//! Slash-command model for the custom structured CLI surface.
//!
//! This module is intentionally pure: it declares the stable command metadata and
//! validates names/prefixes, but it does not execute side effects.

use serde::{Deserialize, Serialize};

use crate::error::DomainError;

/// A slash-command source. Native commands are built into IdeA; plugin commands
/// will be contributed through the same registry contract later.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub enum SlashCommandSource {
    /// Built into IdeA.
    Native,
    /// Contributed by a plugin.
    Plugin {
        /// Opaque plugin id.
        plugin_id: String,
    },
}

/// Whether a command can currently be executed.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "camelCase", tag = "status")]
pub enum SlashCommandAvailability {
    /// The command can be executed now.
    Available,
    /// The command is known but cannot be executed in the current product state.
    Unavailable {
        /// Human-readable reason.
        reason: String,
    },
}

impl SlashCommandAvailability {
    /// Returns whether this availability allows execution.
    #[must_use]
    pub const fn is_available(&self) -> bool {
        matches!(self, Self::Available)
    }
}

/// Built-in command behaviour known to IdeA.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub enum NativeSlashCommand {
    /// Lists commands and help text.
    Help,
    /// Clears the current structured conversation view.
    Clean,
    /// Opens the profile switch flow. Implemented by ticket #164.
    Profile,
}

/// UI-facing slash-command metadata.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct SlashCommand {
    /// Canonical slash name, including the leading `/`.
    pub name: String,
    /// Short UI label/description.
    pub short_description: String,
    /// Whether the UI must ask for confirmation before execution.
    pub requires_confirmation: bool,
    /// Current command availability.
    pub availability: SlashCommandAvailability,
    /// Unified native/plugin source.
    pub source: SlashCommandSource,
    /// Built-in command discriminator when `source == native`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub native: Option<NativeSlashCommand>,
}

impl SlashCommand {
    /// Builds validated command metadata.
    ///
    /// # Errors
    /// Returns [`DomainError::EmptyField`] for an empty/blank name or description,
    /// and [`DomainError::Invariant`] when the name does not start with `/`.
    pub fn new(
        name: impl Into<String>,
        short_description: impl Into<String>,
        requires_confirmation: bool,
        availability: SlashCommandAvailability,
        source: SlashCommandSource,
        native: Option<NativeSlashCommand>,
    ) -> Result<Self, DomainError> {
        let name = name.into();
        let short_description = short_description.into();
        crate::validation::non_empty(&name, "slash_command.name")?;
        crate::validation::non_empty(&short_description, "slash_command.short_description")?;
        if !name.starts_with('/') {
            return Err(DomainError::Invariant(
                "slash command name must start with '/'".to_owned(),
            ));
        }
        Ok(Self {
            name,
            short_description,
            requires_confirmation,
            availability,
            source,
            native,
        })
    }
}

/// Returns the native IdeA slash commands in deterministic UI order.
#[must_use]
pub fn native_slash_commands() -> Vec<SlashCommand> {
    vec![
        SlashCommand::new(
            "/help",
            "Afficher les commandes disponibles",
            false,
            SlashCommandAvailability::Available,
            SlashCommandSource::Native,
            Some(NativeSlashCommand::Help),
        )
        .expect("valid native slash command"),
        SlashCommand::new(
            "/clean",
            "Nettoyer la conversation courante",
            false,
            SlashCommandAvailability::Available,
            SlashCommandSource::Native,
            Some(NativeSlashCommand::Clean),
        )
        .expect("valid native slash command"),
        SlashCommand::new(
            "/profile",
            "Changer le profil de l'agent",
            true,
            SlashCommandAvailability::Available,
            SlashCommandSource::Native,
            Some(NativeSlashCommand::Profile),
        )
        .expect("valid native slash command"),
    ]
}

/// Filters commands by a user-entered slash prefix.
///
/// Blank prefixes return every command. Prefixes without a leading `/` are
/// interpreted as if the slash was present, matching composer input.
#[must_use]
pub fn filter_slash_commands(
    commands: impl IntoIterator<Item = SlashCommand>,
    prefix: Option<&str>,
) -> Vec<SlashCommand> {
    let prefix = prefix.map(str::trim).filter(|p| !p.is_empty()).map(|p| {
        if p.starts_with('/') {
            p.to_owned()
        } else {
            format!("/{p}")
        }
    });
    commands
        .into_iter()
        .filter(|command| {
            prefix
                .as_ref()
                .is_none_or(|prefix| command.name.starts_with(prefix))
        })
        .collect()
}

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

    #[test]
    fn native_registry_exposes_help_clean_and_profile_placeholder() {
        let commands = native_slash_commands();
        let names = commands.iter().map(|c| c.name.as_str()).collect::<Vec<_>>();
        assert_eq!(names, vec!["/help", "/clean", "/profile"]);
        assert!(commands[0].availability.is_available());
        assert!(commands[1].availability.is_available());
        assert!(commands[2].availability.is_available());
        assert!(commands[2].requires_confirmation);
    }

    #[test]
    fn prefix_filter_accepts_with_or_without_leading_slash() {
        let names = filter_slash_commands(native_slash_commands(), Some("cl"))
            .into_iter()
            .map(|c| c.name)
            .collect::<Vec<_>>();
        assert_eq!(names, vec!["/clean"]);

        let names = filter_slash_commands(native_slash_commands(), Some("/pro"))
            .into_iter()
            .map(|c| c.name)
            .collect::<Vec<_>>();
        assert_eq!(names, vec!["/profile"]);
    }
}