//! Configuration (private module)

use std::sync::LazyLock;

use sysinfo::{MemoryRefreshKind, System};

use tracing::warn;

use crate::internal_prelude::*;

/// We want to support at least this many participants with a cache each

///

/// This is not a recommended value; it's probably too lax

const MIN_MAX_PARTICIPANTS: usize = 10;

/// Minimum hysteresis

///

/// This is not a recommended value; it's probably far too lax for sensible performance!

const MAX_LOW_WATER_RATIO: f32 = 0.98;

define_derive_deftly! {

    /// Define setters on the builder for every field of type `Qty`

    ///

    /// The field type must be spelled precisely that way:

    /// we use `approx_equal(...)`.

    QtySetters:

    impl ConfigBuilder {

      $(

        ${when approx_equal($ftype, { Option::<ExplicitOrAuto<Qty>> })}

        ${fattrs doc}

        ///

        /// (Setter method.)

        // We use `value: impl Into<ExplicitOrAuto<usize>>` to avoid breaking users who used the

        // previous `value: usize`. But this isn't 100% foolproof, for example if a user used

        // `$fname(foo.into())`, which will fail type inference.

            self.$fname = Some(value.into().map(Qty));

            self

        }

      )

    }

}

/// Configuration for a memory data tracker

///

/// This is where the quota is specified.

///

/// This type can also represent

/// "memory quota tracking is not supposed to be enabled".

#[derive(Debug, Clone, Eq, PartialEq)]

pub struct Config(pub(crate) IfEnabled<ConfigInner>);

/// Configuration for a memory data tracker (builder)

//

// We could perhaps generate this with `#[derive(Builder)]` on `ConfigInner`,

// but derive-builder would need a *lot* of overriding attributes;

// and, doing it this way lets us write separate docs about

// the invariants on our fields, which are not the same as those in the builder.

#[derive(Serialize, Deserialize, Debug, Clone, Eq, PartialEq, Default, Deftly)]

#[derive_deftly(tor_config::Flattenable, QtySetters)]

pub struct ConfigBuilder {

    /// Maximum memory usage tolerated before reclamation starts

    ///

    /// Setting this to `usize::MAX` disables the memory quota.

    ///

    /// The default is "auto",

    /// which uses a value derived from the total system memory.

    /// It should not be assumed that the value used for "auto"

    /// will remain stable across different versions of this library.

    ///

    /// Note that this is not a hard limit.

    /// See Approximate in [the overview](crate).

    max: Option<ExplicitOrAuto<Qty>>,

    /// Reclamation will stop when memory use is reduced to below this value

    ///

    /// Default is "auto", which uses 75% of the maximum.

    /// It should not be assumed that the value used for "auto"

    /// will remain stable across different versions of this library.

    ///

    /// If set to an explicit value,

    /// then `max` must be set to an explicit value as well.

    low_water: Option<ExplicitOrAuto<Qty>>,

}

/// Configuration, if enabled

#[derive(Debug, Clone, Eq, PartialEq, Deftly)]

#[cfg_attr(

    feature = "testing",

    visibility::make(pub),

    allow(clippy::exhaustive_structs)

)]

pub(crate) struct ConfigInner {

    /// Maximum memory usage

    ///

    /// Guaranteed not to be `MAX`, since we're enabled

    pub max: Qty,

    /// Low water

    ///

    /// Guaranteed to be enough lower than `max`

    pub low_water: Qty,

}

impl Config {

    /// Start building a [`Config`]

    ///

    /// Returns a fresh default [`ConfigBuilder`].

    /// Obtain the actual configuration, if we're enabled, or `None` if not

    ///

    /// Ad-hoc accessor for testing purposes.

    /// (ideally we'd use `visibility` to make fields `pub`, but that doesn't work.)

    #[cfg(any(test, feature = "testing"))]

}

impl ConfigBuilder {

    /// Builds a new `Config` from a builder

    ///

    /// Returns an error if the fields values are invalid or inconsistent.

        // both options default to "auto"

        // `MAX` indicates "disabled".

        // TODO: Should we add a new "enabled" config option instead of using a sentinel value?

        // But this would be a breaking change. Or maybe we should always enable the memquota

        // machinery even if the user chooses an unreasonably large value, and not give users a way

        // to disable it.

            // If it should be disabled, but the user provided an explicit value for `low_water`.

        // We don't want the user to set "auto" for `max`, but an explicit value for `low_water`.

        // Otherwise this config is prone to breaking since a `max` of "auto" may change as system

        // memory is removed (either physically or if running in a VM/container).

            //

        // The general logic is taken from c-tor (see `compute_real_max_mem_in_queues`).

        // NOTE: Relays have an additional lower bound for explicitly given values (64 MiB),

        // but we have no way of knowing whether we are a relay or not here.

        };

        };

        /// Minimum low water.  `const` so that overflows are compile-time.

        const MIN_LOW_WATER: usize = crate::mtracker::MAX_CACHE.as_usize() * MIN_MAX_PARTICIPANTS;

}

/// Determine a max given the system's total available memory.

///

/// This is used when `max` is configured as "auto".

/// It takes a `Result` so that we can handle the case where the total memory isn't available.

    const MIB: usize = 1024 * 1024;

    const GIB: usize = 1024 * 1024 * 1024;

            // Can't get the total available memory,

            // so we return a max depending on whether the architecture is 32-bit or 64-bit.

        }

    };

        // From c-tor:

        //

        // > The idea behind this value is that the amount of RAM is more than enough

        // > for a single relay and should allow the relay operator to run two relays

        // > if they have additional bandwidth available.

    } else {

    };

    // The (min, max) range to clamp `mem` to.

        cfg_if::cfg_if! {

            if #[cfg(target_pointer_width = "64")] {

            } else {

                (256 * MIB, 2 * GIB)

            }

        }

    };

/// The total available memory in bytes.

///

/// This is generally the amount of system RAM,

/// but we may also take into account other OS-specific limits such as cgroups.

///

/// Returns `None` if we were unable to get the total available memory.

/// But see internal comments for details.

    // The sysinfo crate says we should use only one `System` per application.

    // But we're a library, so it's probably best to just make this global and reuse it.

    // In reality getting the system memory probably shouldn't require persistent state,

    // but since the internals of the sysinfo crate are opaque to us,

    // we'll just follow their documentation and cache the `System`.

    //

    // NOTE: The sysinfo crate in practice gets more information than we ask for.

    // For example `System::new()` will always query the `_SC_PAGESIZE` and `_SC_CLK_TCK`

    // on Linux even though we only refresh the memory info below

    // (see https://github.com/GuillaumeGomez/sysinfo/blob/fc31b411eea7b9983176399dc5be162786dec95b/src/unix/linux/system.rs#L152).

    // This means that miri will fail to run on tests that build the config, even if the config uses

    // explicit values.

        // The sysinfo crate has some internal panics which would poison this mutex.

        // But we can easily reset it, rather than panicking ourselves if it's poisoned.

    // It might be possible for 32-bit systems to return >usize::MAX due to PAE (I haven't looked

    // into this), so we just saturate the value and don't consider this an error.

    // The sysinfo crate doesn't report errors, so the best we can do is guess that a value of 0

    // implies that it was unable to get the total memory.

    //

    // We also need to return early to prevent a panic below.

    // Note: The docs for the sysinfo crate say:

    //

    // > You need to have run refresh_memory at least once before calling this method.

    //

    // But as implemented, it also panics if `sys.mem_total == 0` (for example if the refresh

    // silently failed).

        // There is no cgroup (or we're a non-Linux platform).

    };

    // The `cgroup_limits()` surprisingly doesn't actually return the unaltered cgroups limits.

    // It also adjusts them depending on the total memory.

    // Since this is all undocumented, we'll also do the same calculation here.

/// An error when we are unable to obtain the system's total available memory.

#[derive(Clone, Debug, thiserror::Error)]

enum MemQueryError {

    /// The total available memory is unavailable.

    #[error("total available memory is unavailable")]

    Unavailable,

}

/// Convert a `u64` to a `usize`, saturating if the value would overflow.

    // this will be optimized to a no-op on 64-bit systems

#[cfg(test)]

mod test {

    // @@ begin test lint list maintained by maint/add_warning @@

    #![allow(clippy::bool_assert_comparison)]

    #![allow(clippy::clone_on_copy)]

    #![allow(clippy::dbg_macro)]

    #![allow(clippy::mixed_attributes_style)]

    #![allow(clippy::print_stderr)]

    #![allow(clippy::print_stdout)]

    #![allow(clippy::single_char_pattern)]

    #![allow(clippy::unwrap_used)]

    #![allow(clippy::unchecked_duration_subtraction)]

    #![allow(clippy::useless_vec)]

    #![allow(clippy::needless_pass_by_value)]

    //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->

    use super::*;

    use serde_json::json;

    #[test]

    // A value of "auto" depends on the system memory,

    // which typically results in libc calls or syscall that aren't supported by miri.

    #[cfg_attr(miri, ignore)]

    fn configs() {

        let chk_ok_raw = |j, c| {

            let b: ConfigBuilder = serde_json::from_value(j).unwrap();

            assert_eq!(b.build().unwrap(), c);

        };

        #[cfg(feature = "memquota")]

        let chk_ok = |j, max, low_water| {

            const M: usize = 1024 * 1024;

            let exp = IfEnabled::Enabled(

                ConfigInner {

                    max: Qty(max * M),

                    low_water: Qty(low_water * M),

                },

                EnabledToken::new(),

            );

            chk_ok_raw(j, Config(exp));

        };

        let chk_err = |j, exp| {

            let b: ConfigBuilder = serde_json::from_value(j).unwrap();

            let got = b.build().unwrap_err().to_string();

            #[cfg(not(feature = "memquota"))]

            if got.contains("cargo feature `memquota` disabled") {

                return;

            }

            assert!(got.contains(exp), "in {exp:?} in {got:?}");

        };

        #[cfg(not(feature = "memquota"))]

        let chk_ok = |j, max, low_water| {

            chk_err(j, "UNSUPPORTED");

        };

        let chk_builds = |j| {

            cfg_if::cfg_if! {

                if #[cfg(feature = "memquota")] {

                    let b: ConfigBuilder = serde_json::from_value(j).unwrap();

                    b.build().unwrap();

                } else {

                    chk_err(j, "UNSUPPORTED");

                }

            }

        };

        chk_ok(json! {{ "max": "8 MiB" }}, 8, 6);

        chk_ok(json! {{ "max": "8 MiB", "low_water": "auto" }}, 8, 6);

        chk_ok(json! {{ "max": "8 MiB", "low_water": "4 MiB" }}, 8, 4);

        // We don't know what the exact values will be since they are derived from the system

        // memory.

        chk_builds(json! {{ }});

        chk_builds(json! {{ "max": "auto" }});

        chk_builds(json! {{ "low_water": "auto" }});

        chk_builds(json! {{ "max": "auto", "low_water": "auto" }});

        chk_err(

            json! {{ "low_water": "4 MiB" }},

            "max is \"auto\", but low_water is set to an explicit quantity",

        );

        chk_err(

            json! {{ "max": "8 MiB", "low_water": "8 MiB" }},

            "inconsistent: low_water / max",

        );

        // `usize::MAX` is a special value.

        chk_err(

            json! {{ "max": usize::MAX.to_string(), "low_water": "8 MiB" }},

            "low_water supplied, but max indicates that we should disable the memory quota",

        );

        chk_builds(json! {{ "max": (usize::MAX - 1).to_string(), "low_water": "8 MiB" }});

        // check that the builder works as expected

        #[cfg(feature = "memquota")]

        {

            let mut b = Config::builder();

            b.max(ExplicitOrAuto::Explicit(100_000_000));

            if let Some(inner) = b.build().unwrap().inner() {

                assert_eq!(inner.max, Qty(100_000_000));

            }

            let mut b = Config::builder();

            b.max(100_000_000);

            if let Some(inner) = b.build().unwrap().inner() {

                assert_eq!(inner.max, Qty(100_000_000));

            }

            let mut b = ConfigBuilder::default();

            b.max(ExplicitOrAuto::Auto);

            b.build().unwrap();

        }

    }

    /// Test the logic that computes the `max` when configured as "auto".

    #[test]

    // We do some `1 * X` operations below for readability.

    #[allow(clippy::identity_op)]

    fn auto_max() {

        #[allow(unused)]

        fn check_helper(val: Qty, expected_32: Qty, expected_64: Qty) {

            assert_eq!(val, {

                cfg_if::cfg_if! {

                    if #[cfg(target_pointer_width = "64")] {

                        expected_64

                    } else if #[cfg(target_pointer_width = "32")] {

                        expected_32

                    } else {

                        panic!("Unsupported architecture :(");

                    }

                }

            });

        }

        check_helper(

            compute_max_from_total_system_mem(Err(MemQueryError::Unavailable)),

            /* 32-bit */ Qty(1 * 1024 * 1024 * 1024),

            /* 64-bit */ Qty(8 * 1024 * 1024 * 1024),

        );

        check_helper(

            compute_max_from_total_system_mem(Ok(8 * 1024 * 1024 * 1024)),

            /* 32-bit */ Qty(2 * 1024 * 1024 * 1024),

            /* 64-bit */ Qty(3435973836),

        );

        check_helper(

            compute_max_from_total_system_mem(Ok(7 * 1024 * 1024 * 1024)),

            /* 32-bit */ Qty(2 * 1024 * 1024 * 1024),

            /* 64-bit */ Qty(5637144576),

        );

        check_helper(

            compute_max_from_total_system_mem(Ok(1 * 1024 * 1024 * 1024)),

            /* 32-bit */ Qty(805306368),

            /* 64-bit */ Qty(805306368),

        );

        check_helper(

            compute_max_from_total_system_mem(Ok(7 * 1024)),

            /* 32-bit */ Qty(256 * 1024 * 1024),

            /* 64-bit */ Qty(256 * 1024 * 1024),

        );

        check_helper(

            compute_max_from_total_system_mem(Ok(0)),

            /* 32-bit */ Qty(256 * 1024 * 1024),

            /* 64-bit */ Qty(256 * 1024 * 1024),

        );

        check_helper(

            compute_max_from_total_system_mem(Ok(usize::MAX)),

            /* 32-bit */ Qty(2 * 1024 * 1024 * 1024),

            /* 64-bit */ Qty(8 * 1024 * 1024 * 1024),

        );

    }

}