tracematch/sections/

mod.rs

//! # Adaptive Consensus Section Detection
//!
//! Detects frequently-traveled road sections using FULL GPS tracks.
//! Produces smooth, natural polylines that evolve and refine over time
//! as more tracks are observed.
//!
//! ## Algorithm
//! 1. Load full GPS tracks (1000s of points per activity)
//! 2. Find overlapping portions using R-tree spatial indexing
//! 3. Cluster overlaps that represent the same physical section
//! 4. Select initial medoid as the starting reference
//! 5. Compute consensus polyline via weighted averaging of all tracks
//! 6. Track per-point confidence based on observation density
//! 7. Adapt section boundaries based on where tracks consistently overlap
//!
//! ## Consensus Algorithm
//! - Normalize all tracks to common parameterization (by distance)
//! - At each position, collect nearby points from all tracks
//! - Compute weighted average: weight = 1 / (distance_to_reference + epsilon)
//! - Higher observation density → higher confidence → tighter future matching
//!
//! ## Adaptive Boundaries
//! - Track where each activity's overlap starts/ends relative to section
//! - Section can grow if tracks consistently extend beyond current bounds
//! - Section contracts if tracks consistently end before current bounds

mod consensus;
mod evolution;
mod medoid;
mod optimized;
mod overlap;
mod portions;
mod postprocess;
mod rtree;
mod traces;

use crate::matching::calculate_route_distance;
use crate::{GpsPoint, RouteGroup};
use log::info;
#[cfg(feature = "parallel")]
use rayon::prelude::*;
use serde::{Deserialize, Serialize};
use std::collections::{HashMap, HashSet};

#[cfg(feature = "persistence")]
use crate::persistence::SectionDetectionProgress;

// Re-export internal utilities for use across submodules
pub(crate) use consensus::compute_consensus_polyline;
pub(crate) use medoid::select_medoid;
pub(crate) use overlap::{
    FullTrackOverlap, OverlapCluster, cluster_overlaps, find_full_track_overlap,
};
pub(crate) use portions::compute_activity_portions;
pub(crate) use postprocess::{
    consolidate_fragments, filter_low_quality_sections, make_sections_exclusive,
    merge_nearby_sections, remove_overlapping_sections, split_at_gradient_changes,
    split_at_heading_changes, split_folding_sections, split_high_variance_sections,
};
pub(crate) use rtree::{IndexedPoint, bounds_overlap_tracks, build_rtree};
pub(crate) use traces::extract_all_activity_traces;

// Re-export evolution functions for public API
pub use evolution::{
    SectionUpdateResult, merge_overlapping_sections, update_section_with_new_traces,
};

// Re-export optimized detection functions
pub use optimized::{
    IncrementalResult, SectionMatch, SplitResult, detect_sections_incremental,
    detect_sections_optimized, find_sections_in_route, recalculate_section_polyline,
    split_section_at_index, split_section_at_point,
};

/// Compute initial stability score from consensus metrics.
/// Stability increases with more observations and tighter spread.
pub(crate) fn compute_initial_stability(
    observation_count: u32,
    average_spread: f64,
    proximity_threshold: f64,
) -> f64 {
    // Observation factor: saturates at 10 observations
    let obs_factor = (observation_count as f64 / 10.0).min(1.0);

    // Spread factor: lower spread = more stable
    let spread_factor = 1.0 - (average_spread / proximity_threshold).clamp(0.0, 1.0);

    // Combined stability: weighted average
    (obs_factor * 0.6 + spread_factor * 0.4).clamp(0.0, 1.0)
}

/// Scale preset for multi-scale section detection
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
#[cfg_attr(feature = "ffi", derive(uniffi::Record))]
pub struct ScalePreset {
    /// Scale name: "short", "medium", "long"
    pub name: String,
    /// Minimum section length for this scale (meters)
    pub min_length: f64,
    /// Maximum section length for this scale (meters)
    pub max_length: f64,
    /// Minimum activities required at this scale (can be lower for short sections)
    pub min_activities: u32,
}

impl ScalePreset {
    pub fn short() -> Self {
        Self {
            name: "short".to_string(),
            min_length: 100.0,
            max_length: 500.0,
            min_activities: 2,
        }
    }

    pub fn medium() -> Self {
        Self {
            name: "medium".to_string(),
            min_length: 500.0,
            max_length: 2000.0,
            min_activities: 2,
        }
    }

    pub fn long() -> Self {
        Self {
            name: "long".to_string(),
            min_length: 2000.0,
            max_length: 5000.0,
            min_activities: 3,
        }
    }

    pub fn default_presets() -> Vec<Self> {
        vec![Self::short(), Self::medium(), Self::long()]
    }
}

/// Configuration for section detection
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
#[cfg_attr(feature = "ffi", derive(uniffi::Record))]
pub struct SectionConfig {
    /// Maximum distance between tracks to consider overlapping (meters)
    pub proximity_threshold: f64,
    /// Minimum overlap length to consider a section (meters)
    pub min_section_length: f64,
    /// Maximum section length (meters) - prevents sections from becoming full routes
    pub max_section_length: f64,
    /// Minimum number of activities that must share an overlap
    pub min_activities: u32,
    /// Tolerance for clustering similar overlaps (meters)
    pub cluster_tolerance: f64,
    /// Number of sample points for AMD comparison (not for output!)
    pub sample_points: u32,
    /// Detection mode: "discovery" (lower thresholds) or "conservative"
    pub detection_mode: String,
    /// Include potential sections with only 1-2 activities as suggestions
    pub include_potentials: bool,
    /// Scale presets for multi-scale detection (empty = single-scale with min/max_section_length)
    pub scale_presets: Vec<ScalePreset>,
    /// Preserve hierarchical sections (don't deduplicate short sections inside longer ones)
    pub preserve_hierarchy: bool,
}

impl Default for SectionConfig {
    fn default() -> Self {
        Self {
            proximity_threshold: 50.0, // 50m - handles GPS error + wide roads + opposite sides
            min_section_length: 200.0, // 200m minimum section (used when scale_presets is empty)
            max_section_length: 5000.0, // 5km max (used when scale_presets is empty)
            min_activities: 3,         // Need 3+ activities (used when scale_presets is empty)
            cluster_tolerance: 80.0,   // 80m for clustering similar overlaps
            sample_points: 50,         // For AMD comparison only
            detection_mode: "discovery".to_string(),
            include_potentials: true,
            scale_presets: ScalePreset::default_presets(),
            preserve_hierarchy: true,
        }
    }
}

impl SectionConfig {
    /// Create a discovery-mode config (lower thresholds, more sections)
    pub fn discovery() -> Self {
        Self {
            detection_mode: "discovery".to_string(),
            include_potentials: true,
            scale_presets: ScalePreset::default_presets(),
            preserve_hierarchy: true,
            ..Default::default()
        }
    }

    /// Create a conservative config (higher thresholds, fewer sections)
    pub fn conservative() -> Self {
        Self {
            detection_mode: "conservative".to_string(),
            include_potentials: false,
            min_activities: 4,
            scale_presets: vec![ScalePreset::medium(), ScalePreset::long()],
            preserve_hierarchy: false,
            ..Default::default()
        }
    }

    /// Create a legacy single-scale config (for backward compatibility)
    pub fn legacy() -> Self {
        Self {
            detection_mode: "legacy".to_string(),
            include_potentials: false,
            scale_presets: vec![], // Empty = use min/max_section_length directly
            preserve_hierarchy: false,
            min_activities: 3,
            ..Default::default()
        }
    }
}

/// Each activity's portion of a section (for pace comparison)
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
#[cfg_attr(feature = "ffi", derive(uniffi::Record))]
pub struct SectionPortion {
    /// Activity ID
    #[serde(alias = "activity_id")]
    pub activity_id: String,
    /// Start index into the activity's FULL GPS track
    #[serde(alias = "start_index")]
    pub start_index: u32,
    /// End index into the activity's FULL GPS track
    #[serde(alias = "end_index")]
    pub end_index: u32,
    /// Distance of this portion in meters
    #[serde(alias = "distance_meters")]
    pub distance_meters: f64,
    /// Direction relative to representative: "same" or "reverse"
    pub direction: String,
}

/// A frequently-traveled section with adaptive consensus representation
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
#[cfg_attr(feature = "ffi", derive(uniffi::Record))]
pub struct FrequentSection {
    /// Unique section ID
    pub id: String,
    /// Custom name (user-defined, None if not set)
    pub name: Option<String>,
    /// Sport type ("Run", "Ride", etc.)
    #[serde(alias = "sport_type")]
    pub sport_type: String,
    /// The consensus polyline - refined from all overlapping tracks
    /// Initially the medoid, evolves via weighted averaging as more tracks are added
    pub polyline: Vec<GpsPoint>,
    /// Which activity provided the initial representative polyline (medoid)
    #[serde(alias = "representative_activity_id")]
    pub representative_activity_id: String,
    /// All activity IDs that traverse this section
    #[serde(alias = "activity_ids")]
    pub activity_ids: Vec<String>,
    /// Each activity's portion (start/end indices, distance, direction)
    #[serde(alias = "activity_portions")]
    pub activity_portions: Vec<SectionPortion>,
    /// Route group IDs that include this section
    #[serde(alias = "route_ids")]
    pub route_ids: Vec<String>,
    /// Number of times traversed
    #[serde(alias = "visit_count")]
    pub visit_count: u32,
    /// Section length in meters
    #[serde(alias = "distance_meters")]
    pub distance_meters: f64,
    /// Pre-computed GPS traces for each activity's overlapping portion
    /// Key is activity ID, value is the GPS points within proximity of section
    #[serde(alias = "activity_traces")]
    pub activity_traces: HashMap<String, Vec<GpsPoint>>,
    /// Confidence score (0.0-1.0) based on observation density
    /// Higher confidence = more tracks observed, tighter consensus
    pub confidence: f64,
    /// Number of observations (tracks) used to compute consensus
    #[serde(alias = "observation_count")]
    pub observation_count: u32,
    /// Average spread (meters) of track observations from consensus line
    /// Lower spread = more consistent track alignment
    #[serde(alias = "average_spread")]
    pub average_spread: f64,
    /// Per-point observation density (how many activities pass through each point)
    /// Used for detecting high-traffic portions that should become separate sections
    #[serde(alias = "point_density")]
    pub point_density: Vec<u32>,
    /// Scale at which this section was detected: "short", "medium", "long", or "legacy"
    pub scale: Option<String>,

    // === Evolution fields (Phase 3) ===
    /// Section version - incremented each time the section is updated
    pub version: u32,
    /// Whether this section was user-defined (prevents automatic updates)
    #[serde(alias = "is_user_defined")]
    pub is_user_defined: bool,
    /// ISO timestamp when section was created
    #[serde(alias = "created_at")]
    pub created_at: Option<String>,
    /// ISO timestamp when section was last updated
    #[serde(alias = "updated_at")]
    pub updated_at: Option<String>,
    /// Stability score (0.0-1.0) - how stable the consensus has become
    /// High stability = consensus is well-established, unlikely to change significantly
    pub stability: f64,
}

/// A potential section detected from 1-2 activities.
/// These are suggestions that users can promote to full sections.
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
#[cfg_attr(feature = "ffi", derive(uniffi::Record))]
pub struct PotentialSection {
    /// Unique section ID
    pub id: String,
    /// Sport type ("Run", "Ride", etc.)
    #[serde(alias = "sport_type")]
    pub sport_type: String,
    /// The polyline from the representative activity
    pub polyline: Vec<GpsPoint>,
    /// Activity IDs that traverse this potential section (1-2)
    #[serde(alias = "activity_ids")]
    pub activity_ids: Vec<String>,
    /// Number of times traversed (1-2)
    #[serde(alias = "visit_count")]
    pub visit_count: u32,
    /// Section length in meters
    #[serde(alias = "distance_meters")]
    pub distance_meters: f64,
    /// Confidence score (0.0-1.0), lower than FrequentSection
    pub confidence: f64,
    /// Scale at which this was detected
    pub scale: String,
}

/// Result of multi-scale section detection
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
#[cfg_attr(feature = "ffi", derive(uniffi::Record))]
pub struct MultiScaleSectionResult {
    /// Confirmed sections (min_activities met)
    pub sections: Vec<FrequentSection>,
    /// Potential sections (1-2 activities, suggestions for user)
    pub potentials: Vec<PotentialSection>,
    /// Statistics about detection
    pub stats: DetectionStats,
}

/// Statistics from section detection
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
#[cfg_attr(feature = "ffi", derive(uniffi::Record))]
pub struct DetectionStats {
    /// Total activities processed
    pub activities_processed: u32,
    /// Total overlaps found across all scales
    pub overlaps_found: u32,
    /// Sections per scale
    pub sections_by_scale: HashMap<String, u32>,
    /// Potentials per scale
    pub potentials_by_scale: HashMap<String, u32>,
}

/// Process a single cluster into a FrequentSection.
fn process_cluster(
    idx: usize,
    cluster: OverlapCluster,
    sport_type: &str,
    track_map: &HashMap<String, Vec<GpsPoint>>,
    activity_to_route: &HashMap<&str, &str>,
    config: &SectionConfig,
    scale_name: Option<&str>,
) -> Option<FrequentSection> {
    // Select medoid - an ACTUAL GPS trace
    let (representative_id, representative_polyline) = select_medoid(&cluster);

    if representative_polyline.is_empty() {
        return None;
    }

    let distance_meters = calculate_route_distance(&representative_polyline);

    // Filter by max length - sections shouldn't be whole routes
    if distance_meters > config.max_section_length {
        return None;
    }

    // Compute activity portions for pace comparison
    let activity_portions =
        compute_activity_portions(&cluster, &representative_polyline, track_map, config);

    // Collect route IDs
    let route_ids: Vec<String> = cluster
        .activity_ids
        .iter()
        .filter_map(|aid| activity_to_route.get(aid.as_str()).map(|s| s.to_string()))
        .collect::<HashSet<_>>()
        .into_iter()
        .collect();

    // Pre-compute activity traces
    let activity_id_vec: Vec<String> = cluster.activity_ids.iter().cloned().collect();
    let activity_traces =
        extract_all_activity_traces(&activity_id_vec, &representative_polyline, track_map);

    // Collect all traces for consensus computation
    let all_traces: Vec<Vec<GpsPoint>> = activity_traces.values().cloned().collect();

    // Compute consensus polyline from all overlapping tracks
    let consensus = compute_consensus_polyline(
        &representative_polyline,
        &all_traces,
        config.proximity_threshold,
    );

    // Reject sparse sections - a valid LineString requires at least 2 points
    if consensus.polyline.len() < 2 {
        return None;
    }

    // Use consensus polyline and update distance
    let consensus_distance = calculate_route_distance(&consensus.polyline);

    // Filter by min length - consensus might collapse to fewer points
    if consensus_distance < config.min_section_length {
        return None;
    }

    // Compute stability: more observations + tighter spread = more stable
    let stability = compute_initial_stability(
        consensus.observation_count,
        consensus.average_spread,
        config.proximity_threshold,
    );

    // Count activity_ids before moving
    let activity_count = cluster.activity_ids.len();

    Some(FrequentSection {
        id: format!("sec_{}_{}", sport_type.to_lowercase(), idx),
        name: None,
        sport_type: sport_type.to_string(),
        polyline: consensus.polyline,
        representative_activity_id: representative_id,
        activity_ids: cluster.activity_ids.into_iter().collect(),
        activity_portions,
        route_ids,
        // visit_count should equal unique activities
        visit_count: activity_count as u32,
        distance_meters: consensus_distance,
        activity_traces,
        confidence: consensus.confidence,
        observation_count: consensus.observation_count,
        average_spread: consensus.average_spread,
        point_density: consensus.point_density,
        scale: scale_name.map(|s| s.to_string()),
        // Evolution fields (callers should set created_at if needed)
        version: 1,
        is_user_defined: false,
        created_at: None,
        updated_at: None,
        stability,
    })
}

/// Detect frequent sections from FULL GPS tracks.
/// This is the main entry point for section detection.
pub fn detect_sections_from_tracks(
    tracks: &[(String, Vec<GpsPoint>)], // (activity_id, full_gps_points)
    sport_types: &HashMap<String, String>,
    groups: &[RouteGroup],
    config: &SectionConfig,
) -> Vec<FrequentSection> {
    info!("[Sections] Detecting from {} full GPS tracks", tracks.len());

    if tracks.len() < config.min_activities as usize {
        return vec![];
    }

    // Filter to only groups with 2+ activities (these are the ones shown in Routes list)
    let significant_groups: Vec<&RouteGroup> = groups
        .iter()
        .filter(|g| g.activity_ids.len() >= 2)
        .collect();

    // Build activity_id -> route_id mapping (only for significant groups)
    let activity_to_route: HashMap<&str, &str> = significant_groups
        .iter()
        .flat_map(|g| {
            g.activity_ids
                .iter()
                .map(|aid| (aid.as_str(), g.group_id.as_str()))
        })
        .collect();

    // Debug: log the groups we received
    info!(
        "[Sections] Received {} groups, {} with 2+ activities, {} total activity mappings",
        groups.len(),
        significant_groups.len(),
        activity_to_route.len()
    );

    // Build track lookup
    let track_map: HashMap<String, Vec<GpsPoint>> = tracks
        .iter()
        .map(|(id, pts)| (id.clone(), pts.clone()))
        .collect();

    // Group tracks by sport type
    let mut tracks_by_sport: HashMap<String, Vec<(&str, &[GpsPoint])>> = HashMap::new();
    for (activity_id, points) in tracks {
        let sport = sport_types
            .get(activity_id)
            .cloned()
            .unwrap_or_else(|| "Unknown".to_string());
        tracks_by_sport
            .entry(sport)
            .or_default()
            .push((activity_id.as_str(), points.as_slice()));
    }

    let mut all_sections: Vec<FrequentSection> = Vec::new();
    let mut section_counter = 0;

    // Process each sport type
    for (sport_type, sport_tracks) in &tracks_by_sport {
        if sport_tracks.len() < config.min_activities as usize {
            continue;
        }

        info!(
            "[Sections] Processing {} {} tracks",
            sport_tracks.len(),
            sport_type
        );

        let rtree_start = std::time::Instant::now();
        #[cfg(feature = "parallel")]
        let rtrees: Vec<rstar::RTree<IndexedPoint>> = sport_tracks
            .par_iter()
            .map(|(_, pts)| build_rtree(pts))
            .collect();

        #[cfg(not(feature = "parallel"))]
        let rtrees: Vec<rstar::RTree<IndexedPoint>> = sport_tracks
            .iter()
            .map(|(_, pts)| build_rtree(pts))
            .collect();

        info!(
            "[Sections] Built {} R-trees in {}ms",
            rtrees.len(),
            rtree_start.elapsed().as_millis()
        );

        // Find pairwise overlaps - PARALLELIZED with rayon
        let overlap_start = std::time::Instant::now();

        // Generate all pairs
        let pairs: Vec<(usize, usize)> = (0..sport_tracks.len())
            .flat_map(|i| ((i + 1)..sport_tracks.len()).map(move |j| (i, j)))
            .collect();

        let total_pairs = pairs.len();

        // Process pairs (parallel if feature enabled)
        #[cfg(feature = "parallel")]
        let overlaps: Vec<FullTrackOverlap> = pairs
            .into_par_iter()
            .filter_map(|(i, j)| {
                let (id_a, track_a) = sport_tracks[i];
                let (id_b, track_b) = sport_tracks[j];

                // Quick bounding box check
                if !bounds_overlap_tracks(track_a, track_b, config.proximity_threshold) {
                    return None;
                }

                // Find overlap using R-tree
                find_full_track_overlap(id_a, track_a, id_b, track_b, &rtrees[j], config)
            })
            .collect();

        #[cfg(not(feature = "parallel"))]
        let overlaps: Vec<FullTrackOverlap> = pairs
            .into_iter()
            .filter_map(|(i, j)| {
                let (id_a, track_a) = sport_tracks[i];
                let (id_b, track_b) = sport_tracks[j];

                // Quick bounding box check
                if !bounds_overlap_tracks(track_a, track_b, config.proximity_threshold) {
                    return None;
                }

                // Find overlap using R-tree
                find_full_track_overlap(id_a, track_a, id_b, track_b, &rtrees[j], config)
            })
            .collect();

        info!(
            "[Sections] Found {} pairwise overlaps for {} ({} pairs) in {}ms",
            overlaps.len(),
            sport_type,
            total_pairs,
            overlap_start.elapsed().as_millis()
        );

        // Cluster overlaps
        let cluster_start = std::time::Instant::now();
        let clusters = cluster_overlaps(overlaps, config);

        // Filter to clusters with enough activities
        let significant_clusters: Vec<_> = clusters
            .into_iter()
            .filter(|c| c.activity_ids.len() >= config.min_activities as usize)
            .collect();

        info!(
            "[Sections] {} significant clusters ({}+ activities) for {} in {}ms",
            significant_clusters.len(),
            config.min_activities,
            sport_type,
            cluster_start.elapsed().as_millis()
        );

        // Convert clusters to sections - PARALLELIZED with rayon
        let section_convert_start = std::time::Instant::now();

        // Prepare data for parallel processing
        let cluster_data: Vec<_> = significant_clusters.into_iter().enumerate().collect();

        // Process clusters (parallel if feature enabled)
        #[cfg(feature = "parallel")]
        let sport_sections: Vec<FrequentSection> = cluster_data
            .into_par_iter()
            .filter_map(|(idx, cluster)| {
                process_cluster(
                    idx,
                    cluster,
                    sport_type,
                    &track_map,
                    &activity_to_route,
                    config,
                    None,
                )
            })
            .collect();

        #[cfg(not(feature = "parallel"))]
        let sport_sections: Vec<FrequentSection> = cluster_data
            .into_iter()
            .filter_map(|(idx, cluster)| {
                process_cluster(
                    idx,
                    cluster,
                    sport_type,
                    &track_map,
                    &activity_to_route,
                    config,
                    None,
                )
            })
            .collect();

        info!(
            "[Sections] Converted {} sections for {} in {}ms",
            sport_sections.len(),
            sport_type,
            section_convert_start.elapsed().as_millis()
        );

        // Post-process step 1: Split sections that fold back on themselves (out-and-back)
        let fold_start = std::time::Instant::now();
        let fold_sections = split_folding_sections(sport_sections, config);
        info!(
            "[Sections] After fold splitting: {} sections in {}ms",
            fold_sections.len(),
            fold_start.elapsed().as_millis()
        );

        // Post-process step 1b: Split sections at heading inflection points
        let heading_start = std::time::Instant::now();
        let heading_sections = split_at_heading_changes(fold_sections, config);
        info!(
            "[Sections] After heading splitting: {} sections in {}ms",
            heading_sections.len(),
            heading_start.elapsed().as_millis()
        );

        // Post-process step 1c: Split sections at gradient changes (if elevation available)
        let gradient_start = std::time::Instant::now();
        let gradient_sections = split_at_gradient_changes(heading_sections, config);
        info!(
            "[Sections] After gradient splitting: {} sections in {}ms",
            gradient_sections.len(),
            gradient_start.elapsed().as_millis()
        );

        // Post-process step 2: Merge sections that are nearby (reversed, parallel, GPS drift)
        let merge_start = std::time::Instant::now();
        let merged_sections = merge_nearby_sections(gradient_sections, config);
        info!(
            "[Sections] After nearby merge: {} sections in {}ms",
            merged_sections.len(),
            merge_start.elapsed().as_millis()
        );

        // Post-process step 3: Remove sections that contain or are contained by others
        let dedup_start = std::time::Instant::now();
        let deduped_sections = remove_overlapping_sections(merged_sections, config);
        info!(
            "[Sections] After dedup: {} unique sections in {}ms",
            deduped_sections.len(),
            dedup_start.elapsed().as_millis()
        );

        // Post-process step 4: Split sections with high-traffic portions
        // This creates new sections from portions that are used by many activities
        let split_start = std::time::Instant::now();
        let final_sections = split_high_variance_sections(deduped_sections, &track_map, config);
        info!(
            "[Sections] After density splitting: {} sections in {}ms",
            final_sections.len(),
            split_start.elapsed().as_millis()
        );

        // Re-number sections
        for (i, mut section) in final_sections.into_iter().enumerate() {
            section.id = format!("sec_{}_{}", sport_type.to_lowercase(), section_counter + i);
            all_sections.push(section);
        }
        section_counter += all_sections.len();
    }

    // Sort by visit count (most visited first)
    all_sections.sort_by(|a, b| b.visit_count.cmp(&a.visit_count));

    info!("[Sections] Detected {} total sections", all_sections.len());

    all_sections
}

/// Result from processing a single scale preset
struct ScaleResult {
    sections: Vec<FrequentSection>,
    potentials: Vec<PotentialSection>,
    overlaps_found: u32,
    scale_name: String,
}

/// Process a single scale preset (extracted for parallel execution)
fn process_scale_preset(
    preset: &ScalePreset,
    tracks_by_sport: &HashMap<String, Vec<(&str, &[GpsPoint])>>,
    track_map: &HashMap<String, Vec<GpsPoint>>,
    activity_to_route: &HashMap<&str, &str>,
    config: &SectionConfig,
) -> ScaleResult {
    info!(
        "[MultiScale] Processing {} scale: {}-{}m, min {} activities",
        preset.name, preset.min_length, preset.max_length, preset.min_activities
    );

    let scale_config = SectionConfig {
        min_section_length: preset.min_length,
        max_section_length: preset.max_length,
        min_activities: preset.min_activities,
        ..config.clone()
    };

    let mut scale_sections: Vec<FrequentSection> = Vec::new();
    let mut scale_potentials: Vec<PotentialSection> = Vec::new();
    let mut overlaps_found = 0u32;

    // Process each sport type
    for (sport_type, sport_tracks) in tracks_by_sport {
        // For potentials, we only need 1 activity; for sections, use preset.min_activities
        let min_tracks_for_processing = if config.include_potentials {
            1
        } else {
            preset.min_activities as usize
        };
        if sport_tracks.len() < min_tracks_for_processing {
            continue;
        }

        #[cfg(feature = "parallel")]
        let rtrees: Vec<rstar::RTree<IndexedPoint>> = sport_tracks
            .par_iter()
            .map(|(_, pts)| build_rtree(pts))
            .collect();

        #[cfg(not(feature = "parallel"))]
        let rtrees: Vec<rstar::RTree<IndexedPoint>> = sport_tracks
            .iter()
            .map(|(_, pts)| build_rtree(pts))
            .collect();

        // Generate pairs and find overlaps
        let pairs: Vec<(usize, usize)> = (0..sport_tracks.len())
            .flat_map(|i| ((i + 1)..sport_tracks.len()).map(move |j| (i, j)))
            .collect();

        #[cfg(feature = "parallel")]
        let overlaps: Vec<FullTrackOverlap> = pairs
            .into_par_iter()
            .filter_map(|(i, j)| {
                let (id_a, track_a) = sport_tracks[i];
                let (id_b, track_b) = sport_tracks[j];
                if !bounds_overlap_tracks(track_a, track_b, scale_config.proximity_threshold) {
                    return None;
                }
                find_full_track_overlap(id_a, track_a, id_b, track_b, &rtrees[j], &scale_config)
            })
            .collect();

        #[cfg(not(feature = "parallel"))]
        let overlaps: Vec<FullTrackOverlap> = pairs
            .into_iter()
            .filter_map(|(i, j)| {
                let (id_a, track_a) = sport_tracks[i];
                let (id_b, track_b) = sport_tracks[j];
                if !bounds_overlap_tracks(track_a, track_b, scale_config.proximity_threshold) {
                    return None;
                }
                find_full_track_overlap(id_a, track_a, id_b, track_b, &rtrees[j], &scale_config)
            })
            .collect();

        overlaps_found += overlaps.len() as u32;

        // Cluster overlaps
        let clusters = cluster_overlaps(overlaps, &scale_config);

        // Separate into confirmed sections and potential sections
        let (significant, potential): (Vec<_>, Vec<_>) = clusters
            .into_iter()
            .partition(|c| c.activity_ids.len() >= preset.min_activities as usize);

        // Process confirmed sections
        #[cfg(feature = "parallel")]
        let sport_sections: Vec<FrequentSection> = significant
            .into_par_iter()
            .enumerate()
            .filter_map(|(idx, cluster)| {
                process_cluster(
                    idx,
                    cluster,
                    sport_type,
                    track_map,
                    activity_to_route,
                    &scale_config,
                    Some(&preset.name),
                )
            })
            .collect();

        #[cfg(not(feature = "parallel"))]
        let sport_sections: Vec<FrequentSection> = significant
            .into_iter()
            .enumerate()
            .filter_map(|(idx, cluster)| {
                process_cluster(
                    idx,
                    cluster,
                    sport_type,
                    track_map,
                    activity_to_route,
                    &scale_config,
                    Some(&preset.name),
                )
            })
            .collect();

        scale_sections.extend(sport_sections);

        // Process potential sections if enabled
        if config.include_potentials {
            for (idx, cluster) in potential.into_iter().enumerate() {
                // Only include clusters with 1-2 activities
                let activity_count = cluster.activity_ids.len();
                if activity_count >= 1
                    && activity_count < preset.min_activities as usize
                    && let Some((_rep_id, rep_polyline)) = Some(select_medoid(&cluster))
                    && !rep_polyline.is_empty()
                {
                    let distance = calculate_route_distance(&rep_polyline);
                    if distance >= preset.min_length && distance <= preset.max_length {
                        scale_potentials.push(PotentialSection {
                            id: format!(
                                "pot_{}_{}_{}",
                                preset.name,
                                sport_type.to_lowercase(),
                                idx
                            ),
                            sport_type: sport_type.to_string(),
                            polyline: rep_polyline,
                            activity_ids: cluster.activity_ids.into_iter().collect(),
                            visit_count: activity_count as u32,
                            distance_meters: distance,
                            confidence: 0.3 + (activity_count as f64 * 0.2), // 0.5 for 1, 0.7 for 2
                            scale: preset.name.clone(),
                        });
                    }
                }
            }
        }
    }

    info!(
        "[MultiScale] {} scale: {} sections, {} potentials",
        preset.name,
        scale_sections.len(),
        scale_potentials.len()
    );

    ScaleResult {
        sections: scale_sections,
        potentials: scale_potentials,
        overlaps_found,
        scale_name: preset.name.clone(),
    }
}

pub fn detect_sections_multiscale(
    tracks: &[(String, Vec<GpsPoint>)],
    sport_types: &HashMap<String, String>,
    groups: &[RouteGroup],
    config: &SectionConfig,
) -> MultiScaleSectionResult {
    info!(
        "[MultiScale] Detecting from {} tracks with {} scale presets",
        tracks.len(),
        config.scale_presets.len()
    );

    let mut stats = DetectionStats {
        activities_processed: tracks.len() as u32,
        overlaps_found: 0,
        sections_by_scale: HashMap::new(),
        potentials_by_scale: HashMap::new(),
    };

    // If no scale presets, fall back to legacy single-scale detection
    if config.scale_presets.is_empty() {
        let sections = detect_sections_from_tracks(tracks, sport_types, groups, config);
        stats
            .sections_by_scale
            .insert("legacy".to_string(), sections.len() as u32);
        return MultiScaleSectionResult {
            sections,
            potentials: vec![],
            stats,
        };
    }

    // Build shared data structures once
    let track_map: HashMap<String, Vec<GpsPoint>> = tracks
        .iter()
        .map(|(id, pts)| (id.clone(), pts.clone()))
        .collect();

    let significant_groups: Vec<&RouteGroup> = groups
        .iter()
        .filter(|g| g.activity_ids.len() >= 2)
        .collect();

    let activity_to_route: HashMap<&str, &str> = significant_groups
        .iter()
        .flat_map(|g| {
            g.activity_ids
                .iter()
                .map(|aid| (aid.as_str(), g.group_id.as_str()))
        })
        .collect();

    // Group tracks by sport type
    let mut tracks_by_sport: HashMap<String, Vec<(&str, &[GpsPoint])>> = HashMap::new();
    for (activity_id, points) in tracks {
        let sport = sport_types
            .get(activity_id)
            .cloned()
            .unwrap_or_else(|| "Unknown".to_string());
        tracks_by_sport
            .entry(sport)
            .or_default()
            .push((activity_id.as_str(), points.as_slice()));
    }

    // Process all scale presets IN PARALLEL
    #[cfg(feature = "parallel")]
    let scale_results: Vec<ScaleResult> = config
        .scale_presets
        .par_iter()
        .map(|preset| {
            process_scale_preset(
                preset,
                &tracks_by_sport,
                &track_map,
                &activity_to_route,
                config,
            )
        })
        .collect();

    #[cfg(not(feature = "parallel"))]
    let scale_results: Vec<ScaleResult> = config
        .scale_presets
        .iter()
        .map(|preset| {
            process_scale_preset(
                preset,
                &tracks_by_sport,
                &track_map,
                &activity_to_route,
                config,
            )
        })
        .collect();

    // Merge results from all scales
    let mut all_sections: Vec<FrequentSection> = Vec::new();
    let mut all_potentials: Vec<PotentialSection> = Vec::new();

    for result in scale_results {
        stats.overlaps_found += result.overlaps_found;
        stats
            .sections_by_scale
            .insert(result.scale_name.clone(), result.sections.len() as u32);
        stats
            .potentials_by_scale
            .insert(result.scale_name, result.potentials.len() as u32);
        all_sections.extend(result.sections);
        all_potentials.extend(result.potentials);
    }

    // Apply post-processing
    let fold_start = std::time::Instant::now();
    let fold_sections = split_folding_sections(all_sections, config);
    info!(
        "[MultiScale] After fold splitting: {} sections in {}ms",
        fold_sections.len(),
        fold_start.elapsed().as_millis()
    );

    // Split at heading inflection points
    let heading_start = std::time::Instant::now();
    let heading_sections = split_at_heading_changes(fold_sections, config);
    info!(
        "[MultiScale] After heading splitting: {} sections in {}ms",
        heading_sections.len(),
        heading_start.elapsed().as_millis()
    );

    // Split at gradient changes (if elevation available)
    let gradient_start = std::time::Instant::now();
    let gradient_sections = split_at_gradient_changes(heading_sections, config);
    info!(
        "[MultiScale] After gradient splitting: {} sections in {}ms",
        gradient_sections.len(),
        gradient_start.elapsed().as_millis()
    );

    let merge_start = std::time::Instant::now();
    let merged_sections = merge_nearby_sections(gradient_sections, config);
    info!(
        "[MultiScale] After nearby merge: {} sections in {}ms",
        merged_sections.len(),
        merge_start.elapsed().as_millis()
    );

    // Use hierarchical deduplication if preserve_hierarchy is true
    let dedup_start = std::time::Instant::now();
    let deduped_sections = if config.preserve_hierarchy {
        remove_overlapping_sections_hierarchical(merged_sections, config)
    } else {
        remove_overlapping_sections(merged_sections, config)
    };
    info!(
        "[MultiScale] After dedup: {} sections in {}ms",
        deduped_sections.len(),
        dedup_start.elapsed().as_millis()
    );

    let split_start = std::time::Instant::now();
    let final_sections = split_high_variance_sections(deduped_sections, &track_map, config);
    info!(
        "[MultiScale] After density splitting: {} sections in {}ms",
        final_sections.len(),
        split_start.elapsed().as_millis()
    );

    // Sort sections by visit count
    let mut sorted_sections = final_sections;
    sorted_sections.sort_by(|a, b| b.visit_count.cmp(&a.visit_count));

    // Sort potentials by confidence
    let mut sorted_potentials = all_potentials;
    sorted_potentials.sort_by(|a, b| {
        b.confidence
            .partial_cmp(&a.confidence)
            .unwrap_or(std::cmp::Ordering::Equal)
    });

    info!(
        "[MultiScale] Final: {} sections, {} potentials",
        sorted_sections.len(),
        sorted_potentials.len()
    );

    MultiScaleSectionResult {
        sections: sorted_sections,
        potentials: sorted_potentials,
        stats,
    }
}

/// Detect sections at multiple scales with progress reporting.
/// This version accepts a progress tracker for reporting status to the UI.
#[cfg(feature = "persistence")]
pub fn detect_sections_multiscale_with_progress(
    tracks: &[(String, Vec<GpsPoint>)],
    sport_types: &HashMap<String, String>,
    groups: &[RouteGroup],
    config: &SectionConfig,
    progress: &SectionDetectionProgress,
) -> MultiScaleSectionResult {
    info!(
        "[MultiScale] Detecting from {} tracks with {} scale presets (with progress)",
        tracks.len(),
        config.scale_presets.len()
    );

    let mut all_sections: Vec<FrequentSection> = Vec::new();
    let mut all_potentials: Vec<PotentialSection> = Vec::new();
    let mut stats = DetectionStats {
        activities_processed: tracks.len() as u32,
        overlaps_found: 0,
        sections_by_scale: HashMap::new(),
        potentials_by_scale: HashMap::new(),
    };

    // If no scale presets, fall back to legacy single-scale detection
    if config.scale_presets.is_empty() {
        progress.set_phase("finding_overlaps", tracks.len() as u32);
        let sections = detect_sections_from_tracks(tracks, sport_types, groups, config);
        stats
            .sections_by_scale
            .insert("legacy".to_string(), sections.len() as u32);
        progress.set_phase("complete", 0);
        return MultiScaleSectionResult {
            sections,
            potentials: vec![],
            stats,
        };
    }

    // Group tracks by sport type
    let mut tracks_by_sport: HashMap<String, Vec<(&str, &[GpsPoint])>> = HashMap::new();
    for (activity_id, points) in tracks {
        let sport = sport_types
            .get(activity_id)
            .cloned()
            .unwrap_or_else(|| "Unknown".to_string());
        tracks_by_sport
            .entry(sport)
            .or_default()
            .push((activity_id.as_str(), points.as_slice()));
    }

    // Build track lookup and activity_to_route mapping
    let track_map: HashMap<String, Vec<GpsPoint>> = tracks
        .iter()
        .map(|(id, pts)| (id.clone(), pts.clone()))
        .collect();

    let significant_groups: Vec<&RouteGroup> = groups
        .iter()
        .filter(|g| g.activity_ids.len() >= 2)
        .collect();

    let activity_to_route: HashMap<&str, &str> = significant_groups
        .iter()
        .flat_map(|g| {
            g.activity_ids
                .iter()
                .map(|aid| (aid.as_str(), g.group_id.as_str()))
        })
        .collect();

    let total_presets = config.scale_presets.len();
    let mut section_counter = 0;

    // Process each scale preset with progress updates
    for (preset_idx, preset) in config.scale_presets.iter().enumerate() {
        progress.set_phase(&format!("scale_{}", preset.name), total_presets as u32);
        progress
            .completed
            .store(preset_idx as u32, std::sync::atomic::Ordering::Relaxed);

        info!(
            "[MultiScale] Processing {} scale ({}-{}m)",
            preset.name, preset.min_length, preset.max_length
        );

        // Create scale-specific config
        let mut scale_config = config.clone();
        scale_config.min_section_length = preset.min_length;
        scale_config.max_section_length = preset.max_length;
        scale_config.min_activities = preset.min_activities;

        let mut scale_sections = 0u32;
        let mut scale_potentials = 0u32;

        // Process each sport type
        for (sport_type, sport_tracks) in &tracks_by_sport {
            let min_tracks_for_processing = if config.include_potentials {
                1
            } else {
                preset.min_activities as usize
            };
            if sport_tracks.len() < min_tracks_for_processing {
                continue;
            }

            // Update progress for R-tree building
            progress.set_phase("building_rtrees", sport_tracks.len() as u32);

            #[cfg(feature = "parallel")]
            let rtrees: Vec<rstar::RTree<IndexedPoint>> = sport_tracks
                .par_iter()
                .map(|(_, pts)| build_rtree(pts))
                .collect();

            #[cfg(not(feature = "parallel"))]
            let rtrees: Vec<rstar::RTree<IndexedPoint>> = sport_tracks
                .iter()
                .enumerate()
                .map(|(i, (_, pts))| {
                    progress
                        .completed
                        .store(i as u32, std::sync::atomic::Ordering::Relaxed);
                    build_rtree(pts)
                })
                .collect();

            // Generate pairs and find overlaps
            let pairs: Vec<(usize, usize)> = (0..sport_tracks.len())
                .flat_map(|i| ((i + 1)..sport_tracks.len()).map(move |j| (i, j)))
                .collect();

            let total_pairs = pairs.len() as u32;
            progress.set_phase("finding_overlaps", total_pairs);

            #[cfg(feature = "parallel")]
            let overlaps: Vec<FullTrackOverlap> = {
                use std::sync::atomic::AtomicU32;
                let counter = AtomicU32::new(0);

                pairs
                    .into_par_iter()
                    .filter_map(|(i, j)| {
                        let count = counter.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
                        if count.is_multiple_of(100) {
                            progress
                                .completed
                                .store(count, std::sync::atomic::Ordering::Relaxed);
                        }

                        let (id_a, track_a) = sport_tracks[i];
                        let (id_b, track_b) = sport_tracks[j];
                        if !bounds_overlap_tracks(
                            track_a,
                            track_b,
                            scale_config.proximity_threshold,
                        ) {
                            return None;
                        }
                        find_full_track_overlap(
                            id_a,
                            track_a,
                            id_b,
                            track_b,
                            &rtrees[j],
                            &scale_config,
                        )
                    })
                    .collect()
            };

            #[cfg(not(feature = "parallel"))]
            let overlaps: Vec<FullTrackOverlap> = pairs
                .into_iter()
                .enumerate()
                .filter_map(|(idx, (i, j))| {
                    if idx % 50 == 0 {
                        progress
                            .completed
                            .store(idx as u32, std::sync::atomic::Ordering::Relaxed);
                    }

                    let (id_a, track_a) = sport_tracks[i];
                    let (id_b, track_b) = sport_tracks[j];
                    if !bounds_overlap_tracks(track_a, track_b, scale_config.proximity_threshold) {
                        return None;
                    }
                    find_full_track_overlap(id_a, track_a, id_b, track_b, &rtrees[j], &scale_config)
                })
                .collect();

            stats.overlaps_found += overlaps.len() as u32;

            // Cluster overlaps
            progress.set_phase("clustering", overlaps.len() as u32);
            let clusters = cluster_overlaps(overlaps, &scale_config);

            // Separate into confirmed sections and potential sections
            let (significant, potential): (Vec<_>, Vec<_>) = clusters
                .into_iter()
                .partition(|c| c.activity_ids.len() >= preset.min_activities as usize);

            // Process confirmed sections
            let cluster_count = significant.len() as u32;
            progress.set_phase("building_sections", cluster_count);

            #[cfg(feature = "parallel")]
            let sport_sections_vec: Vec<FrequentSection> = {
                use std::sync::atomic::AtomicU32;
                let counter = AtomicU32::new(0);

                significant
                    .into_par_iter()
                    .enumerate()
                    .filter_map(|(idx, cluster)| {
                        let count = counter.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
                        progress
                            .completed
                            .store(count, std::sync::atomic::Ordering::Relaxed);

                        process_cluster(
                            idx,
                            cluster,
                            sport_type,
                            &track_map,
                            &activity_to_route,
                            &scale_config,
                            Some(&preset.name),
                        )
                    })
                    .collect()
            };

            #[cfg(not(feature = "parallel"))]
            let sport_sections_vec: Vec<FrequentSection> = significant
                .into_iter()
                .enumerate()
                .filter_map(|(idx, cluster)| {
                    progress
                        .completed
                        .store(idx as u32, std::sync::atomic::Ordering::Relaxed);
                    process_cluster(
                        idx,
                        cluster,
                        sport_type,
                        &track_map,
                        &activity_to_route,
                        &scale_config,
                        Some(&preset.name),
                    )
                })
                .collect();

            scale_sections += sport_sections_vec.len() as u32;

            // Re-number sections
            for (i, mut section) in sport_sections_vec.into_iter().enumerate() {
                section.id = format!(
                    "sec_{}_{}_{}_{}",
                    sport_type.to_lowercase(),
                    preset.name,
                    section_counter,
                    i
                );
                all_sections.push(section);
            }
            section_counter += 1;

            // Process potential sections if enabled
            if config.include_potentials {
                for (idx, cluster) in potential.into_iter().enumerate() {
                    // Only include clusters with 1-2 activities
                    let activity_count = cluster.activity_ids.len();
                    if activity_count >= 1
                        && activity_count < preset.min_activities as usize
                        && let Some((_rep_id, rep_polyline)) = Some(select_medoid(&cluster))
                        && !rep_polyline.is_empty()
                    {
                        let distance = calculate_route_distance(&rep_polyline);
                        if distance >= preset.min_length && distance <= preset.max_length {
                            all_potentials.push(PotentialSection {
                                id: format!(
                                    "pot_{}_{}_{}",
                                    preset.name,
                                    sport_type.to_lowercase(),
                                    idx
                                ),
                                sport_type: sport_type.to_string(),
                                polyline: rep_polyline,
                                activity_ids: cluster.activity_ids.into_iter().collect(),
                                visit_count: activity_count as u32,
                                distance_meters: distance,
                                confidence: 0.3 + (activity_count as f64 * 0.2),
                                scale: preset.name.clone(),
                            });
                            scale_potentials += 1;
                        }
                    }
                }
            }
        }

        stats
            .sections_by_scale
            .insert(preset.name.clone(), scale_sections);
        stats
            .potentials_by_scale
            .insert(preset.name.clone(), scale_potentials);
    }

    // Post-processing
    progress.set_phase("postprocessing", 4);

    let fold_start = std::time::Instant::now();
    let split_sections = split_folding_sections(all_sections, config);
    progress.increment();
    info!(
        "[MultiScale] After fold splitting: {} sections in {}ms",
        split_sections.len(),
        fold_start.elapsed().as_millis()
    );

    let merge_start = std::time::Instant::now();
    let merged_sections = merge_nearby_sections(split_sections, config);
    progress.increment();
    info!(
        "[MultiScale] After nearby merge: {} sections in {}ms",
        merged_sections.len(),
        merge_start.elapsed().as_millis()
    );

    let dedup_start = std::time::Instant::now();
    let deduped_sections = remove_overlapping_sections_hierarchical(merged_sections, config);
    progress.increment();
    info!(
        "[MultiScale] After hierarchical dedup: {} sections in {}ms",
        deduped_sections.len(),
        dedup_start.elapsed().as_millis()
    );

    let split_start = std::time::Instant::now();
    let final_sections = split_high_variance_sections(deduped_sections, &track_map, config);
    progress.increment();
    info!(
        "[MultiScale] After density splitting: {} sections in {}ms",
        final_sections.len(),
        split_start.elapsed().as_millis()
    );

    // Sort sections by visit count
    let mut sorted_sections = final_sections;
    sorted_sections.sort_by(|a, b| b.visit_count.cmp(&a.visit_count));

    // Sort potentials by confidence
    let mut sorted_potentials = all_potentials;
    sorted_potentials.sort_by(|a, b| {
        b.confidence
            .partial_cmp(&a.confidence)
            .unwrap_or(std::cmp::Ordering::Equal)
    });

    info!(
        "[MultiScale] Final: {} sections, {} potentials",
        sorted_sections.len(),
        sorted_potentials.len()
    );

    progress.set_phase("complete", 0);

    MultiScaleSectionResult {
        sections: sorted_sections,
        potentials: sorted_potentials,
        stats,
    }
}

/// Deduplication that preserves hierarchical sections.
/// Short sections inside longer ones are kept if they're at different scales.
fn remove_overlapping_sections_hierarchical(
    mut sections: Vec<FrequentSection>,
    config: &SectionConfig,
) -> Vec<FrequentSection> {
    if sections.len() <= 1 {
        return sections;
    }

    // Sort by length descending
    sections.sort_by(|a, b| {
        b.distance_meters
            .partial_cmp(&a.distance_meters)
            .unwrap_or(std::cmp::Ordering::Equal)
    });

    // PRE-COMPUTE all R-trees once upfront (O(k) builds instead of O(k²))
    #[cfg(feature = "parallel")]
    let rtrees: Vec<rstar::RTree<IndexedPoint>> = {
        use rayon::prelude::*;
        sections
            .par_iter()
            .map(|s| build_rtree(&s.polyline))
            .collect()
    };

    #[cfg(not(feature = "parallel"))]
    let rtrees: Vec<rstar::RTree<IndexedPoint>> =
        sections.iter().map(|s| build_rtree(&s.polyline)).collect();

    let mut keep = vec![true; sections.len()];

    for i in 0..sections.len() {
        if !keep[i] {
            continue;
        }

        let tree_i = &rtrees[i]; // Use pre-computed R-tree (O(1) lookup)

        for j in (i + 1)..sections.len() {
            if !keep[j] {
                continue;
            }

            // Check if shorter section (j) is contained in longer section (i)
            let containment = compute_polyline_containment_with_rtree(
                &sections[j].polyline,
                tree_i,
                config.proximity_threshold,
            );

            // Length ratio
            let length_ratio = sections[j].distance_meters / sections[i].distance_meters;

            // Only remove if:
            // 1. >90% contained
            // 2. Same length class (ratio > 0.7) - meaning it's a true duplicate, not hierarchical
            // 3. Same scale OR no scale info
            let same_scale = match (&sections[i].scale, &sections[j].scale) {
                (Some(a), Some(b)) => a == b,
                _ => true, // If either has no scale, treat as same
            };

            if containment > 0.9 && length_ratio > 0.7 && same_scale {
                keep[j] = false;
            }
        }
    }

    sections
        .into_iter()
        .zip(keep)
        .filter_map(|(s, k)| if k { Some(s) } else { None })
        .collect()
}

/// Compute what fraction of polyline A is contained within proximity of polyline B (using R-tree).
/// O(a * log b) instead of O(a * b).
fn compute_polyline_containment_with_rtree(
    polyline_a: &[GpsPoint],
    tree_b: &rstar::RTree<IndexedPoint>,
    proximity_threshold: f64,
) -> f64 {
    use rstar::PointDistance;

    if polyline_a.is_empty() {
        return 0.0;
    }

    let threshold_deg = proximity_threshold / 111_000.0;
    let threshold_deg_sq = threshold_deg * threshold_deg;

    let mut contained_count = 0;
    for point_a in polyline_a {
        let query = [point_a.latitude, point_a.longitude];
        if let Some(nearest) = tree_b.nearest_neighbor(&query)
            && nearest.distance_2(&query) <= threshold_deg_sq
        {
            contained_count += 1;
        }
    }

    contained_count as f64 / polyline_a.len() as f64
}

/// Compute what fraction of polyline A is contained within proximity of polyline B
/// (Brute-force version - kept for backward compatibility)
#[allow(dead_code)]
fn compute_polyline_containment(
    polyline_a: &[GpsPoint],
    polyline_b: &[GpsPoint],
    proximity_threshold: f64,
) -> f64 {
    use crate::geo_utils::haversine_distance;

    if polyline_a.is_empty() || polyline_b.is_empty() {
        return 0.0;
    }

    let mut contained_count = 0;
    for point_a in polyline_a {
        let min_dist = polyline_b
            .iter()
            .map(|point_b| haversine_distance(point_a, point_b))
            .fold(f64::MAX, |a, b| a.min(b));

        if min_dist <= proximity_threshold {
            contained_count += 1;
        }
    }

    contained_count as f64 / polyline_a.len() as f64
}