การคิดเรื่อง Collections และ Enumerable

orders.sum { |order| order[:amount] }

invoices.each_with_object({}) do |invoice, totals|
  key = invoice[:currency]
  totals[key] ||= 0
  totals[key] += invoice[:amount]
end

orders.sum { |o| o[:amount] }
orders.select { |o| o[:amount] >= 100 }
orders.map { |o| o[:customer] }
items.max_by { |i| i[:score] }

invoices.each_with_object({}) do |invoice, totals|
  currency = invoice[:currency]
  totals[currency] ||= 0
  totals[currency] += invoice[:amount]
end

# EXAMPLE CODE
# Topic: topic_03_collections_enumerable
#
# Purpose:
# - This file demonstrates reference implementation for the concept.
# - It should pass tests from the beginning.
# - Read and understand it before solving exercises.

class OrderReport
  def total_amount(orders)
    orders.sum { |o| o[:amount] }
  end

  def high_value_orders(orders, min: 100)
    orders.select { |o| o[:amount] >= min }
  end

  def customer_names(orders)
    orders.map { |o| o[:customer] }.uniq.sort
  end
end

# STUDENT TASK (BASIC)
# Topic: topic_03_collections_enumerable
#
# What to do:
# - Implement or improve the class/methods in this file.
# - Read tests in tests/topic_03_collections_enumerable_spec.rb under the "basic exercise" examples.
# - Make tests pass without breaking the example/advanced sections.
#
# Expected outcome:
# - You can run this topic tests and see all examples green after implementation.

class ScoreAnalyzer
  def average_score(items)
    return 0.0 if items.empty?

    items.sum { |i| i[:score] }.to_f / items.size
  end

  def passing_names(items, threshold: 60)
    items.select { |i| i[:score] >= threshold }.map { |i| i[:name] }
  end

  def top_scorer(items)
    items.max_by { |i| i[:score] }&.dig(:name)
  end
end

# STUDENT TASK (ADVANCED)
# Topic: topic_03_collections_enumerable
#
# Academic purpose:
# - Practice turning a reporting requirement into a declarative collection transformation.
# - Understand why Ruby developers reach for Enumerable when shaping business data.
#
# Real-world use case:
# - Multi-currency invoice reporting is common in billing, analytics, and finance tools.
# - Teams often need "totals by group" answers for dashboards or exports.
# - This is a realistic place where Ruby's collection methods feel powerful rather than decorative.
#
# Why Ruby is beautiful here:
# - `each_with_object` makes the accumulator explicit without boilerplate loop setup.
# - The code mirrors the business question: "group totals by currency".
# - The method stays close to the domain language.
#
# What to do:
# - Complete the challenge behavior requested by the guide.
# - Focus on why the chosen Enumerable style matches the reporting requirement.
# - Use tests in tests/topic_03_collections_enumerable_spec.rb under the "advanced exercise" examples.
#
# Expected outcome:
# - Advanced tests pass and you can defend your use of Enumerable.

class InvoiceSummarizer
  def group_total_by_currency(invoices)
    invoices.each_with_object({}) do |invoice, totals|
      key = invoice[:currency]
      totals[key] ||= 0
      totals[key] += invoice[:amount]
    end
  end
end

# ANSWER KEY (BASIC)
# Topic: topic_03_collections_enumerable
#
# Solution idea:
# - Choose the Enumerable method that matches the job:
#   average -> `sum`
#   pass list -> `select` + `map`
#   top result -> `max_by`
# - The code reads better when each method expresses one kind of collection work.

class ScoreAnalyzer
  def average_score(items)
    return 0.0 if items.empty?

    items.sum { |item| item[:score] }.to_f / items.size
  end

  def passing_names(items, threshold: 60)
    items.select { |item| item[:score] >= threshold }.map { |item| item[:name] }
  end

  def top_scorer(items)
    items.max_by { |item| item[:score] }&.dig(:name)
  end
end

# ANSWER KEY (ADVANCED)
# Topic: topic_03_collections_enumerable
#
# Solution idea:
# - Build a hash accumulator explicitly with `each_with_object`.
# - Each invoice contributes its amount into the bucket for its currency.
# - This mirrors how grouped totals are computed in reporting code.

class InvoiceSummarizer
  def group_total_by_currency(invoices)
    invoices.each_with_object({}) do |invoice, totals|
      currency = invoice[:currency]
      totals[currency] ||= 0
      totals[currency] += invoice[:amount]
    end
  end
end

# This spec is your learning companion for topic_03_collections_enumerable.
#
# How to use this file:
# 1) Run tests and observe failures/successes.
# 2) Keep EXAMPLE specs green from the beginning.
# 3) Implement BASIC exercise until BASIC specs pass.
# 4) Implement ADVANCED exercise and pass edge cases.
#
# Expected final result:
# - All examples in this file pass.
# - You understand both the concept and the implementation tradeoffs.

require_relative "../example"
require_relative "../basic_exercise"
require_relative "../adv_exercise"

RSpec.describe "topic_03_collections_enumerable" do
  describe "EXAMPLE purpose: understand the reference implementation" do
    it "builds report totals and names" do
      orders = [
        { customer: "Ann", amount: 120 },
        { customer: "Bob", amount: 80 },
        { customer: "Ann", amount: 30 }
      ]

      r = OrderReport.new
      expect(r.total_amount(orders)).to eq(230)
      expect(r.high_value_orders(orders, min: 80).size).to eq(2)
      expect(r.customer_names(orders)).to eq(%w[Ann Bob])
    end
  end

  describe "BASIC EXERCISE purpose: implement the comparable task" do
    it "analyzes score data" do
      s = ScoreAnalyzer.new
      scores = [{ name: "A", score: 80 }, { name: "B", score: 60 }, { name: "C", score: 40 }]
      expect(s.average_score(scores)).to eq(60.0)
      expect(s.passing_names(scores, threshold: 60)).to eq(%w[A B])
      expect(s.top_scorer(scores)).to eq("A")
    end
  end

  describe "ADVANCED EXERCISE purpose: solve challenge and edge cases" do
    it "groups invoice totals by currency" do
      i = InvoiceSummarizer.new
      invoices = [{ currency: "USD", amount: 10 }, { currency: "THB", amount: 700 }, { currency: "USD", amount: 40 }]
      expect(i.group_total_by_currency(invoices)).to eq({ "USD" => 50, "THB" => 700 })
    end
  end
end

#!/usr/bin/env bash
set -euo pipefail

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
ROOT_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"

exec "${ROOT_DIR}/run_tests.sh" "$(basename "${SCRIPT_DIR}")"