const std = @import("std");
const ObjCopy = @This();

const Allocator = std.mem.Allocator;
const ArenaAllocator = std.heap.ArenaAllocator;
const File = std.Io.File;
const InstallDir = std.Build.InstallDir;
const Step = std.Build.Step;
const elf = std.elf;
const fs = std.fs;
const sort = std.sort;

pub const base_id: Step.Id = .objcopy;

pub const RawFormat = enum {
    bin,
    hex,
    elf,
};

pub const Strip = enum {
    none,
    debug,
    debug_and_symbols,
};

pub const SectionFlags = packed struct {
    /// add SHF_ALLOC
    alloc: bool = false,

    /// if section is SHT_NOBITS, set SHT_PROGBITS, otherwise do nothing
    contents: bool = false,

    /// if section is SHT_NOBITS, set SHT_PROGBITS, otherwise do nothing (same as contents)
    load: bool = false,

    /// readonly: clear default SHF_WRITE flag
    readonly: bool = false,

    /// add SHF_EXECINSTR
    code: bool = false,

    /// add SHF_EXCLUDE
    exclude: bool = false,

    /// add SHF_X86_64_LARGE. Fatal error if target is not x86_64
    large: bool = false,

    /// add SHF_MERGE
    merge: bool = false,

    /// add SHF_STRINGS
    strings: bool = false,
};

pub const AddSection = struct {
    section_name: []const u8,
    file_path: std.Build.LazyPath,
};

pub const SetSectionAlignment = struct {
    section_name: []const u8,
    alignment: u32,
};

pub const SetSectionFlags = struct {
    section_name: []const u8,
    flags: SectionFlags,
};

step: Step,
input_file: std.Build.LazyPath,
basename: []const u8,
output_file: std.Build.GeneratedFile,
output_file_debug: ?std.Build.GeneratedFile,

format: ?RawFormat,
only_section: ?[]const u8,
pad_to: ?u64,
strip: Strip,
compress_debug: bool,

add_section: ?AddSection,
set_section_alignment: ?SetSectionAlignment,
set_section_flags: ?SetSectionFlags,

pub const Options = struct {
    basename: ?[]const u8 = null,
    format: ?RawFormat = null,
    only_section: ?[]const u8 = null,
    pad_to: ?u64 = null,

    compress_debug: bool = false,
    strip: Strip = .none,

    /// Put the stripped out debug sections in a separate file.
    /// note: the `basename` is baked into the elf file to specify the link to the separate debug file.
    /// see https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html
    extract_to_separate_file: bool = false,

    add_section: ?AddSection = null,
    set_section_alignment: ?SetSectionAlignment = null,
    set_section_flags: ?SetSectionFlags = null,
};

pub fn create(
    owner: *std.Build,
    input_file: std.Build.LazyPath,
    options: Options,
) *ObjCopy {
    const objcopy = owner.allocator.create(ObjCopy) catch @panic("OOM");
    objcopy.* = ObjCopy{
        .step = Step.init(.{
            .id = base_id,
            .name = owner.fmt("objcopy {s}", .{input_file.getDisplayName()}),
            .owner = owner,
            .makeFn = make,
        }),
        .input_file = input_file,
        .basename = options.basename orelse input_file.getDisplayName(),
        .output_file = std.Build.GeneratedFile{ .step = &objcopy.step },
        .output_file_debug = if (options.strip != .none and options.extract_to_separate_file) std.Build.GeneratedFile{ .step = &objcopy.step } else null,
        .format = options.format,
        .only_section = options.only_section,
        .pad_to = options.pad_to,
        .strip = options.strip,
        .compress_debug = options.compress_debug,
        .add_section = options.add_section,
        .set_section_alignment = options.set_section_alignment,
        .set_section_flags = options.set_section_flags,
    };
    input_file.addStepDependencies(&objcopy.step);
    return objcopy;
}

pub fn getOutput(objcopy: *const ObjCopy) std.Build.LazyPath {
    return .{ .generated = .{ .file = &objcopy.output_file } };
}
pub fn getOutputSeparatedDebug(objcopy: *const ObjCopy) ?std.Build.LazyPath {
    return if (objcopy.output_file_debug) |*file| .{ .generated = .{ .file = file } } else null;
}

fn make(step: *Step, options: Step.MakeOptions) !void {
    const prog_node = options.progress_node;
    const b = step.owner;
    const io = b.graph.io;
    const objcopy: *ObjCopy = @fieldParentPtr("step", step);
    try step.singleUnchangingWatchInput(objcopy.input_file);

    var man = b.graph.cache.obtain();
    defer man.deinit();

    const full_src_path = objcopy.input_file.getPath2(b, step);
    _ = try man.addFile(full_src_path, null);
    man.hash.addOptionalBytes(objcopy.only_section);
    man.hash.addOptional(objcopy.pad_to);
    man.hash.addOptional(objcopy.format);
    man.hash.add(objcopy.compress_debug);
    man.hash.add(objcopy.strip);
    man.hash.add(objcopy.output_file_debug != null);

    if (try step.cacheHit(&man)) {
        // Cache hit, skip subprocess execution.
        const digest = man.final();
        objcopy.output_file.path = try b.cache_root.join(b.allocator, &.{
            "o", &digest, objcopy.basename,
        });
        if (objcopy.output_file_debug) |*file| {
            file.path = try b.cache_root.join(b.allocator, &.{
                "o", &digest, b.fmt("{s}.debug", .{objcopy.basename}),
            });
        }
        return;
    }

    const digest = man.final();
    const cache_path = "o" ++ fs.path.sep_str ++ digest;
    const full_dest_path = try b.cache_root.join(b.allocator, &.{ cache_path, objcopy.basename });
    const full_dest_path_debug = try b.cache_root.join(b.allocator, &.{ cache_path, b.fmt("{s}.debug", .{objcopy.basename}) });
    b.cache_root.handle.createDirPath(io, cache_path) catch |err| {
        return step.fail("unable to make path {s}: {s}", .{ cache_path, @errorName(err) });
    };

    var argv = std.array_list.Managed([]const u8).init(b.allocator);
    try argv.appendSlice(&.{ b.graph.zig_exe, "objcopy" });

    if (objcopy.only_section) |only_section| {
        try argv.appendSlice(&.{ "-j", only_section });
    }
    switch (objcopy.strip) {
        .none => {},
        .debug => try argv.appendSlice(&.{"--strip-debug"}),
        .debug_and_symbols => try argv.appendSlice(&.{"--strip-all"}),
    }
    if (objcopy.pad_to) |pad_to| {
        try argv.appendSlice(&.{ "--pad-to", b.fmt("{d}", .{pad_to}) });
    }
    if (objcopy.format) |format| switch (format) {
        .bin => try argv.appendSlice(&.{ "-O", "binary" }),
        .hex => try argv.appendSlice(&.{ "-O", "hex" }),
        .elf => try argv.appendSlice(&.{ "-O", "elf" }),
    };
    if (objcopy.compress_debug) {
        try argv.appendSlice(&.{"--compress-debug-sections"});
    }
    if (objcopy.output_file_debug != null) {
        try argv.appendSlice(&.{b.fmt("--extract-to={s}", .{full_dest_path_debug})});
    }
    if (objcopy.add_section) |section| {
        try argv.append("--add-section");
        try argv.appendSlice(&.{b.fmt("{s}={s}", .{ section.section_name, section.file_path.getPath2(b, step) })});
    }
    if (objcopy.set_section_alignment) |set_align| {
        try argv.append("--set-section-alignment");
        try argv.appendSlice(&.{b.fmt("{s}={d}", .{ set_align.section_name, set_align.alignment })});
    }
    if (objcopy.set_section_flags) |set_flags| {
        const f = set_flags.flags;
        // trailing comma is allowed
        try argv.append("--set-section-flags");
        try argv.appendSlice(&.{b.fmt("{s}={s}{s}{s}{s}{s}{s}{s}{s}{s}", .{
            set_flags.section_name,
            if (f.alloc) "alloc," else "",
            if (f.contents) "contents," else "",
            if (f.load) "load," else "",
            if (f.readonly) "readonly," else "",
            if (f.code) "code," else "",
            if (f.exclude) "exclude," else "",
            if (f.large) "large," else "",
            if (f.merge) "merge," else "",
            if (f.strings) "strings," else "",
        })});
    }

    try argv.appendSlice(&.{ full_src_path, full_dest_path });

    try argv.append("--listen=-");
    _ = try step.evalZigProcess(argv.items, prog_node, false, options.web_server, options.gpa);

    objcopy.output_file.path = full_dest_path;
    if (objcopy.output_file_debug) |*file| file.path = full_dest_path_debug;
    try man.writeManifest();
}
