#!/usr/bin/env ruby
# frozen_string_literal: true

require "json"
require "open3"
require "shellwords"

class UpcomingChangeStatusPRs
  def initialize(env: ENV)
    @report_file = env.fetch("REPORT_FILE") { abort "REPORT_FILE is required" }
    @base_branch = env.fetch("BASE_BRANCH") { abort "BASE_BRANCH is required" }
    @dry_run = env.fetch("DRY_RUN", "true") == "true"
    @stale_after_days = env.fetch("STALE_AFTER_DAYS", "14")
    @github_repository = env.fetch("GITHUB_REPOSITORY", "")
    @github_step_summary = env.fetch("GITHUB_STEP_SUMMARY", "/dev/stdout")
    @rails_command = env.fetch("RAILS_COMMAND", "bin/rails")
  end

  def run
    if !@dry_run && @github_repository != "discourse/discourse"
      abort "Refusing to create pull requests outside discourse/discourse."
    end

    run!("git", "fetch", "origin", @base_branch)

    eligible_changes.each { |change| process(change) }
  end

  private

  def eligible_changes
    JSON.parse(File.read(@report_file)).select { |change| change["eligible"] }
  end

  def process(change)
    name = change["name"]
    settings_path = change["settings_path"]
    original_pr_number = change["original_pr_number"]
    branch = change["branch"]
    title = change["title"]
    pr_label = change["pr_label"]
    body_file = "/tmp/upcoming-change-#{name}-body.md"
    assignee = resolve_assignee(original_pr_number)

    File.write(body_file, change["pr_body"])

    if @dry_run
      write_dry_run_summary(
        name:,
        branch:,
        title:,
        body_file:,
        assignee:,
        settings_path:,
        pr_label:,
      )
      return
    end

    if open_pr_exists?(branch)
      puts "Open PR already exists for #{branch}; skipping."
      return
    end

    run!("git", "checkout", "-B", branch, "origin/#{@base_branch}")
    rails_runner(
      "script/upcoming_changes_status_report",
      "--",
      "--stale-after-days",
      @stale_after_days,
      "--apply",
      name,
    )
    run!("git", "add", settings_path)
    run!("git", "commit", "-m", title)
    run!("git", "push", "-f", "origin", branch)

    create_pr(branch:, title:, body_file:, pr_label:, assignee:)
  end

  def resolve_assignee(original_pr_number)
    return if original_pr_number.nil? || original_pr_number.to_s.empty?

    login, status =
      Open3.capture2(
        "gh",
        "pr",
        "view",
        original_pr_number.to_s,
        "--json",
        "author",
        "--jq",
        ".author.login",
      )
    status.success? ? login.strip : nil
  end

  def open_pr_exists?(branch)
    count =
      capture!(
        "gh",
        "pr",
        "list",
        "--head",
        branch,
        "--state",
        "open",
        "--json",
        "number",
        "--jq",
        "length",
      ).strip
    count != "0"
  end

  def create_pr(branch:, title:, body_file:, pr_label:, assignee:)
    args = [
      "gh",
      "pr",
      "create",
      "--base",
      @base_branch,
      "--head",
      branch,
      "--title",
      title,
      "--body-file",
      body_file,
      "--label",
      pr_label,
    ]
    args.push("--assignee", assignee) if assignee && !assignee.empty?
    run!(*args)
  end

  def rails_runner(*args)
    run!(@rails_command, "runner", *args, env: { "SKIP_DB_AND_REDIS" => "1", "RAILS_DB" => "nonexistent" })
  end

  def write_dry_run_summary(name:, branch:, title:, body_file:, assignee:, settings_path:, pr_label:)
    create_pr_line =
      if assignee && !assignee.empty?
        "gh pr create --base #{@base_branch} --head #{branch} --title \"#{title}\" --body-file #{body_file} --label #{pr_label} --assignee #{assignee}"
      else
        "gh pr create --base #{@base_branch} --head #{branch} --title \"#{title}\" --body-file #{body_file} --label #{pr_label}"
      end

    summary = <<~SUMMARY
      ### #{name}

      ```bash
      git checkout -B #{branch} origin/#{@base_branch}
      SKIP_DB_AND_REDIS=1 RAILS_DB=nonexistent bin/rails runner script/upcoming_changes_status_report -- --stale-after-days #{@stale_after_days} --apply #{name}
      git add #{settings_path}
      git commit -m "#{title}"
      git push -f origin #{branch}
      #{create_pr_line}
      ```

    SUMMARY

    File.open(@github_step_summary, "a") { |file| file.write(summary) }
  end

  # Runs a command, streaming output, and aborts on failure (set -e equivalent).
  def run!(*args, env: {})
    args = args.map(&:to_s)
    unless system(env, *args)
      abort "Command failed (#{$?.exitstatus}): #{args.shelljoin}"
    end
  end

  # Runs a command and returns its stdout, aborting on failure (set -e + pipefail).
  def capture!(*args)
    args = args.map(&:to_s)
    stdout, status = Open3.capture2(*args)
    abort "Command failed (#{status.exitstatus}): #{args.shelljoin}" unless status.success?
    stdout
  end
end

UpcomingChangeStatusPRs.new.run if $PROGRAM_NAME == __FILE__