//! This file is shared among Zig code running in wildly different contexts:
//! * The build runner, running on the host computer
//! * The build system web interface Wasm code, running in the browser
//! * `libfuzzer`, compiled alongside unit tests
//!
//! All of these components interface to some degree via an ABI:
//! * The build runner communicates with the web interface over a WebSocket connection
//! * The build runner communicates with `libfuzzer` over a shared memory-mapped file
const std = @import("std");

// Check that no WebSocket message type has implicit padding bits. This ensures we never send any
// undefined bits over the wire, and also helps validate that the layout doesn't differ between, for
// instance, the web server in `std.Build` and the Wasm client.
comptime {
    const check = struct {
        fn check(comptime T: type) void {
            std.debug.assert(@typeInfo(T) == .@"struct");
            std.debug.assert(@typeInfo(T).@"struct".layout == .@"extern");
            std.debug.assert(std.meta.hasUniqueRepresentation(T));
        }
    }.check;

    // server->client
    check(Hello);
    check(StatusUpdate);
    check(StepUpdate);
    check(fuzz.SourceIndexHeader);
    check(fuzz.CoverageUpdateHeader);
    check(fuzz.EntryPointHeader);
    check(time_report.GenericResult);
    check(time_report.CompileResult);

    // client->server
    check(Rebuild);
}

/// All WebSocket messages sent by the server to the client begin with a `ToClientTag` byte. This
/// enum is non-exhaustive only to avoid Illegal Behavior when malformed messages are sent over the
/// socket; unnamed tags are an error condition and should terminate the connection.
///
/// Every tag has a curresponding `extern struct` representing the full message (or a header of the
/// message if it is variable-length). For instance, `.hello` corresponds to `Hello`.
///
/// When introducing a tag, make sure to add a corresponding `extern struct` whose first field is
/// this enum, and `check` its layout in the `comptime` block above.
pub const ToClientTag = enum(u8) {
    hello,
    status_update,
    step_update,

    // `--fuzz`
    fuzz_source_index,
    fuzz_coverage_update,
    fuzz_entry_points,

    // `--time-report`
    time_report_generic_result,
    time_report_compile_result,
    time_report_run_test_result,

    _,
};

/// Like `ToClientTag`, but for messages sent by the client to the server.
pub const ToServerTag = enum(u8) {
    rebuild,

    _,
};

/// The current overall status of the build runner.
/// Keep in sync with indices in web UI `main.js:updateBuildStatus`.
pub const BuildStatus = enum(u8) {
    idle,
    watching,
    running,
    fuzz_init,
};

/// WebSocket server->client.
///
/// Sent by the server as the first message after a WebSocket connection opens to provide basic
/// information about the server, the build graph, etc.
///
/// Trailing:
/// * `step_name_len: u32` for each `steps_len`
/// * `step_name: [step_name_len]u8` for each `step_name_len`
/// * `step_status: u8` for every 4 `steps_len`; every 2 bits is a `StepUpdate.Status`, LSBs first
pub const Hello = extern struct {
    tag: ToClientTag = .hello,

    status: BuildStatus,
    flags: Flags,

    /// Any message containing a timestamp represents it as a number of nanoseconds relative to when
    /// the build began. This field is the current timestamp, represented in that form.
    timestamp: i64 align(4),

    /// The number of steps in the build graph which are reachable from the top-level step[s] being
    /// run; in other words, the number of steps which will be executed by this build. The name of
    /// each step trails this message.
    steps_len: u32 align(1),

    pub const Flags = packed struct(u16) {
        /// Whether time reporting is enabled.
        time_report: bool,
        _: u15 = 0,
    };
};
/// WebSocket server->client.
///
/// Indicates that the build status has changed.
pub const StatusUpdate = extern struct {
    tag: ToClientTag = .status_update,
    new: BuildStatus,
};
/// WebSocket server->client.
///
/// Indicates a change in a step's status.
pub const StepUpdate = extern struct {
    tag: ToClientTag = .step_update,
    step_idx: u32 align(1),
    bits: packed struct(u8) {
        status: Status,
        _: u6 = 0,
    },
    /// Keep in sync with indices in web UI `main.js:updateStepStatus`.
    pub const Status = enum(u2) {
        pending,
        wip,
        success,
        failure,
    };
};

pub const Rebuild = extern struct {
    tag: ToServerTag = .rebuild,
};

/// ABI bits specifically relating to the fuzzer interface.
pub const fuzz = struct {
    /// Returns if `error.SkipZigTest` was indicated
    pub const TestOne = *const fn () callconv(.c) bool;

    /// A unique value to identify the related requests across runs
    pub const Uid = packed struct(u32) {
        kind: enum(u1) { int, bytes },
        hash: u31,

        pub const hashmap_ctx = struct {
            pub fn hash(_: @This(), u: Uid) u32 {
                // We can ignore `kind` since `hash` should be unique regardless
                return u.hash;
            }

            pub fn eql(_: @This(), a: Uid, b: Uid, _: usize) bool {
                return a == b;
            }
        };
    };

    pub extern fn fuzzer_init(cache_dir_path: Slice) void;
    /// `fuzzer_init` must be called first.
    pub extern fn fuzzer_coverage() Coverage;
    pub extern fn fuzzer_unslide_address(addr: usize) usize;

    /// Performs all the fuzzing work and selects tests to run
    ///
    /// `fuzzer_init` must be called first.
    pub extern fn fuzzer_main(
        n_tests: u32,
        seed: u32,
        limit_kind: LimitKind,
        amount_or_instance: u64,
    ) void;
    pub extern fn runner_test_run(i: u32) void;
    pub extern fn runner_test_name(i: u32) Slice;
    // Since the runner owns the `std.zig.Server` instance, it also controls the
    // concurrent Io instance so reads can be canceled. As such, the fuzzer has
    // to call into the runner for any zig server / concurrent operation.
    pub extern fn runner_start_input_poller() void;
    pub extern fn runner_stop_input_poller() void;
    /// Returns if cancelation has been indicated.
    pub extern fn runner_futex_wait(*const u32, expected: u32) bool;
    pub extern fn runner_futex_wake(*const u32, waiters: u32) void;
    pub extern fn runner_broadcast_input(test_i: u32, bytes: Slice) void;
    /// `fuzzer_main` must be called first.
    ///
    /// Called concurrently with `fuzzer_main`. Returns if cancelation has been indicated.
    pub extern fn fuzzer_receive_input(test_i: u32, bytes: Slice) bool;

    /// Must be called from inside a test function
    pub extern fn fuzzer_set_test(test_one: TestOne) void;
    /// Must be called from inside a test function where `fuzzer_set_test` has been called first.
    pub extern fn fuzzer_new_input(bytes: Slice) void;
    /// Must be called from inside a test function where `fuzzer_set_test` has been called first.
    pub extern fn fuzzer_start_test() void;

    pub extern fn fuzzer_int(uid: Uid, weights: Weights) u64;
    pub extern fn fuzzer_eos(uid: Uid, weights: Weights) bool;
    pub extern fn fuzzer_bytes(uid: Uid, out: MutSlice, weights: Weights) void;
    pub extern fn fuzzer_slice(
        uid: Uid,
        buf: MutSlice,
        len_weights: Weights,
        byte_weights: Weights,
    ) u32;

    pub const Slice = extern struct {
        ptr: [*]const u8,
        len: usize,

        pub fn toSlice(s: Slice) []const u8 {
            return s.ptr[0..s.len];
        }

        pub fn fromSlice(s: []const u8) Slice {
            return .{ .ptr = s.ptr, .len = s.len };
        }
    };

    pub const MutSlice = extern struct {
        ptr: [*]u8,
        len: usize,

        pub fn toSlice(s: MutSlice) []u8 {
            return s.ptr[0..s.len];
        }

        pub fn fromSlice(s: []u8) MutSlice {
            return .{ .ptr = s.ptr, .len = s.len };
        }
    };

    pub const Weights = extern struct {
        ptr: [*]const Weight,
        len: usize,

        pub fn toSlice(s: Weights) []const Weight {
            return s.ptr[0..s.len];
        }

        pub fn fromSlice(s: []const Weight) Weights {
            return .{ .ptr = s.ptr, .len = s.len };
        }
    };

    /// Increases the probability of values being selected by the fuzzer.
    ///
    /// `weight` applies to each value in the range (i.e. not evenly across
    /// the range) and must be nonzero.
    ///
    /// In a set of weights, the total weight must not exceed 2^64 and be
    /// nonzero.
    pub const Weight = extern struct {
        /// Inclusive
        min: u64,
        /// Inclusive
        max: u64,
        weight: u64,

        /// `inline` to propogate comptimeness
        inline fn intFromValue(x: anytype) u64 {
            const T = @TypeOf(x);
            return switch (@typeInfo(T)) {
                .comptime_int => x,
                .bool => @intFromBool(x),
                .@"enum" => @intFromEnum(x),
                else => @as(std.meta.Int(.unsigned, @bitSizeOf(T)), @bitCast(x)),

                .int => |i| x: {
                    comptime {
                        if (i.signedness == .signed) {
                            @compileError("type does not have a continous range: " ++ @typeName(T));
                        }
                        // Reject types that don't have a fixed bitsize (esp. usize)
                        // since they are not gauraunteed to fit in a u64 across targets.
                        //
                        // std.mem.indexOfScalar is not used to avoid backward branches
                        // and preserve the eval branch quota.
                        if (T == usize or T == c_char or T == c_ushort or
                            T == c_uint or T == c_ulong or T == c_ulonglong)
                        {
                            @compileError("type does not have a fixed bitsize: " ++ @typeName(T));
                        }
                    }
                    break :x x;
                },

                .comptime_float,
                .float,
                => @compileError("type does not have a continous range: " ++ @typeName(T)),
                .pointer => @compileError("type does not have a fixed bitsize: " ++ @typeName(T)),
            };
        }

        /// `inline` to propogate comptimeness
        pub inline fn value(T: type, x: T, weight: u64) Weight {
            return .{ .min = intFromValue(x), .max = intFromValue(x), .weight = weight };
        }

        /// `inline` to propogate comptimeness
        pub inline fn rangeAtMost(T: type, at_least: T, at_most: T, weight: u64) Weight {
            std.debug.assert(intFromValue(at_least) <= intFromValue(at_most));
            return .{
                .min = intFromValue(at_least),
                .max = intFromValue(at_most),
                .weight = weight,
            };
        }

        /// `inline` to propogate comptimeness
        pub inline fn rangeLessThan(T: type, at_least: T, less_than: T, weight: u64) Weight {
            std.debug.assert(intFromValue(at_least) < intFromValue(less_than));
            return .{
                .min = intFromValue(at_least),
                .max = intFromValue(less_than) - 1,
                .weight = weight,
            };
        }
    };

    pub const LimitKind = enum(u8) { forever, iterations };

    /// libfuzzer uses this and its usize is the one that counts. To match the ABI,
    /// make the ints be the size of the target used with libfuzzer.
    ///
    /// Trailing:
    /// * 1 bit per pc_addr, usize elements
    /// * pc_addr: usize for each pcs_len
    pub const SeenPcsHeader = extern struct {
        n_runs: usize,
        unique_runs: usize,
        pcs_len: usize,

        /// Used for comptime assertions. Provides a mechanism for strategically
        /// causing compile errors.
        pub const trailing = .{
            .pc_bits_usize,
            .pc_addr,
        };

        pub fn headerEnd(header: *const SeenPcsHeader) []const usize {
            const ptr: [*]align(@alignOf(usize)) const u8 = @ptrCast(header);
            const header_end_ptr: [*]const usize = @ptrCast(ptr + @sizeOf(SeenPcsHeader));
            const pcs_len = header.pcs_len;
            return header_end_ptr[0 .. pcs_len + seenElemsLen(pcs_len)];
        }

        pub fn seenBits(header: *const SeenPcsHeader) []const usize {
            return header.headerEnd()[0..seenElemsLen(header.pcs_len)];
        }

        pub fn seenElemsLen(pcs_len: usize) usize {
            return (pcs_len + @bitSizeOf(usize) - 1) / @bitSizeOf(usize);
        }

        pub fn pcAddrs(header: *const SeenPcsHeader) []const usize {
            const pcs_len = header.pcs_len;
            return header.headerEnd()[seenElemsLen(pcs_len)..][0..pcs_len];
        }
    };

    /// Fields are little-endian
    pub const MmapInputHeader = extern struct {
        pc_digest: u64 align(4), // aligned so header does not have padding
        instance_id: u32,
        test_i: u32,
        len: u32,
    };

    /// WebSocket server->client.
    ///
    /// Sent once, when fuzzing starts, to indicate the available coverage data.
    ///
    /// Trailing:
    /// * std.debug.Coverage.String for each directories_len
    /// * std.debug.Coverage.File for each files_len
    /// * std.debug.Coverage.SourceLocation for each source_locations_len
    /// * u8 for each string_bytes_len
    pub const SourceIndexHeader = extern struct {
        tag: ToClientTag = .fuzz_source_index,
        _: [3]u8 = @splat(0),
        directories_len: u32,
        files_len: u32,
        source_locations_len: u32,
        string_bytes_len: u32,
        /// When, according to the server, fuzzing started.
        start_timestamp: i64 align(4),
        start_n_runs: u64 align(4),
    };

    /// WebSocket server->client.
    ///
    /// Sent whenever the set of covered source locations is updated.
    ///
    /// Trailing:
    /// * one bit per source_locations_len, contained in u64 elements
    pub const CoverageUpdateHeader = extern struct {
        tag: ToClientTag = .fuzz_coverage_update,
        _: [7]u8 = @splat(0),
        n_runs: u64,
        unique_runs: u64,

        pub const trailing = .{
            .pc_bits_usize,
        };
    };

    /// WebSocket server->client.
    ///
    /// Sent whenever the set of entry points is updated.
    ///
    /// Trailing:
    /// * one u32 index of source_locations per locsLen()
    pub const EntryPointHeader = extern struct {
        tag: ToClientTag = .fuzz_entry_points,
        locs_len_raw: [3]u8,

        pub fn locsLen(hdr: EntryPointHeader) u24 {
            return @bitCast(hdr.locs_len_raw);
        }
        pub fn init(locs_len: u24) EntryPointHeader {
            return .{ .locs_len_raw = @bitCast(locs_len) };
        }
    };

    /// Sent by lib/fuzzer to test_runner to obtain information about the
    /// active memory mapped input file and cumulative stats about previous
    /// fuzzing runs.
    pub const Coverage = extern struct {
        id: u64,
        runs: u64,
        unique: u64,
        seen: u64,
    };
};

/// ABI bits specifically relating to the time report interface.
pub const time_report = struct {
    /// WebSocket server->client.
    ///
    /// Sent after a `Step` finishes, providing the time taken to execute the step.
    pub const GenericResult = extern struct {
        tag: ToClientTag = .time_report_generic_result,
        step_idx: u32 align(1),
        ns_total: u64 align(1),
    };

    /// WebSocket server->client.
    ///
    /// Sent after a `Step.Compile` finishes, providing the step's time report.
    ///
    /// Trailing:
    /// * `llvm_pass_timings: [llvm_pass_timings_len]u8` (ASCII-encoded)
    /// * for each `files_len`:
    ///   * `name` (null-terminated UTF-8 string)
    /// * for each `decls_len`:
    ///   * `name` (null-terminated UTF-8 string)
    ///   * `file: u32` (index of file this decl is in)
    ///   * `sema_ns: u64` (nanoseconds spent semantically analyzing this decl)
    ///   * `codegen_ns: u64` (nanoseconds spent semantically analyzing this decl)
    ///   * `link_ns: u64` (nanoseconds spent semantically analyzing this decl)
    pub const CompileResult = extern struct {
        tag: ToClientTag = .time_report_compile_result,

        step_idx: u32 align(1),

        flags: Flags,
        stats: Stats align(1),
        ns_total: u64 align(1),

        llvm_pass_timings_len: u32 align(1),
        files_len: u32 align(1),
        decls_len: u32 align(1),

        pub const Flags = packed struct(u8) {
            use_llvm: bool,
            _: u7 = 0,
        };

        pub const Stats = extern struct {
            n_reachable_files: u32,
            n_imported_files: u32,
            n_generic_instances: u32,
            n_inline_calls: u32,

            cpu_ns_parse: u64,
            cpu_ns_astgen: u64,
            cpu_ns_sema: u64,
            cpu_ns_codegen: u64,
            cpu_ns_link: u64,

            real_ns_files: u64,
            real_ns_decls: u64,
            real_ns_llvm_emit: u64,
            real_ns_link_flush: u64,

            pub const init: Stats = .{
                .n_reachable_files = 0,
                .n_imported_files = 0,
                .n_generic_instances = 0,
                .n_inline_calls = 0,
                .cpu_ns_parse = 0,
                .cpu_ns_astgen = 0,
                .cpu_ns_sema = 0,
                .cpu_ns_codegen = 0,
                .cpu_ns_link = 0,
                .real_ns_files = 0,
                .real_ns_decls = 0,
                .real_ns_llvm_emit = 0,
                .real_ns_link_flush = 0,
            };
        };
    };

    /// WebSocket server->client.
    ///
    /// Sent after a `Step.Run` for a Zig test executable finishes, providing the test's time report.
    ///
    /// Trailing:
    /// * for each `tests_len`:
    ///   * `test_ns: u64` (nanoseconds spent running this test)
    /// * for each `tests_len`:
    ///   * `name` (null-terminated UTF-8 string)
    pub const RunTestResult = extern struct {
        tag: ToClientTag = .time_report_run_test_result,
        step_idx: u32 align(1),
        tests_len: u32 align(1),
    };
};