defmodule Mv.Membership.Import.CsvParserTest do
  use ExUnit.Case, async: true

  alias Mv.Membership.Import.CsvParser

  describe "parse/1" do
    test "returns {:ok, headers, rows} for valid CSV with semicolon delimiter" do
      csv_content = "email;first_name\njohn@example.com;John"

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      assert headers == ["email", "first_name"]
      assert rows == [{2, ["john@example.com", "John"]}]
    end

    test "returns {:ok, headers, rows} for valid CSV with comma delimiter" do
      csv_content = "email,first_name\njohn@example.com,John"

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      assert headers == ["email", "first_name"]
      assert rows == [{2, ["john@example.com", "John"]}]
    end

    test "detects semicolon delimiter when both delimiters present" do
      csv_content = "email;first_name,last_name\njohn@example.com;John,Doe"

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      # Should detect semicolon as primary delimiter
      assert length(headers) >= 2
      assert length(rows) == 1
    end

    test "prefers semicolon delimiter when recognition is tied" do
      # CSV where both delimiters would yield same number of fields
      csv_content = "email;name\njohn@example.com;John"

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      # Should prefer semicolon
      assert headers == ["email", "name"]
      assert rows == [{2, ["john@example.com", "John"]}]
    end

    test "defaults to semicolon delimiter when no headers recognized" do
      csv_content = "unknown1;unknown2\nvalue1;value2"

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      # Should default to semicolon
      assert headers == ["unknown1", "unknown2"]
      assert rows == [{2, ["value1", "value2"]}]
    end
  end

  describe "BOM handling" do
    test "strips UTF-8 BOM from file content" do
      bom = <<0xEF, 0xBB, 0xBF>>
      csv_content = bom <> "email;first_name\njohn@example.com;John"

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      assert headers == ["email", "first_name"]
      assert rows == [{2, ["john@example.com", "John"]}]
    end

    test "parses CSV with BOM correctly (Excel export compatibility)" do
      bom = <<0xEF, 0xBB, 0xBF>>

      csv_content =
        bom <>
          "email;first_name;last_name\njohn@example.com;John;Doe\njane@example.com;Jane;Smith"

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      assert headers == ["email", "first_name", "last_name"]
      assert length(rows) == 2
      assert Enum.at(rows, 0) == {2, ["john@example.com", "John", "Doe"]}
      assert Enum.at(rows, 1) == {3, ["jane@example.com", "Jane", "Smith"]}
    end
  end

  describe "line number handling" do
    test "header row is line 1, first data row is line 2" do
      csv_content = "email\njohn@example.com"

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      assert headers == ["email"]
      assert rows == [{2, ["john@example.com"]}]
    end

    test "preserves correct line numbers when empty lines are skipped" do
      csv_content = "email;first_name\n\njohn@example.com;John\n\njane@example.com;Jane"

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      assert headers == ["email", "first_name"]
      # Line 2 is empty (skipped), line 3 has data
      assert Enum.at(rows, 0) == {3, ["john@example.com", "John"]}
      # Line 4 is empty (skipped), line 5 has data
      assert Enum.at(rows, 1) == {5, ["jane@example.com", "Jane"]}
    end

    test "skips completely empty rows but preserves line numbers" do
      csv_content = "email\n\n\njohn@example.com"

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      assert headers == ["email"]
      # Lines 2 & 3 are empty (skipped), line 4 has data
      assert rows == [{4, ["john@example.com"]}]
    end
  end

  describe "line ending handling" do
    test "handles \\r\\n line endings correctly" do
      csv_content = "email;first_name\r\njohn@example.com;John\r\njane@example.com;Jane"

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      assert headers == ["email", "first_name"]
      assert length(rows) == 2
      assert Enum.at(rows, 0) == {2, ["john@example.com", "John"]}
      assert Enum.at(rows, 1) == {3, ["jane@example.com", "Jane"]}
    end

    test "handles \\n line endings correctly" do
      csv_content = "email;first_name\njohn@example.com;John\njane@example.com;Jane"

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      assert headers == ["email", "first_name"]
      assert length(rows) == 2
      assert Enum.at(rows, 0) == {2, ["john@example.com", "John"]}
      assert Enum.at(rows, 1) == {3, ["jane@example.com", "Jane"]}
    end
  end

  describe "quoted fields" do
    test "parses quoted fields correctly" do
      csv_content = "email;name\njohn@example.com;\"John Doe\""

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      assert headers == ["email", "name"]
      assert rows == [{2, ["john@example.com", "John Doe"]}]
    end

    test "handles escaped quotes (\"\") inside quoted fields" do
      csv_content = "email;name\njohn@example.com;\"John \"\"Johnny\"\" Doe\""

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      assert headers == ["email", "name"]
      assert rows == [{2, ["john@example.com", "John \"Johnny\" Doe"]}]
    end

    test "handles multiline quoted fields with correct line numbering" do
      # Header line 1
      # Data record starts line 2, contains "foo\nbar" in a field
      # Record ends physically at line 3
      # Expected: row gets line number 2 (start line)
      csv_content = "email;description\njohn@example.com;\"foo\nbar\""

      assert {:ok, headers, rows} = CsvParser.parse(csv_content)

      assert headers == ["email", "description"]
      assert rows == [{2, ["john@example.com", "foo\nbar"]}]
    end
  end

  describe "error handling" do
    test "returns {:error, reason} for empty file" do
      assert {:error, reason} = CsvParser.parse("")
      assert reason =~ "empty"
    end

    test "returns {:error, reason} when no header row found" do
      # Only whitespace after BOM strip
      assert {:error, reason} = CsvParser.parse("   \n  ")
      assert reason =~ "CSV file is empty"
    end

    test "returns {:error, reason} for invalid UTF-8 content" do
      # Invalid UTF-8 sequence
      invalid_utf8 = <<0xFF, 0xFE, 0xFD>>

      assert {:error, reason} = CsvParser.parse(invalid_utf8)
      assert reason =~ "UTF-8"
    end

    test "returns {:error, reason} for unparsable data row" do
      # Malformed CSV row that cannot be parsed
      # NimbleCSV will throw an exception for unclosed quotes
      csv_content = "email;name\njohn@example.com;\"unclosed quote"

      assert {:error, reason} = CsvParser.parse(csv_content)
      assert is_binary(reason)
      # Error message should indicate parsing failure
      assert reason =~ "parse" or reason =~ "CSV"
    end
  end

  describe "module documentation" do
    test "module has @moduledoc" do
      assert Code.ensure_loaded?(CsvParser)

      {:docs_v1, _, _, _, %{"en" => moduledoc}, _, _} = Code.fetch_docs(CsvParser)
      assert is_binary(moduledoc)
      assert String.length(moduledoc) > 0
    end
  end
end