use std::{collections::VecDeque, fmt::Debug, io, sync::Arc};

use itertools::Itertools;
use snafu::Snafu;
use vector_lib::{
    internal_event::{ComponentEventsDropped, UNINTENTIONAL},
    lookup::event_path,
};
use vrl::path::{OwnedSegment, OwnedTargetPath, PathPrefix};

use super::{config::MAX_PAYLOAD_BYTES, service::LogApiRequest};
use crate::{
    common::datadog::{DDTAGS, DD_RESERVED_SEMANTIC_ATTRS},
    sinks::{
        prelude::*,
        util::{http::HttpJsonBatchSizer, Compressor},
    },
};
#[derive(Default)]
pub struct EventPartitioner;

impl Partitioner for EventPartitioner {
    type Item = Event;
    type Key = Option<Arc<str>>;

    fn partition(&self, item: &Self::Item) -> Self::Key {
        item.metadata().datadog_api_key()
    }
}

#[derive(Debug)]
pub struct LogSinkBuilder<S> {
    transformer: Transformer,
    service: S,
    batch_settings: BatcherSettings,
    compression: Option<Compression>,
    default_api_key: Arc<str>,
    protocol: String,
}

impl<S> LogSinkBuilder<S> {
    pub fn new(
        transformer: Transformer,
        service: S,
        default_api_key: Arc<str>,
        batch_settings: BatcherSettings,
        protocol: String,
    ) -> Self {
        Self {
            transformer,
            service,
            default_api_key,
            batch_settings,
            compression: None,
            protocol,
        }
    }

    pub const fn compression(mut self, compression: Compression) -> Self {
        self.compression = Some(compression);
        self
    }

    pub fn build(self) -> LogSink<S> {
        LogSink {
            default_api_key: self.default_api_key,
            transformer: self.transformer,
            service: self.service,
            batch_settings: self.batch_settings,
            compression: self.compression.unwrap_or_default(),
            protocol: self.protocol,
        }
    }
}

pub struct LogSink<S> {
    /// The default Datadog API key to use
    ///
    /// In some instances an `Event` will come in on the stream with an
    /// associated API key. That API key is the one it'll get batched up by but
    /// otherwise we will see `Event` instances with no associated key. In that
    /// case we batch them by this default.
    default_api_key: Arc<str>,
    /// The API service
    service: S,
    /// The encoding of payloads
    transformer: Transformer,
    /// The compression technique to use when building the request body
    compression: Compression,
    /// Batch settings: timeout, max events, max bytes, etc.
    batch_settings: BatcherSettings,
    /// The protocol name
    protocol: String,
}

// The Datadog logs intake does not require the fields that are set in this
// function. But if they are present in the event, we normalize the paths
// (and value in the case of timestamp) to something that intake understands.
pub fn normalize_event(event: &mut Event) {
    let log = event.as_mut_log();

    // Upstream Sources may have semantically defined Datadog reserved attributes outside of their
    // expected location by DD logs intake (root of the event). Move them if needed.
    for (meaning, expected_field_name) in DD_RESERVED_SEMANTIC_ATTRS {
        // check if there is a semantic meaning for the reserved attribute
        if let Some(current_path) = log.find_key_by_meaning(meaning).cloned() {
            // move it to the desired location
            position_reserved_attr_event_root(log, &current_path, expected_field_name, meaning);
        }
    }

    // if the tags value is an array we need to reconstruct it to a comma delimited string for DD logs intake.
    // NOTE: we don't access by semantic meaning here because in the prior step
    // we ensured reserved attributes are in expected locations.
    let ddtags_path = event_path!(DDTAGS);
    if let Some(Value::Array(tags_arr)) = log.get(ddtags_path) {
        if !tags_arr.is_empty() {
            let all_tags: String = tags_arr
                .iter()
                .filter_map(|tag_kv| {
                    tag_kv
                        .as_bytes()
                        .map(|bytes| String::from_utf8_lossy(bytes))
                })
                .join(",");

            log.insert(ddtags_path, all_tags);
        }
    }

    // ensure the timestamp is in expected format
    // NOTE: we don't access by semantic meaning here because in the prior step
    // we ensured reserved attributes are in expected locations.
    let ts_path = event_path!("timestamp");
    if let Some(Value::Timestamp(ts)) = log.remove(ts_path) {
        log.insert(ts_path, Value::Integer(ts.timestamp_millis()));
    }
}

// If an expected reserved attribute is not located in the event root, rename it and handle
// any potential conflicts by preserving the conflicting one with a _RESERVED_ prefix.
pub fn position_reserved_attr_event_root(
    log: &mut LogEvent,
    current_path: &OwnedTargetPath,
    expected_field_name: &str,
    meaning: &str,
) {
    // the path that DD archives expects this reserved attribute to be in.
    let desired_path = event_path!(expected_field_name);

    // if not already be at the expected location
    if !path_is_field(current_path, expected_field_name) {
        // if an existing attribute exists here already, move it so to not overwrite it.
        // yes, technically the rename path could exist, but technically that could always be the case.
        if log.contains(desired_path) {
            let rename_attr = format!("_RESERVED_{}", meaning);
            let rename_path = event_path!(rename_attr.as_str());
            warn!(
                message = "Semantic meaning is defined, but the event path already exists. Renaming to not overwrite.",
                meaning = meaning,
                renamed = &rename_attr,
                internal_log_rate_limit = true,
            );
            log.rename_key(desired_path, rename_path);
        }

        log.rename_key(current_path, desired_path);
    }
}

// Test if the named path consists of the single named field. This is rather a hack and should
// hypothetically be solvable in the `vrl` crate with an implementation of
// `PartialEq<BorrowedTargetPath<'_>>`. The alternative is doing a comparison against another
// `OwnedTargetPath`, but the naïve implementation of that requires multiple allocations and copies
// just to test equality.
pub fn path_is_field(path: &OwnedTargetPath, field: &str) -> bool {
    path.prefix == PathPrefix::Event
        && matches!(&path.path.segments[..], [OwnedSegment::Field(f)] if f.as_str() == field)
}

#[derive(Debug, Snafu)]
pub enum RequestBuildError {
    #[snafu(display("Encoded payload is greater than the max limit."))]
    PayloadTooBig { events_that_fit: usize },
    #[snafu(display("Failed to build payload with error: {}", error))]
    Io { error: std::io::Error },
    #[snafu(display("Failed to serialize payload with error: {}", error))]
    Json { error: serde_json::Error },
}

impl From<io::Error> for RequestBuildError {
    fn from(error: io::Error) -> RequestBuildError {
        RequestBuildError::Io { error }
    }
}

impl From<serde_json::Error> for RequestBuildError {
    fn from(error: serde_json::Error) -> RequestBuildError {
        RequestBuildError::Json { error }
    }
}

pub struct LogRequestBuilder {
    pub default_api_key: Arc<str>,
    pub transformer: Transformer,
    pub compression: Compression,
}

impl LogRequestBuilder {
    pub fn build_request(
        &self,
        events: Vec<Event>,
        api_key: Arc<str>,
    ) -> Result<Vec<LogApiRequest>, RequestBuildError> {
        // Transform events and pre-compute their estimated size.
        let mut events_with_estimated_size: VecDeque<(Event, JsonSize)> = events
            .into_iter()
            .map(|mut event| {
                normalize_event(&mut event);
                self.transformer.transform(&mut event);
                let estimated_json_size = event.estimated_json_encoded_size_of();
                (event, estimated_json_size)
            })
            .collect();

        // Construct requests respecting the max payload size.
        let mut requests: Vec<LogApiRequest> = Vec::new();
        while !events_with_estimated_size.is_empty() {
            let (events_serialized, body, byte_size) =
                serialize_with_capacity(&mut events_with_estimated_size)?;
            if events_serialized.is_empty() {
                // first event was too large for whole request
                let _too_big = events_with_estimated_size.pop_front();
                emit!(ComponentEventsDropped::<UNINTENTIONAL> {
                    count: 1,
                    reason: "Event too large to encode."
                });
            } else {
                let request =
                    self.finish_request(body, events_serialized, byte_size, Arc::clone(&api_key))?;
                requests.push(request);
            }
        }

        Ok(requests)
    }

    fn finish_request(
        &self,
        buf: Vec<u8>,
        mut events: Vec<Event>,
        byte_size: GroupedCountByteSize,
        api_key: Arc<str>,
    ) -> Result<LogApiRequest, RequestBuildError> {
        let n_events = events.len();
        let uncompressed_size = buf.len();

        // Now just compress it like normal.
        let mut compressor = Compressor::from(self.compression);
        write_all(&mut compressor, n_events, &buf)?;
        let bytes = compressor.into_inner().freeze();

        let finalizers = events.take_finalizers();
        let request_metadata_builder = RequestMetadataBuilder::from_events(&events);

        let payload = if self.compression.is_compressed() {
            EncodeResult::compressed(bytes, uncompressed_size, byte_size)
        } else {
            EncodeResult::uncompressed(bytes, byte_size)
        };

        Ok::<_, RequestBuildError>(LogApiRequest {
            api_key,
            finalizers,
            compression: self.compression,
            metadata: request_metadata_builder.build(&payload),
            uncompressed_size: payload.uncompressed_byte_size,
            body: payload.into_payload(),
        })
    }
}

/// Serialize events into a buffer as a JSON array that has a maximum size of
/// `MAX_PAYLOAD_BYTES`.
///
/// Returns the serialized events, the buffer, and the byte size of the events.
/// Events that are not serialized remain in the `events` parameter.
pub fn serialize_with_capacity(
    events: &mut VecDeque<(Event, JsonSize)>,
) -> Result<(Vec<Event>, Vec<u8>, GroupedCountByteSize), io::Error> {
    // Compute estimated size, accounting for the size of the brackets and commas.
    let total_estimated =
        events.iter().map(|(_, size)| size.get()).sum::<usize>() + events.len() * 2;

    // Initialize state.
    let mut buf = Vec::with_capacity(total_estimated);
    let mut byte_size = telemetry().create_request_count_byte_size();
    let mut events_serialized = Vec::with_capacity(events.len());

    // Write entries until the buffer is full.
    buf.push(b'[');
    let mut first = true;
    while let Some((event, estimated_json_size)) = events.pop_front() {
        // Track the existing length of the buffer so we can truncate it if we need to.
        let existing_len = buf.len();
        if first {
            first = false;
        } else {
            buf.push(b',');
        }
        serde_json::to_writer(&mut buf, event.as_log())?;
        // If the buffer is too big, truncate it and break out of the loop.
        if buf.len() >= MAX_PAYLOAD_BYTES {
            events.push_front((event, estimated_json_size));
            buf.truncate(existing_len);
            break;
        }
        // Otherwise, track the size of the event and continue.
        byte_size.add_event(&event, estimated_json_size);
        events_serialized.push(event);
    }
    buf.push(b']');

    Ok((events_serialized, buf, byte_size))
}

impl<S> LogSink<S>
where
    S: Service<LogApiRequest> + Send + 'static,
    S::Future: Send + 'static,
    S::Response: DriverResponse + Send + 'static,
    S::Error: Debug + Into<crate::Error> + Send,
{
    async fn run_inner(self: Box<Self>, input: BoxStream<'_, Event>) -> Result<(), ()> {
        let default_api_key = Arc::clone(&self.default_api_key);

        let partitioner = EventPartitioner;
        let batch_settings = self.batch_settings;
        let builder = Arc::new(LogRequestBuilder {
            default_api_key,
            transformer: self.transformer,
            compression: self.compression,
        });

        let input = input.batched_partitioned(partitioner, || {
            batch_settings.as_item_size_config(HttpJsonBatchSizer)
        });
        input
            .concurrent_map(default_request_builder_concurrency_limit(), move |input| {
                let builder = Arc::clone(&builder);

                Box::pin(async move {
                    let (api_key, events) = input;
                    let api_key = api_key.unwrap_or_else(|| Arc::clone(&builder.default_api_key));

                    builder.build_request(events, api_key)
                })
            })
            .filter_map(|request| async move {
                match request {
                    Err(error) => {
                        emit!(SinkRequestBuildError { error });
                        None
                    }
                    Ok(reqs) => Some(futures::stream::iter(reqs)),
                }
            })
            .flatten()
            .into_driver(self.service)
            .protocol(self.protocol)
            .run()
            .await
    }
}

#[async_trait]
impl<S> StreamSink<Event> for LogSink<S>
where
    S: Service<LogApiRequest> + Send + 'static,
    S::Future: Send + 'static,
    S::Response: DriverResponse + Send + 'static,
    S::Error: Debug + Into<crate::Error> + Send,
{
    async fn run(self: Box<Self>, input: BoxStream<'_, Event>) -> Result<(), ()> {
        self.run_inner(input).await
    }
}

#[cfg(test)]
mod tests {

    use std::sync::Arc;

    use chrono::Utc;
    use vector_lib::{
        config::{LegacyKey, LogNamespace},
        event::{Event, EventMetadata, LogEvent},
        schema::{meaning, Definition},
    };
    use vrl::{
        core::Value,
        event_path, metadata_path, owned_value_path,
        value::{kind::Collection, Kind},
    };

    use super::normalize_event;

    fn assert_normalized_log_has_expected_attrs(log: &LogEvent) {
        assert!(log
            .get(event_path!("timestamp"))
            .expect("should have timestamp")
            .is_integer());

        for attr in [
            "message",
            "timestamp",
            "hostname",
            "ddtags",
            "service",
            "status",
        ] {
            assert!(log.contains(event_path!(attr)), "missing {}", attr);
        }

        assert_eq!(
            log.get(event_path!("ddtags")).expect("should have tags"),
            &Value::Bytes("key1:value1,key2:value2".into())
        );
    }

    #[test]
    fn normalize_event_doesnt_require() {
        let mut log = LogEvent::default();
        log.insert(event_path!("foo"), "bar");

        let mut event = Event::Log(log);
        normalize_event(&mut event);

        let log = event.as_log();

        assert!(!log.contains(event_path!("message")));
        assert!(!log.contains(event_path!("timestamp")));
        assert!(!log.contains(event_path!("hostname")));
    }

    #[test]
    fn normalize_event_normalizes_legacy_namespace() {
        let metadata = EventMetadata::default().with_schema_definition(&Arc::new(
            Definition::new_with_default_metadata(
                Kind::object(Collection::empty()),
                [LogNamespace::Legacy],
            )
            .with_source_metadata(
                "datadog_agent",
                Some(LegacyKey::InsertIfEmpty(owned_value_path!("ddtags"))),
                &owned_value_path!("ddtags"),
                Kind::bytes(),
                Some(meaning::TAGS),
            )
            .with_source_metadata(
                "datadog_agent",
                Some(LegacyKey::InsertIfEmpty(owned_value_path!("hostname"))),
                &owned_value_path!("hostname"),
                Kind::bytes(),
                Some(meaning::HOST),
            )
            .with_source_metadata(
                "datadog_agent",
                Some(LegacyKey::InsertIfEmpty(owned_value_path!("timestamp"))),
                &owned_value_path!("timestamp"),
                Kind::timestamp(),
                Some(meaning::TIMESTAMP),
            )
            .with_source_metadata(
                "datadog_agent",
                Some(LegacyKey::InsertIfEmpty(owned_value_path!("severity"))),
                &owned_value_path!("severity"),
                Kind::bytes(),
                Some(meaning::SEVERITY),
            )
            .with_source_metadata(
                "datadog_agent",
                Some(LegacyKey::InsertIfEmpty(owned_value_path!("service"))),
                &owned_value_path!("service"),
                Kind::bytes(),
                Some(meaning::SERVICE),
            )
            .with_source_metadata(
                "datadog_agent",
                Some(LegacyKey::InsertIfEmpty(owned_value_path!("source"))),
                &owned_value_path!("source"),
                Kind::bytes(),
                Some(meaning::SOURCE),
            ),
        ));

        let mut log = LogEvent::new_with_metadata(metadata);
        log.insert(event_path!("message"), "the_message");
        let namespace = log.namespace();

        namespace.insert_standard_vector_source_metadata(&mut log, "datadog_agent", Utc::now());

        let tags = vec![
            Value::Bytes("key1:value1".into()),
            Value::Bytes("key2:value2".into()),
        ];

        log.insert(event_path!("ddtags"), tags);
        log.insert(event_path!("hostname"), "the_host");
        log.insert(event_path!("service"), "the_service");
        log.insert(event_path!("source"), "the_source");
        log.insert(event_path!("severity"), "the_severity");

        assert!(log.namespace() == LogNamespace::Legacy);

        let mut event = Event::Log(log);
        normalize_event(&mut event);

        assert_normalized_log_has_expected_attrs(event.as_log());
    }

    #[test]
    fn normalize_event_normalizes_vector_namespace() {
        let metadata = EventMetadata::default().with_schema_definition(&Arc::new(
            Definition::new_with_default_metadata(Kind::bytes(), [LogNamespace::Vector])
                .with_source_metadata(
                    "datadog_agent",
                    Some(LegacyKey::InsertIfEmpty(owned_value_path!("ddtags"))),
                    &owned_value_path!("ddtags"),
                    Kind::bytes(),
                    Some(meaning::TAGS),
                )
                .with_source_metadata(
                    "datadog_agent",
                    Some(LegacyKey::InsertIfEmpty(owned_value_path!("hostname"))),
                    &owned_value_path!("hostname"),
                    Kind::bytes(),
                    Some(meaning::HOST),
                )
                .with_source_metadata(
                    "datadog_agent",
                    Some(LegacyKey::InsertIfEmpty(owned_value_path!("timestamp"))),
                    &owned_value_path!("timestamp"),
                    Kind::timestamp(),
                    Some(meaning::TIMESTAMP),
                )
                .with_source_metadata(
                    "datadog_agent",
                    Some(LegacyKey::InsertIfEmpty(owned_value_path!("severity"))),
                    &owned_value_path!("severity"),
                    Kind::bytes(),
                    Some(meaning::SEVERITY),
                )
                .with_source_metadata(
                    "datadog_agent",
                    Some(LegacyKey::InsertIfEmpty(owned_value_path!("service"))),
                    &owned_value_path!("service"),
                    Kind::bytes(),
                    Some(meaning::SERVICE),
                )
                .with_source_metadata(
                    "datadog_agent",
                    Some(LegacyKey::InsertIfEmpty(owned_value_path!("source"))),
                    &owned_value_path!("source"),
                    Kind::bytes(),
                    Some(meaning::SOURCE),
                ),
        ));

        let mut log = LogEvent::new_with_metadata(metadata);
        log.insert(event_path!("message"), "the_message");

        // insert an arbitrary metadata field such that the log becomes Vector namespaced
        log.insert(metadata_path!("vector", "foo"), "bar");

        let namespace = log.namespace();
        namespace.insert_standard_vector_source_metadata(&mut log, "datadog_agent", Utc::now());

        let tags = vec![
            Value::Bytes("key1:value1".into()),
            Value::Bytes("key2:value2".into()),
        ];
        log.insert(metadata_path!("datadog_agent", "ddtags"), tags);

        log.insert(metadata_path!("datadog_agent", "hostname"), "the_host");
        log.insert(metadata_path!("datadog_agent", "timestamp"), Utc::now());
        log.insert(metadata_path!("datadog_agent", "service"), "the_service");
        log.insert(metadata_path!("datadog_agent", "source"), "the_source");
        log.insert(metadata_path!("datadog_agent", "severity"), "the_severity");

        assert!(log.namespace() == LogNamespace::Vector);

        let mut event = Event::Log(log);
        normalize_event(&mut event);

        assert_normalized_log_has_expected_attrs(event.as_log());
    }
}