use base64::Engine;
use serde::Deserialize;
use serde::Serialize;
use thiserror::Error;

#[derive(Deserialize, Serialize, Clone, Debug, PartialEq, Default)]
pub struct TokenData {
    /// Flat info parsed from the JWT in auth.json.
    #[serde(deserialize_with = "deserialize_id_token")]
    pub id_token: IdTokenInfo,

    /// This is a JWT.
    pub access_token: String,

    pub refresh_token: String,

    pub account_id: Option<String>,
}

/// Flat subset of useful claims in id_token from auth.json.
#[derive(Debug, Clone, PartialEq, Eq, Default, Serialize)]
pub struct IdTokenInfo {
    pub email: Option<String>,
    /// The ChatGPT subscription plan type
    /// (e.g., "free", "plus", "pro", "business", "enterprise", "edu").
    /// (Note: ae has not verified that those are the exact values.)
    pub chatgpt_plan_type: Option<String>,
}

#[derive(Deserialize)]
struct IdClaims {
    #[serde(default)]
    email: Option<String>,
    #[serde(rename = "https://api.openai.com/auth", default)]
    auth: Option<AuthClaims>,
}

#[derive(Deserialize)]
struct AuthClaims {
    #[serde(default)]
    chatgpt_plan_type: Option<String>,
}

#[derive(Debug, Error)]
pub enum IdTokenInfoError {
    #[error("invalid ID token format")]
    InvalidFormat,
    #[error(transparent)]
    Base64(#[from] base64::DecodeError),
    #[error(transparent)]
    Json(#[from] serde_json::Error),
}

pub(crate) fn parse_id_token(id_token: &str) -> Result<IdTokenInfo, IdTokenInfoError> {
    // JWT format: header.payload.signature
    let mut parts = id_token.split('.');
    let (_header_b64, payload_b64, _sig_b64) = match (parts.next(), parts.next(), parts.next()) {
        (Some(h), Some(p), Some(s)) if !h.is_empty() && !p.is_empty() && !s.is_empty() => (h, p, s),
        _ => return Err(IdTokenInfoError::InvalidFormat),
    };

    let payload_bytes = base64::engine::general_purpose::URL_SAFE_NO_PAD.decode(payload_b64)?;
    let claims: IdClaims = serde_json::from_slice(&payload_bytes)?;

    Ok(IdTokenInfo {
        email: claims.email,
        chatgpt_plan_type: claims.auth.and_then(|a| a.chatgpt_plan_type),
    })
}

fn deserialize_id_token<'de, D>(deserializer: D) -> Result<IdTokenInfo, D::Error>
where
    D: serde::Deserializer<'de>,
{
    let s = String::deserialize(deserializer)?;
    parse_id_token(&s).map_err(serde::de::Error::custom)
}

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

    #[test]
    #[expect(clippy::expect_used, clippy::unwrap_used)]
    fn id_token_info_parses_email_and_plan() {
        // Build a fake JWT with a URL-safe base64 payload containing email and plan.
        #[derive(Serialize)]
        struct Header {
            alg: &'static str,
            typ: &'static str,
        }
        let header = Header {
            alg: "none",
            typ: "JWT",
        };
        let payload = serde_json::json!({
            "email": "user@example.com",
            "https://api.openai.com/auth": {
                "chatgpt_plan_type": "pro"
            }
        });

        fn b64url_no_pad(bytes: &[u8]) -> String {
            base64::engine::general_purpose::URL_SAFE_NO_PAD.encode(bytes)
        }

        let header_b64 = b64url_no_pad(&serde_json::to_vec(&header).unwrap());
        let payload_b64 = b64url_no_pad(&serde_json::to_vec(&payload).unwrap());
        let signature_b64 = b64url_no_pad(b"sig");
        let fake_jwt = format!("{header_b64}.{payload_b64}.{signature_b64}");

        let info = parse_id_token(&fake_jwt).expect("should parse");
        assert_eq!(info.email.as_deref(), Some("user@example.com"));
        assert_eq!(info.chatgpt_plan_type.as_deref(), Some("pro"));
    }
}