//! # OpenTelemetry Metrics API

use std::any::Any;
use std::result;
use std::sync::PoisonError;
use std::{borrow::Cow, sync::Arc};
use thiserror::Error;

mod instruments;
mod meter;
pub mod noop;

use crate::ExportError;
pub use instruments::{
    counter::{Counter, ObservableCounter, SyncCounter},
    gauge::ObservableGauge,
    histogram::{Histogram, SyncHistogram},
    up_down_counter::{ObservableUpDownCounter, SyncUpDownCounter, UpDownCounter},
    AsyncInstrument, AsyncInstrumentBuilder, Callback, InstrumentBuilder,
};
pub use meter::{CallbackRegistration, Meter, MeterProvider, Observer};

/// A specialized `Result` type for metric operations.
pub type Result<T> = result::Result<T, MetricsError>;

/// Errors returned by the metrics API.
#[derive(Error, Debug)]
#[non_exhaustive]
pub enum MetricsError {
    /// Other errors not covered by specific cases.
    #[error("Metrics error: {0}")]
    Other(String),
    /// Invalid configuration
    #[error("Config error {0}")]
    Config(String),
    /// Fail to export metrics
    #[error("Metrics exporter {} failed with {0}", .0.exporter_name())]
    ExportErr(Box<dyn ExportError>),
    /// Invalid instrument configuration such invalid instrument name, invalid instrument description, invalid instrument unit, etc.
    /// See [spec](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/api.md#general-characteristics)
    /// for full list of requirements.
    #[error("Invalid instrument configuration: {0}")]
    InvalidInstrumentConfiguration(&'static str),
}

impl<T: ExportError> From<T> for MetricsError {
    fn from(err: T) -> Self {
        MetricsError::ExportErr(Box::new(err))
    }
}

impl<T> From<PoisonError<T>> for MetricsError {
    fn from(err: PoisonError<T>) -> Self {
        MetricsError::Other(err.to_string())
    }
}

/// Units denote underlying data units tracked by `Meter`s.
#[derive(Clone, Default, Debug, PartialEq, Eq, Hash)]
pub struct Unit(Cow<'static, str>);

impl Unit {
    /// Create a new `Unit` from an `Into<String>`
    pub fn new<S>(value: S) -> Self
    where
        S: Into<Cow<'static, str>>,
    {
        Unit(value.into())
    }

    /// View unit as &str
    pub fn as_str(&self) -> &str {
        self.0.as_ref()
    }
}

impl AsRef<str> for Unit {
    #[inline]
    fn as_ref(&self) -> &str {
        self.0.as_ref()
    }
}

/// SDK implemented trait for creating instruments
pub trait InstrumentProvider {
    /// creates an instrument for recording increasing values.
    fn u64_counter(
        &self,
        _name: Cow<'static, str>,
        _description: Option<Cow<'static, str>>,
        _unit: Option<Unit>,
    ) -> Result<Counter<u64>> {
        Ok(Counter::new(Arc::new(noop::NoopSyncInstrument::new())))
    }

    /// creates an instrument for recording increasing values.
    fn f64_counter(
        &self,
        _name: Cow<'static, str>,
        _description: Option<Cow<'static, str>>,
        _unit: Option<Unit>,
    ) -> Result<Counter<f64>> {
        Ok(Counter::new(Arc::new(noop::NoopSyncInstrument::new())))
    }

    /// creates an instrument for recording increasing values via callback.
    fn u64_observable_counter(
        &self,
        _name: Cow<'static, str>,
        _description: Option<Cow<'static, str>>,
        _unit: Option<Unit>,
        _callback: Vec<Callback<u64>>,
    ) -> Result<ObservableCounter<u64>> {
        Ok(ObservableCounter::new(Arc::new(
            noop::NoopAsyncInstrument::new(),
        )))
    }

    /// creates an instrument for recording increasing values via callback.
    fn f64_observable_counter(
        &self,
        _name: Cow<'static, str>,
        _description: Option<Cow<'static, str>>,
        _unit: Option<Unit>,
        _callback: Vec<Callback<f64>>,
    ) -> Result<ObservableCounter<f64>> {
        Ok(ObservableCounter::new(Arc::new(
            noop::NoopAsyncInstrument::new(),
        )))
    }

    /// creates an instrument for recording changes of a value.
    fn i64_up_down_counter(
        &self,
        _name: Cow<'static, str>,
        _description: Option<Cow<'static, str>>,
        _unit: Option<Unit>,
    ) -> Result<UpDownCounter<i64>> {
        Ok(UpDownCounter::new(
            Arc::new(noop::NoopSyncInstrument::new()),
        ))
    }

    /// creates an instrument for recording changes of a value.
    fn f64_up_down_counter(
        &self,
        _name: Cow<'static, str>,
        _description: Option<Cow<'static, str>>,
        _unit: Option<Unit>,
    ) -> Result<UpDownCounter<f64>> {
        Ok(UpDownCounter::new(
            Arc::new(noop::NoopSyncInstrument::new()),
        ))
    }

    /// creates an instrument for recording changes of a value.
    fn i64_observable_up_down_counter(
        &self,
        _name: Cow<'static, str>,
        _description: Option<Cow<'static, str>>,
        _unit: Option<Unit>,
        _callback: Vec<Callback<i64>>,
    ) -> Result<ObservableUpDownCounter<i64>> {
        Ok(ObservableUpDownCounter::new(Arc::new(
            noop::NoopAsyncInstrument::new(),
        )))
    }

    /// creates an instrument for recording changes of a value via callback.
    fn f64_observable_up_down_counter(
        &self,
        _name: Cow<'static, str>,
        _description: Option<Cow<'static, str>>,
        _unit: Option<Unit>,
        _callback: Vec<Callback<f64>>,
    ) -> Result<ObservableUpDownCounter<f64>> {
        Ok(ObservableUpDownCounter::new(Arc::new(
            noop::NoopAsyncInstrument::new(),
        )))
    }

    /// creates an instrument for recording the current value via callback.
    fn u64_observable_gauge(
        &self,
        _name: Cow<'static, str>,
        _description: Option<Cow<'static, str>>,
        _unit: Option<Unit>,
        _callback: Vec<Callback<u64>>,
    ) -> Result<ObservableGauge<u64>> {
        Ok(ObservableGauge::new(Arc::new(
            noop::NoopAsyncInstrument::new(),
        )))
    }

    /// creates an instrument for recording the current value via callback.
    fn i64_observable_gauge(
        &self,
        _name: Cow<'static, str>,
        _description: Option<Cow<'static, str>>,
        _unit: Option<Unit>,
        _callback: Vec<Callback<i64>>,
    ) -> Result<ObservableGauge<i64>> {
        Ok(ObservableGauge::new(Arc::new(
            noop::NoopAsyncInstrument::new(),
        )))
    }

    /// creates an instrument for recording the current value via callback.
    fn f64_observable_gauge(
        &self,
        _name: Cow<'static, str>,
        _description: Option<Cow<'static, str>>,
        _unit: Option<Unit>,
        _callback: Vec<Callback<f64>>,
    ) -> Result<ObservableGauge<f64>> {
        Ok(ObservableGauge::new(Arc::new(
            noop::NoopAsyncInstrument::new(),
        )))
    }

    /// creates an instrument for recording a distribution of values.
    fn f64_histogram(
        &self,
        _name: Cow<'static, str>,
        _description: Option<Cow<'static, str>>,
        _unit: Option<Unit>,
    ) -> Result<Histogram<f64>> {
        Ok(Histogram::new(Arc::new(noop::NoopSyncInstrument::new())))
    }

    /// creates an instrument for recording a distribution of values.
    fn u64_histogram(
        &self,
        _name: Cow<'static, str>,
        _description: Option<Cow<'static, str>>,
        _unit: Option<Unit>,
    ) -> Result<Histogram<u64>> {
        Ok(Histogram::new(Arc::new(noop::NoopSyncInstrument::new())))
    }

    /// creates an instrument for recording a distribution of values.
    fn i64_histogram(
        &self,
        _name: Cow<'static, str>,
        _description: Option<Cow<'static, str>>,
        _unit: Option<Unit>,
    ) -> Result<Histogram<i64>> {
        Ok(Histogram::new(Arc::new(noop::NoopSyncInstrument::new())))
    }

    /// Captures the function that will be called during data collection.
    ///
    /// It is only valid to call `observe` within the scope of the passed function.
    fn register_callback(
        &self,
        instruments: &[Arc<dyn Any>],
        callbacks: Box<MultiInstrumentCallback>,
    ) -> Result<Box<dyn CallbackRegistration>>;
}

type MultiInstrumentCallback = dyn Fn(&dyn Observer) + Send + Sync;