const root = @import("@build");
const std = @import("std");
const builtin = @import("builtin");
const io = std.io;
const fmt = std.fmt;
const Builder = std.build.Builder;
const mem = std.mem;
const process = std.process;
const ArrayList = std.ArrayList;
const warn = std.debug.warn;
const File = std.fs.File;

pub fn main() !void {
    // Here we use an ArenaAllocator backed by a DirectAllocator because a build is a short-lived,
    // one shot program. We don't need to waste time freeing memory and finding places to squish
    // bytes into. So we free everything all at once at the very end.
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer arena.deinit();

    const allocator = &arena.allocator;
    var args = try process.argsAlloc(allocator);
    defer process.argsFree(allocator, args);

    // skip my own exe name
    var arg_idx: usize = 1;

    const zig_exe = nextArg(args, &arg_idx) orelse {
        warn("Expected first argument to be path to zig compiler\n", .{});
        return error.InvalidArgs;
    };
    const build_root = nextArg(args, &arg_idx) orelse {
        warn("Expected second argument to be build root directory path\n", .{});
        return error.InvalidArgs;
    };
    const cache_root = nextArg(args, &arg_idx) orelse {
        warn("Expected third argument to be cache root directory path\n", .{});
        return error.InvalidArgs;
    };

    const builder = try Builder.create(allocator, zig_exe, build_root, cache_root);
    defer builder.destroy();

    var targets = ArrayList([]const u8).init(allocator);

    const stderr_stream = io.getStdErr().outStream();
    const stdout_stream = io.getStdOut().outStream();

    while (nextArg(args, &arg_idx)) |arg| {
        if (mem.startsWith(u8, arg, "-D")) {
            const option_contents = arg[2..];
            if (option_contents.len == 0) {
                warn("Expected option name after '-D'\n\n", .{});
                return usageAndErr(builder, false, stderr_stream);
            }
            if (mem.indexOfScalar(u8, option_contents, '=')) |name_end| {
                const option_name = option_contents[0..name_end];
                const option_value = option_contents[name_end + 1 ..];
                if (try builder.addUserInputOption(option_name, option_value))
                    return usageAndErr(builder, false, stderr_stream);
            } else {
                if (try builder.addUserInputFlag(option_contents))
                    return usageAndErr(builder, false, stderr_stream);
            }
        } else if (mem.startsWith(u8, arg, "-")) {
            if (mem.eql(u8, arg, "--verbose")) {
                builder.verbose = true;
            } else if (mem.eql(u8, arg, "--help")) {
                return usage(builder, false, stdout_stream);
            } else if (mem.eql(u8, arg, "--prefix")) {
                builder.install_prefix = nextArg(args, &arg_idx) orelse {
                    warn("Expected argument after --prefix\n\n", .{});
                    return usageAndErr(builder, false, stderr_stream);
                };
            } else if (mem.eql(u8, arg, "--search-prefix")) {
                const search_prefix = nextArg(args, &arg_idx) orelse {
                    warn("Expected argument after --search-prefix\n\n", .{});
                    return usageAndErr(builder, false, stderr_stream);
                };
                builder.addSearchPrefix(search_prefix);
            } else if (mem.eql(u8, arg, "--override-lib-dir")) {
                builder.override_lib_dir = nextArg(args, &arg_idx) orelse {
                    warn("Expected argument after --override-lib-dir\n\n", .{});
                    return usageAndErr(builder, false, stderr_stream);
                };
            } else if (mem.eql(u8, arg, "--verbose-tokenize")) {
                builder.verbose_tokenize = true;
            } else if (mem.eql(u8, arg, "--verbose-ast")) {
                builder.verbose_ast = true;
            } else if (mem.eql(u8, arg, "--verbose-link")) {
                builder.verbose_link = true;
            } else if (mem.eql(u8, arg, "--verbose-ir")) {
                builder.verbose_ir = true;
            } else if (mem.eql(u8, arg, "--verbose-llvm-ir")) {
                builder.verbose_llvm_ir = true;
            } else if (mem.eql(u8, arg, "--verbose-cimport")) {
                builder.verbose_cimport = true;
            } else if (mem.eql(u8, arg, "--verbose-cc")) {
                builder.verbose_cc = true;
            } else if (mem.eql(u8, arg, "--verbose-llvm-cpu-features")) {
                builder.verbose_llvm_cpu_features = true;
            } else if (mem.eql(u8, arg, "--")) {
                builder.args = argsRest(args, arg_idx);
                break;
            } else {
                warn("Unrecognized argument: {}\n\n", .{arg});
                return usageAndErr(builder, false, stderr_stream);
            }
        } else {
            try targets.append(arg);
        }
    }

    builder.resolveInstallPrefix();
    try runBuild(builder);

    if (builder.validateUserInputDidItFail())
        return usageAndErr(builder, true, stderr_stream);

    builder.make(targets.toSliceConst()) catch |err| {
        switch (err) {
            error.InvalidStepName => {
                return usageAndErr(builder, true, stderr_stream);
            },
            error.UncleanExit => process.exit(1),
            else => return err,
        }
    };
}

fn runBuild(builder: *Builder) anyerror!void {
    switch (@typeInfo(@TypeOf(root.build).ReturnType)) {
        .Void => root.build(builder),
        .ErrorUnion => try root.build(builder),
        else => @compileError("expected return type of build to be 'void' or '!void'"),
    }
}

fn usage(builder: *Builder, already_ran_build: bool, out_stream: var) !void {
    // run the build script to collect the options
    if (!already_ran_build) {
        builder.setInstallPrefix(null);
        builder.resolveInstallPrefix();
        try runBuild(builder);
    }

    try out_stream.print(
        \\Usage: {} build [steps] [options]
        \\
        \\Steps:
        \\
    , .{builder.zig_exe});

    const allocator = builder.allocator;
    for (builder.top_level_steps.toSliceConst()) |top_level_step| {
        const name = if (&top_level_step.step == builder.default_step)
            try fmt.allocPrint(allocator, "{} (default)", .{top_level_step.step.name})
        else
            top_level_step.step.name;
        try out_stream.print("  {s:22} {}\n", .{ name, top_level_step.description });
    }

    try out_stream.writeAll(
        \\
        \\General Options:
        \\  --help                 Print this help and exit
        \\  --verbose              Print commands before executing them
        \\  --prefix [path]        Override default install prefix
        \\  --search-prefix [path] Add a path to look for binaries, libraries, headers
        \\
        \\Project-Specific Options:
        \\
    );

    if (builder.available_options_list.len == 0) {
        try out_stream.print("  (none)\n", .{});
    } else {
        for (builder.available_options_list.toSliceConst()) |option| {
            const name = try fmt.allocPrint(allocator, "  -D{}=[{}]", .{
                option.name,
                Builder.typeIdName(option.type_id),
            });
            defer allocator.free(name);
            try out_stream.print("{s:24} {}\n", .{ name, option.description });
        }
    }

    try out_stream.writeAll(
        \\
        \\Advanced Options:
        \\  --build-file [file]         Override path to build.zig
        \\  --cache-dir [path]          Override path to zig cache directory
        \\  --override-lib-dir [arg]    Override path to Zig lib directory
        \\  --verbose-tokenize          Enable compiler debug output for tokenization
        \\  --verbose-ast               Enable compiler debug output for parsing into an AST
        \\  --verbose-link              Enable compiler debug output for linking
        \\  --verbose-ir                Enable compiler debug output for Zig IR
        \\  --verbose-llvm-ir           Enable compiler debug output for LLVM IR
        \\  --verbose-cimport           Enable compiler debug output for C imports
        \\  --verbose-cc                Enable compiler debug output for C compilation
        \\  --verbose-llvm-cpu-features Enable compiler debug output for LLVM CPU features
        \\
    );
}

fn usageAndErr(builder: *Builder, already_ran_build: bool, out_stream: var) void {
    usage(builder, already_ran_build, out_stream) catch {};
    process.exit(1);
}

fn nextArg(args: [][]const u8, idx: *usize) ?[]const u8 {
    if (idx.* >= args.len) return null;
    defer idx.* += 1;
    return args[idx.*];
}

fn argsRest(args: [][]const u8, idx: usize) ?[][]const u8 {
    if (idx >= args.len) return null;
    return args[idx..];
}