package bytes

import "core:io"
import "core:unicode/utf8"

MIN_READ :: 512;

@(private)
SMALL_BUFFER_SIZE :: 64;

// A Buffer is a variable-sized buffer of bytes with a io.Stream interface
// The zero value for Buffer is an empty buffer ready to use.
Buffer :: struct {
	buf: [dynamic]byte,
	off: int,
	last_read: Read_Op,
}

@(private)
Read_Op :: enum i8 {
	Read       = -1,
	Invalid    =  0,
	Read_Rune1 =  1,
	Read_Rune2 =  2,
	Read_Rune3 =  3,
	Read_Rune4 =  4,
}


buffer_init :: proc(b: ^Buffer, buf: []byte) {
	resize(&b.buf, len(buf));
	copy(b.buf[:], buf);
}

buffer_init_string :: proc(b: ^Buffer, s: string) {
	resize(&b.buf, len(s));
	copy(b.buf[:], s);
}

buffer_init_allocator :: proc(b: ^Buffer, len, cap: int, allocator := context.allocator) {
	b.buf.allocator = allocator;
	reserve(&b.buf, cap);
	resize(&b.buf, len);
}

buffer_destroy :: proc(b: ^Buffer) {
	delete(b.buf);
	buffer_reset(b);
}

buffer_to_bytes :: proc(b: ^Buffer) -> []byte {
	return b.buf[b.off:];
}

buffer_to_string :: proc(b: ^Buffer) -> string {
	if b == nil {
		return "<nil>";
	}
	return string(b.buf[b.off:]);
}

buffer_is_empty :: proc(b: ^Buffer) -> bool {
	return len(b.buf) <= b.off;
}

buffer_length :: proc(b: ^Buffer) -> int {
	return len(b.buf) - b.off;
}

buffer_capacity :: proc(b: ^Buffer) -> int {
	return cap(b.buf);
}

buffer_reset :: proc(b: ^Buffer) {
	clear(&b.buf);
	b.off = 0;
	b.last_read = .Invalid;
}


buffer_truncate :: proc(b: ^Buffer, n: int) {
	if n == 0 {
		buffer_reset(b);
		return;
	}
	b.last_read = .Invalid;
	if n < 0 || n > buffer_length(b) {
		panic("bytes.truncate: truncation out of range");
	}
	resize(&b.buf, b.off+n);
}

@(private)
_buffer_try_grow :: proc(b: ^Buffer, n: int) -> (int, bool) {
	if l := len(b.buf); n <= cap(b.buf)-l {
		resize(&b.buf, l+n);
		return l, true;
	}
	return 0, false;
}

@(private)
_buffer_grow :: proc(b: ^Buffer, n: int) -> int {
	m := buffer_length(b);
	if m == 0 && b.off != 0 {
		buffer_reset(b);
	}
	if i, ok := _buffer_try_grow(b, n); ok {
		return i;
	}
	if b.buf == nil && n <= SMALL_BUFFER_SIZE {
		b.buf = make([dynamic]byte, n, SMALL_BUFFER_SIZE);
		return 0;
	}

	c := cap(b.buf);
	if n <= c/2 - m {
		copy(b.buf[:], b.buf[b.off:]);
	} else if c > max(int) - c - n {
		panic("bytes.Buffer: too large");
	} else {
		resize(&b.buf, 2*c + n);
		copy(b.buf[:], b.buf[b.off:]);
	}
	b.off = 0;
	resize(&b.buf, m+n);
	return m;
}

buffer_grow :: proc(b: ^Buffer, n: int) {
	if n < 0 {
		panic("bytes.buffer_grow: negative count");
	}
	m := _buffer_grow(b, n);
	resize(&b.buf, m);
}

buffer_write_at :: proc(b: ^Buffer, p: []byte, offset: int) -> (n: int, err: io.Error) {
	b.last_read = .Invalid;
	if offset < 0 {
		err = .Invalid_Offset;
		return;
	}
	_, ok := _buffer_try_grow(b, offset+len(p));
	if !ok {
		_ = _buffer_grow(b, offset+len(p));
	}
	if len(b.buf) <= offset {
		return 0, .Short_Write;
	}
	return copy(b.buf[offset:], p), nil;
}


buffer_write :: proc(b: ^Buffer, p: []byte) -> (n: int, err: io.Error) {
	b.last_read = .Invalid;
	m, ok := _buffer_try_grow(b, len(p));
	if !ok {
		m = _buffer_grow(b, len(p));
	}
	return copy(b.buf[m:], p), nil;
}

buffer_write_string :: proc(b: ^Buffer, s: string) -> (n: int, err: io.Error) {
	b.last_read = .Invalid;
	m, ok := _buffer_try_grow(b, len(s));
	if !ok {
		m = _buffer_grow(b, len(s));
	}
	return copy(b.buf[m:], s), nil;
}

buffer_write_byte :: proc(b: ^Buffer, c: byte) -> io.Error {
	b.last_read = .Invalid;
	m, ok := _buffer_try_grow(b, 1);
	if !ok {
		m = _buffer_grow(b, 1);
	}
	b.buf[m] = c;
	return nil;
}

buffer_write_rune :: proc(b: ^Buffer, r: rune) -> (n: int, err: io.Error) {
	if r < utf8.RUNE_SELF {
		buffer_write_byte(b, byte(r));
		return 1, nil;
	}
	b.last_read = .Invalid;
	m, ok := _buffer_try_grow(b, utf8.UTF_MAX);
	if !ok {
		m = _buffer_grow(b, utf8.UTF_MAX);
	}
	res: [4]byte;
	res, n = utf8.encode_rune(r);
	copy(b.buf[m:][:utf8.UTF_MAX], res[:n]);
	resize(&b.buf, m+n);
	return;
}

buffer_next :: proc(b: ^Buffer, n: int) -> []byte {
	n := n;
	b.last_read = .Invalid;
	m := buffer_length(b);
	if n > m {
		n = m;
	}
	data := b.buf[b.off : b.off + n];
	b.off += n;
	if n > 0 {
		b.last_read = .Read;
	}
	return data;
}

buffer_read :: proc(b: ^Buffer, p: []byte) -> (n: int, err: io.Error) {
	b.last_read = .Invalid;
	if buffer_is_empty(b) {
		buffer_reset(b);
		if len(p) == 0 {
			return 0, nil;
		}
		return 0, .EOF;
	}
	n = copy(p, b.buf[b.off:]);
	b.off += n;
	if n > 0 {
		b.last_read = .Read;
	}
	return;
}

buffer_read_at :: proc(b: ^Buffer, p: []byte, offset: int) -> (n: int, err: io.Error) {
	b.last_read = .Invalid;

	if offset < 0 || offset >= len(b.buf) {
		err = .Invalid_Offset;
		return;
	}

	if 0 <= offset && offset < len(b.buf) {
		n = copy(p, b.buf[offset:]);
	}
	if n > 0 {
		b.last_read = .Read;
	}
	return;
}


buffer_read_byte :: proc(b: ^Buffer) -> (byte, io.Error) {
	if buffer_is_empty(b) {
		buffer_reset(b);
		return 0, .EOF;
	}
	c := b.buf[b.off];
	b.off += 1;
	b.last_read = .Read;
	return c, nil;
}

buffer_read_rune :: proc(b: ^Buffer) -> (r: rune, size: int, err: io.Error) {
	if buffer_is_empty(b) {
		buffer_reset(b);
		return 0, 0, .EOF;
	}
	c := b.buf[b.off];
	if c < utf8.RUNE_SELF {
		b.off += 1;
		b.last_read = .Read_Rune1;
		return rune(c), 1, nil;
	}
	r, size = utf8.decode_rune(b.buf[b.off:]);
	b.off += size;
	b.last_read = Read_Op(i8(size));
	return;
}

buffer_unread_byte :: proc(b: ^Buffer) -> io.Error {
	if b.last_read == .Invalid {
		return .Invalid_Unread;
	}
	b.last_read = .Invalid;
	if b.off > 0 {
		b.off -= 1;
	}
	return nil;
}

buffer_unread_rune :: proc(b: ^Buffer) -> io.Error {
	if b.last_read <= .Invalid {
		return .Invalid_Unread;
	}
	if b.off >= int(b.last_read) {
		b.off -= int(i8(b.last_read));
	}
	b.last_read = .Invalid;
	return nil;
}


buffer_read_bytes :: proc(b: ^Buffer, delim: byte) -> (line: []byte, err: io.Error) {
	i := index_byte(b.buf[b.off:], delim);
	end := b.off + i + 1;
	if i < 0 {
		end = len(b.buf);
		err = .EOF;
	}
	line = b.buf[b.off:end];
	b.off = end;
	b.last_read = .Read;
	return;
}

buffer_read_string :: proc(b: ^Buffer, delim: byte) -> (line: string, err: io.Error) {
	slice: []byte;
	slice, err = buffer_read_bytes(b, delim);
	return string(slice), err;
}

buffer_write_to :: proc(b: ^Buffer, w: io.Writer) -> (n: i64, err: io.Error) {
	b.last_read = .Invalid;
	if byte_count := buffer_length(b); byte_count > 0 {
		m, e := io.write(w, b.buf[b.off:]);
		if m > byte_count {
			panic("bytes.buffer_write_to: invalid io.write count");
		}
		b.off += m;
		n = i64(m);
		if e != nil {
			err = e;
			return;
		}
		if m != byte_count {
			err = .Short_Write;
			return;
		}
	}
	buffer_reset(b);
	return;
}

buffer_read_from :: proc(b: ^Buffer, r: io.Reader) -> (n: i64, err: io.Error) #no_bounds_check {
	b.last_read = .Invalid;
	for {
		i := _buffer_grow(b, MIN_READ);
		resize(&b.buf, i);
		m, e := io.read(r, b.buf[i:cap(b.buf)]);
		if m < 0 {
			err = .Negative_Read;
			return;
		}

		resize(&b.buf, i+m);
		n += i64(m);
		if e == .EOF {
			return;
		}
		if e != nil {
			err = e;
			return;
		}
	}
	return;
}


buffer_to_stream :: proc(b: ^Buffer) -> (s: io.Stream) {
	s.stream_data = b;
	s.stream_vtable = _buffer_vtable;
	return;
}

@(private)
_buffer_vtable := &io.Stream_VTable{
	impl_size = proc(s: io.Stream) -> i64 {
		b := (^Buffer)(s.stream_data);
		return i64(buffer_capacity(b));
	},
	impl_read = proc(s: io.Stream, p: []byte) -> (n: int, err: io.Error) {
		b := (^Buffer)(s.stream_data);
		return buffer_read(b, p);
	},
	impl_read_at = proc(s: io.Stream, p: []byte, offset: i64) -> (n: int, err: io.Error) {
		b := (^Buffer)(s.stream_data);
		return buffer_read_at(b, p, int(offset));
	},
	impl_read_byte = proc(s: io.Stream) -> (byte, io.Error) {
		b := (^Buffer)(s.stream_data);
		return buffer_read_byte(b);
	},
	impl_read_rune = proc(s: io.Stream) -> (r: rune, size: int, err: io.Error) {
		b := (^Buffer)(s.stream_data);
		return buffer_read_rune(b);
	},
	impl_write = proc(s: io.Stream, p: []byte) -> (n: int, err: io.Error) {
		b := (^Buffer)(s.stream_data);
		return buffer_write(b, p);
	},
	impl_write_at = proc(s: io.Stream, p: []byte, offset: i64) -> (n: int, err: io.Error) {
		b := (^Buffer)(s.stream_data);
		return buffer_write_at(b, p, int(offset));
	},
	impl_write_byte = proc(s: io.Stream, c: byte) -> io.Error {
		b := (^Buffer)(s.stream_data);
		return buffer_write_byte(b, c);
	},
	impl_write_rune = proc(s: io.Stream, r: rune) -> (int, io.Error) {
		b := (^Buffer)(s.stream_data);
		return buffer_write_rune(b, r);
	},
	impl_unread_byte = proc(s: io.Stream) -> io.Error {
		b := (^Buffer)(s.stream_data);
		return buffer_unread_byte(b);
	},
	impl_unread_rune = proc(s: io.Stream) -> io.Error {
		b := (^Buffer)(s.stream_data);
		return buffer_unread_rune(b);
	},
	impl_destroy = proc(s: io.Stream) -> io.Error {
		b := (^Buffer)(s.stream_data);
		buffer_destroy(b);
		return nil;
	},
	impl_write_to = proc(s: io.Stream, w: io.Writer) -> (n: i64, err: io.Error) {
		b := (^Buffer)(s.stream_data);
		return buffer_write_to(b, w);
	},
	impl_read_from = proc(s: io.Stream, r: io.Reader) -> (n: i64, err: io.Error) {
		b := (^Buffer)(s.stream_data);
		return buffer_read_from(b, r);
	},
};