use ra_mcp_domain::types::{InvariantViolation, WorkspaceRoot};
use std::{path::PathBuf, time::Duration};

/// Exponential backoff policy for worker restart attempts.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct BackoffPolicy {
    /// Minimum delay between restart attempts.
    pub floor: Duration,
    /// Maximum delay between restart attempts.
    pub ceiling: Duration,
}

impl BackoffPolicy {
    /// Builds a validated backoff policy.
    pub fn try_new(floor: Duration, ceiling: Duration) -> Result<Self, InvariantViolation> {
        if floor.is_zero() {
            return Err(InvariantViolation::new("backoff floor must be non-zero"));
        }
        if ceiling < floor {
            return Err(InvariantViolation::new(
                "backoff ceiling must be greater than or equal to floor",
            ));
        }
        Ok(Self { floor, ceiling })
    }
}

/// Runtime engine configuration.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct EngineConfig {
    /// Absolute workspace root used for rust-analyzer process cwd/root URI.
    pub workspace_root: WorkspaceRoot,
    /// rust-analyzer executable path.
    pub rust_analyzer_binary: PathBuf,
    /// Additional rust-analyzer process arguments.
    pub rust_analyzer_args: Vec<String>,
    /// Additional rust-analyzer process environment variables.
    pub rust_analyzer_env: Vec<(String, String)>,
    /// Startup handshake timeout.
    pub startup_timeout: Duration,
    /// Timeout for ordinary requests.
    pub request_timeout: Duration,
    /// Restart backoff policy.
    pub backoff_policy: BackoffPolicy,
}

impl EngineConfig {
    /// Builds validated engine configuration.
    pub fn try_new(
        workspace_root: WorkspaceRoot,
        rust_analyzer_binary: PathBuf,
        rust_analyzer_args: Vec<String>,
        rust_analyzer_env: Vec<(String, String)>,
        startup_timeout: Duration,
        request_timeout: Duration,
        backoff_policy: BackoffPolicy,
    ) -> Result<Self, InvariantViolation> {
        if rust_analyzer_binary.as_os_str().is_empty() {
            return Err(InvariantViolation::new(
                "rust-analyzer binary path must be non-empty",
            ));
        }
        if startup_timeout.is_zero() {
            return Err(InvariantViolation::new("startup timeout must be non-zero"));
        }
        if request_timeout.is_zero() {
            return Err(InvariantViolation::new("request timeout must be non-zero"));
        }
        Ok(Self {
            workspace_root,
            rust_analyzer_binary,
            rust_analyzer_args,
            rust_analyzer_env,
            startup_timeout,
            request_timeout,
            backoff_policy,
        })
    }
}