#!/usr/bin/env python3
"""Emit core/generated/velox_proto.{hpp,cpp} from contracts/schema/.

Design notes that matter to the CORE and DAEMON lanes:

* **No exceptions.** nlohmann's own throwing `get<T>()` / ADL `from_json` are deliberately
  not used and not emitted. Parsing goes through `velox::proto::parse<T>(json)` which
  returns `std::expected<T, ParseError>`, so a malformed frame from the wire is an ordinary
  value the RPC loop handles, not a throw unwinding through the transfer path.
* **Serialisation is ADL `to_json`,** so `nlohmann::json j = task;` works as expected.
  Only the outbound direction is allowed to be implicit; the wire is never trusted.
* **`libveloxproto`, not `libveloxcore`.** This code includes nlohmann/json, which
  CLAUDE.md forbids inside core. It is a separate target that core and daemon both link;
  the layering rule constrains `libveloxcore`, and `core/generated/` is not part of it.
  See docs/adr/0009-generated-protocol-library.md.

Run: python3 contracts/codegen/gen_cpp.py
"""

from __future__ import annotations

import json
import sys
from pathlib import Path

sys.path.insert(0, str(Path(__file__).resolve().parent))

from schema_ir import Contract, Field, TypeDef, TypeRef, load, pascal, topo_sorted  # noqa: E402

OUT_DIR = Path(__file__).resolve().parent.parent.parent / "core" / "generated"

BANNER = """// ---------------------------------------------------------------------------
// GENERATED FILE — DO NOT EDIT.
//
// Source:    contracts/schema/**
// Generator: contracts/codegen/gen_cpp.py
// Contract:  v{version}
//
// Hand-editing this file is a merge blocker. Fix the schema and regenerate:
//     python3 contracts/codegen/gen_cpp.py
// Only lane PROTO commits to contracts/.
// ---------------------------------------------------------------------------
"""


def cpp_type(ref: TypeRef) -> str:
    if ref.kind == "named":
        return ref.name or "void"
    if ref.kind == "string":
        return "std::string"
    if ref.kind == "integer":
        return "std::int64_t"
    if ref.kind == "number":
        return "double"
    if ref.kind == "boolean":
        return "bool"
    if ref.kind == "json":
        return "nlohmann::json"
    if ref.kind == "array":
        return f"std::vector<{cpp_type(ref.inner)}>"
    if ref.kind == "map":
        return f"std::map<std::string, {cpp_type(ref.inner)}>"
    raise AssertionError(ref.kind)


def cpp_constraints(ref: TypeRef, var: str, path: str, indent: str) -> list[str]:
    """Range, length and pattern checks. The wire is untrusted: a `maximum` in the schema
    has to be a check here, or -32602 would never fire for an out-of-range value."""
    lim = ref.limits
    if not lim:
        return []
    i = indent
    o: list[str] = []

    def bail(msg: str) -> str:
        return f'return std::unexpected(ParseError{{std::string({path}), "{msg}"}});'

    if ref.kind in ("integer", "number"):
        if "minimum" in lim:
            o.append(f'{i}if ({var} < {lim["minimum"]}) {bail("value is below the minimum of " + str(lim["minimum"]))}')
        if "maximum" in lim:
            o.append(f'{i}if ({var} > {lim["maximum"]}) {bail("value is above the maximum of " + str(lim["maximum"]))}')
    elif ref.kind == "string":
        if "minLength" in lim:
            o.append(f'{i}if ({var}.size() < {lim["minLength"]}u) {bail("value is shorter than " + str(lim["minLength"]) + " characters")}')
        if "maxLength" in lim:
            o.append(f'{i}if ({var}.size() > {lim["maxLength"]}u) {bail("value is longer than " + str(lim["maxLength"]) + " characters")}')
        if "pattern" in lim:
            lit = json.dumps(lim["pattern"])
            o.append(f"{i}{{")
            o.append(f"{i}    static const std::regex re({lit}, std::regex::ECMAScript);")
            o.append(f'{i}    if (!std::regex_match({var}, re)) {bail("value does not match the required pattern")}')
            o.append(f"{i}}}")
    elif ref.kind == "array":
        if "minItems" in lim:
            o.append(f'{i}if ({var}.size() < {lim["minItems"]}u) {bail("fewer than " + str(lim["minItems"]) + " items")}')
        if "maxItems" in lim:
            o.append(f'{i}if ({var}.size() > {lim["maxItems"]}u) {bail("more than " + str(lim["maxItems"]) + " items")}')
    return o


def field_type(f: Field) -> str:
    inner = cpp_type(f.type)
    return f"std::optional<{inner}>" if f.optional else inner


def ident(name: str) -> str:
    """A JSON property name as a C++ member name."""
    out = name.replace(".", "_").replace("-", "_")
    reserved = {"class", "delete", "namespace", "operator", "template", "new", "auto"}
    return out + "_" if out in reserved else out


def doc_comment(text: str, indent: str = "") -> list[str]:
    if not text:
        return []
    lines: list[str] = []
    words = text.split()
    cur = ""
    for w in words:
        if len(cur) + len(w) + 1 > 92:
            lines.append(cur)
            cur = w
        else:
            cur = f"{cur} {w}".strip()
    if cur:
        lines.append(cur)
    return [f"{indent}/// {ln}" for ln in lines]


def method_ident(name: str) -> str:
    return pascal(name)


def handler_name(name: str) -> str:
    return "on_" + name.replace(".", "_")


# ------------------------------------------------------------------ header


def emit_header(c: Contract) -> str:
    o: list[str] = [BANNER.format(version=c.version), "#pragma once", ""]
    o += [
        "#include <cstdint>",
        "#include <expected>",
        "#include <map>",
        "#include <optional>",
        "#include <string>",
        "#include <string_view>",
        "#include <vector>",
        "",
        "#include <nlohmann/json.hpp>",
        "",
        "// This is libveloxproto, NOT libveloxcore. The layering rule in CLAUDE.md forbids",
        "// JSON inside the engine; the engine does not link this target. See",
        "// docs/adr/0009-generated-protocol-library.md.",
        "namespace velox::proto {",
        "",
        f'inline constexpr std::string_view kProtocolVersion = "{c.version}";',
        "",
        "/// Why a payload could not be turned into a typed value. `path` is a JSON Pointer",
        "/// into the offending document, so a conformance failure names the exact field.",
        "struct ParseError {",
        "    std::string path;",
        "    std::string message;",
        "};",
        "",
        "/// Every parse in this file returns one of these. Nothing here throws.",
        "template <class T>",
        "using Result = std::expected<T, ParseError>;",
        "",
        "/// Which listener a request arrived on. Decides whether a privileged method is",
        "/// allowed: see `is_allowed_on`.",
        "enum class Transport { Uds, Ws };",
        "",
    ]

    # ---- enums
    for t in topo_sorted(c.types):
        if t.kind == "string_enum":
            o += doc_comment(t.doc)
            o.append(f"enum class {t.name} {{")
            for v in t.values:
                o.append(f"    {v.name},  // \"{v.wire}\"")
            o.append("};")
            o.append(f"std::string_view to_string({t.name} v) noexcept;")
            o.append(f"Result<{t.name}> parse_{t.name}(std::string_view s);")
            o.append("")
        elif t.kind == "int_enum":
            o += doc_comment(t.doc)
            o.append(f"enum class {t.name} : std::int32_t {{")
            for v in t.values:
                o += doc_comment(v.doc, "    ")
                o.append(f"    {v.name} = {v.wire},")
            o.append("};")
            o.append(f"std::string_view to_string({t.name} v) noexcept;")
            o.append(f"std::optional<{t.name}> {t.name.lower()}_from_int(std::int32_t v) noexcept;")
            o.append("")
        elif t.kind == "map_alias":
            o += doc_comment(t.doc)
            o.append(f"using {t.name} = {cpp_type(t.alias)};")
            o.append("")

    # ---- structs
    for t in topo_sorted(c.types):
        if t.kind != "struct":
            continue
        o += doc_comment(t.doc)
        o.append(f"struct {t.name} {{")
        if not t.fields:
            o.append("    // No fields: this method takes no parameters.")
        for f in t.fields:
            o += doc_comment(f.doc, "    ")
            o.append(f"    {field_type(f)} {ident(f.name)}{{}};")
        o.append("};")
        o.append("")

    o += [
        "// --- serialisation ---------------------------------------------------------",
        "// ADL hooks, so `nlohmann::json j = value;` works. Outbound only: there is no",
        "// generated from_json, because nlohmann's inbound path throws and the wire is",
        "// never trusted. Use parse<T> below.",
        "",
    ]
    for t in topo_sorted(c.types):
        if t.kind in ("struct", "string_enum", "int_enum"):
            o.append(f"void to_json(nlohmann::json& j, const {t.name}& v);")
    o.append("")

    o += [
        "// --- parsing ---------------------------------------------------------------",
        "",
        "/// Turn an untrusted JSON value into a typed one. Specialised below for every",
        "/// contract type; the primary template is intentionally not defined, so asking",
        "/// for a type the contract does not have is a compile error, not a runtime one.",
        "template <class T>",
        "Result<T> parse(const nlohmann::json& j, std::string_view path = \"\");",
        "",
    ]
    for t in topo_sorted(c.types):
        if t.kind in ("struct", "string_enum", "int_enum", "map_alias"):
            o.append(f"template <> Result<{t.name}> parse<{t.name}>(const nlohmann::json& j, std::string_view path);")
    o.append("")

    # ---- method / event enums
    o += [
        "// --- method surface --------------------------------------------------------",
        "",
        "/// Every method in the contract. Generated, so a daemon cannot answer a method",
        "/// the contract does not define, and cannot silently fail to answer one it does.",
        "enum class Method {",
    ]
    for m in c.methods:
        o.append(f"    {method_ident(m.name)},  // {m.name}")
    o += ["};", "",
          "inline constexpr std::size_t kMethodCount = " + str(len(c.methods)) + ";",
          "",
          "std::string_view to_string(Method m) noexcept;",
          "std::optional<Method> method_from_string(std::string_view s) noexcept;",
          "",
          "/// True for methods refused over the WebSocket transport with -32003. The",
          "/// extension is not allowed to reconfigure the daemon or destroy user data.",
          "bool is_privileged(Method m) noexcept;",
          "bool is_allowed_on(Method m, Transport t) noexcept;",
          "",
          "/// The contract's answer deadline. capture.offer's 750 ms is the one that",
          "/// matters: past it the extension has already let Firefox take the download.",
          "std::int32_t deadline_ms(Method m) noexcept;",
          ""]

    o += ["/// Server-to-client notifications.", "enum class Event {"]
    for e in c.events:
        o.append(f"    {pascal(e.name[len('event.'):])},  // {e.name}")
    o += ["};", "",
          "std::string_view to_string(Event e) noexcept;",
          "std::optional<Event> event_from_string(std::string_view s) noexcept;",
          "",
          "// --- dispatch --------------------------------------------------------------",
          "",
          "/// Build a JSON-RPC error response. `id` may be null for a request that could",
          "/// not be parsed far enough to have one.",
          "nlohmann::json make_error(const nlohmann::json& id, ErrorCode code, std::string_view message,",
          "                         nlohmann::json data = nullptr);",
          "nlohmann::json make_result(const nlohmann::json& id, nlohmann::json result);",
          "nlohmann::json make_notification(Event e, nlohmann::json params);",
          "",
          "/// One virtual per method. The daemon implements this; `dispatch` below does the",
          "/// envelope handling, the transport check and the parameter parsing, so a handler",
          "/// only ever sees a validated, typed params struct.",
          "class Dispatcher {",
          "public:",
          "    virtual ~Dispatcher() = default;",
          ""]
    for m in c.methods:
        o += doc_comment(m.doc, "    ")
        o.append(f"    virtual Result<{cpp_type(m.result)}> {handler_name(m.name)}(const {cpp_type(m.params)}& params) = 0;")
        o.append("")
    o += ["};", "",
          "/// Parse one JSON-RPC request, route it, and return the response to write back.",
          "/// Never throws. Returns a null json for a notification that needs no reply.",
          "nlohmann::json dispatch(Dispatcher& handler, Transport transport, const nlohmann::json& request);",
          "",
          "}  // namespace velox::proto",
          ""]
    return "\n".join(o)


# ------------------------------------------------------------------ source


def emit_source(c: Contract) -> str:
    o: list[str] = [BANNER.format(version=c.version),
                    '#include "velox_proto.hpp"', "", "#include <algorithm>", "#include <regex>", "",
                    "namespace velox::proto {", "", "namespace {", "",
                    'std::string join(std::string_view path, std::string_view key) {',
                    '    std::string out(path);',
                    '    out += "/";',
                    '    out += key;',
                    '    return out;',
                    '}', "", "}  // namespace", ""]

    # enum conversions
    for t in topo_sorted(c.types):
        if t.kind == "string_enum":
            o.append(f"std::string_view to_string({t.name} v) noexcept {{")
            o.append("    switch (v) {")
            for v in t.values:
                o.append(f'        case {t.name}::{v.name}: return "{v.wire}";')
            o.append("    }")
            o.append('    return "";')
            o.append("}")
            o.append("")
            o.append(f"Result<{t.name}> parse_{t.name}(std::string_view s) {{")
            for v in t.values:
                o.append(f'    if (s == "{v.wire}") return {t.name}::{v.name};')
            o.append(f'    return std::unexpected(ParseError{{"", "not a valid {t.name}: \'" + std::string(s) + "\'"}});')
            o.append("}")
            o.append("")
            o.append(f"void to_json(nlohmann::json& j, const {t.name}& v) {{ j = to_string(v); }}")
            o.append("")
            o.append(f"template <> Result<{t.name}> parse<{t.name}>(const nlohmann::json& j, std::string_view path) {{")
            o.append('    if (!j.is_string()) return std::unexpected(ParseError{std::string(path), "expected a string"});')
            o.append(f"    auto r = parse_{t.name}(j.get_ref<const std::string&>());")
            o.append("    if (!r) return std::unexpected(ParseError{std::string(path), r.error().message});")
            o.append("    return *r;")
            o.append("}")
            o.append("")
        elif t.kind == "int_enum":
            o.append(f"std::string_view to_string({t.name} v) noexcept {{")
            o.append("    switch (v) {")
            for v in t.values:
                o.append(f'        case {t.name}::{v.name}: return "{v.name}";')
            o.append("    }")
            o.append('    return "";')
            o.append("}")
            o.append("")
            o.append(f"std::optional<{t.name}> {t.name.lower()}_from_int(std::int32_t v) noexcept {{")
            o.append("    switch (v) {")
            for v in t.values:
                o.append(f"        case {v.wire}: return {t.name}::{v.name};")
            o.append("        default: return std::nullopt;")
            o.append("    }")
            o.append("}")
            o.append("")
            o.append(f"void to_json(nlohmann::json& j, const {t.name}& v) {{ j = static_cast<std::int32_t>(v); }}")
            o.append("")
            o.append(f"template <> Result<{t.name}> parse<{t.name}>(const nlohmann::json& j, std::string_view path) {{")
            o.append('    if (!j.is_number_integer()) return std::unexpected(ParseError{std::string(path), "expected an integer"});')
            o.append(f"    auto v = {t.name.lower()}_from_int(j.get<std::int32_t>());")
            o.append('    if (!v) return std::unexpected(ParseError{std::string(path), "not a contract error code"});')
            o.append("    return *v;")
            o.append("}")
            o.append("")

    # map aliases: a parse specialisation only. The alias is a std::map, which nlohmann
    # already serialises, so an emitted to_json here would be an ambiguous overload.
    for t in topo_sorted(c.types):
        if t.kind != "map_alias":
            continue
        o.append(f"template <> Result<{t.name}> parse<{t.name}>(const nlohmann::json& j, std::string_view path) {{")
        o += emit_value_parse(t.alias, "j", "out", "path", "    ")
        o.append("    return out;")
        o.append("}")
        o.append("")

    # struct to_json / parse
    for t in topo_sorted(c.types):
        if t.kind != "struct":
            continue
        # A no-parameter method's struct has nothing to read, so the parameter goes
        # unnamed: the project builds with -Wall -Wextra -Werror.
        vname = "v" if t.fields else "/*v*/"
        o.append(f"void to_json(nlohmann::json& j, const {t.name}& {vname}) {{")
        o.append("    j = nlohmann::json::object();")
        for f in t.fields:
            m = ident(f.name)
            if f.optional:
                o.append(f'    if (v.{m}.has_value()) j["{f.name}"] = *v.{m};')
                if f.required:
                    o.append(f'    else j["{f.name}"] = nullptr;')
            else:
                o.append(f'    j["{f.name}"] = v.{m};')
        o.append("}")
        o.append("")

        pname = "path" if t.fields else "/*path*/"
        o.append(f"template <> Result<{t.name}> parse<{t.name}>(const nlohmann::json& j, std::string_view {pname}) {{")
        if t.fields:
            o.append('    if (!j.is_object()) return std::unexpected(ParseError{std::string(path), "expected an object"});')
        else:
            o.append('    if (!j.is_object()) return std::unexpected(ParseError{"", "expected an object"});')
        o.append(f"    {t.name} out;")
        for f in t.fields:
            o += emit_field_parse(f, indent="    ")
        o.append("    return out;")
        o.append("}")
        o.append("")

    o += emit_tables(c)
    o += emit_dispatch(c)
    o += ["}  // namespace velox::proto", ""]
    return "\n".join(o)


def emit_value_parse(ref: TypeRef, src: str, dst: str, path: str, indent: str) -> list[str]:
    """Statements that parse json expression `src` into a fresh variable named `dst`."""
    i = indent
    o: list[str] = []
    if ref.kind == "named":
        o.append(f"{i}auto {dst}_r = parse<{ref.name}>({src}, {path});")
        o.append(f"{i}if (!{dst}_r) return std::unexpected({dst}_r.error());")
        o.append(f"{i}auto {dst} = std::move(*{dst}_r);")
    elif ref.kind == "string":
        o.append(f"{i}if (!{src}.is_string()) return std::unexpected(ParseError{{std::string({path}), \"expected a string\"}});")
        o.append(f"{i}auto {dst} = {src}.get<std::string>();")
    elif ref.kind == "integer":
        o.append(f"{i}if (!{src}.is_number_integer()) return std::unexpected(ParseError{{std::string({path}), \"expected an integer\"}});")
        o.append(f"{i}auto {dst} = {src}.get<std::int64_t>();")
    elif ref.kind == "number":
        o.append(f"{i}if (!{src}.is_number()) return std::unexpected(ParseError{{std::string({path}), \"expected a number\"}});")
        o.append(f"{i}auto {dst} = {src}.get<double>();")
    elif ref.kind == "boolean":
        o.append(f"{i}if (!{src}.is_boolean()) return std::unexpected(ParseError{{std::string({path}), \"expected a boolean\"}});")
        o.append(f"{i}auto {dst} = {src}.get<bool>();")
    elif ref.kind == "json":
        o.append(f"{i}auto {dst} = {src};")
    elif ref.kind == "array":
        et = cpp_type(ref.inner)
        o.append(f"{i}if (!{src}.is_array()) return std::unexpected(ParseError{{std::string({path}), \"expected an array\"}});")
        o.append(f"{i}std::vector<{et}> {dst};")
        o.append(f"{i}{dst}.reserve({src}.size());")
        o.append(f"{i}for (std::size_t idx = 0; idx < {src}.size(); ++idx) {{")
        o.append(f'{i}    const std::string ip = join({path}, std::to_string(idx));')
        o += emit_value_parse(ref.inner, f"{src}[idx]", f"{dst}_e", "ip", i + "    ")
        o.append(f"{i}    {dst}.push_back(std::move({dst}_e));")
        o.append(f"{i}}}")
    elif ref.kind == "map":
        et = cpp_type(ref.inner)
        o.append(f"{i}if (!{src}.is_object()) return std::unexpected(ParseError{{std::string({path}), \"expected an object\"}});")
        o.append(f"{i}std::map<std::string, {et}> {dst};")
        o.append(f"{i}for (const auto& [mk, mv] : {src}.items()) {{")
        o.append(f'{i}    const std::string mp = join({path}, mk);')
        o += emit_value_parse(ref.inner, "mv", f"{dst}_e", "mp", i + "    ")
        o.append(f"{i}    {dst}.emplace(mk, std::move({dst}_e));")
        o.append(f"{i}}}")
    else:
        raise AssertionError(ref.kind)
    o += cpp_constraints(ref, dst, path, indent)
    return o


def emit_field_parse(f: Field, indent: str) -> list[str]:
    i = indent
    m = ident(f.name)
    o = [f'{i}{{',
         f'{i}    const std::string fp = join(path, "{f.name}");',
         f'{i}    const auto it = j.find("{f.name}");']
    if f.optional:
        # Absent and null mean the same thing: the field is not set. A client that omits
        # a nullable field and one that sends null are treated identically on purpose.
        o.append(f"{i}    if (it != j.end() && !it->is_null()) {{")
        o += emit_value_parse(f.type, "(*it)", "val", "fp", i + "        ")
        o.append(f"{i}        out.{m} = std::move(val);")
        o.append(f"{i}    }}")
    else:
        o.append(f"{i}    if (it == j.end() || it->is_null())")
        o.append(f'{i}        return std::unexpected(ParseError{{fp, "required field is missing"}});')
        o += emit_value_parse(f.type, "(*it)", "val", "fp", i + "    ")
        o.append(f"{i}    out.{m} = std::move(val);")
    o.append(f"{i}}}")
    return o


def emit_tables(c: Contract) -> list[str]:
    o = ["std::string_view to_string(Method m) noexcept {", "    switch (m) {"]
    for m in c.methods:
        o.append(f'        case Method::{method_ident(m.name)}: return "{m.name}";')
    o += ["    }", '    return "";', "}", ""]

    o += ["std::optional<Method> method_from_string(std::string_view s) noexcept {"]
    for m in c.methods:
        o.append(f'    if (s == "{m.name}") return Method::{method_ident(m.name)};')
    o += ["    return std::nullopt;", "}", ""]

    o += ["bool is_privileged(Method m) noexcept {", "    switch (m) {"]
    for m in c.methods:
        o.append(f"        case Method::{method_ident(m.name)}: return {str(m.privileged).lower()};")
    o += ["    }", "    return true;  // unknown means refuse", "}", ""]

    o += ["bool is_allowed_on(Method m, Transport t) noexcept {", "    switch (m) {"]
    for m in c.methods:
        uds = "true" if "uds" in m.transports else "false"
        ws = "true" if "ws" in m.transports else "false"
        o.append(f"        case Method::{method_ident(m.name)}: return t == Transport::Uds ? {uds} : {ws};")
    o += ["    }", "    return false;", "}", ""]

    o += ["std::int32_t deadline_ms(Method m) noexcept {", "    switch (m) {"]
    for m in c.methods:
        o.append(f"        case Method::{method_ident(m.name)}: return {m.deadline_ms};")
    o += ["    }", "    return 5000;", "}", ""]

    o += ["std::string_view to_string(Event e) noexcept {", "    switch (e) {"]
    for e in c.events:
        o.append(f'        case Event::{pascal(e.name[len("event."):])}: return "{e.name}";')
    o += ["    }", '    return "";', "}", ""]

    o += ["std::optional<Event> event_from_string(std::string_view s) noexcept {"]
    for e in c.events:
        o.append(f'    if (s == "{e.name}") return Event::{pascal(e.name[len("event."):])};')
    o += ["    return std::nullopt;", "}", ""]
    return o


def emit_dispatch(c: Contract) -> list[str]:
    o = [
        "nlohmann::json make_error(const nlohmann::json& id, ErrorCode code, std::string_view message,",
        "                         nlohmann::json data) {",
        "    nlohmann::json err = {{\"code\", static_cast<std::int32_t>(code)}, {\"message\", std::string(message)}};",
        "    if (!data.is_null()) err[\"data\"] = std::move(data);",
        "    return {{\"jsonrpc\", \"2.0\"}, {\"id\", id}, {\"error\", std::move(err)}};",
        "}",
        "",
        "nlohmann::json make_result(const nlohmann::json& id, nlohmann::json result) {",
        "    return {{\"jsonrpc\", \"2.0\"}, {\"id\", id}, {\"result\", std::move(result)}};",
        "}",
        "",
        "nlohmann::json make_notification(Event e, nlohmann::json params) {",
        "    return {{\"jsonrpc\", \"2.0\"}, {\"method\", std::string(to_string(e))}, {\"params\", std::move(params)}};",
        "}",
        "",
        "nlohmann::json dispatch(Dispatcher& handler, Transport transport, const nlohmann::json& request) {",
        "    const nlohmann::json id = request.contains(\"id\") ? request.at(\"id\") : nlohmann::json(nullptr);",
        "",
        "    if (!request.is_object() || request.value(\"jsonrpc\", \"\") != \"2.0\" || !request.contains(\"method\"))",
        "        return make_error(id, ErrorCode::InvalidRequest, \"not a JSON-RPC 2.0 request\");",
        "    if (!request.at(\"method\").is_string())",
        "        return make_error(id, ErrorCode::InvalidRequest, \"method must be a string\");",
        "",
        "    const auto method = method_from_string(request.at(\"method\").get_ref<const std::string&>());",
        "    if (!method)",
        "        return make_error(id, ErrorCode::MethodNotFound, \"no such method\");",
        "    if (!is_allowed_on(*method, transport))",
        "        return make_error(id, ErrorCode::TransportForbidden,",
        "                          \"method is not permitted on this transport\");",
        "",
        "    const nlohmann::json params =",
        "        request.contains(\"params\") ? request.at(\"params\") : nlohmann::json::object();",
        "",
        "    switch (*method) {",
    ]
    for m in c.methods:
        pt, rt = cpp_type(m.params), cpp_type(m.result)
        o += [
            f"    case Method::{method_ident(m.name)}: {{",
            f'        auto p = parse<{pt}>(params, "params");',
            "        if (!p)",
            "            return make_error(id, ErrorCode::InvalidParams, p.error().message,",
            '                              nlohmann::json{{"path", p.error().path}});',
            f"        auto r = handler.{handler_name(m.name)}(*p);",
            "        if (!r)",
            "            return make_error(id, ErrorCode::InternalError, r.error().message,",
            '                              nlohmann::json{{"path", r.error().path}});',
            "        nlohmann::json out = *r;",
            "        return make_result(id, std::move(out));",
            "    }",
        ]
    o += ["    }", "",
          "    return make_error(id, ErrorCode::MethodNotFound, \"no such method\");",
          "}", ""]
    return o


def main() -> int:
    c = load()
    OUT_DIR.mkdir(parents=True, exist_ok=True)
    (OUT_DIR / "velox_proto.hpp").write_text(emit_header(c))
    (OUT_DIR / "velox_proto.cpp").write_text(emit_source(c))
    print(f"gen_cpp: {len(c.types)} types, {len(c.methods)} methods, {len(c.events)} events -> {OUT_DIR}")
    return 0


if __name__ == "__main__":
    raise SystemExit(main())