/// Predefined runtime profiles matching the plan targets.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RuntimeProfile {
    /// Qwen3.5-4B – maximum TPS, text-only, flash attention, moderate context.
    Turbo4B,
    /// Qwen3.5-9B – balanced quality/speed, tuned KV cache.
    Balanced9B,
    /// CPU-only fallback for machines without a GPU.
    CpuFallback,
}

impl RuntimeProfile {
    /// Returns sensible defaults for each profile.
    ///
    /// `n_ctx` sets the KV cache / context window size. Larger values allow longer
    /// conversations but consume more VRAM. Override at runtime with `LOCALLLM_CTX`.
    /// `n_batch` controls the prefill chunk size — kept independent of `n_ctx` to
    /// avoid pre-allocating the full window as a single batch buffer (OOM risk).
    pub fn defaults(&self) -> ProfileDefaults {
        match self {
            Self::Turbo4B => ProfileDefaults {
                n_gpu_layers: 999,
                n_ctx: 131_072, // 128 K — covers very long conversations; needs ~4 GB KV VRAM at FP16
                n_batch: 2048,  // prefill chunk size; independent of n_ctx
                n_ubatch: 512,
                flash_attn: true,
                n_threads: 8,
            },
            Self::Balanced9B => ProfileDefaults {
                n_gpu_layers: 999,
                n_ctx: 65_536, // 64 K
                n_batch: 2048,
                n_ubatch: 256,
                flash_attn: true,
                n_threads: 8,
            },
            Self::CpuFallback => ProfileDefaults {
                n_gpu_layers: 0,
                n_ctx: 16_384, // 16 K — CPU KV cache is RAM-backed; keep conservative
                n_batch: 512,
                n_ubatch: 128,
                flash_attn: false,
                n_threads: num_cpus(),
            },
        }
    }
}

fn num_cpus() -> i32 {
    // Simple fallback; replace with `num_cpus` crate if needed.
    std::thread::available_parallelism()
        .map(|n| n.get() as i32)
        .unwrap_or(4)
}

#[derive(Debug, Clone)]
pub struct ProfileDefaults {
    pub n_gpu_layers: i32,
    pub n_ctx: u32,
    pub n_batch: u32,
    pub n_ubatch: u32,
    pub flash_attn: bool,
    pub n_threads: i32,
}