//! Typed errors mapped onto the OpenAI error payload.

use std::path::PathBuf;

/// Convenience alias used across the crate.
pub type Result<T, E = GatewayError> = std::result::Result<T, E>;

/// Every failure mode the gateway can surface to a client.
#[derive(Debug, thiserror::Error)]
pub enum GatewayError {
    #[error("model '{0}' does not match any configured provider")]
    UnknownProvider(String),

    /// The model string named a provider, but not one of its accounts.
    #[error("{0}")]
    UnknownAccount(String),

    #[error("parameter '{param}' {detail}")]
    UnsupportedParameter { param: String, detail: String },

    #[error("{0}")]
    UnsupportedContentType(String),

    #[error("{0}")]
    InvalidRequest(String),

    #[error("invalid API key")]
    InvalidApiKey,

    #[error(
        "provider '{provider}' is not signed in: run 'llm-gateway login {provider} --manual', sign in inside the window it opens, then close it (Google refuses browsers it sees as automated, so this path avoids that)"
    )]
    RequiresLogin { provider: String },

    #[error(
        "provider '{provider}' is showing a captcha challenge; solve it in the browser window"
    )]
    Captcha { provider: String },

    #[error("provider '{provider}' is busy, retry later")]
    ProviderBusy { provider: String, waited_ms: u64 },

    #[error("provider '{provider}' is rate limiting: {detail}")]
    UpstreamRateLimited { provider: String, detail: String },

    #[error("browser profile {path} is locked by another browser instance; close it and retry")]
    BrowserProfileLocked { path: PathBuf },

    #[error("selector '{selector}' not found ({step})")]
    SelectorMissing { selector: String, step: String },

    #[error("provider '{provider}' reported an error: {message}")]
    UpstreamError { provider: String, message: String },

    #[error("browser engine unavailable: {0}")]
    BrowserUnavailable(String),

    #[error("timed out while {stage} after {timeout_s}s")]
    CaptureTimeout { stage: String, timeout_s: u64 },

    #[error("provider '{provider}' is misconfigured: {detail}")]
    ProviderMisconfigured { provider: String, detail: String },

    #[error("unsupported browser '{0}': only Chromium-based browsers speak CDP")]
    UnsupportedBrowser(String),

    #[error("provider '{0}' is not configured")]
    ProviderNotConfigured(String),

    #[error("HTTP request to {url} failed: {source}")]
    Http {
        url: String,
        #[source]
        source: reqwest::Error,
    },

    #[error("I/O error: {0}")]
    Io(#[from] std::io::Error),

    #[error("invalid configuration: {0}")]
    Config(String),

    #[error("internal error: {0}")]
    Internal(String),

    /// The caller went away before the answer was captured. Never serialised:
    /// there is no client left to read it.
    #[error("client disconnected before the answer was captured")]
    Cancelled,
}

impl GatewayError {
    pub fn invalid_request(msg: impl Into<String>) -> Self {
        Self::InvalidRequest(msg.into())
    }

    pub fn unsupported_param(param: impl Into<String>, detail: impl Into<String>) -> Self {
        Self::UnsupportedParameter {
            param: param.into(),
            detail: detail.into(),
        }
    }

    pub fn internal(msg: impl Into<String>) -> Self {
        Self::Internal(msg.into())
    }

    /// HTTP status returned to the OpenAI-compatible client.
    pub fn http_status(&self) -> u16 {
        match self {
            Self::UnknownProvider(_) | Self::UnknownAccount(_) => 404,
            Self::UnsupportedParameter { .. }
            | Self::UnsupportedContentType(_)
            | Self::InvalidRequest(_) => 400,
            Self::InvalidApiKey | Self::RequiresLogin { .. } => 401,
            Self::Captcha { .. } => 403,
            Self::ProviderBusy { .. } | Self::UpstreamRateLimited { .. } => 429,
            Self::BrowserProfileLocked { .. } => 409,
            Self::BrowserUnavailable(_) | Self::ProviderMisconfigured { .. } => 503,
            Self::CaptureTimeout { .. } => 504,
            Self::Cancelled => 499,
            _ => 500,
        }
    }

    /// OpenAI-compatible error type field.
    pub fn error_type(&self) -> &'static str {
        match self.http_status() {
            400 | 401 | 403 | 404 => "invalid_request_error",
            429 => "rate_limit_error",
            _ => "api_error",
        }
    }

    /// Stable machine-readable code, also used as a log field.
    pub fn code(&self) -> &'static str {
        match self {
            Self::UnknownProvider(_) => "model_not_found",
            Self::UnknownAccount(_) => "account_not_found",
            Self::UnsupportedParameter { .. } => "unsupported_parameter",
            Self::UnsupportedContentType(_) => "unsupported_content_type",
            Self::InvalidRequest(_) => "invalid_request",
            Self::InvalidApiKey => "invalid_api_key",
            Self::RequiresLogin { .. } => "requires_login",
            Self::Captcha { .. } => "captcha_required",
            Self::ProviderBusy { .. } => "provider_busy",
            Self::UpstreamRateLimited { .. } => "upstream_rate_limit",
            Self::BrowserProfileLocked { .. } => "browser_profile_locked",
            Self::SelectorMissing { .. } => "selector_missing",
            Self::UpstreamError { .. } => "upstream_error",
            Self::BrowserUnavailable(_) => "browser_unavailable",
            Self::CaptureTimeout { .. } => "upstream_timeout",
            Self::ProviderMisconfigured { .. } => "provider_misconfigured",
            Self::UnsupportedBrowser(_) => "unsupported_browser",
            Self::ProviderNotConfigured(_) => "provider_not_configured",
            Self::Http { .. } => "upstream_http_error",
            Self::Io(_) => "io_error",
            Self::Config(_) => "invalid_configuration",
            Self::Internal(_) => "internal_error",
            Self::Cancelled => "client_disconnected",
        }
    }

    /// Name of the offending parameter, when the error is parameter-specific.
    pub fn param(&self) -> Option<&str> {
        match self {
            Self::UnsupportedParameter { param, .. } => Some(param.as_str()),
            _ => None,
        }
    }
}

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

    #[test]
    fn codes_and_statuses_are_stable() {
        let e = GatewayError::RequiresLogin {
            provider: "chatgpt".into(),
        };
        assert_eq!(e.http_status(), 401);
        assert_eq!(e.code(), "requires_login");
        assert_eq!(e.error_type(), "invalid_request_error");
        assert!(e.to_string().contains("llm-gateway login chatgpt"));

        let e = GatewayError::CaptureTimeout {
            stage: "waiting for the answer".into(),
            timeout_s: 180,
        };
        assert_eq!(e.http_status(), 504);
        assert_eq!(e.code(), "upstream_timeout");

        let e = GatewayError::unsupported_param("tools", "is not supported by the browser backend");
        assert_eq!(e.param(), Some("tools"));
        assert_eq!(e.http_status(), 400);

        let e = GatewayError::BrowserProfileLocked {
            path: PathBuf::from("/p"),
        };
        assert_eq!(e.http_status(), 409);

        let e = GatewayError::UnknownAccount("provider 'chatgpt' has no account 'x'".into());
        assert_eq!(e.http_status(), 404);
        assert_eq!(e.code(), "account_not_found");
        assert_eq!(e.error_type(), "invalid_request_error");
        assert!(e.to_string().contains("no account 'x'"));
    }
}