#!/usr/bin/env python
# 9p/generate - Generate C marshalers/unmarshalers for a .txt file
#               defining a 9P protocol variant.
#
# Copyright (C) 2024  Luke T. Shumaker <lukeshu@lukeshu.com>
# SPDX-Licence-Identifier: AGPL-3.0-or-later

import enum
import re

PROGRAM = "./9p/generate"

# Parse the *.txt ##############################################################


class Atom(enum.Enum):
    u8 = 1
    u16 = 2
    u32 = 4
    u64 = 8

    @property
    def name(self) -> str:
        return str(self.value)

    @property
    def static_size(self) -> int:
        return self.value


# `msgid/structname = "member1 member2..."`
# `structname = "member1 member2..."`
# `structname += "member1 member2..."`
class Struct:
    msgid: int | None = None
    name: str
    members: list["Member"]

    @property
    def static_size(self) -> int | None:
        size = 0
        for member in self.members:
            msize = member.static_size
            if msize is None:
                return None
            size += msize
        return size


# `cnt*(name[typ])`
# the `cnt*(...)` wrapper is optional
class Member:
    cnt: str | None = None
    name: str
    typ: Atom | Struct

    @property
    def static_size(self) -> int | None:
        if self.cnt:
            return None
        return self.typ.static_size


re_membername = "(?:[a-zA-Z_][a-zA-Z_0-9]*)"
re_memberspec = (
    f"(?:(?P<cnt>{re_membername})\\*\\()?(?P<name>{re_membername})\\[(?P<typ>.*)\\]\\)?"
)


def parse_members(
    env: dict[str, Atom | Struct], existing: list[Member], specs: str
) -> list[Member]:
    ret = existing
    for spec in specs.split():
        m = re.fullmatch(re_memberspec, spec)
        if not m:
            raise SyntaxError(f"invalid member spec {repr(spec)}")

        member = Member()

        member.name = m.group("name")
        if any(x.name == member.name for x in ret):
            raise ValueError(f"duplicate member name {repr(member.name)}")

        if m.group("typ") not in env:
            raise NameError(f"Unknown type {repr(m.group(2))}")
        member.typ = env[m.group("typ")]

        if cnt := m.group("cnt"):
            if len(ret) == 0 or ret[-1].name != cnt:
                raise ValueError(f"list count must be previous item: {repr(cnt)}")
            if not isinstance(ret[-1].typ, Atom):
                raise ValueError(f"list count must be an integer type: {repr(cnt)}")
            member.cnt = cnt

        ret += [member]
    return ret


re_version = r'version\s+"(?P<version>[^"]+)"'
re_structspec = (
    r'(?:(?P<msgid>[0-9]+)/)?(?P<name>\S+)\s*(?P<op>\+?=)\s*"(?P<members>[^"]*)"'
)
re_structspec_cont = r'"(?P<members>[^"]*)"'


def parse_file(filename: str) -> tuple[str, list[Struct]]:
    version: str | None = None
    env: dict[str, Atom | Struct] = {
        "1": Atom.u8,
        "2": Atom.u16,
        "4": Atom.u32,
        "8": Atom.u64,
    }
    with open(filename, "r") as fh:
        prev: Struct | None = None
        for line in fh:
            line = line.split("#", 1)[0].strip()
            if not line:
                continue
            if m := re.fullmatch(re_version, line):
                if version:
                    raise SyntaxError("must have exactly 1 version line")
                version = m.group("version")
            elif m := re.fullmatch(re_structspec, line):
                if m.group("op") == "+=" and m.group("msgid"):
                    raise SyntaxError("cannot += to a message that is not yet defined")
                match m.group("op"):
                    case "=":
                        struct = Struct()
                        if m.group("msgid"):
                            struct.msgid = int(m.group("msgid"))
                        struct.name = m.group("name")
                        struct.members = parse_members(env, [], m.group("members"))
                        env[struct.name] = struct
                        prev = struct
                    case "+=":
                        if m.group("name") not in env:
                            raise NameError(f"Unknown type {repr(m.group('name'))}")
                        _struct = env[m.group("name")]
                        if not isinstance(_struct, Struct):
                            raise NameError(
                                f"Type {repr(m.group('name'))} is not a struct"
                            )
                        struct = _struct
                        struct.members = parse_members(
                            env, struct.members, m.group("members")
                        )
                        prev = struct
            elif m := re.fullmatch(re_structspec_cont, line):
                if not prev:
                    raise SyntaxError("continuation line must come after a struct line")
                prev.members = parse_members(env, prev.members, m.group("members"))
            else:
                raise SyntaxError(f"invalid line {repr(line)}")
    if not version:
        raise SyntaxError("must have exactly 1 version line")
    structs = [x for x in env.values() if isinstance(x, Struct)]
    return version, structs


# Generate C ###################################################################


def c_typename(idprefix: str, typ: Atom | Struct) -> str:
    match typ:
        case Atom():
            return f"uint{typ.value*8}_t"
        case Struct():
            if typ.msgid is not None:
                return f"struct {idprefix}msg_{typ.name}"
            return f"struct {idprefix}{typ.name}"
        case _:
            raise ValueError(f"not a type: {typ.__class__.__name__}")


def gen_h(txtname: str, idprefix: str, structs: list[Struct]) -> str:
    guard = (
        "_"
        + txtname.replace(".txt", ".h").upper().replace("/", "_").replace(".", "_")
        + "_"
    )
    ret = f"""/* Generated by `{PROGRAM} {txtname}`.  DO NOT EDIT!  */

#ifndef {guard}
#define {guard}

#define {idprefix.upper()}MIN_MSGLEN 7
"""
    ret += """
/* non-message structs ********************************************************/

"""
    for struct in structs:
        if struct.msgid is not None:
            continue
        ret += c_typename(idprefix, struct) + " {\n"
        typewidth = max(
            len(c_typename(idprefix, member.typ)) for member in struct.members
        )
        for member in struct.members:
            ret += f"\t{c_typename(idprefix, member.typ).ljust(typewidth)}  {'*' if member.cnt else ' '}{member.name};\n"
        ret += "};\n"

    ret += """
/* message types **************************************************************/

"""
    ret += f"enum {idprefix}msg_type {{ /* uint8_t */\n"
    namewidth = max(len(msg.name) for msg in structs if msg.msgid is not None)
    for msg in structs:
        if msg.msgid is None:
            continue
        ret += f"\t{idprefix.upper()}TYP_{msg.name.ljust(namewidth)} = {msg.msgid},\n"
    ret += "};\n"

    ret += """
/* message structs ************************************************************/

"""
    for msg in structs:
        if msg.msgid is None:
            continue
        if not msg.members:
            ret += c_typename(idprefix, msg) + " {};\n"
            continue
        ret += c_typename(idprefix, msg) + " {\n"
        typewidth = max(len(c_typename(idprefix, member.typ)) for member in msg.members)
        for member in msg.members:
            ret += f"\t{c_typename(idprefix, member.typ).ljust(typewidth)}  {'*' if member.cnt else ' '}{member.name};\n"
        ret += "};\n"

    ret += f"""
/* functions ******************************************************************/

/**
 * @param net_bytes : the complete request, starting with the "size[4]"
 * @param out_tag : the message-ID tag
 * @param out_body : a pointer that get set to the parsed body, whose
 *                   type is known by the return value, will need to
 *                   be free()d
 * @return -{idprefix.upper()}E{{error}} on error, {idprefix.upper()}TYP_{{type}} on success
 */
int {idprefix}unmarshal_msg(uint8_t *net_bytes, uint16_t *out_tag, void **out_body);

/**
 * @param uint16_t in_msgid : the message-ID tag
 * @param struct {idprefix}msg_{{type}} in_msg : the message to encode
 * @param uint8_t *out_buf : the buffer to encode to
 * @return uint32_t : the encoded length
 */
#define {idprefix}marshal_msg(in_msgid, in_msg, out_buf) _Generic((in_msg)"""
    for msg in structs:
        if msg.msgid is None:
            continue
        ret += f", \\\n\t\t{c_typename(idprefix, msg)}: _{idprefix}marshal_{msg.name}(in_msgid, in_msg, out_buf)"
    ret += "\\\n\t)(in_msg)\n"
    for msg in structs:
        if msg.msgid is None:
            continue
        ret += f"uint32_t _{idprefix}marshal_{msg.name}(uint16_t in_msgid, {c_typename(idprefix, msg)} in_msg, uint8_t *out_buf);\n"

    ret += "\n"
    ret += f"#endif /* {guard} */\n"
    return ret


def gen_c(txtname: str, idprefix: str, structs: list[Struct]) -> str:
    ret = f"""/* Generated by `{PROGRAM} {txtname}`.  DO NOT EDIT!  */

#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h> /* for malloc() */

#include "{txtname.replace('.txt', '.h')}"
"""

    # basic utilities ##########################################################
    ret += """
/* basic utilities ************************************************************/

#define UNUSED(name) /* name __attribute__ ((unused)) */

static inline uint8_t decode_u8le(uint8_t *in) {
	return in[0];
}
static inline uint16_t decode_u16le(uint8_t *in) {
	return (((uint16_t)(in[0])) <<	0)
		 | (((uint16_t)(in[1])) <<	8)
		 ;
}
static inline uint32_t decode_u32le(uint8_t *in) {
	return (((uint32_t)(in[0])) <<	0)
		 | (((uint32_t)(in[1])) <<	8)
		 | (((uint32_t)(in[2])) << 16)
		 | (((uint32_t)(in[3])) << 24)
		 ;
}
static inline uint64_t decode_u64le(uint8_t *in) {
	return (((uint64_t)(in[0])) <<	0)
		 | (((uint64_t)(in[1])) <<	8)
		 | (((uint64_t)(in[2])) << 16)
		 | (((uint64_t)(in[3])) << 24)
		 | (((uint64_t)(in[4])) << 32)
		 | (((uint64_t)(in[5])) << 40)
		 | (((uint64_t)(in[6])) << 48)
		 | (((uint64_t)(in[7])) << 56)
		 ;
}

static inline void encode_u8le(uint8_t in, uint8_t *out) {
	out[0] = in;
}
static inline void encode_u16le(uint16_t in, uint8_t *out) {
	out[0] = (uint8_t)((in >>  0) & 0xFF);
	out[1] = (uint8_t)((in >>  8) & 0xFF);
}
static inline void encode_u32le(uint32_t in, uint8_t *out) {
	out[0] = (uint8_t)((in >>  0) & 0xFF);
	out[1] = (uint8_t)((in >>  8) & 0xFF);
	out[2] = (uint8_t)((in >> 16) & 0xFF);
	out[3] = (uint8_t)((in >> 24) & 0xFF);
}
static inline void encode_u64le(uint64_t in, uint8_t *out) {
	out[0] = (uint8_t)((in >>  0) & 0xFF);
	out[1] = (uint8_t)((in >>  8) & 0xFF);
	out[2] = (uint8_t)((in >> 16) & 0xFF);
	out[3] = (uint8_t)((in >> 24) & 0xFF);
	out[4] = (uint8_t)((in >> 32) & 0xFF);
	out[5] = (uint8_t)((in >> 40) & 0xFF);
	out[6] = (uint8_t)((in >> 48) & 0xFF);
	out[7] = (uint8_t)((in >> 56) & 0xFF);
}
"""

    def used(arg: str) -> str:
        return arg

    def unused(arg: str) -> str:
        return f"UNUSED({arg})"

    # checksize_* ##############################################################
    ret += """
/* checksize_* ****************************************************************/

typedef bool (*_checksize_fn_t)(uint32_t net_len, uint8_t *net_bytes, uint32_t *mut_net_offset, size_t *mut_host_extra);
static inline bool _checksize_list(size_t cnt, _checksize_fn_t fn, size_t host_size,
                                   uint32_t net_len, uint8_t *net_bytes, uint32_t *mut_net_offset, size_t *mut_host_extra) {
	for (size_t i = 0; i < cnt; i++)
		if (__builtin_add_overflow(*mut_host_extra, host_size, mut_host_extra)
		 || fn(net_len, net_bytes, mut_net_offset, mut_host_extra))
			return true;
	return false;
}
static inline bool checksize_1(uint32_t net_len, uint8_t *UNUSED(net_bytes), uint32_t *mut_net_offset, size_t *UNUSED(mut_host_extra)) {
	return __builtin_add_overflow(*mut_net_offset, 1, mut_net_offset) || net_len < *mut_net_offset;
}
static inline bool checksize_2(uint32_t net_len, uint8_t *UNUSED(net_bytes), uint32_t *mut_net_offset, size_t *UNUSED(mut_host_extra)) {
	return __builtin_add_overflow(*mut_net_offset, 2, mut_net_offset) || net_len < *mut_net_offset;
}
static inline bool checksize_4(uint32_t net_len, uint8_t *UNUSED(net_bytes), uint32_t *mut_net_offset, size_t *UNUSED(mut_host_extra)) {
	return __builtin_add_overflow(*mut_net_offset, 4, mut_net_offset) || net_len < *mut_net_offset;
}
static inline bool checksize_8(uint32_t net_len, uint8_t *UNUSED(net_bytes), uint32_t *mut_net_offset, size_t *UNUSED(mut_host_extra)) {
	return __builtin_add_overflow(*mut_net_offset, 8, mut_net_offset) || net_len < *mut_net_offset;
}
"""
    for struct in structs:
        argfn = used if struct.members else unused
        ret += f"static inline bool checksize_{struct.name}(uint32_t {argfn('net_len')}, uint8_t *{argfn('net_bytes')}, uint32_t *{argfn('mut_net_offset')}, size_t *{argfn('mut_host_extra')}) {{\n"
        if len(struct.members) == 0:
            ret += "\treturn false;\n"
            ret += "}\n"
            continue
        prefix0 = "\treturn "
        prefix1 = "\t    || "
        prefix2 = "\t       "
        prefix = prefix0
        prev_size: int | None = None
        for member in struct.members:
            if member.cnt is not None:
                assert prev_size
                ret += f"\n{prefix }_checksize_list(decode_u{prev_size*8}le(&net_bytes[(*mut_net_offset)-{prev_size}]), checksize_{member.typ.name}, sizeof({c_typename(idprefix, member.typ)}),"
                ret += f"\n{prefix2}                net_len, net_bytes, mut_net_offset, mut_host_extra)"
            else:
                ret += f"\n{prefix}checksize_{member.typ.name}(net_len, net_bytes, mut_net_offset, mut_host_extra)"
            prefix = prefix1
            prev_size = member.static_size
        if struct.name == "s":
            ret += (
                f"\n{prefix}__builtin_add_overflow(*mut_host_extra, 1, mut_host_extra)"
            )
        ret += ";\n}\n"

    # unmarshal_* ##############################################################
    ret += """
/* unmarshal_* ****************************************************************/
/* checksize_XXX() should be called before unmarshal_XXX().  */

static inline void unmarshal_1(uint8_t *net_bytes, uint32_t *mut_net_offset, void **UNUSED(mut_host_extra), uint8_t *out) {
	*out = decode_u8le(&net_bytes[*mut_net_offset]);
	*mut_net_offset += 1;
}
static inline void unmarshal_2(uint8_t *net_bytes, uint32_t *mut_net_offset, void **UNUSED(mut_host_extra), uint16_t *out) {
	*out = decode_u16le(&net_bytes[*mut_net_offset]);
	*mut_net_offset += 2;
}
static inline void unmarshal_4(uint8_t *net_bytes, uint32_t *mut_net_offset, void **UNUSED(mut_host_extra), uint32_t *out) {
	*out = decode_u32le(&net_bytes[*mut_net_offset]);
	*mut_net_offset += 4;
}
static inline void unmarshal_8(uint8_t *net_bytes, uint32_t *mut_net_offset, void **UNUSED(mut_host_extra), uint64_t *out) {
	*out = decode_u64le(&net_bytes[*mut_net_offset]);
	*mut_net_offset += 8;
}
"""
    for struct in structs:
        argfn = used if struct.members else unused
        ret += f"static inline void unmarshal_{struct.name}(uint8_t *{argfn('net_bytes')}, uint32_t *{argfn('mut_net_offset')}, void **{argfn('mut_host_extra')}, {c_typename(idprefix, struct)} *{argfn('out')}) {{"
        if len(struct.members) == 0:
            ret += "}\n"
            continue
        ret += "\n"
        for member in struct.members:
            if member.cnt:
                ret += f"\tout->{member.name} = *mut_host_extra;\n"
                ret += f"\t*mut_host_extra += sizeof(*out->{member.name}) * out->{member.cnt};\n"
                ret += f"\tfor (typeof(out->{member.cnt}) i = 0; i < out->{member.cnt}; i++)\n"
                ret += f"\t\tunmarshal_{member.typ.name}(net_bytes, mut_net_offset, mut_host_extra, &(out->{member.name}[i]));\n"
            else:
                ret += f"\tunmarshal_{member.typ.name}(net_bytes, mut_net_offset, mut_host_extra, &(out->{member.name}));\n"
        ret += "}\n"

    # unmarshal_msg ############################################################
    ret += f"""
/* unmarshal_msg **************************************************************/

int {idprefix}unmarshal_msg(uint8_t *net_bytes, uint16_t *out_tag, void **out_body) {{
	uint32_t net_len = decode_u32le(net_bytes);
	if (net_len < 7)
		return -LINUX_EWRONGSIZE;
	uint8_t typ = net_bytes[4];
	*out_tag = decode_u16le(&net_bytes[5]);

	uint32_t net_offset = 7;
	size_t host_size;
	void *host_extra;
	switch (typ) {{
"""
    for msg in structs:
        if msg.msgid is None:
            continue
        ret += f"\tcase {idprefix.upper()}TYP_{msg.name}:\n"
        ret += f"\t\thost_size = sizeof({c_typename(idprefix, msg)});\n"
        ret += f"\t\tif (checksize_{msg.name}(net_len, net_bytes, &net_offset, &host_size))\n"
        ret += "\t\t\treturn -LINUX_EWRONGSIZE;\n"
        ret += "\n"
        ret += "\t\t*out_body = malloc(host_size);"
        ret += "\n"
        ret += "\t\tnet_offset = 7;\n"
        ret += f"\t\thost_extra = *out_body + sizeof({c_typename(idprefix, msg)});\n"
        ret += f"\t\tunmarshal_{msg.name}(net_bytes, &net_offset, &host_extra, *out_body);\n"
        ret += "\n"
        ret += "\t\tbreak;\n"
    ret += """
	default:
		return -LINUX_EOPNOTSUPP;
	}
	return typ;
}
"""

    # marshal_* ################################################################
    ret += """
/* marshal_* ******************************************************************/

static inline void marshal_1(uint8_t val, uint8_t *out_net_bytes, uint32_t *mut_net_offset) {
    out_net_bytes[*mut_net_offset] = val;
	*mut_net_offset += 1;
}
static inline void marshal_2(uint16_t val, uint8_t *out_net_bytes, uint32_t *mut_net_offset) {
	encode_u16le(val, &out_net_bytes[*mut_net_offset]);
	*mut_net_offset += 2;
}
static inline void marshal_4(uint32_t val, uint8_t *out_net_bytes, uint32_t *mut_net_offset) {
	encode_u32le(val, &out_net_bytes[*mut_net_offset]);
	*mut_net_offset += 4;
}
static inline void marshal_8(uint64_t val, uint8_t *out_net_bytes, uint32_t *mut_net_offset) {
	encode_u64le(val, &out_net_bytes[*mut_net_offset]);
	*mut_net_offset += 8;
}
"""
    for struct in structs:
        argfn = used if struct.members else unused
        ret += f"static inline void marshal_{struct.name}({c_typename(idprefix, struct)} {argfn('val')}, uint8_t *{argfn('out_net_bytes')}, uint32_t *{argfn('mut_net_offset')}) {{"
        if len(struct.members) == 0:
            ret += "}\n"
            continue
        ret += "\n"
        for member in struct.members:
            if member.cnt:
                ret += f"\tfor (typeof(val.{member.cnt}) i = 0; i < val.{member.cnt}; i++)\n"
                ret += f"\t\tmarshal_{member.typ.name}(val.{member.name}[i], out_net_bytes, mut_net_offset);\n"
            else:
                ret += f"\tmarshal_{member.typ.name}(val.{member.name}, out_net_bytes, mut_net_offset);\n"
        ret += "}\n"

    # _marshal_msg_* ###########################################################
    ret += """
/* _marshal_msg_* *************************************************************/

"""
    for msg in structs:
        if msg.msgid is None:
            continue
        ret += f"uint32_t _{idprefix}marshal_{msg.name}(uint16_t in_msgid, {c_typename(idprefix, msg)} in_msg, uint8_t *out_buf) {{\n"
        ret += "\tuint32_t offset = 4;\n"
        ret += f"\tmarshal_1({idprefix.upper()}TYP_{msg.name}, out_buf, &offset);\n"
        ret += "\tmarshal_2(in_msgid, out_buf, &offset);\n"
        ret += f"\tmarshal_{msg.name}(in_msg, out_buf, &offset);\n"
        ret += "\tencode_u32le(offset, out_buf);\n"
        ret += "\treturn offset;\n"
        ret += "}\n"
    ret += "\n"

    ############################################################################
    return ret


################################################################################

if __name__ == "__main__":
    import sys

    for txtname in sys.argv[1:]:
        version, structs = parse_file(txtname)
        with open(txtname.replace(".txt", ".h"), "w") as fh:
            fh.write(gen_h(txtname, "p9_", structs))
        with open(txtname.replace(".txt", ".c"), "w") as fh:
            fh.write(gen_c(txtname, "p9_", structs))