# frozen_string_literal: true

class Assistant::Function::GetAccountStatement < Assistant::Function
  include Assistant::Function::StatementVaultSupport

  DOWNLOAD_URL_TTL = 15.minutes

  class << self
    def name
      "get_account_statement"
    end

    def description
      <<~INSTRUCTIONS
        Fetch one Statement Vault document by ID: its identity (SHA-256, filename,
        period), the balances read off the document, and the reconciliation checks
        comparing those balances against the ledger.

        The reconciliation checks are the trustworthy part. Each compares a figure
        printed on the statement against the account's recorded balance:

        - `opening_balance` / `closing_balance` — the statement's figure vs the ledger's
        - `period_movement` — the change across the period, both sides

        Each check reports `matched` or `mismatched` (tolerance: 0.01). A mismatch
        means the ledger and the document disagree — report it, and do not paper
        over it by adjusting the number to fit.

        Also returns a short-lived download URL (valid #{DOWNLOAD_URL_TTL.inspect})
        for the original file when one is attached.

        Example:

        ```
        get_account_statement({ statement_id: "abc123-def456" })
        ```
      INSTRUCTIONS
    end
  end

  def strict_mode?
    false
  end

  def params_schema
    build_schema(
      required: [ "statement_id" ],
      properties: {
        statement_id: {
          type: "string",
          description: "UUID of the statement, as returned by list_account_statements or upload_account_statement."
        }
      }
    )
  end

  def call(params = {})
    return not_a_statement_manager unless statement_manager?

    statement = find_statement(params["statement_id"])

    unless statement&.viewable_by?(user)
      return error("not_found", "No statement found with that ID that this user can view.")
    end

    {
      success: true,
      statement: statement_payload(statement).merge(
        reconciliation_status: statement.reconciliation_status,
        reconciliation_checks: reconciliation_payload(statement),
        download_url: download_url(statement)
      ).compact
    }
  end

  private
    def reconciliation_payload(statement)
      statement.reconciliation_checks.map do |check|
        {
          check: check[:key],
          statement_amount: check[:statement_amount].to_s,
          ledger_amount: check[:ledger_amount].to_s,
          difference: check[:difference].to_s,
          status: check[:status]
        }
      end
    end

    # Chat and MCP clients render outside the request that produced the record, so
    # the URL has to be absolute. Falls back to nil when no host is configured
    # (e.g. a self-hosted worker with no APP_DOMAIN) rather than handing back a
    # relative path an external agent cannot resolve.
    def download_url(statement)
      return nil unless statement.original_file.attached?

      host_opts = Rails.application.config.action_mailer.default_url_options || {}
      return nil if host_opts[:host].blank?

      Rails.application.routes.url_helpers.rails_blob_url(
        statement.original_file,
        host_opts.merge(disposition: "attachment", expires_in: DOWNLOAD_URL_TTL)
      )
    end
end