use poem::{
    http::{Method, header},
    middleware::Cors,
};

/// CORS (Cross-Origin Resource Sharing) configuration for the HTTP API.
///
/// Controls which origins can access the API from browsers. In development,
/// use permissive settings (`allowed_origins: ["*"]`). In production, use
/// restrictive settings with specific origins.
///
/// # Security Constraint
///
/// When `allow_credentials` is `true`, `allowed_origins` MUST NOT contain
/// wildcard `"*"`. This is enforced by browser security policy and will be
/// validated by the `build_cors()` function.
#[derive(Debug, serde::Deserialize, Clone)]
pub struct CorsSettings {
    /// List of allowed origin URLs (e.g., `["https://sta.example.com"]`).
    ///
    /// Use `["*"]` for development to allow all origins.
    /// In production, specify exact origins to prevent unauthorized access.
    #[serde(default)]
    pub allowed_origins: Vec<String>,
    /// Whether to allow credentials (cookies, authorization headers) in CORS requests.
    ///
    /// Set to `true` in production when using Authelia authentication.
    /// MUST be `false` when using wildcard `"*"` in `allowed_origins`.
    #[serde(default)]
    pub allow_credentials: bool,
    /// Duration in seconds that browsers can cache CORS preflight responses.
    ///
    /// Typical value: `3600` (1 hour). Higher values reduce preflight requests
    /// but delay policy changes from taking effect.
    #[serde(default = "default_max_age_secs")]
    pub max_age_secs: i32,
}

impl Default for CorsSettings {
    fn default() -> Self {
        Self {
            allowed_origins: vec![],
            allow_credentials: false,
            max_age_secs: 3600,
        }
    }
}

/// Default value for CORS max age in seconds (1 hour).
const fn default_max_age_secs() -> i32 {
    3600
}

impl From<CorsSettings> for Cors {
    fn from(val: CorsSettings) -> Self {
        assert!(
            !(val.allow_credentials && val.allowed_origins.contains(&"*".to_string())),
            "CORS misconfiguration: wildcard origin not allowed with credentials=true"
        );
        let mut cors = Self::new();
        for origin in &val.allowed_origins {
            cors = cors.allow_origin(origin);
        }
        cors = cors.allow_methods(vec![
            Method::GET,
            Method::POST,
            Method::PUT,
            Method::PATCH,
            Method::DELETE,
            Method::OPTIONS,
        ]);
        cors = cors.allow_headers(vec![header::CONTENT_TYPE, header::AUTHORIZATION]);
        cors = cors
            .allow_credentials(val.allow_credentials)
            .max_age(val.max_age_secs);
        tracing::info!(
            target: "backend::settings::cors",
            allowed_origins = ?val.allowed_origins,
            allow_credentials = ?val.allow_credentials,
            max_age_secs = ?val.max_age_secs,
            "CORS middleware configured"
        );
        cors
    }
}

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

    // T009: Tests for CorsSettings struct deserialization
    #[test]
    fn cors_settings_deserialize_from_yaml() {
        let yaml = r#"
            allowed_origins:
              - "http://localhost:5173"
              - "https://sta.example.com"
            allow_credentials: true
            max_age_secs: 7200
        "#;
        let settings: CorsSettings = serde_yaml::from_str(yaml).unwrap();
        assert_eq!(settings.allowed_origins.len(), 2);
        assert_eq!(settings.allowed_origins[0], "http://localhost:5173");
        assert_eq!(settings.allowed_origins[1], "https://sta.example.com");
        assert!(settings.allow_credentials);
        assert_eq!(settings.max_age_secs, 7200);
    }

    #[test]
    fn cors_settings_default_has_empty_origins() {
        let settings = CorsSettings::default();
        assert!(
            settings.allowed_origins.is_empty(),
            "Default CorsSettings should have empty allowed_origins for restrictive fail-safe"
        );
        assert!(
            !settings.allow_credentials,
            "Default CorsSettings should have credentials disabled"
        );
        assert_eq!(
            settings.max_age_secs, 3600,
            "Default CorsSettings should have 1 hour max_age"
        );
    }

    #[test]
    fn cors_settings_with_wildcard_deserializes() {
        let yaml = r#"
            allowed_origins:
              - "*"
            allow_credentials: false
            max_age_secs: 3600
        "#;
        let settings: CorsSettings = serde_yaml::from_str(yaml).unwrap();
        assert_eq!(settings.allowed_origins.len(), 1);
        assert_eq!(settings.allowed_origins[0], "*");
        assert!(!settings.allow_credentials);
        assert_eq!(settings.max_age_secs, 3600);
    }

    #[test]
    fn cors_settings_deserialize_with_defaults() {
        // Test partial deserialization using serde defaults
        let yaml = r#"
            allowed_origins:
              - "https://example.com"
        "#;
        let settings: CorsSettings = serde_yaml::from_str(yaml).unwrap();
        assert_eq!(settings.allowed_origins.len(), 1);
        assert_eq!(settings.allowed_origins[0], "https://example.com");
        // These should use defaults
        assert!(!settings.allow_credentials);
        assert_eq!(settings.max_age_secs, 3600);
    }

    // T013: Tests for From<CorsSettings> for Cors trait implementation
    #[test]
    fn cors_conversion_with_wildcard_origin() {
        let settings = CorsSettings {
            allowed_origins: vec!["*".to_string()],
            allow_credentials: false,
            max_age_secs: 3600,
        };

        // Should successfully convert without panic
        let _cors: Cors = settings.into();
    }

    #[test]
    fn cors_conversion_with_specific_origin() {
        let settings = CorsSettings {
            allowed_origins: vec!["https://sta.example.com".to_string()],
            allow_credentials: true,
            max_age_secs: 7200,
        };

        // Should successfully convert without panic
        let _cors: Cors = settings.into();
    }

    #[test]
    fn cors_conversion_with_multiple_origins() {
        let settings = CorsSettings {
            allowed_origins: vec![
                "http://localhost:5173".to_string(),
                "https://sta.example.com".to_string(),
            ],
            allow_credentials: false,
            max_age_secs: 3600,
        };

        // Should successfully convert without panic
        let _cors: Cors = settings.into();
    }

    #[test]
    #[should_panic(
        expected = "CORS misconfiguration: wildcard origin not allowed with credentials=true"
    )]
    fn cors_conversion_panics_on_wildcard_with_credentials() {
        let settings = CorsSettings {
            allowed_origins: vec!["*".to_string()],
            allow_credentials: true, // Invalid combination!
            max_age_secs: 3600,
        };

        // This should panic due to browser security constraint violation
        let _cors: Cors = settings.into();
    }

    #[test]
    fn cors_conversion_with_empty_origins() {
        let settings = CorsSettings::default();

        // Should successfully convert even with empty origins (restrictive CORS)
        let _cors: Cors = settings.into();
    }
}