use serde::{Deserialize, Serialize};
use serde_json::Value;

pub const API_VERSION: &str = "2026-04-08";
pub const API_RESPONSE_ENVELOPE_HEADER: &str = "x-genarrative-response-envelope";
pub const X_REQUEST_ID_HEADER: &str = "x-request-id";
pub const API_VERSION_HEADER: &str = "x-api-version";
pub const ROUTE_VERSION_HEADER: &str = "x-route-version";
pub const RESPONSE_TIME_HEADER: &str = "x-response-time-ms";

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq)]
pub struct ApiResponseMeta {
    #[serde(rename = "apiVersion")]
    pub api_version: String,
    #[serde(rename = "requestId", skip_serializing_if = "Option::is_none")]
    pub request_id: Option<String>,
    #[serde(rename = "routeVersion")]
    pub route_version: String,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub operation: Option<String>,
    #[serde(rename = "latencyMs")]
    pub latency_ms: u64,
    pub timestamp: String,
}

impl ApiResponseMeta {
    pub fn new(
        api_version: impl Into<String>,
        request_id: Option<String>,
        route_version: impl Into<String>,
        operation: Option<String>,
        latency_ms: u64,
        timestamp: impl Into<String>,
    ) -> Self {
        Self {
            api_version: api_version.into(),
            request_id,
            route_version: route_version.into(),
            operation,
            latency_ms,
            timestamp: timestamp.into(),
        }
    }
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
pub struct ApiErrorPayload {
    pub code: String,
    pub message: String,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub details: Option<Value>,
}

impl ApiErrorPayload {
    pub fn new(
        code: impl Into<String>,
        message: impl Into<String>,
        details: Option<Value>,
    ) -> Self {
        Self {
            code: code.into(),
            message: message.into(),
            details,
        }
    }
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
pub struct ApiSuccessEnvelope<T> {
    pub ok: bool,
    pub data: T,
    pub error: Option<ApiErrorPayload>,
    pub meta: ApiResponseMeta,
}

impl<T> ApiSuccessEnvelope<T> {
    pub fn new(data: T, meta: ApiResponseMeta) -> Self {
        Self {
            ok: true,
            data,
            error: None,
            meta,
        }
    }
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
pub struct ApiErrorEnvelope {
    pub ok: bool,
    pub data: Option<Value>,
    pub error: ApiErrorPayload,
    pub meta: ApiResponseMeta,
}

impl ApiErrorEnvelope {
    pub fn new(error: ApiErrorPayload, meta: ApiResponseMeta) -> Self {
        Self {
            ok: false,
            data: None,
            error,
            meta,
        }
    }
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
pub struct LegacyApiErrorResponse {
    pub error: ApiErrorPayload,
    pub meta: ApiResponseMeta,
}

impl LegacyApiErrorResponse {
    pub fn new(error: ApiErrorPayload, meta: ApiResponseMeta) -> Self {
        Self { error, meta }
    }
}

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

    #[test]
    fn success_envelope_serializes_null_error_field() {
        let payload = serde_json::to_value(ApiSuccessEnvelope::new(
            json!({ "service": "genarrative" }),
            ApiResponseMeta::new(
                API_VERSION,
                Some("req-1".to_string()),
                API_VERSION,
                Some("GET /healthz".to_string()),
                12,
                "2026-04-21T00:00:00Z",
            ),
        ))
        .expect("payload should serialize");

        assert_eq!(payload["ok"], Value::Bool(true));
        assert_eq!(payload["error"], Value::Null);
        assert_eq!(
            payload["meta"]["apiVersion"],
            Value::String(API_VERSION.to_string())
        );
    }

    #[test]
    fn error_envelope_serializes_null_data_field() {
        let payload = serde_json::to_value(ApiErrorEnvelope::new(
            ApiErrorPayload::new("BAD_REQUEST", "请求参数不合法", None),
            ApiResponseMeta::new(
                API_VERSION,
                Some("req-2".to_string()),
                API_VERSION,
                Some("POST /api/test".to_string()),
                21,
                "2026-04-21T00:00:01Z",
            ),
        ))
        .expect("payload should serialize");

        assert_eq!(payload["ok"], Value::Bool(false));
        assert_eq!(payload["data"], Value::Null);
        assert_eq!(
            payload["error"]["code"],
            Value::String("BAD_REQUEST".to_string())
        );
    }
}