// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.

use crate::error_recording::{record_error, ErrorType};
use crate::histogram::{Functional, Histogram};
use crate::metrics::memory_unit::MemoryUnit;
use crate::metrics::{DistributionData, Metric, MetricType};
use crate::storage::StorageManager;
use crate::CommonMetricData;
use crate::Glean;

// The base of the logarithm used to determine bucketing
const LOG_BASE: f64 = 2.0;

// The buckets per each order of magnitude of the logarithm.
const BUCKETS_PER_MAGNITUDE: f64 = 16.0;

// Set a maximum recordable value of 1 terabyte so the buckets aren't
// completely unbounded.
const MAX_BYTES: u64 = 1 << 40;

/// A memory distribution metric.
///
/// Memory distributions are used to accumulate and store memory sizes.
#[derive(Debug)]
pub struct MemoryDistributionMetric {
    meta: CommonMetricData,
    memory_unit: MemoryUnit,
}

/// Create a snapshot of the histogram.
///
/// The snapshot can be serialized into the payload format.
pub(crate) fn snapshot(hist: &Histogram<Functional>) -> DistributionData {
    DistributionData {
        // **Caution**: This cannot use `Histogram::snapshot_values` and needs to use the more
        // specialized snapshot function.
        values: hist.snapshot(),
        sum: hist.sum(),
    }
}

impl MetricType for MemoryDistributionMetric {
    fn meta(&self) -> &CommonMetricData {
        &self.meta
    }

    fn meta_mut(&mut self) -> &mut CommonMetricData {
        &mut self.meta
    }
}

// IMPORTANT:
//
// When changing this implementation, make sure all the operations are
// also declared in the related trait in `../traits/`.
impl MemoryDistributionMetric {
    /// Creates a new memory distribution metric.
    pub fn new(meta: CommonMetricData, memory_unit: MemoryUnit) -> Self {
        Self { meta, memory_unit }
    }

    /// Accumulates the provided sample in the metric.
    ///
    /// # Arguments
    ///
    /// * `sample` - The sample to be recorded by the metric. The sample is assumed to be in the
    ///   configured memory unit of the metric.
    ///
    /// ## Notes
    ///
    /// Values bigger than 1 Terabyte (2<sup>40</sup> bytes) are truncated
    /// and an [`ErrorType::InvalidValue`] error is recorded.
    pub fn accumulate(&self, glean: &Glean, sample: u64) {
        if !self.should_record(glean) {
            return;
        }

        let mut sample = self.memory_unit.as_bytes(sample);

        if sample > MAX_BYTES {
            let msg = "Sample is bigger than 1 terabyte";
            record_error(glean, &self.meta, ErrorType::InvalidValue, msg, None);
            sample = MAX_BYTES;
        }

        glean
            .storage()
            .record_with(glean, &self.meta, |old_value| match old_value {
                Some(Metric::MemoryDistribution(mut hist)) => {
                    hist.accumulate(sample);
                    Metric::MemoryDistribution(hist)
                }
                _ => {
                    let mut hist = Histogram::functional(LOG_BASE, BUCKETS_PER_MAGNITUDE);
                    hist.accumulate(sample);
                    Metric::MemoryDistribution(hist)
                }
            });
    }

    /// Accumulates the provided signed samples in the metric.
    ///
    /// This is required so that the platform-specific code can provide us with
    /// 64 bit signed integers if no `u64` comparable type is available. This
    /// will take care of filtering and reporting errors for any provided negative
    /// sample.
    ///
    /// Please note that this assumes that the provided samples are already in
    /// the "unit" declared by the instance of the metric type (e.g. if the the
    /// instance this method was called on is using [`MemoryUnit::Kilobyte`], then
    /// `samples` are assumed to be in that unit).
    ///
    /// # Arguments
    ///
    /// * `samples` - The vector holding the samples to be recorded by the metric.
    ///
    /// ## Notes
    ///
    /// Discards any negative value in `samples` and report an [`ErrorType::InvalidValue`]
    /// for each of them.
    ///
    /// Values bigger than 1 Terabyte (2<sup>40</sup> bytes) are truncated
    /// and an [`ErrorType::InvalidValue`] error is recorded.
    pub fn accumulate_samples_signed(&self, glean: &Glean, samples: Vec<i64>) {
        if !self.should_record(glean) {
            return;
        }

        let mut num_negative_samples = 0;
        let mut num_too_log_samples = 0;

        glean.storage().record_with(glean, &self.meta, |old_value| {
            let mut hist = match old_value {
                Some(Metric::MemoryDistribution(hist)) => hist,
                _ => Histogram::functional(LOG_BASE, BUCKETS_PER_MAGNITUDE),
            };

            for &sample in samples.iter() {
                if sample < 0 {
                    num_negative_samples += 1;
                } else {
                    let sample = sample as u64;
                    let mut sample = self.memory_unit.as_bytes(sample);
                    if sample > MAX_BYTES {
                        num_too_log_samples += 1;
                        sample = MAX_BYTES;
                    }

                    hist.accumulate(sample);
                }
            }
            Metric::MemoryDistribution(hist)
        });

        if num_negative_samples > 0 {
            let msg = format!("Accumulated {} negative samples", num_negative_samples);
            record_error(
                glean,
                &self.meta,
                ErrorType::InvalidValue,
                msg,
                num_negative_samples,
            );
        }

        if num_too_log_samples > 0 {
            let msg = format!(
                "Accumulated {} samples larger than 1TB",
                num_too_log_samples
            );
            record_error(
                glean,
                &self.meta,
                ErrorType::InvalidValue,
                msg,
                num_too_log_samples,
            );
        }
    }

    /// **Test-only API (exported for FFI purposes).**
    ///
    /// Gets the currently stored value as an integer.
    ///
    /// This doesn't clear the stored value.
    pub fn test_get_value(&self, glean: &Glean, storage_name: &str) -> Option<DistributionData> {
        match StorageManager.snapshot_metric_for_test(
            glean.storage(),
            storage_name,
            &self.meta.identifier(glean),
            self.meta.lifetime,
        ) {
            Some(Metric::MemoryDistribution(hist)) => Some(snapshot(&hist)),
            _ => None,
        }
    }

    /// **Test-only API (exported for FFI purposes).**
    ///
    /// Gets the currently-stored histogram as a JSON String of the serialized value.
    ///
    /// This doesn't clear the stored value.
    pub fn test_get_value_as_json_string(
        &self,
        glean: &Glean,
        storage_name: &str,
    ) -> Option<String> {
        self.test_get_value(glean, storage_name)
            .map(|snapshot| serde_json::to_string(&snapshot).unwrap())
    }
}