//! Length-prefixed JSON over a unix socket: u32 big-endian frame length,
//! then the serialized request/response.

use serde::{Deserialize, Serialize};
use tokio::io::{AsyncReadExt, AsyncWriteExt};
use uuid::Uuid;

use crate::BrokerError;

const MAX_FRAME: u32 = 1024 * 1024;

#[derive(Debug, Serialize, Deserialize)]
#[serde(tag = "op", rename_all = "snake_case")]
pub enum Request {
    StoreSecret {
        workspace_id: Uuid,
        kind: String,
        plaintext: String,
    },
    SecretKind {
        secret_id: Uuid,
    },
    /// Verifies a Slack request signature (v0 HMAC-SHA256) against the
    /// connection's signing secret — which never leaves the broker.
    VerifySlackSignature {
        secret_id: Uuid,
        timestamp: String,
        body: String,
        signature: String,
    },
    /// Performs an HTTP POST with the secret injected as a bearer token.
    /// Requires consuming the approval's single-use execution grant.
    InvokeHttp {
        approval_id: Uuid,
        secret_id: Uuid,
        url: String,
        #[serde(default)]
        body: serde_json::Value,
    },
    /// Read-only HTTP GET with the secret injected as a bearer token. Returns
    /// the response body as JSON without ever exposing the credential to the
    /// caller. Used by low-privilege data-fetching flows (listing an org's
    /// repositories on GitHub / Gitea / GitLab) that don't need the
    /// single-use grant `InvokeHttp` demands. The URL scheme is still
    /// restricted to http(s).
    FetchAuthorized {
        secret_id: Uuid,
        url: String,
    },
}

#[derive(Debug, Serialize, Deserialize)]
#[serde(tag = "result", rename_all = "snake_case")]
pub enum Response {
    SecretStored {
        secret_id: Uuid,
    },
    SecretKind {
        kind: String,
    },
    HttpDone {
        status: u16,
    },
    /// Response to a `FetchAuthorized`: HTTP status + parsed JSON body.
    /// Body is `null` when the response wasn't JSON-parseable.
    HttpJson {
        status: u16,
        body: serde_json::Value,
    },
    Verified {
        valid: bool,
    },
    Error {
        kind: ErrorKind,
        message: String,
    },
}

#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum ErrorKind {
    GrantRefused,
    Invalid,
    NotFound,
    Internal,
}

impl Response {
    pub fn from_error(err: &BrokerError) -> Response {
        let (kind, message) = match err {
            BrokerError::GrantRefused => (ErrorKind::GrantRefused, err.to_string()),
            BrokerError::Invalid(m) => (ErrorKind::Invalid, m.clone()),
            BrokerError::NotFound => (ErrorKind::NotFound, err.to_string()),
            BrokerError::Crypto(m) | BrokerError::Io(m) => (ErrorKind::Internal, m.clone()),
        };
        Response::Error { kind, message }
    }

    pub fn into_result(self) -> Result<Response, BrokerError> {
        match self {
            Response::Error { kind, message } => Err(match kind {
                ErrorKind::GrantRefused => BrokerError::GrantRefused,
                ErrorKind::Invalid => BrokerError::Invalid(message),
                ErrorKind::NotFound => BrokerError::NotFound,
                ErrorKind::Internal => BrokerError::Io(message),
            }),
            ok => Ok(ok),
        }
    }
}

pub async fn write_frame<W, T>(writer: &mut W, value: &T) -> Result<(), BrokerError>
where
    W: AsyncWriteExt + Unpin,
    T: Serialize,
{
    let payload = serde_json::to_vec(value).map_err(|e| BrokerError::Io(e.to_string()))?;
    let len = u32::try_from(payload.len()).map_err(|_| BrokerError::Invalid("frame".into()))?;
    if len > MAX_FRAME {
        return Err(BrokerError::Invalid("frame too large".into()));
    }
    writer
        .write_all(&len.to_be_bytes())
        .await
        .map_err(|e| BrokerError::Io(e.to_string()))?;
    writer
        .write_all(&payload)
        .await
        .map_err(|e| BrokerError::Io(e.to_string()))?;
    Ok(())
}

pub async fn read_frame<R, T>(reader: &mut R) -> Result<T, BrokerError>
where
    R: AsyncReadExt + Unpin,
    T: for<'de> Deserialize<'de>,
{
    let mut len_bytes = [0u8; 4];
    reader
        .read_exact(&mut len_bytes)
        .await
        .map_err(|e| BrokerError::Io(e.to_string()))?;
    let len = u32::from_be_bytes(len_bytes);
    if len > MAX_FRAME {
        return Err(BrokerError::Invalid("frame too large".into()));
    }
    let mut payload = vec![0u8; len as usize];
    reader
        .read_exact(&mut payload)
        .await
        .map_err(|e| BrokerError::Io(e.to_string()))?;
    serde_json::from_slice(&payload).map_err(|e| BrokerError::Io(e.to_string()))
}