use ascii;
use bufio;
use encoding::utf8;
use fmt;
use io;
use strings;

// List of HTTP headers.
// TODO: [](str, []str)
export type header = [](str, str);

// Adds a given HTTP header, which may be added more than once. The name should
// be canonicalized by the caller.
export fn header_add(head: *header, name: str, val: str) void = {
	assert(len(name) >= 1 && len(val) >= 1);
	let name = ascii::strlower(name);
	append(head, (name, strings::dup(val)));
};

// Sets the value of a given HTTP header, removing any previous values. The name
// should be canonicalized by the caller.
export fn header_set(head: *header, name: str, val: str) void = {
	header_del(head, name);
	header_add(head, name, val);
};

// Removes an HTTP header from a list of [[header]]. If multiple headers match
// the given name, all matching headers are removed.
export fn header_del(head: *header, name: str) void = {
	for (let i = 0z; i < len(head); i += 1) {
		if (ascii::strcasecmp(head[i].0, name) == 0) {
			free(head[i].0);
			free(head[i].1);
			delete(head[i]);
			i -= 1;
		};
	};
};

// Retrieves a value, or values, from a header. An empty string indicates the
// absence of a header.
export fn header_get(head: *header, name: str) str = {
	for (let i = 0z; i < len(head); i += 1) {
		const (key, val) = head[i];
		if (ascii::strcasecmp(key, name) == 0) {
			return val;
		};
	};
	return "";
};

// Frees state associated with an HTTP [[header]].
export fn header_free(head: *header) void = {
	for (let i = 0z; i < len(head); i += 1) {
		free(head[i].0);
		free(head[i].1);
	};
	free(*head);
};

// Duplicates a set of HTTP headers.
export fn header_dup(head: *header) header = {
	let new: header = [];
	for (let i = 0z; i < len(head); i += 1) {
		const (key, val) = head[i];
		header_add(&new, key, val);
	};
	return new;
};

// Writes a list of HTTP headers to the provided I/O handle in the HTTP wire
// format.
export fn write_header(sink: io::handle, head: *header) (size | io::error) = {
	let z = 0z;
	for (let i = 0z; i < len(head); i += 1) {
		const (name, val) = head[i];
		z += fmt::fprintf(sink, "{}: {}\r\n", name, val)?;
	};
	return z;
};

fn read_header(head: *header, scan: *bufio::scanner) (void | io::error | protoerr) = {
	for (true) {
		const item = match (bufio::scan_string(scan, "\r\n")) {
		case let line: const str =>
			yield line;
		case io::EOF =>
			break;
		case let err: io::error =>
			return err;
		case utf8::invalid =>
			return protoerr;
		};
		if (item == "") {
			break;
		};

		let (name, val) = strings::cut(item, ":");
		val = strings::trim(val);
		if (val == "") {
			continue;
		};
		// TODO: validate field-name

		header_add(head, name, val);
	};
};