//! LLM provider registry (issue #88): resolution helpers over the
//! `settings.providers` map — the default provider, its default model and
//! name validation. Tokens are deliberately out of scope here: they live in
//! the OS keyring under `providers/<name>/api_key` (issue #89).
//!
//! The install-time configuration (issues #90, #92) will resolve the
//! provider/model of an agent through these helpers.

use crate::config::{Config, ProviderDef};
use std::collections::BTreeMap;

/// Empty provider map shared by the helpers below (never mutated).
static EMPTY: BTreeMap<String, Option<ProviderDef>> = BTreeMap::new();

/// Every provider of the effective configuration (empty when unset).
/// `None` values are the YAML null-deletion markers and are skipped.
pub fn all(config: &Config) -> &BTreeMap<String, Option<ProviderDef>> {
    config.settings.providers.as_ref().unwrap_or(&EMPTY)
}

/// The providers actually defined (null markers filtered out).
pub fn defined(config: &Config) -> impl Iterator<Item = (&String, &ProviderDef)> {
    all(config)
        .iter()
        .filter_map(|(k, v)| v.as_ref().map(|def| (k, def)))
}

/// Look up one provider by name.
pub fn get<'a>(config: &'a Config, name: &str) -> Option<&'a ProviderDef> {
    config.settings.provider(name)
}

/// Name of the default provider, when set and defined.
pub fn default_name(config: &Config) -> Option<&str> {
    let (name, _) = config.settings.default_provider()?;
    Some(name.as_str())
}

/// The default provider entry (name + definition).
pub fn default(config: &Config) -> Option<(&String, &ProviderDef)> {
    config.settings.default_provider()
}

/// Model to use for a provider: the explicit model when given, otherwise
/// the provider's default model.
pub fn model_for<'a>(provider: &'a ProviderDef, explicit: Option<&'a str>) -> Option<&'a str> {
    explicit
        .filter(|m| !m.is_empty())
        .or(provider.default_model.as_deref())
}

/// Sorted provider names (for error messages listing the registry).
pub fn names(config: &Config) -> Vec<String> {
    let mut v: Vec<String> = defined(config).map(|(k, _)| k.clone()).collect();
    v.sort();
    v
}

/// Resolve the provider + model of an agent at install time (issue #90):
/// `flag --provider` > `agent.provider` > `settings.default_provider` ;
/// `flag --model` > `agent.model` > `provider.default_model`.
/// Returns None when no provider is configured at all.
pub fn resolve_for<'a>(
    config: &'a Config,
    agent_provider: Option<&'a str>,
    agent_model: Option<&'a str>,
    flag_provider: Option<&'a str>,
    flag_model: Option<&'a str>,
) -> Option<(&'a str, &'a ProviderDef, Option<&'a str>)> {
    let provider_name = flag_provider
        .filter(|p| !p.is_empty())
        .or(agent_provider.filter(|p| !p.is_empty()))
        .or_else(|| default_name(config))?;
    let def = get(config, provider_name)?;
    let model = model_for(
        def,
        flag_model
            .filter(|m| !m.is_empty())
            .or(agent_model.filter(|m| !m.is_empty())),
    );
    Some((provider_name, def, model))
}

/// Provider names accept the same slug rule as agent names: [a-z0-9_-].
pub fn is_valid_name(name: &str) -> bool {
    !name.is_empty()
        && name
            .chars()
            .all(|c| c.is_ascii_lowercase() || c.is_ascii_digit() || c == '-' || c == '_')
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::config::{Config, ProviderDef};

    fn config_with() -> Config {
        let mut c = Config::default();
        c.settings.default_provider = Some("openai".to_string());
        let mut providers = BTreeMap::new();
        providers.insert(
            "openai".to_string(),
            Some(ProviderDef {
                base_url: "https://api.openai.com/v1".to_string(),
                default_model: Some("gpt-5.2".to_string()),
                models: vec!["gpt-5.2".to_string(), "gpt-5.1-mini".to_string()],
            }),
        );
        providers.insert(
            "deepseek".to_string(),
            Some(ProviderDef {
                base_url: "https://api.deepseek.com".to_string(),
                default_model: None,
                models: vec!["deepseek-chat".to_string()],
            }),
        );
        c.settings.providers = Some(providers);
        c
    }

    #[test]
    fn resolves_the_default_provider() {
        let c = config_with();
        let (name, def) = default(&c).expect("default provider");
        assert_eq!(name, "openai");
        assert_eq!(def.base_url, "https://api.openai.com/v1");
        assert_eq!(default_name(&c), Some("openai"));
    }

    #[test]
    fn explicit_model_wins_over_the_default() {
        let c = config_with();
        let def = get(&c, "deepseek").unwrap();
        assert_eq!(model_for(def, None), None);
        assert_eq!(model_for(def, Some("deepseek-reasoner")), Some("deepseek-reasoner"));
        let openai = get(&c, "openai").unwrap();
        assert_eq!(model_for(openai, None), Some("gpt-5.2"));
        assert_eq!(model_for(openai, Some("gpt-5.1-mini")), Some("gpt-5.1-mini"));
    }

    #[test]
    fn default_missing_provider_is_none() {
        let mut c = config_with();
        c.settings.default_provider = Some("nope".to_string());
        assert!(default(&c).is_none());
        assert!(default_name(&c).is_none());
    }

    #[test]
    fn name_validation_follows_the_slug_rule() {
        assert!(is_valid_name("openai"));
        assert!(is_valid_name("deep-seek_2"));
        assert!(!is_valid_name("OpenAI"));
        assert!(!is_valid_name(""));
        assert!(!is_valid_name("has space"));
    }

    #[test]
    fn resolve_for_flag_beats_agent_beats_default() {
        let c = config_with();
        // 1. Rien de précisé → default_provider (openai) + son default_model.
        let (p, _, m) = resolve_for(&c, None, None, None, None).unwrap();
        assert_eq!(p, "openai");
        assert_eq!(m, Some("gpt-5.2"));
        // 2. Le provider déclaré par l'agent gagne sur le défaut.
        let (p, _, m) = resolve_for(&c, Some("deepseek"), None, None, None).unwrap();
        assert_eq!(p, "deepseek");
        assert_eq!(m, None, "deepseek n'a pas de default_model");
        // 3. Le flag --provider gagne sur tout.
        let (p, _, m) = resolve_for(&c, Some("openai"), None, Some("deepseek"), None).unwrap();
        assert_eq!(p, "deepseek");
        // 4. --model flag > agent.model > default_model.
        let (_, _, m) = resolve_for(&c, None, Some("o4-mini"), None, None).unwrap();
        assert_eq!(m, Some("o4-mini"));
        let (_, _, m) = resolve_for(&c, None, Some("o4-mini"), None, Some("gpt-5.1-mini")).unwrap();
        assert_eq!(m, Some("gpt-5.1-mini"));
    }

    #[test]
    fn resolve_for_none_without_any_provider() {
        let mut c = config_with();
        c.settings.default_provider = None;
        c.settings.providers = None;
        assert!(resolve_for(&c, None, None, None, None).is_none());
        // Un agent qui déclare son provider résout même sans défaut.
        assert!(resolve_for(&c, Some("openai"), None, None, None).is_none());
        let mut c2 = config_with();
        c2.settings.default_provider = None;
        assert_eq!(resolve_for(&c2, Some("openai"), None, None, None).unwrap().0, "openai");
    }

    #[test]
    fn names_are_sorted() {
        let c = config_with();
        assert_eq!(names(&c), vec!["deepseek".to_string(), "openai".to_string()]);
    }
}