// This source code is released into the public domain.
export module nihil.util:tabulate;

import nihil.std;
import nihil.error;
import :ctype;

namespace nihil {

// tabulate: format the given range in an ASCII table and write the output
// to the given output iterator.  The range's values will be converted to
// strings as if by std::format.
//
// tabulate is implemented by copying the range; this allows it to work on
// input/forward ranges at the cost of slightly increased memory use.
//
// The table spec is a string consisting of zero or more field formats,
// formatted as {flags:fieldname}; both flags and fieldname are optional.
// If there are fewer field formats than fields, the remaining fields
// are formatted as if by {:}.
//
// The following flags are supported:
//
// 	<	left-align this column (default)
// 	>	right-align this column

// Exception thrown when a table spec is invalid.
export struct table_spec_error : error {
	explicit table_spec_error(std::string_view what)
		: error(what)
	{
	}
};

// The specification for a single field.
template<typename Char>
struct field_spec {
	enum align_t { left, right };

	// Get the name of this field.
	auto name(this field_spec const &self)
		-> std::basic_string_view<Char>
	{
		return self.m_name;
	}

	// Set the name of this field.
	auto name(this field_spec &self,
		  std::basic_string_view<Char> new_name)
		-> void
	{
		self.m_name = new_name;
	}

	// Set this field's alignment.
	auto align(this field_spec &self, align_t new_align) -> void
	{
		self.m_align = new_align;
	}

	// Ensure the length of this field is at least the given width.
	auto ensure_width(this field_spec &self, std::size_t newwidth)
		-> void
	{
		self.m_width = std::max(self.m_width, newwidth);
	}

	// Format an object to a string based on our field spec.
	[[nodiscard]] auto format(this field_spec const &, auto &&obj)
		-> std::basic_string<Char>
	{
		auto format_string = std::basic_string<Char>{'{', '}'};
		return std::format(std::runtime_format(format_string), obj);
	}

	// Print a column value to an output iterator according to our field
	// spec.  If is_last is true, this is the last field on the line, so
	// we won't output any trailling padding.
	auto print(this field_spec const &self,
		   std::basic_string_view<Char> value,
		   std::output_iterator<Char> auto &out,
		   bool is_last)
		-> void
	{
		auto padding = self.m_width - value.size();

		if (self.m_align == right)
			for (std::size_t i = 0; i < padding; ++i)
				*out++ = ' ';

		std::ranges::copy(value, out);

		if (!is_last && self.m_align == left)
			for (std::size_t i = 0; i < padding; ++i)
				*out++ = ' ';
	}

private:
	std::basic_string_view<Char>	m_name;
	std::size_t			m_width = 0;
	align_t				m_align = left;
};

/*
 * The specification for an entire table.
 */
template<typename Char>
struct table_spec {
	// Add a new field spec to this table.
	auto add(this table_spec &self, field_spec<Char> field) -> void
	{
		self.m_fields.emplace_back(std::move(field));
	}

	// Return the field spec for a given field.  If the field doesn't
	// exist, this field and any intermediate fields will be created.
	[[nodiscard]] auto field(this table_spec &self, std::size_t fieldnr)
		-> field_spec<Char> &
	{
		if (fieldnr >= self.m_fields.size())
			self.m_fields.resize(fieldnr + 1);
		return self.m_fields.at(fieldnr);
	}

	// The number of columns in this table.
	[[nodiscard]] auto columns(this table_spec const &self) -> std::size_t
	{
		return self.m_fields.size();
	}

	// Return all the fields in this table.
	[[nodiscard]] auto fields(this table_spec const &self)
		    -> std::vector<field_spec<Char>> const &
	{
		return self.m_fields;
	}

private:
	std::vector<field_spec<Char>> m_fields;
};

// Parse the field flags, e.g. '<'.
template<typename Char,
	 std::input_iterator Iterator, std::sentinel_for<Iterator> Sentinel>
auto parse_field_flags(field_spec<Char> &field, Iterator &pos, Sentinel end)
	-> void
{
	while (pos < end) {
		switch (*pos) {
		case '<':
			field.align(field_spec<Char>::left);
			break;
		case '>':
			field.align(field_spec<Char>::right);
			break;
		case ':':
			++pos;
			/*FALLTHROUGH*/
		case '}':
			return;
		default:
			throw table_spec_error("Invalid table spec: "
					       "unknown flag character");
		}

		if (++pos == end)
			throw table_spec_error("Invalid table spec: "
					       "unterminated field");
	}
}

// Parse a complete field spec, e.g. "{<:NAME}".
template<typename Char,
	std::input_iterator Iterator, std::sentinel_for<Iterator> Sentinel>
[[nodiscard]] auto parse_field(Iterator &pos, Sentinel end)
	-> field_spec<Char>
{
	auto field = field_spec<Char>{};

	if (pos == end)
		throw table_spec_error("Invalid table spec: empty field");

	// The field spec should start with a '{'.
	if (*pos != '{')
		throw table_spec_error("Invalid table spec: expected '{'");

	if (++pos == end)
		throw table_spec_error("Invalid table spec: unterminated field");

	// This consumes 'pos' up to and including the ':'.
	parse_field_flags(field, pos, end);

	auto brace = std::ranges::find(pos, end, '}');
	if (brace == end)
		throw table_spec_error("Invalid table spec: expected '}'");

	field.name(std::basic_string_view<Char>(pos, brace));
	pos = std::next(brace);

	// The field must be at least as wide as its header.
	field.ensure_width(field.name().size());

	return field;
}

template<typename Char>
[[nodiscard]] auto parse_table_spec(std::basic_string_view<Char> spec)
	-> table_spec<Char>
{
	auto table = table_spec<Char>();

	auto pos = std::ranges::begin(spec);
	auto end = std::ranges::end(spec);

	for (;;) {
		// Skip leading whitespace
		while (pos < end && is_c_space(*pos))
			++pos;

		if (pos == end)
			break;

		table.add(parse_field<Char>(pos, end));
	}

	return table;
}

export template<typename Char,
		std::ranges::range Range,
		std::output_iterator<Char> Iterator>
auto basic_tabulate(std::basic_string_view<Char> table_spec,
		    Range &&range,
		    Iterator &&out)
	-> void
{
	// Parse the table spec.
	auto table = parse_table_spec(table_spec);

	// Create our copy of the input data.
	auto data = std::vector<std::vector<std::basic_string<Char>>>();
	// Reserve the first row for the header.
	data.resize(1);

	// Find the required length of each field.
	for (auto &&row : range) {
		// LLVM doesn't have std::enumerate_view yet
		auto i = std::size_t{0};
		auto &this_row = data.emplace_back();

		for (auto &&column : row) {
			auto &field = table.field(i);
			auto &str = this_row.emplace_back(field.format(column));
			field.ensure_width(str.size());
			++i;
		}
	}

	// Add the header row.
	for (auto &&field : table.fields())
		data.at(0).emplace_back(std::from_range, field.name());

	// Print the values.
	for (auto &&row : data) {
		for (std::size_t i = 0; i < row.size(); ++i) {
			auto &field = table.field(i);
			bool is_last = (i == row.size() - 1);

			field.print(row[i], out, is_last);

			if (!is_last)
				*out++ = ' ';
		}

		*out++ = '\n';
	}
}

export auto tabulate(std::string_view table_spec,
		     std::ranges::range auto &&range,
		     std::output_iterator<char> auto &&out)
{
	return basic_tabulate<char>(table_spec,
				    std::forward<decltype(range)>(range),
				    std::forward<decltype(out)>(out));
}

export auto wtabulate(std::wstring_view table_spec,
		      std::ranges::range auto &&range,
		      std::output_iterator<wchar_t> auto &&out)
{
	return basic_tabulate<wchar_t>(table_spec,
				       std::forward<decltype(range)>(range),
				       std::forward<decltype(out)>(out));
}

} // namespace nihil