const std = @import("std");

fn usage(file: std.Io.File, io: std.Io) !void {
    var buf: [1024]u8 = undefined;
    var w = file.writer(io, &buf);
    try w.interface.writeAll(
        \\usage: have [NAME...]
        \\
        \\List executable command names found in PATH, one per line.
        \\With NAME args, print the names that are available and exit 1 if any are missing.
        \\This inspects PATH only; it does not know shell builtins, aliases, functions, or packages.
        \\
        \\stdout:
        \\  one command name per line
        \\
        \\examples:
        \\  have | grep '^zig$'
        \\  have zig git curl
        \\
    );
    try w.interface.flush();
}

fn die(io: std.Io, comptime fmt: []const u8, args: anytype) noreturn {
    var buf: [512]u8 = undefined;
    var w = std.Io.File.stderr().writer(io, &buf);
    w.interface.print(fmt, args) catch {};
    w.interface.flush() catch {};
    std.process.exit(1);
}

fn pathEnv() []const u8 {
    const raw = std.c.getenv("PATH") orelse return "";
    return std.mem.span(raw);
}

fn commandName(name: []const u8) bool {
    return name.len != 0 and std.mem.indexOfScalar(u8, name, '/') == null;
}

fn executableFileInDir(dir: std.Io.Dir, io: std.Io, name: []const u8) bool {
    const stat = dir.statFile(io, name, .{}) catch return false;
    if (stat.kind != .file) return false;
    dir.access(io, name, .{ .execute = true }) catch return false;
    return true;
}

fn haveOne(io: std.Io, name: []const u8) bool {
    if (!commandName(name)) return false;

    var dirs = std.mem.splitScalar(u8, pathEnv(), ':');
    while (dirs.next()) |dir_path| {
        const actual_dir = if (dir_path.len == 0) "." else dir_path;
        var dir = std.Io.Dir.cwd().openDir(io, actual_dir, .{}) catch continue;
        defer dir.close(io);
        if (executableFileInDir(dir, io, name)) return true;
    }
    return false;
}

fn listDir(io: std.Io, writer: *std.Io.Writer, seen: *std.StringHashMap(void), dir_path: []const u8) !void {
    var dir = std.Io.Dir.cwd().openDir(io, dir_path, .{ .iterate = true }) catch return;
    defer dir.close(io);

    var it = dir.iterate();
    while (try it.next(io)) |entry| {
        if (!commandName(entry.name)) continue;
        if (seen.contains(entry.name)) continue;
        if (!executableFileInDir(dir, io, entry.name)) continue;

        const owned = try seen.allocator.dupe(u8, entry.name);
        errdefer seen.allocator.free(owned);
        try seen.put(owned, {});
        try writer.print("{s}\n", .{entry.name});
    }
}

fn listAll(allocator: std.mem.Allocator, io: std.Io, writer: *std.Io.Writer) !void {
    var seen = std.StringHashMap(void).init(allocator);
    defer {
        var keys = seen.keyIterator();
        while (keys.next()) |key| allocator.free(key.*);
        seen.deinit();
    }

    var dirs = std.mem.splitScalar(u8, pathEnv(), ':');
    while (dirs.next()) |dir_path| {
        const actual_dir = if (dir_path.len == 0) "." else dir_path;
        try listDir(io, writer, &seen, actual_dir);
    }
}

pub fn main(init: std.process.Init) !void {
    const allocator = init.gpa;
    var args = try std.process.Args.Iterator.initAllocator(init.minimal.args, allocator);
    defer args.deinit();
    _ = args.skip();

    var out_buf: [8192]u8 = undefined;
    var out = std.Io.File.stdout().writer(init.io, &out_buf);

    var names = std.ArrayList([]const u8).empty;
    defer names.deinit(allocator);
    while (args.next()) |arg| {
        if (std.mem.eql(u8, arg, "--help") or std.mem.eql(u8, arg, "-h")) {
            try usage(std.Io.File.stdout(), init.io);
            return;
        }
        try names.append(allocator, arg);
    }

    if (names.items.len == 0) {
        listAll(allocator, init.io, &out.interface) catch |err| die(init.io, "have: {s}\n", .{@errorName(err)});
        try out.interface.flush();
        return;
    }

    var missing = false;
    for (names.items) |name| {
        if (haveOne(init.io, name)) {
            try out.interface.print("{s}\n", .{name});
        } else {
            missing = true;
        }
    }
    try out.interface.flush();
    if (missing) std.process.exit(1);
}

test commandName {
    try std.testing.expect(commandName("zig"));
    try std.testing.expect(commandName("."));
    try std.testing.expect(!commandName(""));
    try std.testing.expect(!commandName("./zig"));
    try std.testing.expect(!commandName("bin/zig"));
}