use axum::http::StatusCode;
use axum::response::{IntoResponse, Response};
use axum::Json;
use serde_json::json;

/// API-surface errors with their HTTP mapping. Internal causes are logged
/// server-side, never echoed to clients.
#[derive(Debug, thiserror::Error)]
pub enum ApiError {
    #[error("bad request")]
    BadRequest,
    #[error("unauthorized")]
    Unauthorized,
    #[error("forbidden")]
    Forbidden,
    #[error("not found")]
    NotFound,
    #[error("conflict")]
    Conflict,
    #[error("{0}")]
    Quota(String),
    /// A 400 whose REASON the caller needs.
    ///
    /// Same argument as `Unavailable` below, one status code down. The
    /// proposal decide handlers each computed a precise refusal — "the mission
    /// is running, not a draft", "no node can boot that backend any more" —
    /// logged it to stderr, and returned a bare `BadRequest`. The person who
    /// needed the sentence was the one clicking Approve, and they got
    /// "bad request". `mission_plan::Refusal` exists and is written as
    /// human-readable copy; this is how it reaches them.
    #[error("{0}")]
    Refused(String),
    /// A dependency is temporarily refusing work and will accept it later —
    /// today, the Claude Code subscription's rate limit. Distinct from
    /// `Internal` because the operator's next action is different: wait and
    /// press the button again, rather than read a server log. A 500 with
    /// "internal error" sent them looking for a bug that was not there.
    #[error("{0}")]
    Unavailable(String),
    #[error("internal error")]
    Internal,
}

impl From<cm_db::DbError> for ApiError {
    fn from(err: cm_db::DbError) -> Self {
        match err {
            cm_db::DbError::NotFound => ApiError::NotFound,
            _ => ApiError::Internal,
        }
    }
}

impl From<sqlx::Error> for ApiError {
    fn from(err: sqlx::Error) -> Self {
        ApiError::from(cm_db::DbError::from(err))
    }
}

impl From<cm_auth::AuthError> for ApiError {
    fn from(err: cm_auth::AuthError) -> Self {
        match err {
            cm_auth::AuthError::InvalidCredentials | cm_auth::AuthError::Unauthenticated => {
                ApiError::Unauthorized
            }
            _ => ApiError::Internal,
        }
    }
}

impl IntoResponse for ApiError {
    fn into_response(self) -> Response {
        let status = match self {
            ApiError::BadRequest | ApiError::Refused(_) => StatusCode::BAD_REQUEST,
            ApiError::Unauthorized => StatusCode::UNAUTHORIZED,
            ApiError::Forbidden => StatusCode::FORBIDDEN,
            ApiError::NotFound => StatusCode::NOT_FOUND,
            ApiError::Conflict => StatusCode::CONFLICT,
            ApiError::Quota(_) => StatusCode::PAYMENT_REQUIRED,
            ApiError::Unavailable(_) => StatusCode::SERVICE_UNAVAILABLE,
            ApiError::Internal => StatusCode::INTERNAL_SERVER_ERROR,
        };
        (status, Json(json!({ "error": self.to_string() }))).into_response()
    }
}

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

    /// A refusal must carry its reason into the response body.
    ///
    /// The proposal decide handlers each computed a precise sentence and then
    /// returned a bare `BadRequest`, so the person clicking Approve saw
    /// "bad request" while the reason went to a server log they cannot read.
    #[tokio::test]
    async fn a_refusal_reaches_the_caller_and_a_bare_bad_request_does_not_pretend_to() {
        let refused = ApiError::Refused("this mission is running, not a draft".into());
        let response = refused.into_response();
        assert_eq!(response.status(), StatusCode::BAD_REQUEST);
        let body = to_bytes(response.into_body(), 64 * 1024).await.unwrap();
        let text = String::from_utf8_lossy(&body);
        assert!(
            text.contains("running, not a draft"),
            "the reason must be in the body, not only in the server log: {text}"
        );

        // The bare variant stays as it was — same status, no invented detail.
        let bare = ApiError::BadRequest.into_response();
        assert_eq!(bare.status(), StatusCode::BAD_REQUEST);
    }
}