From a0e2915c3df09e3f5740d98870494a9bb7241ed7 Mon Sep 17 00:00:00 2001
From: Valentin Haudiquet <valentin.haudiquet@canonical.com>
Date: Thu, 30 Apr 2026 20:16:00 +0200
Subject: [PATCH] fix/match_collector: fix splitting of boots and first backs

---
 match_collector/src/champion_stat.ts | 55 ++++++++++++++++++++++++----
 match_collector/src/types.ts         |  1 +
 2 files changed, 48 insertions(+), 8 deletions(-)

diff --git a/match_collector/src/champion_stat.ts b/match_collector/src/champion_stat.ts
index 58bc1c8..4196851 100644
--- a/match_collector/src/champion_stat.ts
+++ b/match_collector/src/champion_stat.ts
@@ -177,7 +177,7 @@ function handleMatchBuilds(
   participantIndex: number,
   builds: Builds,
   platform?: string
-): Build {
+): { build: Build; startItemId: number | undefined } {
   const timeline: Timeline = match.timeline
 
   // Find or create the build for this participant's rune configuration
@@ -185,6 +185,7 @@ function handleMatchBuilds(
   build.count += 1
 
   const items: Array<{ itemId: number; goldAdvantage: GoldAdvantageTag; platform?: string }> = []
+  let startItemId: number | undefined = undefined
   for (const frame of timeline.info.frames) {
     for (const event of frame.events) {
       if (event.participantId != participantIndex) continue
@@ -267,9 +268,11 @@ function handleMatchBuilds(
   // This tree includes start item as the root, then branching paths
   if (items.length > 0) {
     treeMerge(build.items, items)
+    // The first item is the starter item
+    startItemId = items[0].itemId
   }
 
-  return build
+  return { build, startItemId }
 }
 
 function handleMatch(match: Match, champions: Map<number, ChampionData>, platform?: string) {
@@ -365,14 +368,22 @@ function handleMatch(match: Match, champions: Map<number, ChampionData>, platfor
     }
 
     // Items and runes (builds)
-    const build = handleMatchBuilds(match, participant, participantIndex, lane.builds, platform)
+    const { build, startItemId } = handleMatchBuilds(
+      match,
+      participant,
+      participantIndex,
+      lane.builds,
+      platform
+    )
 
-    // First back data - store at build level
+    // First back data - store at build level with start item tracking
     const firstBackData = extractFirstBackFromMatch(match, participantIndex)
     if (firstBackData) {
       if (!build.firstBacksRaw) {
         build.firstBacksRaw = []
       }
+      // Include the starter item ID for proper filtering when splitting builds
+      firstBackData.startItemId = startItemId
       build.firstBacksRaw.push(firstBackData)
     }
   }
@@ -445,16 +456,44 @@ function splitMergeOnStarterItem(build: Build, championName: string): BuildWithS
     console.log(`Warning: for champion ${championName}, start item splits build variant.`)
     const builds = []
     for (const c of build.items.children) {
+      // Calculate the ratio for proportional distribution
+      const ratio = c.count / build.count
+
+      // Proportionally distribute boots counts
+      const scaledBoots = build.boots.map(b => ({
+        data: b.data,
+        count: Math.round(b.count * ratio)
+      }))
+
+      // Proportionally distribute suppItems counts
+      const scaledSuppItems = build.suppItems.map(s => ({
+        data: s.data,
+        count: Math.round(s.count * ratio)
+      }))
+
+      // Proportionally distribute bootsFirstCount
+      const scaledBootsFirstCount = Math.round(build.bootsFirstCount * ratio)
+
+      // Filter firstBacksRaw by starter item
+      let filteredFirstBacksRaw: FirstBackData[] | undefined
+      if (build.firstBacksRaw && build.firstBacksRaw.length > 0) {
+        // Filter by the starter item ID that was tracked when storing firstBacksRaw
+        filteredFirstBacksRaw = build.firstBacksRaw.filter(fb => fb.startItemId === c.data)
+        if (filteredFirstBacksRaw.length === 0) {
+          filteredFirstBacksRaw = undefined
+        }
+      }
+
       builds.push({
         runeKeystone: build.runeKeystone,
         runes: build.runes,
         items: c,
-        bootsFirstCount: build.bootsFirstCount,
+        bootsFirstCount: scaledBootsFirstCount,
         count: c.count,
         startItems: [{ data: c.data!, count: c.count }],
-        suppItems: build.suppItems,
-        boots: build.boots,
-        firstBacksRaw: build.firstBacksRaw
+        suppItems: scaledSuppItems,
+        boots: scaledBoots,
+        firstBacksRaw: filteredFirstBacksRaw
       })
       c.data = undefined
     }
diff --git a/match_collector/src/types.ts b/match_collector/src/types.ts
index 6175a7f..7786996 100644
--- a/match_collector/src/types.ts
+++ b/match_collector/src/types.ts
@@ -82,6 +82,7 @@ export interface ItemSet {
 export interface FirstBackData {
   timestamp: number
   itemSet: ItemSet
+  startItemId?: number
 }
 
 /**