use anyhow::{Context, Result};
use std::{
    io::Write,
    path::{Path, PathBuf},
};

use serde::{Deserialize, Serialize};
use statrs::statistics::{Data, Distribution, Max, Min, OrderStatistics};

use crate::utils::generate_unique_id;

const IQR_OUTLIER_FACTOR: f64 = 1.5;
const STDEV_OUTLIER_FACTOR: f64 = 3.0;

#[derive(Debug, Serialize, Deserialize)]
pub struct BenchmarkMetadata {
    pub name: String,
    pub uri: String,
}

#[derive(Debug, Serialize, Deserialize)]
struct BenchmarkStats {
    min_ns: f64,
    max_ns: f64,
    mean_ns: f64,
    stdev_ns: f64,

    q1_ns: f64,
    median_ns: f64,
    q3_ns: f64,

    rounds: u64,
    total_time: f64,
    iqr_outlier_rounds: u64,
    stdev_outlier_rounds: u64,
    iter_per_round: u64,
    warmup_iters: u64,
}

#[derive(Debug, Serialize, Deserialize, Default)]
struct BenchmarkConfig {
    warmup_time_ns: Option<f64>,
    min_round_time_ns: Option<f64>,
    max_time_ns: Option<f64>,
    max_rounds: Option<u64>,
}

#[derive(Debug, Serialize, Deserialize)]
pub struct WalltimeBenchmark {
    #[serde(flatten)]
    metadata: BenchmarkMetadata,

    config: BenchmarkConfig,
    stats: BenchmarkStats,
}

impl WalltimeBenchmark {
    /// Entry point called in patched integration to harvest raw walltime data
    ///
    /// `CODSPEED_CARGO_WORKSPACE_ROOT` is expected to be set for this to work
    ///
    /// # Arguments
    ///
    /// - `scope`: The used integration, e.g. "divan" or "criterion"
    /// - `name`: The name of the benchmark
    /// - `uri`: The URI of the benchmark
    /// - `iters_per_round`: The number of iterations for each round (=sample_size), e.g. `[1, 2, 3]` (variable) or `[2, 2, 2, 2]` (constant).
    /// - `times_per_round_ns`: The measured time for each round in nanoseconds, e.g. `[1000, 2000, 3000]`
    /// - `max_time_ns`: The time limit for the benchmark in nanoseconds (if defined)
    ///
    /// # Pseudo-code
    ///
    /// ```text
    /// let sample_count = /* The number of executions for the same benchmark. */
    /// let sample_size = iters_per_round = vec![/* The number of iterations within each sample. */];
    /// for round in 0..sample_count {
    ///     let times_per_round_ns = 0;
    ///     for iteration in 0..sample_size[round] {
    ///         run_benchmark();
    ///         times_per_round_ns += /* measured execution time */;
    ///     }
    /// }
    /// ```
    ///
    pub fn collect_raw_walltime_results(
        scope: &str,
        name: String,
        uri: String,
        iters_per_round: Vec<u128>,
        times_per_round_ns: Vec<u128>,
        max_time_ns: Option<u128>,
    ) {
        if !crate::utils::running_with_codspeed_runner() {
            return;
        }
        let workspace_root = std::env::var("CODSPEED_CARGO_WORKSPACE_ROOT").map(PathBuf::from);
        let Ok(workspace_root) = workspace_root else {
            eprintln!("codspeed failed to get workspace root. skipping");
            return;
        };
        let data = WalltimeBenchmark::from_runtime_data(
            name,
            uri,
            iters_per_round,
            times_per_round_ns,
            max_time_ns,
        );
        data.dump_to_results(&workspace_root, scope);
    }

    pub fn from_runtime_data(
        name: String,
        uri: String,
        iters_per_round: Vec<u128>,
        times_per_round_ns: Vec<u128>,
        max_time_ns: Option<u128>,
    ) -> Self {
        let total_time = times_per_round_ns.iter().sum::<u128>() as f64 / 1_000_000_000.0;
        let time_per_iteration_per_round_ns: Vec<_> = times_per_round_ns
            .into_iter()
            .zip(&iters_per_round)
            .map(|(time_per_round, iter_per_round)| time_per_round / iter_per_round)
            .map(|t| t as f64)
            .collect::<Vec<f64>>();

        let mut data = Data::new(time_per_iteration_per_round_ns);
        let rounds = data.len() as u64;

        let mean_ns = data.mean().unwrap();

        let stdev_ns = if data.len() < 2 {
            // std_dev() returns f64::NAN if data has less than two entries, so we have to
            // manually handle this case.
            0.0
        } else {
            data.std_dev().unwrap()
        };

        let q1_ns = data.quantile(0.25);
        let median_ns = data.median();
        let q3_ns = data.quantile(0.75);

        let iqr_ns = q3_ns - q1_ns;
        let iqr_outlier_rounds = data
            .iter()
            .filter(|&&t| {
                t < q1_ns - IQR_OUTLIER_FACTOR * iqr_ns || t > q3_ns + IQR_OUTLIER_FACTOR * iqr_ns
            })
            .count() as u64;

        let stdev_outlier_rounds = data
            .iter()
            .filter(|&&t| {
                t < mean_ns - STDEV_OUTLIER_FACTOR * stdev_ns
                    || t > mean_ns + STDEV_OUTLIER_FACTOR * stdev_ns
            })
            .count() as u64;

        let min_ns = data.min();
        let max_ns = data.max();

        // TODO(COD-1056): We currently only support single iteration count per round
        let iter_per_round =
            (iters_per_round.iter().sum::<u128>() / iters_per_round.len() as u128) as u64;
        let warmup_iters = 0; // FIXME: add warmup detection

        let stats = BenchmarkStats {
            min_ns,
            max_ns,
            mean_ns,
            stdev_ns,
            q1_ns,
            median_ns,
            q3_ns,
            rounds,
            total_time,
            iqr_outlier_rounds,
            stdev_outlier_rounds,
            iter_per_round,
            warmup_iters,
        };

        WalltimeBenchmark {
            metadata: BenchmarkMetadata { name, uri },
            config: BenchmarkConfig {
                max_time_ns: max_time_ns.map(|t| t as f64),
                ..Default::default()
            },
            stats,
        }
    }

    fn dump_to_results(&self, workspace_root: &Path, scope: &str) {
        let output_dir = result_dir_from_workspace_root(workspace_root).join(scope);
        std::fs::create_dir_all(&output_dir).unwrap();
        let bench_id = generate_unique_id();
        let output_path = output_dir.join(format!("{bench_id}.json"));
        let mut writer = std::fs::File::create(&output_path).expect("Failed to create the file");
        serde_json::to_writer_pretty(&mut writer, self).expect("Failed to write the data");
        writer.flush().expect("Failed to flush the writer");
    }

    pub fn is_invalid(&self) -> bool {
        self.stats.min_ns < f64::EPSILON
    }

    pub fn name(&self) -> &str {
        &self.metadata.name
    }
}

#[derive(Debug, Serialize, Deserialize)]
struct Instrument {
    #[serde(rename = "type")]
    type_: String,
}

#[derive(Debug, Serialize, Deserialize)]
struct Creator {
    name: String,
    version: String,
    pid: u32,
}

#[derive(Debug, Serialize, Deserialize)]
pub struct WalltimeResults {
    creator: Creator,
    instrument: Instrument,
    benchmarks: Vec<WalltimeBenchmark>,
}

impl WalltimeResults {
    pub fn collect_walltime_results(workspace_root: &Path) -> Result<Self> {
        // retrieve data from `{workspace_root}/target/codspeed/raw_results/{scope}/*.json
        let benchmarks = glob::glob(&format!(
            "{}/**/*.json",
            result_dir_from_workspace_root(workspace_root)
                .to_str()
                .unwrap(),
        ))?
        .map(|sample| -> Result<_> {
            let sample = sample?;
            serde_json::from_reader::<_, WalltimeBenchmark>(std::fs::File::open(&sample)?)
                .context("Failed to read benchmark data")
        })
        .collect::<Result<Vec<_>>>()?;

        Ok(WalltimeResults {
            instrument: Instrument {
                type_: "walltime".to_string(),
            },
            creator: Creator {
                name: "codspeed-rust".to_string(),
                version: env!("CARGO_PKG_VERSION").to_string(),
                pid: std::process::id(),
            },
            benchmarks,
        })
    }

    pub fn clear(workspace_root: &Path) -> Result<()> {
        let raw_results_dir = result_dir_from_workspace_root(workspace_root);
        std::fs::remove_dir_all(&raw_results_dir).ok(); // ignore errors when the directory does not exist
        std::fs::create_dir_all(&raw_results_dir)
            .context("Failed to create raw_results directory")?;
        Ok(())
    }

    pub fn benchmarks(&self) -> &[WalltimeBenchmark] {
        &self.benchmarks
    }
}

// FIXME: This assumes that the cargo target dir is `target`, and duplicates information with
// `cargo-codspeed::helpers::get_codspeed_target_dir`
fn result_dir_from_workspace_root(workspace_root: &Path) -> PathBuf {
    workspace_root
        .join("target")
        .join("codspeed")
        .join("walltime")
        .join("raw_results")
}

#[cfg(test)]
mod tests {
    use super::*;

    const NAME: &str = "benchmark";
    const URI: &str = "test::benchmark";

    #[test]
    fn test_parse_single_benchmark() {
        let benchmark = WalltimeBenchmark::from_runtime_data(
            NAME.to_string(),
            URI.to_string(),
            vec![1],
            vec![42],
            None,
        );
        assert_eq!(benchmark.stats.stdev_ns, 0.);
        assert_eq!(benchmark.stats.min_ns, 42.);
        assert_eq!(benchmark.stats.max_ns, 42.);
        assert_eq!(benchmark.stats.mean_ns, 42.);
    }

    #[test]
    fn test_parse_bench_with_variable_iterations() {
        let iters_per_round = vec![1, 2, 3, 4, 5, 6];
        let total_rounds = iters_per_round.iter().sum::<u128>() as f64;

        let benchmark = WalltimeBenchmark::from_runtime_data(
            NAME.to_string(),
            URI.to_string(),
            iters_per_round,
            vec![42, 42 * 2, 42 * 3, 42 * 4, 42 * 5, 42 * 6],
            None,
        );

        assert_eq!(benchmark.stats.stdev_ns, 0.);
        assert_eq!(benchmark.stats.min_ns, 42.);
        assert_eq!(benchmark.stats.max_ns, 42.);
        assert_eq!(benchmark.stats.mean_ns, 42.);
        assert_eq!(
            benchmark.stats.total_time,
            42. * total_rounds / 1_000_000_000.0
        );
    }
}
