//! Interval-based reporting: aggregate per-measurement data into coarse
//! time buckets (monthly, weekly, daily, or fixed durations) for summary
//! charts and tables.
//!
//! This is a separate concern from LTTB decimation:
//!
//! - **LTTB** picks representative sample points to fit a chart's pixel
//!   budget. No aggregation — original values are preserved.
//! - **Interval reporting** aggregates every observation in a bucket into
//!   one output value (mean, sum, max, …) using the measurement's
//!   configured `signal_aggregation` (or a per-request override).
//!
//! Each output cell carries its own *N* (count of non-null contributing
//! observations), which varies by measurement because native sample rates
//! differ. A monthly report over mixed-rate measurements produces the
//! same number of rows per measurement (one per bucket) but different N
//! per cell — SCADA at 60s has ~43,200 contributors per month, while
//! historical precipitation at 1h has ~720. N is observed-only: nulls
//! (including those that weren't filled because no `null_value` was
//! configured) never contribute.
//!
//! # Module layout
//!
//! - [`planner`] — pure decision logic: given a measurement + interval,
//!   produce a [`ResamplingPlan`] describing how its data maps to the
//!   report grid. No polars work — fully unit-testable in isolation.
//! - `aggregate` (future) — the imperative side that applies the plan
//!   to a DataFrame and captures per-cell N in diagnostics.
//! - `diag` (future) — `IntervalCellDiag` roll-up surfaced on
//!   `SubsetInfo`.

pub mod aggregate;
pub mod planner;

use std::collections::HashMap;

use serde::{Deserialize, Serialize};

use crate::{CanonicalColumnName, aggregation::Aggregate, unit::NullValue};

pub use aggregate::{
    IntervalAggregateOutput, IntervalStats, apply_interval, build_resampling_plans, run_interval,
};
pub use planner::{AggregationSource, ResamplingPath, ResamplingPlan, ResamplingPlanner};

// ============================================================================
// ReportInterval — what the request asks for
// ============================================================================

/// Request-side specification of a report interval. When present on an
/// `EtlUnitSubsetRequest`, the subset pipeline aggregates each
/// measurement into buckets described by `bucket`.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ReportInterval {
    pub bucket: IntervalBucket,
    #[serde(default)]
    pub strategy: RateStrategy,
    /// Override each measurement's `signal_aggregation` for this request.
    /// Keyed by the measurement's canonical name. Absent keys fall back
    /// to the schema-configured aggregation.
    #[serde(default)]
    pub aggregation_override: Option<HashMap<CanonicalColumnName, Aggregate>>,
    #[serde(default)]
    pub empty_bucket: EmptyBucketPolicy,
}

/// How time is bucketed for aggregation. Calendar-aware variants
/// (`Months`/`Weeks`/`Days`/`Hours`) use Polars' `dt.truncate` downstream
/// so bucket boundaries land on real calendar edges. `Fixed` produces
/// uniform, epoch-aligned buckets. `WholeWindow` collapses every
/// observation per subject into a single bucket — useful paired with
/// `group_by` to produce one value per group across the full request
/// window ("mean sump per parish for the last month").
#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
#[serde(tag = "type", rename_all = "snake_case")]
pub enum IntervalBucket {
    Months(u32),
    Weeks(u32),
    Days(u32),
    Hours(u32),
    Fixed {
        duration_ms: i64,
    },
    /// Single bucket spanning the entire observed window **per subject**.
    /// Each subject's `bucket_start_ms` in stats is that subject's earliest
    /// observation time; the aggregation folds every observation for that
    /// subject into one value. Combined with `group_by`, this produces
    /// "one value per group for the whole request window".
    WholeWindow,
}

impl IntervalBucket {
    /// Approximate duration in milliseconds. Months/weeks use canonical
    /// averages (30-day month, 7-day week) — fine for the *ordering*
    /// comparisons the planner makes against a measurement's native
    /// sample rate. The imperative bucket boundary math uses Polars'
    /// calendar-aware `dt.truncate`, not this value.
    /// Parse a human-friendly shorthand string into an `IntervalBucket`.
    ///
    /// Accepted forms (case-insensitive):
    /// - `"whole_window"` / `"whole"` → [`Self::WholeWindow`]
    /// - `"<n>mo"` → [`Self::Months`]
    /// - `"<n>w"`  → [`Self::Weeks`]
    /// - `"<n>d"`  → [`Self::Days`]
    /// - `"<n>h"`  → [`Self::Hours`]
    /// - `"<n>m"`  → [`Self::Fixed { n*60_000 }`] (minutes)
    /// - `"<n>s"`  → [`Self::Fixed { n*1_000 }`]  (seconds)
    /// - `"<n>ms"` → [`Self::Fixed { n }`]         (milliseconds, verbatim)
    pub fn parse(s: &str) -> Result<Self, String> {
        let trimmed = s.trim().to_ascii_lowercase();
        if matches!(trimmed.as_str(), "whole_window" | "whole") {
            return Ok(Self::WholeWindow);
        }
        // Order matters: longer suffixes first so "mo" / "ms" beat "m" / "s".
        for (suffix, build) in [
            (
                "mo",
                Box::new(|n: i64| Self::Months(n as u32)) as Box<dyn Fn(i64) -> Self>,
            ),
            (
                "ms",
                Box::new(|n: i64| Self::Fixed { duration_ms: n }) as Box<_>,
            ),
            ("w", Box::new(|n: i64| Self::Weeks(n as u32)) as Box<_>),
            ("d", Box::new(|n: i64| Self::Days(n as u32)) as Box<_>),
            ("h", Box::new(|n: i64| Self::Hours(n as u32)) as Box<_>),
            (
                "m",
                Box::new(|n: i64| Self::Fixed {
                    duration_ms: n * 60_000,
                }) as Box<_>,
            ),
            (
                "s",
                Box::new(|n: i64| Self::Fixed {
                    duration_ms: n * 1_000,
                }) as Box<_>,
            ),
        ] {
            if let Some(num_str) = trimmed.strip_suffix(suffix)
                && let Ok(n) = num_str.trim().parse::<i64>()
                && n > 0
            {
                return Ok(build(n));
            }
        }
        Err(format!(
            "unrecognized interval '{s}'. Use '1h', '1d', '1mo', 'whole_window', etc."
        ))
    }

    pub fn approximate_ms(&self) -> i64 {
        const MS_PER_SECOND: i64 = 1_000;
        const MS_PER_MINUTE: i64 = 60 * MS_PER_SECOND;
        const MS_PER_HOUR: i64 = 60 * MS_PER_MINUTE;
        const MS_PER_DAY: i64 = 24 * MS_PER_HOUR;
        const MS_PER_WEEK: i64 = 7 * MS_PER_DAY;
        const MS_PER_MONTH_AVG: i64 = 30 * MS_PER_DAY;

        match self {
            Self::Months(n) => i64::from(*n) * MS_PER_MONTH_AVG,
            Self::Weeks(n) => i64::from(*n) * MS_PER_WEEK,
            Self::Days(n) => i64::from(*n) * MS_PER_DAY,
            Self::Hours(n) => i64::from(*n) * MS_PER_HOUR,
            Self::Fixed { duration_ms } => *duration_ms,
            // Effectively unbounded — by construction always coarser than
            // any native rate, so the planner picks Aggregate.
            Self::WholeWindow => i64::MAX,
        }
    }
}

/// How each measurement should be resampled into the interval grid when
/// the native rate doesn't match. Applied per-measurement by the
/// planner. Strategies differ only in the middle case
/// (`native > interval`); for `native <= interval` every strategy
/// aggregates, and for `native == interval` every strategy passes through.
#[derive(Debug, Clone, Copy, Default, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum RateStrategy {
    /// Aggregate where native ≤ interval; sparse where native > interval.
    /// Most honest default — no fabricated values.
    #[default]
    Auto,
    /// Aggregate where possible; upsample (per the measurement's declared
    /// `upsample_strategy`) where native > interval. Falls back to sparse
    /// if no upsample strategy is configured.
    Upsample,
    /// Keep every measurement at its native rate — cells outside the
    /// native cadence on the interval grid are null.
    Native,
    /// Aggregate where possible, sparse otherwise. Identical to `Auto`
    /// today; exists as an explicit override when `Auto`'s default
    /// changes in the future.
    AggregateOrSparse,
}

/// What goes in a bucket that no observation landed in.
#[derive(Debug, Clone, Default, Serialize, Deserialize)]
#[serde(tag = "type", rename_all = "snake_case")]
pub enum EmptyBucketPolicy {
    /// Leave the bucket's value as null.
    #[default]
    Null,
    /// Use each measurement's configured `null_value` (if any).
    FromConfig,
    /// Fill every empty bucket with this explicit value.
    Value(NullValue),
}
