buildpath/match_collector/src/item_tree.ts

import {
  REGION_KEYS,
  initPlatformCounts,
  mergePlatformCounts,
  singlePlatformCount
} from './platform'

import type { PlatformCounts } from './platform'

type GoldAdvantageTag = 'ahead' | 'behind' | 'even'

// Item tags that can be derived from purchase patterns
type ItemTag = 'ahead' | 'behind' | 'region_euw' | 'region_eun' | 'region_na' | 'region_kr'

type ItemTree = {
  data: number | undefined
  count: number
  children: Array<ItemTree>

  // Gold advantage tracking
  boughtWhen: {
    aheadCount: number
    behindCount: number
    evenCount: number
    meanGold: number
  }

  // Platform tracking
  platformCount: PlatformCounts

  // Derived tags for display
  tags: Array<ItemTag>
}

function treeInit(): ItemTree {
  return {
    data: undefined,
    count: 0,
    children: [],
    boughtWhen: { aheadCount: 0, behindCount: 0, evenCount: 0, meanGold: 0 },
    platformCount: initPlatformCounts(),
    tags: []
  }
}

/*
 * Merge a node with an item tree
 */
function nodeMerge(itemtree: ItemTree, node: ItemTree) {
  const item = node.data
  const count = node.count
  let next: ItemTree | null = null

  // Try to find an existing node in this tree level with same item
  for (const child of itemtree.children) {
    if (child.data == item) {
      child.count += 1

      child.boughtWhen.aheadCount += node.boughtWhen.aheadCount
      child.boughtWhen.evenCount += node.boughtWhen.evenCount
      child.boughtWhen.behindCount += node.boughtWhen.behindCount

      // Merge platform counts
      mergePlatformCounts(child.platformCount, node.platformCount)

      next = child
      break
    }
  }

  // If not found, add item node at this level
  if (next == null && item !== undefined) {
    next = {
      data: item,
      count: count,
      children: [],
      boughtWhen: { ...node.boughtWhen },
      platformCount: { ...node.platformCount },
      tags: []
    }
    itemtree.children.push(next)
  }

  return next!
}

/*
 * Merge a full build path with an existing item tree
 */
function treeMerge(
  itemtree: ItemTree,
  items: Array<{ itemId: number; goldAdvantage: GoldAdvantageTag; platform?: string }>
) {
  let current = itemtree

  for (const item of items) {
    current = nodeMerge(current, {
      data: item.itemId,
      count: 1,
      boughtWhen: {
        aheadCount: item.goldAdvantage == 'ahead' ? 1 : 0,
        evenCount: item.goldAdvantage == 'even' ? 1 : 0,
        behindCount: item.goldAdvantage == 'behind' ? 1 : 0,
        meanGold: 0
      },
      children: [],
      platformCount: item.platform ? singlePlatformCount(item.platform) : initPlatformCounts(),
      tags: []
    })
  }
}

function treeCutBranches(itemtree: ItemTree, thresholdCount: number, thresholdPerc: number) {
  // Remove branches that are above threshold count
  while (itemtree.children.length > thresholdCount) {
    const leastUsedBranch = itemtree.children.reduce(
      (a, b) => (Math.min(a.count, b.count) == a.count ? a : b),
      {
        data: undefined,
        count: +Infinity,
        children: [],
        boughtWhen: { aheadCount: 0, behindCount: 0, evenCount: 0, meanGold: 0 },
        platformCount: initPlatformCounts(),
        tags: []
      }
    )
    itemtree.children.splice(itemtree.children.indexOf(leastUsedBranch), 1)
  }

  // Remove branches that are of too low usage
  const toRemove: Array<ItemTree> = []
  for (const child of itemtree.children) {
    if (child.count / itemtree.count < thresholdPerc) {
      toRemove.push(child)
    }
  }
  for (const tr of toRemove) {
    itemtree.children.splice(itemtree.children.indexOf(tr), 1)
  }

  itemtree.children.map(x => treeCutBranches(x, thresholdCount, thresholdPerc))
}

function treeSort(itemtree: ItemTree) {
  itemtree.children.sort((a, b) => b.count - a.count)

  for (const item of itemtree.children) {
    treeSort(item)
  }
}

/*
 * Deep clone an ItemTree
 */
function treeClone(tree: ItemTree): ItemTree {
  return {
    data: tree.data,
    count: tree.count,
    children: tree.children.map(child => treeClone(child)),
    boughtWhen: {
      aheadCount: tree.boughtWhen.aheadCount,
      behindCount: tree.boughtWhen.behindCount,
      evenCount: tree.boughtWhen.evenCount,
      meanGold: tree.boughtWhen.meanGold
    },
    platformCount: { ...tree.platformCount },
    tags: [...tree.tags]
  }
}

/*
 * Merge two ItemTrees into one
 */
function treeMergeTree(t1: ItemTree, t2: ItemTree): ItemTree {
  // Merge counts for the root
  t1.count += t2.count

  // Merge platform counts
  mergePlatformCounts(t1.platformCount, t2.platformCount)

  // Merge boughtWhen
  t1.boughtWhen.aheadCount += t2.boughtWhen.aheadCount
  t1.boughtWhen.evenCount += t2.boughtWhen.evenCount
  t1.boughtWhen.behindCount += t2.boughtWhen.behindCount

  // Merge children from t2 into t1
  for (const child2 of t2.children) {
    // Find matching child in t1 (same data value)
    const matchingChild = t1.children.find(child1 => child1.data === child2.data)

    if (matchingChild) {
      // Recursively merge matching children
      treeMergeTree(matchingChild, child2)
    } else {
      // Add a deep copy of child2 to t1
      t1.children.push(treeClone(child2))
    }
  }

  return t1
}

/*
 * Flatten an ItemTree into a Set of item numbers
 */
function treeToSet(itemtree: ItemTree): Set<number> {
  const items: Set<number> = new Set()

  function traverse(node: ItemTree) {
    if (node.data !== undefined) {
      items.add(node.data)
    }
    for (const child of node.children) {
      traverse(child)
    }
  }

  traverse(itemtree)
  return items
}

/*
 * Calculate similarity between two trees as item sets.
 * Returns a number between 0 and 1, where 1 means identical and 0 means completely different.
 * Uses Jaccard similarity: |A ∩ B| / |A ∪ B|
 * Sets included in one another will have similarity close to 1.
 */
function areTreeSimilars(t1: ItemTree, t2: ItemTree): number {
  const set1 = treeToSet(t1)
  const set2 = treeToSet(t2)

  // Handle empty sets
  if (set1.size === 0 && set2.size === 0) {
    return 1.0
  }

  // Calculate intersection
  const intersection = new Set<number>()
  for (const item of Array.from(set1)) {
    if (set2.has(item)) {
      intersection.add(item)
    }
  }

  // Calculate union
  const union = new Set<number>()
  for (const item of Array.from(set1)) {
    union.add(item)
  }
  for (const item of Array.from(set2)) {
    union.add(item)
  }

  // Jaccard similarity: |intersection| / |union|
  const similarity = intersection.size / Math.min(set1.size, set2.size)

  // Ensure result is between 0 and 1
  return Math.max(0, Math.min(1, similarity))
}

/*
 * Derive tags for an item based on purchase patterns
 * Tags are derived when a specific condition is dominant (>= 60% threshold)
 * For region tags, we compare against expected distribution to find items that are
 * significantly more popular in a region than expected
 */
function deriveTags(node: ItemTree, expectedRegionDistribution?: PlatformCounts): void {
  const tags: Array<ItemTag> = []

  // Derive gold situation tags
  const totalGoldSituations =
    node.boughtWhen.aheadCount + node.boughtWhen.behindCount + node.boughtWhen.evenCount
  if (totalGoldSituations > 0) {
    const aheadPct = node.boughtWhen.aheadCount / totalGoldSituations
    const behindPct = node.boughtWhen.behindCount / totalGoldSituations

    // Only tag if there's a dominant pattern (>= 60%)
    if (aheadPct >= 0.6) {
      tags.push('ahead')
    } else if (behindPct >= 0.6) {
      tags.push('behind')
    }
  }

  // Derive region tags by comparing against expected distribution
  const totalRegionCount = REGION_KEYS.reduce((sum, key) => sum + node.platformCount[key], 0)
  if (totalRegionCount > 0 && expectedRegionDistribution) {
    const totalExpected = REGION_KEYS.reduce((sum, key) => sum + expectedRegionDistribution[key], 0)

    if (totalExpected > 0) {
      // Tag if the item is significantly more popular in a region (>= 1.5x expected rate)
      // and has a minimum absolute percentage (>= 10%)
      const SIGNIFICANCE_THRESHOLD = 1.5
      const MINIMUM_PCT = 0.1

      // Loop through all regions to derive tags
      const regionTags: Array<{ key: keyof PlatformCounts; tag: ItemTag }> = [
        { key: 'euw', tag: 'region_euw' },
        { key: 'eun', tag: 'region_eun' },
        { key: 'na', tag: 'region_na' },
        { key: 'kr', tag: 'region_kr' }
      ]

      for (const { key, tag } of regionTags) {
        const expectedPct = expectedRegionDistribution[key] / totalExpected
        const actualPct = node.platformCount[key] / totalRegionCount

        if (actualPct >= expectedPct * SIGNIFICANCE_THRESHOLD && actualPct >= MINIMUM_PCT) {
          tags.push(tag)
        }
      }
    }
  }

  node.tags = tags

  // Recursively derive tags for children
  for (const child of node.children) {
    deriveTags(child, expectedRegionDistribution)
  }
}

/*
 * Apply tag derivation to an entire tree
 * expectedRegionDistribution: the total region distribution for the champion/lane,
 * used to detect items that are region-specific
 */
function treeDeriveTags(itemtree: ItemTree, expectedRegionDistribution?: PlatformCounts): void {
  deriveTags(itemtree, expectedRegionDistribution)
}

export {
  ItemTree,
  PlatformCounts,
  GoldAdvantageTag,
  ItemTag,
  treeMerge,
  treeInit,
  treeCutBranches,
  treeSort,
  treeMergeTree,
  areTreeSimilars,
  treeDeriveTags
}