use std::cell::RefCell;
use std::time::{Duration, Instant};
use std::mem;
use std::io::{stderr, Write};
use std::iter::repeat;
use std::collections::{HashSet};
use std::default::Default;
use std::iter::FromIterator;
use std::sync::{RwLock, atomic::{AtomicBool, Ordering}};
use lazy_static::lazy_static;

/// Set profiling filter. It specifies descriptions allowed to profile.
/// This is helpful when call stack has too many nested profiling scopes.
/// Additionally filter can specify maximum depth of profiling scopes nesting.
///
/// #Example
/// ```
/// use ra_prof::{set_filter, Filter};
/// let f = Filter::from_spec("profile1|profile2@2");
/// set_filter(f);
/// ```
pub fn set_filter(f: Filter) {
    PROFILING_ENABLED.store(f.depth > 0, Ordering::SeqCst);
    let set = HashSet::from_iter(f.allowed.iter().cloned());
    let mut old = FILTER.write().unwrap();
    let filter_data = FilterData {
        depth: f.depth,
        allowed: set,
        longer_than: f.longer_than,
        version: old.version + 1,
    };
    *old = filter_data;
}

/// This function starts a profiling scope in the current execution stack with a given description.
/// It returns a Profile structure and measure elapsed time between this method invocation and Profile structure drop.
/// It supports nested profiling scopes in case when this function invoked multiple times at the execution stack. In this case the profiling information will be nested at the output.
/// Profiling information is being printed in the stderr.
///
/// #Example
/// ```
/// use ra_prof::{profile, set_filter, Filter};
///
/// let f = Filter::from_spec("profile1|profile2@2");
/// set_filter(f);
/// profiling_function1();
///
/// fn profiling_function1() {
///     let _p = profile("profile1");
///     profiling_function2();
/// }
///
/// fn profiling_function2() {
///     let _p = profile("profile2");
/// }
/// ```
/// This will print in the stderr the following:
/// ```text
///  0ms - profile
///      0ms - profile2
/// ```
pub fn profile(desc: &str) -> Profiler {
    assert!(!desc.is_empty());
    if !PROFILING_ENABLED.load(Ordering::Relaxed) {
        return Profiler { desc: None };
    }

    PROFILE_STACK.with(|stack| {
        let mut stack = stack.borrow_mut();
        if stack.starts.is_empty() {
            if let Ok(f) = FILTER.try_read() {
                if f.version > stack.filter_data.version {
                    stack.filter_data = f.clone();
                }
            };
        }

        if stack.starts.len() > stack.filter_data.depth {
            return Profiler { desc: None };
        }

        if stack.filter_data.allowed.is_empty() || stack.filter_data.allowed.contains(desc) {
            stack.starts.push(Instant::now());
            Profiler { desc: Some(desc.to_string()) }
        } else {
            Profiler { desc: None }
        }
    })
}

pub struct Profiler {
    desc: Option<String>,
}

pub struct Filter {
    depth: usize,
    allowed: Vec<String>,
    longer_than: Duration,
}

impl Filter {
    // Filtering syntax
    // env RA_PROFILE=*             // dump everything
    // env RA_PROFILE=foo|bar|baz   // enabled only selected entries
    // env RA_PROFILE=*@3>10        // dump everything, up to depth 3, if it takes more than 10 ms
    pub fn from_spec(mut spec: &str) -> Filter {
        let longer_than = if let Some(idx) = spec.rfind('>') {
            let longer_than = spec[idx + 1..].parse().expect("invalid profile longer_than");
            spec = &spec[..idx];
            Duration::from_millis(longer_than)
        } else {
            Duration::new(0, 0)
        };

        let depth = if let Some(idx) = spec.rfind('@') {
            let depth: usize = spec[idx + 1..].parse().expect("invalid profile depth");
            spec = &spec[..idx];
            depth
        } else {
            999
        };
        let allowed =
            if spec == "*" { Vec::new() } else { spec.split('|').map(String::from).collect() };
        Filter::new(depth, allowed, longer_than)
    }

    pub fn disabled() -> Filter {
        Filter::new(0, Vec::new(), Duration::new(0, 0))
    }

    pub fn new(depth: usize, allowed: Vec<String>, longer_than: Duration) -> Filter {
        Filter { depth, allowed, longer_than }
    }
}

struct ProfileStack {
    starts: Vec<Instant>,
    messages: Vec<Message>,
    filter_data: FilterData,
}

struct Message {
    level: usize,
    duration: Duration,
    message: String,
}

impl ProfileStack {
    fn new() -> ProfileStack {
        ProfileStack { starts: Vec::new(), messages: Vec::new(), filter_data: Default::default() }
    }
}

#[derive(Default, Clone)]
struct FilterData {
    depth: usize,
    version: usize,
    allowed: HashSet<String>,
    longer_than: Duration,
}

static PROFILING_ENABLED: AtomicBool = AtomicBool::new(false);

lazy_static! {
    static ref FILTER: RwLock<FilterData> = RwLock::new(Default::default());
}

thread_local!(static PROFILE_STACK: RefCell<ProfileStack> = RefCell::new(ProfileStack::new()));

impl Drop for Profiler {
    fn drop(&mut self) {
        match self {
            Profiler { desc: Some(desc) } => {
                PROFILE_STACK.with(|stack| {
                    let mut stack = stack.borrow_mut();
                    let start = stack.starts.pop().unwrap();
                    let duration = start.elapsed();
                    let level = stack.starts.len();
                    let message = mem::replace(desc, String::new());
                    stack.messages.push(Message { level, duration, message });
                    if level == 0 {
                        let stdout = stderr();
                        if duration >= stack.filter_data.longer_than {
                            print(0, &stack.messages, &mut stdout.lock());
                        }
                        stack.messages.clear();
                    }
                });
            }
            Profiler { desc: None } => (),
        }
    }
}

fn print(lvl: usize, msgs: &[Message], out: &mut impl Write) {
    let mut last = 0;
    let indent = repeat("    ").take(lvl + 1).collect::<String>();
    for (i, &Message { level: l, duration: dur, message: ref msg }) in msgs.iter().enumerate() {
        if l != lvl {
            continue;
        }
        writeln!(out, "{} {:6}ms - {}", indent, dur.as_millis(), msg)
            .expect("printing profiling info to stdout");

        print(lvl + 1, &msgs[last..i], out);
        last = i;
    }
}

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

    #[test]
    fn test_basic_profile() {
        let s = vec!["profile1".to_string(), "profile2".to_string()];
        let f = Filter::new(2, s, Duration::new(0, 0));
        set_filter(f);
        profiling_function1();
    }

    fn profiling_function1() {
        let _p = profile("profile1");
        profiling_function2();
    }

    fn profiling_function2() {
        let _p = profile("profile2");
    }
}