// Copyright 2019-2023 Tauri Programme within The Commons Conservancy
// SPDX-License-Identifier: Apache-2.0
// SPDX-License-Identifier: MIT

use std::time::Instant;

// The TransferStats struct is used to track and calculate the transfer speed of data chunks over time.
pub struct TransferStats {
    accumulated_chunk_len: usize, // Total length of chunks transferred in the current period
    accumulated_time: u128,       // Total time taken for the transfers in the current period
    pub transfer_speed: u64,      // Calculated transfer speed in bytes per second
    start_time: Instant,          // Time when the current period started
    granularity: u32, // Time period (in milliseconds) over which the transfer speed is calculated
}

impl TransferStats {
    // Initializes a new TransferStats instance with the specified granularity.
    pub fn start(granularity: u32) -> Self {
        Self {
            accumulated_chunk_len: 0,
            accumulated_time: 0,
            transfer_speed: 0,
            start_time: Instant::now(),
            granularity,
        }
    }
    // Records the transfer of a data chunk and updates the transfer speed if the granularity period has elapsed.
    pub fn record_chunk_transfer(&mut self, chunk_len: usize) {
        let now = Instant::now();
        let it_took = now.duration_since(self.start_time).as_millis();
        self.accumulated_chunk_len += chunk_len;
        self.accumulated_time += it_took;

        // If the accumulated time exceeds the granularity, calculate the transfer speed.
        if self.accumulated_time >= self.granularity as u128 {
            self.transfer_speed =
                (self.accumulated_chunk_len as u128 / self.accumulated_time * 1024) as u64;
            self.accumulated_chunk_len = 0;
            self.accumulated_time = 0;
        }

        // Reset the start time for the next period.
        self.start_time = now;
    }
}

// Provides a default implementation for TransferStats with a granularity of 500 milliseconds.
impl Default for TransferStats {
    fn default() -> Self {
        Self::start(500) // Default granularity is 500
    }
}