ไฟล์ CSV, งานข้อมูลขนาดเล็ก และการค้นข้อมูลแบบง่าย

reader.load("inventory.csv")
# => [{"sku"=>"B100", "name"=>"Ruby Book", "price"=>"30", "category"=>"books"}]

CSV.read(path, headers: true).map(&:to_h)

CSV.open(path, "w") do |csv|
  csv << %w[sku name price]
  rows.each { |row| csv << [row[:sku], row[:name], row[:price]] }
end

rows.select { |row| row["category"] == "books" }
rows.find { |row| row["sku"] == "B100" }
rows.map { |row| row["name"] }

# EXAMPLE CODE
# Topic: topic_11_csv_files_queries
#
# Purpose:
# - This file demonstrates a reference implementation for reading CSV data from a file.
# - It should pass tests from the beginning.
# - Read it before solving the writer and query exercises.

require "csv"

class InventoryCsvReader
  def load(path)
    CSV.read(path, headers: true).map(&:to_h)
  end
end

# STUDENT TASK (BASIC)
# Topic: topic_11_csv_files_queries
#
# What to do:
# - Write structured rows to a CSV file.
# - Keep header order stable so tests and downstream readers are predictable.
# - Return the path so the caller knows what was written.
#
# Expected outcome:
# - You can export rows to CSV in a small, focused writer object.

require "csv"

class InventoryCsvWriter
  HEADERS = %w[sku name price category].freeze

  def write(path, rows)
    CSV.open(path, "w") do |csv|
      csv << HEADERS
      rows.each do |row|
        csv << [row[:sku], row[:name], row[:price], row[:category]]
      end
    end

    path
  end
end

# STUDENT TASK (ADVANCED)
# Topic: topic_11_csv_files_queries
#
# Academic purpose:
# - Practice turning imported CSV rows into a small query service.
# - Learn to keep file reading separate from business questions.
#
# Real-world use case:
# - Admin tools and back-office systems often import CSV files and then need quick lookups
#   such as "find this SKU" or "list all rows in this category."
# - A query object keeps those questions away from low-level file handling.
#
# Why Ruby is beautiful here:
# - Arrays of hashes are easy to query with Enumerable.
# - An injected reader makes the service easier to test and replace later.
# - The code stays compact while still describing a real workflow.
#
# What to do:
# - Build a service that loads rows through the reader.
# - Provide a couple of focused query methods.
# - Keep the service about querying, not parsing.
#
# Expected outcome:
# - Advanced tests pass and you can explain the reader/query separation.

class InventoryQueryService
  def initialize(reader:)
    @reader = reader
  end

  def find_by_sku(path, sku)
    @reader.load(path).find { |row| row["sku"] == sku }
  end

  def names_in_category(path, category)
    @reader.load(path)
           .select { |row| row["category"] == category }
           .map { |row| row["name"] }
  end
end

# ANSWER KEY (BASIC)
# Topic: topic_11_csv_files_queries
#
# Solution idea:
# - Use a dedicated writer object so file export stays separate from parsing and queries.
# - Fix the header order up front.
# - Write one row at a time from the hash values in that order.

require "csv"

class InventoryCsvWriter
  HEADERS = %w[sku name price category].freeze

  def write(path, rows)
    CSV.open(path, "w") do |csv|
      csv << HEADERS
      rows.each do |row|
        csv << [row[:sku], row[:name], row[:price], row[:category]]
      end
    end

    path
  end
end

# ANSWER KEY (ADVANCED)
# Topic: topic_11_csv_files_queries
#
# Solution idea:
# - Inject the reader so the query service asks for rows instead of reading files directly.
# - Use `find` for a single lookup and `select` + `map` for category listing.
# - Keep the methods small and clearly tied to one business question each.

class InventoryQueryService
  def initialize(reader:)
    @reader = reader
  end

  def find_by_sku(path, sku)
    @reader.load(path).find { |row| row["sku"] == sku }
  end

  def names_in_category(path, category)
    @reader.load(path)
           .select { |row| row["category"] == category }
           .map { |row| row["name"] }
  end
end

# This spec is your learning companion for topic_11_csv_files_queries.
#
# How to use this file:
# 1) Run tests and observe failures or successes.
# 2) Keep the EXAMPLE specs green from the beginning.
# 3) Implement the BASIC exercise as sprint 2: writing rows.
# 4) Implement the ADVANCED exercise as sprint 3: querying imported rows.
#
# Expected final result:
# - All examples in this file pass.
# - You understand CSV work as a small pipeline rather than isolated syntax.

require "tempfile"

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

RSpec.describe "topic_11_csv_files_queries" do
  describe "EXAMPLE purpose: read rows from a CSV file before adding more behavior" do
    it "loads rows as hashes using headers" do
      file = Tempfile.new(["inventory", ".csv"])
      file.write("sku,name,price,category\nB100,Ruby Book,30,books\nA200,Desk Lamp,45,home\n")
      file.flush

      reader = InventoryCsvReader.new

      expect(reader.load(file.path)).to eq(
        [
          { "sku" => "B100", "name" => "Ruby Book", "price" => "30", "category" => "books" },
          { "sku" => "A200", "name" => "Desk Lamp", "price" => "45", "category" => "home" }
        ]
      )
    ensure
      file.close!
    end
  end

  describe "BASIC EXERCISE purpose: write structured rows in a small export sprint" do
    it "writes rows with a stable header order" do
      file = Tempfile.new(["inventory_export", ".csv"])
      rows = [
        { sku: "B100", name: "Ruby Book", price: 30, category: "books" },
        { sku: "A200", name: "Desk Lamp", price: 45, category: "home" }
      ]

      writer = InventoryCsvWriter.new
      writer.write(file.path, rows)

      expect(File.read(file.path)).to eq(
        "sku,name,price,category\nB100,Ruby Book,30,books\nA200,Desk Lamp,45,home\n"
      )
    ensure
      file.close!
    end
  end

  describe "ADVANCED EXERCISE purpose: query imported data through a focused service" do
    it "uses an injected reader to find rows and list names by category" do
      file = Tempfile.new(["inventory_query", ".csv"])
      file.write("sku,name,price,category\nB100,Ruby Book,30,books\nB200,Refactoring,50,books\nA200,Desk Lamp,45,home\n")
      file.flush

      service = InventoryQueryService.new(reader: InventoryCsvReader.new)

      expect(service.find_by_sku(file.path, "B200")).to eq(
        { "sku" => "B200", "name" => "Refactoring", "price" => "50", "category" => "books" }
      )
      expect(service.names_in_category(file.path, "books")).to eq(["Ruby Book", "Refactoring"])
    ensure
      file.close!
    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}")"