// imports
const std = @import("std");
const Builder = std.build.Builder;

// Alloc stuff
var GPAAlloc = std.heap.GeneralPurposeAllocator(.{}){};
var alloc = &GPAAlloc.allocator;

// Target enumeration stuff
const Target = struct {
    parent: ?*const Target = null,
    cpu_arch: ?std.Target.Cpu.Arch = null,
    cpu_model: ?std.build.Target.CpuModel = null,
    archdir: ?[]const u8 = null,
    linkscript: ?[]const u8 = null,
    name: []const u8,
};

const x86 = Target{
    .archdir = "x86",
    .name = "x86-generic"
};
const x86_64 = Target {
    .parent = &x86,
    .cpu_arch = std.Target.Cpu.Arch.x86_64,
    .archdir = "x86_64",
    .name = "x86_64-generic"
};
const x86_64_stivale2 = Target {
    .parent = &x86_64,
    // .archdir = "x86_64/stivale2",
    .linkscript = "make/x86_64/linker.ld",
    .name = "x86_64-stivale2",
};

const Targets = enum {
    x86_64,
    x86_64_stivale2,

    pub fn getTarget(self: Targets) Target {
        return switch(self) {
            .x86_64 => x86_64_stivale2,
            .x86_64_stivale2 => x86_64_stivale2,
        };
    }
    pub fn default() Targets {
        return Targets.x86_64_stivale2;
    }
};

fn getCpuArch(t: Target) std.Target.Cpu.Arch {
    return t.cpu_arch orelse getCpuArch(t.parent.?.*);
}

fn getCpuModel(t: Target) std.build.Target.CpuModel {
    if(t.cpu_model) |m| {
        return m;
    } else if (t.parent) |p| {
        return getCpuModel(t.parent.?.*);
    } else {
        return std.build.Target.CpuModel.baseline;
    }
}

fn getLinkerScript(t: Target) []const u8 {
    return t.linkscript orelse getLinkerScript(t.parent.?.*);
}

fn getTarget(t: Target) std.zig.CrossTarget {
    return .{
        .cpu_arch = getCpuArch(t),
        .cpu_model = getCpuModel(t),
        .os_tag = std.Target.Os.Tag.freestanding,
    };
}

// Directory traversal stuff
const Files = struct {
    generic_c: [][]const u8,
    archspecific_c: [][]const u8,
    archspecific_s: [][]const u8,
    nasm: [][]const u8,
};
fn strPrefix(str: []const u8, prefix: []const u8) bool {
    if (str.len < prefix.len) return false;
    return std.mem.eql(u8, str[0..prefix.len], prefix);
}
fn fileExtEql(name: []const u8, ext: []const u8) bool {
    std.debug.assert(ext[0] == '.');
    if(name.len <= ext.len) return false;
    const file_ext = name[name.len - ext.len..];
    return std.mem.eql(u8, file_ext, ext);
}
fn findSources(dir: []const u8, ext: []const u8, prefix: ?[]const u8) ![][] const u8 {
    var files = std.ArrayList([]const u8).init(alloc);
    var walker = try std.fs.walkPath(alloc, dir);
    while (try walker.next()) |entry| {
        if(entry.kind != std.fs.Dir.Entry.Kind.File) continue;

        if(prefix != null and strPrefix(entry.path, prefix.?)) {
            // std.debug.print("Ignoring {}\n", .{entry.path});
        } else {
            if(fileExtEql(entry.basename, ext)) {
                // std.debug.print("Adding file {}\n", .{entry.path});
                var p = std.ArrayList(u8).init(alloc);
                try p.appendSlice(entry.path);
                try files.append(p.toOwnedSlice());
            } else {
                // std.debug.print("wrong file extension: {}\n", .{entry.basename});
            }
        }
    }
    walker.deinit();
    return files.toOwnedSlice();
}
fn findArch(t: Target, ext: []const u8) ![][] const u8 {
    var arch_c = std.ArrayList([]const u8).init(alloc);
    if (t.parent) |parent| {
        const parentfiles = findArch(parent.*, ext) catch unreachable;
        try arch_c.appendSlice( parentfiles );
    }
    if (t.archdir) |archdir| {
        const dir = try std.fmt.allocPrint(alloc, "src/arch/{}", .{archdir});
        const files = try findSources(dir, ext, null);
        try arch_c.appendSlice(files);
    }
    return arch_c.items;
}
fn findFiles(t: Target) !Files {
    const generic_c = try findSources("src", ".c", "src/arch/");
    const arch_c = try findArch(t, ".c");
    const arch_s = try findArch(t, ".s");
    const nasm = try findArch(t, ".nasm");

    return Files {
        .generic_c = generic_c,
        .archspecific_c = arch_c,
        .archspecific_s = arch_s,
        .nasm = nasm
    };
}

pub fn build(b: *Builder) !void {
    const target_option = b.option(Targets, "target", "The kernel target") orelse Targets.default();
    const ktarget = target_option.getTarget();

    // Standard release options allow the person running `zig build` to select
    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall.
    const mode = b.standardReleaseOptions();
 
    b.cache_root = "zig-cache";

    const files = try findFiles(ktarget);

    const cflags = [_][]const u8{"-Wall", "-Wextra", "-pedantic", "-std=gnu11", "-I../ext", "-Isrc", "-fPIE", "-mno-red-zone"};

    const exename = try std.fmt.allocPrint(alloc, "kernel-{}", .{ktarget.name});
    const exe = b.addExecutable(exename, "src/main.zig");
    var cfiles = std.ArrayList([]const u8).init(alloc);
    try cfiles.appendSlice(files.generic_c);
    try cfiles.appendSlice(files.archspecific_c);
    for (cfiles.items) |c_file| {
        // std.debug.print("CC: {}\n", .{c_file});
        exe.addCSourceFile(c_file, &cflags);
    }
    for(files.archspecific_s) |s_file| {
        // std.debug.print("zig as: {}\n", .{s_file});
        exe.addAssemblyFile(s_file);
    }
    for(files.nasm) |nasm_file| {
        // std.debug.print("nasm: {}\n", .{nasm_file});
        const output = try std.fmt.allocPrint(alloc, "zig-cache/nasm/{}.o", .{nasm_file});
        const output_folder = std.fs.cwd().makePath(std.fs.path.dirname(output).?);
        const assX = b.addSystemCommand(&[_][]const u8{"nasm", "-Isrc", "-felf64", nasm_file, "-o", output});
        exe.step.dependOn(&assX.step);
        exe.addObjectFile(output);
    }

    exe.setTarget(getTarget(ktarget));
    exe.setBuildMode(mode);
    exe.setLinkerScriptPath(getLinkerScript(ktarget));
    // exe.setOutputDir("bin");
    exe.install();

    const run_cmd = exe.run();
    run_cmd.step.dependOn(b.getInstallStep());
    if (b.args) |args| {
        run_cmd.addArgs(args);
    }


    // const run_step = b.step("run", "Run the app");
    // run_step.dependOn(&run_cmd.step);
}