/// Error types with semantic exit codes.
///
/// Every error maps to an exit code (1-4), a machine-readable code, and a
/// recovery suggestion that agents can follow literally.

#[derive(thiserror::Error, Debug)]
#[allow(dead_code)] // Some variants demonstrate the full exit code contract (0-4)
pub enum AppError {
    #[error("Invalid input: {0}")]
    InvalidInput(String),

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

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

    #[error("Rate limited: {0}")]
    RateLimited(String),

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

    #[error("Update failed: {0}")]
    Update(String),

    /// Audit score is below the `--fail-under` threshold. Not really an
    /// error — the audit succeeded, the page just didn't clear the gate.
    /// Stdout already holds the full JSON; this only flips the exit code
    /// so CI / agents can branch on it.
    #[error("Audit score {score} below threshold {threshold}")]
    QualityGate { score: u32, threshold: u32 },

    /// `aiseo verify` ran cleanly but the diff says the agent's claimed
    /// fix did not land. Stdout already holds the structured diff;
    /// exit 1 so the calling loop can branch.
    #[error("Verify failed: {still_present} still present, {regressed} regressed")]
    VerifyFailed {
        still_present: usize,
        regressed: usize,
    },
}

impl AppError {
    pub fn exit_code(&self) -> i32 {
        match self {
            Self::InvalidInput(_) => 3,
            Self::Config(_) => 2,
            Self::RateLimited(_) => 4,
            Self::Transient(_) | Self::Io(_) | Self::Update(_) => 1,
            Self::QualityGate { .. } | Self::VerifyFailed { .. } => 1,
        }
    }

    pub fn error_code(&self) -> &str {
        match self {
            Self::InvalidInput(_) => "invalid_input",
            Self::Config(_) => "config_error",
            Self::Transient(_) => "transient_error",
            Self::RateLimited(_) => "rate_limited",
            Self::Io(_) => "io_error",
            Self::Update(_) => "update_error",
            Self::QualityGate { .. } => "quality_gate",
            Self::VerifyFailed { .. } => "verify_failed",
        }
    }

    pub fn suggestion(&self) -> &str {
        match self {
            Self::InvalidInput(_) => {
                concat!("Check arguments with: ", env!("CARGO_PKG_NAME"), " --help")
            }
            Self::Config(_) => concat!(
                "Check config with: ",
                env!("CARGO_PKG_NAME"),
                " config path"
            ),
            Self::Transient(_) | Self::Io(_) => "Retry the command",
            Self::RateLimited(_) => "Wait a moment and retry",
            Self::Update(_) => concat!(
                "Retry later, or install manually via cargo install ",
                env!("CARGO_PKG_NAME")
            ),
            Self::QualityGate { .. } => {
                "Review stdout `.suggestions[]` and re-run after applying the fixes"
            }
            Self::VerifyFailed { .. } => {
                "Review stdout `.delta.regressed[]` and `.delta.still_present[]`, then re-run"
            }
        }
    }
}
