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// Copyright 2021 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use crate::writer::{
    ArithmeticArrayProperty, ArrayProperty, DoubleArrayProperty, HistogramProperty, Node,
    StringReference,
};
use diagnostics_hierarchy::{ArrayFormat, ExponentialHistogramParams};
use inspect_format::constants;
use tracing::error;

#[derive(Debug, Default)]
/// An exponential histogram property for double values.
pub struct DoubleExponentialHistogramProperty {
    array: DoubleArrayProperty,
    floor: f64,
    initial_step: f64,
    step_multiplier: f64,
    slots: usize,
}

impl DoubleExponentialHistogramProperty {
    pub(crate) fn new(
        name: StringReference,
        params: ExponentialHistogramParams<f64>,
        parent: &Node,
    ) -> Self {
        let slots = params.buckets + constants::EXPONENTIAL_HISTOGRAM_EXTRA_SLOTS;
        let array =
            parent.create_double_array_internal(name, slots, ArrayFormat::ExponentialHistogram);
        array.set(0, params.floor);
        array.set(1, params.initial_step);
        array.set(2, params.step_multiplier);
        Self {
            floor: params.floor,
            initial_step: params.initial_step,
            step_multiplier: params.step_multiplier,
            slots,
            array,
        }
    }

    fn get_index(&self, value: f64) -> usize {
        let mut current_floor = self.floor;
        let mut offset = self.initial_step;
        // Start in the underflow index.
        let mut index = constants::EXPONENTIAL_HISTOGRAM_EXTRA_SLOTS - 2;
        while value >= current_floor && index < self.slots - 1 {
            current_floor = self.floor + offset;
            offset *= self.step_multiplier;
            index += 1;
        }
        index as usize
    }
}

impl HistogramProperty for DoubleExponentialHistogramProperty {
    type Type = f64;

    fn insert(&self, value: f64) {
        self.insert_multiple(value, 1);
    }

    fn insert_multiple(&self, value: f64, count: usize) {
        self.array.add(self.get_index(value), count as f64);
    }

    fn clear(&self) {
        if let Some(ref inner_ref) = self.array.inner.inner_ref() {
            // Ensure we don't delete the array slots that contain histogram metadata.
            inner_ref
                .state
                .try_lock()
                .and_then(|mut state| {
                    // -2 = the overflow and underflow slots which still need to be cleared.
                    state.clear_array(
                        inner_ref.block_index,
                        constants::EXPONENTIAL_HISTOGRAM_EXTRA_SLOTS - 2,
                    )
                })
                .unwrap_or_else(|err| {
                    error!(?err, "Failed to clear property");
                });
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::writer::{testing_utils::GetBlockExt, Inspector};

    #[fuchsia::test]
    fn test_double_exp_histogram() {
        let inspector = Inspector::default();
        let root = inspector.root();
        let node = root.create_child("node");
        {
            let double_histogram = node.create_double_exponential_histogram(
                "double-histogram",
                ExponentialHistogramParams {
                    floor: 1.0,
                    initial_step: 1.0,
                    step_multiplier: 2.0,
                    buckets: 4,
                },
            );
            double_histogram.insert_multiple(0.0, 2); // underflow
            double_histogram.insert(8.3);
            double_histogram.insert(500.0); // overflow
            double_histogram.array.get_block(|block| {
                for (i, value) in [1.0, 1.0, 2.0, 2.0, 0.0, 0.0, 0.0, 1.0, 1.0].iter().enumerate() {
                    assert_eq!(block.array_get_double_slot(i).unwrap(), *value);
                }
            });

            node.get_block(|node_block| {
                assert_eq!(node_block.child_count().unwrap(), 1);
            });
        }
        node.get_block(|node_block| {
            assert_eq!(node_block.child_count().unwrap(), 0);
        });
    }
}