    const std = @import("std");
    const builtin = @import("builtin");
    const mem = std.mem;
    const io = std.io;
    const fs = std.fs;
    const fmt = std.fmt;
    const testing = std.testing;

    const Target = std.Target;
    const CrossTarget = std.zig.CrossTarget;

    const assert = std.debug.assert;

    const SparcCpuinfoImpl = struct {
        model: ?*const Target.Cpu.Model = null,
        is_64bit: bool = false,

        const cpu_names = .{
            .{ "SuperSparc", &Target.sparc.cpu.supersparc },
            .{ "HyperSparc", &Target.sparc.cpu.hypersparc },
            .{ "SpitFire", &Target.sparc.cpu.ultrasparc },
            .{ "BlackBird", &Target.sparc.cpu.ultrasparc },
            .{ "Sabre", &Target.sparc.cpu.ultrasparc },
            .{ "Hummingbird", &Target.sparc.cpu.ultrasparc },
            .{ "Cheetah", &Target.sparc.cpu.ultrasparc3 },
            .{ "Jalapeno", &Target.sparc.cpu.ultrasparc3 },
            .{ "Jaguar", &Target.sparc.cpu.ultrasparc3 },
            .{ "Panther", &Target.sparc.cpu.ultrasparc3 },
            .{ "Serrano", &Target.sparc.cpu.ultrasparc3 },
            .{ "UltraSparc T1", &Target.sparc.cpu.niagara },
            .{ "UltraSparc T2", &Target.sparc.cpu.niagara2 },
            .{ "UltraSparc T3", &Target.sparc.cpu.niagara3 },
            .{ "UltraSparc T4", &Target.sparc.cpu.niagara4 },
            .{ "UltraSparc T5", &Target.sparc.cpu.niagara4 },
            .{ "LEON", &Target.sparc.cpu.leon3 },
        };

        fn line_hook(self: *SparcCpuinfoImpl, key: []const u8, value: []const u8) !bool {
            if (mem.eql(u8, key, "cpu")) {
                inline for (cpu_names) |pair| {
                    if (mem.indexOfPos(u8, value, 0, pair[0]) != null) {
                        self.model = pair[1];
                        break;
                    }
                }
            } else if (mem.eql(u8, key, "type")) {
                self.is_64bit = mem.eql(u8, value, "sun4u") or mem.eql(u8, value, "sun4v");
            }

            return true;
        }

        fn finalize(self: *const SparcCpuinfoImpl, arch: Target.Cpu.Arch) ?Target.Cpu {
            // At the moment we only support 64bit SPARC systems.

            assert(self.is_64bit);

            const model = self.model orelse return null;
            return Target.Cpu{
                .arch = arch,
                .model = model,
                .features = model.features,
            };
        }
    };

    const SparcCpuinfoParser = CpuinfoParser(SparcCpuinfoImpl);

    test "cpuinfo: SPARC" {
        try testParser(SparcCpuinfoParser, .sparc64, &Target.sparc.cpu.niagara2,
            \\cpu             : UltraSparc T2 (Niagara2)

            \\fpu             : UltraSparc T2 integrated FPU

            \\pmu             : niagara2

            \\type            : sun4v

        );
    }

    const PowerpcCpuinfoImpl = struct {
        model: ?*const Target.Cpu.Model = null,

        const cpu_names = .{
            .{ "604e", &Target.powerpc.cpu.@"604e" },
            .{ "604", &Target.powerpc.cpu.@"604" },
            .{ "7400", &Target.powerpc.cpu.@"7400" },
            .{ "7410", &Target.powerpc.cpu.@"7400" },
            .{ "7447", &Target.powerpc.cpu.@"7400" },
            .{ "7455", &Target.powerpc.cpu.@"7450" },
            .{ "G4", &Target.powerpc.cpu.@"g4" },
            .{ "POWER4", &Target.powerpc.cpu.@"970" },
            .{ "PPC970FX", &Target.powerpc.cpu.@"970" },
            .{ "PPC970MP", &Target.powerpc.cpu.@"970" },
            .{ "G5", &Target.powerpc.cpu.@"g5" },
            .{ "POWER5", &Target.powerpc.cpu.@"g5" },
            .{ "A2", &Target.powerpc.cpu.@"a2" },
            .{ "POWER6", &Target.powerpc.cpu.@"pwr6" },
            .{ "POWER7", &Target.powerpc.cpu.@"pwr7" },
            .{ "POWER8", &Target.powerpc.cpu.@"pwr8" },
            .{ "POWER8E", &Target.powerpc.cpu.@"pwr8" },
            .{ "POWER8NVL", &Target.powerpc.cpu.@"pwr8" },
            .{ "POWER9", &Target.powerpc.cpu.@"pwr9" },
            .{ "POWER10", &Target.powerpc.cpu.@"pwr10" },
        };

        fn line_hook(self: *PowerpcCpuinfoImpl, key: []const u8, value: []const u8) !bool {
            if (mem.eql(u8, key, "cpu")) {
                // The model name is often followed by a comma or space and extra

                // info.

                inline for (cpu_names) |pair| {
                    const end_index = mem.indexOfAny(u8, value, ", ") orelse value.len;
                    if (mem.eql(u8, value[0..end_index], pair[0])) {
                        self.model = pair[1];
                        break;
                    }
                }

                // Stop the detection once we've seen the first core.

                return false;
            }

            return true;
        }

        fn finalize(self: *const PowerpcCpuinfoImpl, arch: Target.Cpu.Arch) ?Target.Cpu {
            const model = self.model orelse return null;
            return Target.Cpu{
                .arch = arch,
                .model = model,
                .features = model.features,
            };
        }
    };

    const PowerpcCpuinfoParser = CpuinfoParser(PowerpcCpuinfoImpl);

    test "cpuinfo: PowerPC" {
        try testParser(PowerpcCpuinfoParser, .powerpc, &Target.powerpc.cpu.@"970",
            \\processor	: 0

            \\cpu		: PPC970MP, altivec supported

            \\clock		: 1250.000000MHz

            \\revision	: 1.1 (pvr 0044 0101)

        );
        try testParser(PowerpcCpuinfoParser, .powerpc64le, &Target.powerpc.cpu.pwr8,
            \\processor	: 0

            \\cpu		: POWER8 (raw), altivec supported

            \\clock		: 2926.000000MHz

            \\revision	: 2.0 (pvr 004d 0200)

        );
    }

    const ArmCpuinfoImpl = struct {
        cores: [4]CoreInfo = undefined,
        core_no: usize = 0,
        have_fields: usize = 0,

        const CoreInfo = struct {
            architecture: u8 = 0,
            implementer: u8 = 0,
            variant: u8 = 0,
            part: u16 = 0,
            is_really_v6: bool = false,
        };

        const cpu_models = @import("arm.zig").cpu_models;

        fn addOne(self: *ArmCpuinfoImpl) void {
            if (self.have_fields == 4 and self.core_no < self.cores.len) {
                if (self.core_no > 0) {
                    // Deduplicate the core info.

                    for (self.cores[0..self.core_no]) |it| {
                        if (std.meta.eql(it, self.cores[self.core_no]))
                            return;
                    }
                }
                self.core_no += 1;
            }
        }

        fn line_hook(self: *ArmCpuinfoImpl, key: []const u8, value: []const u8) !bool {
            const info = &self.cores[self.core_no];

            if (mem.eql(u8, key, "processor")) {
                // Handle both old-style and new-style cpuinfo formats.

                // The former prints a sequence of "processor: N" lines for each

                // core and then the info for the core that's executing this code(!)

                // while the latter prints the infos for each core right after the

                // "processor" key.

                self.have_fields = 0;
                self.cores[self.core_no] = .{};
            } else if (mem.eql(u8, key, "CPU implementer")) {
                info.implementer = try fmt.parseInt(u8, value, 0);
                self.have_fields += 1;
            } else if (mem.eql(u8, key, "CPU architecture")) {
                // "AArch64" on older kernels.

                info.architecture = if (mem.startsWith(u8, value, "AArch64"))
                    8
                else
                    try fmt.parseInt(u8, value, 0);
                self.have_fields += 1;
            } else if (mem.eql(u8, key, "CPU variant")) {
                info.variant = try fmt.parseInt(u8, value, 0);
                self.have_fields += 1;
            } else if (mem.eql(u8, key, "CPU part")) {
                info.part = try fmt.parseInt(u16, value, 0);
                self.have_fields += 1;
            } else if (mem.eql(u8, key, "model name")) {
                // ARMv6 cores report "CPU architecture" equal to 7.

                if (mem.indexOf(u8, value, "(v6l)")) |_| {
                    info.is_really_v6 = true;
                }
            } else if (mem.eql(u8, key, "CPU revision")) {
                // This field is always the last one for each CPU section.

                _ = self.addOne();
            }

            return true;
        }

        fn finalize(self: *ArmCpuinfoImpl, arch: Target.Cpu.Arch) ?Target.Cpu {
            if (self.core_no == 0) return null;

            const is_64bit = switch (arch) {
                .aarch64, .aarch64_be, .aarch64_32 => true,
                else => false,
            };

            var known_models: [self.cores.len]?*const Target.Cpu.Model = undefined;
            for (self.cores[0..self.core_no]) |core, i| {
                known_models[i] = cpu_models.isKnown(.{
                    .architecture = core.architecture,
                    .implementer = core.implementer,
                    .variant = core.variant,
                    .part = core.part,
                }, is_64bit);
            }

            // XXX We pick the first core on big.LITTLE systems, hopefully the

            // LITTLE one.

            const model = known_models[0] orelse return null;
            return Target.Cpu{
                .arch = arch,
                .model = model,
                .features = model.features,
            };
        }
    };

    const ArmCpuinfoParser = CpuinfoParser(ArmCpuinfoImpl);

    test "cpuinfo: ARM" {
        try testParser(ArmCpuinfoParser, .arm, &Target.arm.cpu.arm1176jz_s,
            \\processor       : 0

            \\model name      : ARMv6-compatible processor rev 7 (v6l)

            \\BogoMIPS        : 997.08

            \\Features        : half thumb fastmult vfp edsp java tls

            \\CPU implementer : 0x41

            \\CPU architecture: 7

            \\CPU variant     : 0x0

            \\CPU part        : 0xb76

            \\CPU revision    : 7

        );
        try testParser(ArmCpuinfoParser, .arm, &Target.arm.cpu.cortex_a7,
            \\processor	: 0

            \\model name	: ARMv7 Processor rev 3 (v7l)

            \\BogoMIPS	: 18.00

            \\Features	: half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae

            \\CPU implementer	: 0x41

            \\CPU architecture: 7

            \\CPU variant	: 0x0

            \\CPU part	: 0xc07

            \\CPU revision	: 3

            \\

            \\processor	: 4

            \\model name	: ARMv7 Processor rev 3 (v7l)

            \\BogoMIPS	: 90.00

            \\Features	: half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae

            \\CPU implementer	: 0x41

            \\CPU architecture: 7

            \\CPU variant	: 0x2

            \\CPU part	: 0xc0f

            \\CPU revision	: 3

        );
        try testParser(ArmCpuinfoParser, .aarch64, &Target.aarch64.cpu.cortex_a72,
            \\processor       : 0

            \\BogoMIPS        : 108.00

            \\Features        : fp asimd evtstrm crc32 cpuid

            \\CPU implementer : 0x41

            \\CPU architecture: 8

            \\CPU variant     : 0x0

            \\CPU part        : 0xd08

            \\CPU revision    : 3

        );
    }

    fn testParser(
        parser: anytype,
        arch: Target.Cpu.Arch,
        expected_model: *const Target.Cpu.Model,
        input: []const u8,
    ) !void {
        var fbs = io.fixedBufferStream(input);
        const result = try parser.parse(arch, fbs.reader());
        try testing.expectEqual(expected_model, result.?.model);
        try testing.expect(expected_model.features.eql(result.?.features));
    }

    // The generic implementation of a /proc/cpuinfo parser.

    // For every line it invokes the line_hook method with the key and value strings

    // as first and second parameters. Returning false from the hook function stops

    // the iteration without raising an error.

    // When all the lines have been analyzed the finalize method is called.

    fn CpuinfoParser(comptime impl: anytype) type {
        return struct {
            fn parse(arch: Target.Cpu.Arch, reader: anytype) anyerror!?Target.Cpu {
                var line_buf: [1024]u8 = undefined;
                var obj: impl = .{};

                while (true) {
                    const line = (try reader.readUntilDelimiterOrEof(&line_buf, '\n')) orelse break;
                    const colon_pos = mem.indexOfScalar(u8, line, ':') orelse continue;
                    const key = mem.trimRight(u8, line[0..colon_pos], " \t");
                    const value = mem.trimLeft(u8, line[colon_pos + 1 ..], " \t");

                    if (!try obj.line_hook(key, value))
                        break;
                }

                return obj.finalize(arch);
            }
        };
    }

    pub fn detectNativeCpuAndFeatures() ?Target.Cpu {
        var f = fs.openFileAbsolute("/proc/cpuinfo", .{ .intended_io_mode = .blocking }) catch |err| switch (err) {
            else => return null,
        };
        defer f.close();

        const current_arch = builtin.cpu.arch;
        switch (current_arch) {
            .arm, .armeb, .thumb, .thumbeb, .aarch64, .aarch64_be, .aarch64_32 => {
                return ArmCpuinfoParser.parse(current_arch, f.reader()) catch null;
            },
            .sparc64 => {
                return SparcCpuinfoParser.parse(current_arch, f.reader()) catch null;
            },
            .powerpc, .powerpcle, .powerpc64, .powerpc64le => {
                return PowerpcCpuinfoParser.parse(current_arch, f.reader()) catch null;
            },
            else => {},
        }

        return null;
    }