prefix) {
        return None;
    }
    let rest = &text[prefix.len()..];
    // Must be at end or followed by non-alphanumeric
    match rest.chars().next() {
        None => Some(rest), // exact match, empty remainder
        Some(c) if c.is_alphanumeric() || c == '-' || c == '_' => None, // not a word boundary
        _ => Some(rest),
    }
}

// ---------------------------------------------------------------------------
// Built-in command handlers
// ---------------------------------------------------------------------------

fn handle_help(ctx: &CommandContext) -> String {
    let mut output = format!("**{} Commands**\n\n", ctx.bot_name);
    for cmd in commands() {
        output.push_str(&format!("- **{}** — {}\n", cmd.name, cmd.description));
    }
    output
}

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

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

    // -- strip_bot_mention --------------------------------------------------

    #[test]
    fn strip_mention_full_user_id() {
        let rest = strip_bot_mention(
            "@timmy:homeserver.local help",
            "Timmy",
            "@timmy:homeserver.local",
        );
        assert_eq!(rest.trim(), "help");
    }

    #[test]
    fn strip_mention_localpart() {
        let rest = strip_bot_mention("@timmy help me", "Timmy", "@timmy:homeserver.local");
        assert_eq!(rest.trim(), "help me");
    }

    #[test]
    fn strip_mention_display_name() {
        let rest = strip_bot_mention("Timmy help", "Timmy", "@timmy:homeserver.local");
        assert_eq!(rest.trim(), "help");
    }

    #[test]
    fn strip_mention_display_name_case_insensitive() {
        let rest = strip_bot_mention("timmy help", "Timmy", "@timmy:homeserver.local");
        assert_eq!(rest.trim(), "help");
    }

    #[test]
    fn strip_mention_no_match_returns_original() {
        let rest = strip_bot_mention("hello world", "Timmy", "@timmy:homeserver.local");
        assert_eq!(rest, "hello world");
    }

    #[test]
    fn strip_mention_does_not_match_longer_name() {
        // "@timmybot" should NOT match "@timmy"
        let rest = strip_bot_mention("@timmybot help", "Timmy", "@timmy:homeserver.local");
        assert_eq!(rest, "@timmybot help");
    }

    #[test]
    fn strip_mention_comma_after_name() {
        let rest = strip_bot_mention("@timmy, help", "Timmy", "@timmy:homeserver.local");
        assert_eq!(rest.trim().trim_start_matches(',').trim(), "help");
    }

    // -- try_handle_command -------------------------------------------------

    #[test]
    fn help_command_matches() {
        let result = try_handle_command("Timmy", "@timmy:homeserver.local", "@timmy help");
        assert!(result.is_some(), "help command should match");
    }

    #[test]
    fn help_command_case_insensitive() {
        let result = try_handle_command("Timmy", "@timmy:homeserver.local", "@timmy HELP");
        assert!(result.is_some(), "HELP should match case-insensitively");
    }

    #[test]
    fn unknown_command_returns_none() {
        let result = try_handle_command(
            "Timmy",
            "@timmy:homeserver.local",
            "@timmy what is the weather?",
        );
        assert!(result.is_none(), "non-command should return None");
    }

    #[test]
    fn help_output_contains_all_commands() {
        let result = try_handle_command("Timmy", "@timmy:homeserver.local", "@timmy help");
        let output = result.unwrap();
        for cmd in commands() {
            assert!(
                output.contains(cmd.name),
                "help output must include command '{}'",
                cmd.name
            );
            assert!(
                output.contains(cmd.description),
                "help output must include description for '{}'",
                cmd.name
            );
        }
    }

    #[test]
    fn help_output_uses_bot_name() {
        let result = try_handle_command("HAL", "@hal:example.com", "@hal help");
        let output = result.unwrap();
        assert!(
            output.contains("HAL Commands"),
            "help output should use bot name: {output}"
        );
    }

    #[test]
    fn help_output_formatted_as_markdown() {
        let result = try_handle_command("Timmy", "@timmy:homeserver.local", "@timmy help");
        let output = result.unwrap();
        assert!(
            output.contains("**help**"),
            "command name should be bold: {output}"
        );
        assert!(
            output.contains("- **"),
            "commands should be in a list: {output}"
        );
    }

    #[test]
    fn empty_message_after_mention_returns_none() {
        let result = try_handle_command("Timmy", "@timmy:homeserver.local", "@timmy");
        assert!(
            result.is_none(),
            "bare mention with no command should fall through to LLM"
        );
    }

    // -- strip_prefix_ci ----------------------------------------------------

    #[test]
    fn strip_prefix_ci_basic() {
        assert_eq!(strip_prefix_ci("Hello world", "hello"), Some(" world"));
    }

    #[test]
    fn strip_prefix_ci_no_match() {
        assert_eq!(strip_prefix_ci("goodbye", "hello"), None);
    }

    #[test]
    fn strip_prefix_ci_word_boundary_required() {
        assert_eq!(strip_prefix_ci("helloworld", "hello"), None);
    }

    #[test]
    fn strip_prefix_ci_exact_match() {
        assert_eq!(strip_prefix_ci("hello", "hello"), Some(""));
    }

    // -- commands registry --------------------------------------------------

    #[test]
    fn commands_registry_is_not_empty() {
        assert!(
            !commands().is_empty(),
            "command registry must contain at least one command"
        );
    }

    #[test]
    fn all_command_names_are_lowercase() {
        for cmd in commands() {
            assert_eq!(
                cmd.name,
                cmd.name.to_ascii_lowercase(),
                "command name '{}' must be lowercase",
                cmd.name
            );
        }
    }

    #[test]
    fn all_commands_have_descriptions() {
        for cmd in commands() {
            assert!(
                !cmd.description.is_empty(),
                "command '{}' must have a description",
                cmd.name
            );
        }
    }
}