use crate::metric_primitive::MetricPrimitive;
use crate::timestamp::Timestamp;
use serde::Serialize;
use std::collections::BTreeMap;

/// Key type for the engine's primary index.
///
/// Variants are ordered top to bottom as declared (derived `Ord` compares the
/// discriminant first), which is what carves the map into contiguous ranges:
/// logs, then params, then metric declarations, then buckets.
#[allow(dead_code)]
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Serialize)]
pub enum IndexKey {
    /// Marker for the start of the whole range. Never inserted, only navigated to.
    Start,
    IngestedLog {
        sequence: u64,
        timestamp: Timestamp,
    },
    /// Marker between the log range and the param range.
    LogParamSplit,
    ParamDeclaration {
        name: String,
    },
    /// Marker between the param range and the metric declaration range.
    ParamMetricSplit,
    MetricDeclaration {
        name: String,
    },
    /// Marker between metric declarations and their buckets.
    MetricBucketSplit,
    Bucket {
        metric_name: String,
        labels: BTreeMap<String, MetricPrimitive>,
    },
    /// Ticket 023: internal bookkeeping (never returned by a query) tracking
    /// the timestamp of the most recent counter event for one metric+label
    /// combination, independent of whether that event actually pushed a
    /// `Bucket` value — a `Duration`-kind `Value` param's *first* occurrence
    /// of a label set has no previous event to diff against and pushes no
    /// `Bucket` entry, but must still be recorded here so the *next*
    /// occurrence can compute its elapsed time.
    LastMetricEvent {
        metric_name: String,
        labels: BTreeMap<String, MetricPrimitive>,
    },
    /// Marker for the end of the whole range. Nothing sorts after this.
    End,
}