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: facts [PATH...]
        \\
        \\Print file metadata as TSV. With no PATH args, reads one path per stdin line.
        \\Columns: path kind size mode mtime_ns
        \\
        \\stdout is records only; diagnostics go to stderr.
        \\No filtering, sorting, deletion, exec, expression language, JSON, color, or hidden writes.
        \\
        \\examples:
        \\  files src | facts | pick --header path size
        \\  facts README.md build.zig
        \\
    );
    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 isHelp(arg: []const u8) bool {
    return std.mem.eql(u8, arg, "--help") or std.mem.eql(u8, arg, "-h");
}

fn kindName(kind: std.Io.File.Kind) []const u8 {
    return switch (kind) {
        .file => "file",
        .directory => "dir",
        .sym_link => "symlink",
        .block_device => "block",
        .character_device => "char",
        .named_pipe => "fifo",
        .unix_domain_socket => "socket",
        .whiteout => "whiteout",
        .door => "door",
        .event_port => "eventport",
        .unknown => "unknown",
    };
}

fn modeValue(stat: std.Io.File.Stat) u64 {
    if (@hasDecl(std.Io.File.Permissions, "toMode")) return @intCast(stat.permissions.toMode());
    return 0;
}

fn printError(io: std.Io, path: []const u8, err: anyerror) !void {
    var err_buf: [512]u8 = undefined;
    var errw = std.Io.File.stderr().writer(io, &err_buf);
    try errw.interface.print("facts: {s}: {s}\n", .{ path, @errorName(err) });
    try errw.interface.flush();
}

fn unsupportedPathByte(path: []const u8) ?[]const u8 {
    for (path) |byte| switch (byte) {
        '\t' => return "tab",
        '\n' => return "newline",
        '\r' => return "carriage return",
        else => {},
    };
    return null;
}

fn printUnsupportedPath(io: std.Io, byte_name: []const u8) !void {
    var err_buf: [512]u8 = undefined;
    var errw = std.Io.File.stderr().writer(io, &err_buf);
    try errw.interface.print("facts: unsupported path: contains {s}\n", .{byte_name});
    try errw.interface.flush();
}

fn printFact(io: std.Io, writer: *std.Io.Writer, path: []const u8) !bool {
    if (unsupportedPathByte(path)) |byte_name| {
        try printUnsupportedPath(io, byte_name);
        return false;
    }
    const st = std.Io.Dir.cwd().statFile(io, path, .{}) catch |err| {
        try printError(io, path, err);
        return false;
    };
    try writer.print("{s}\t{s}\t{}\t{o}\t{}\n", .{ path, kindName(st.kind), st.size, modeValue(st), st.mtime.nanoseconds });
    return true;
}

fn printStdinError(io: std.Io, comptime message: []const u8) !void {
    var err_buf: [512]u8 = undefined;
    var errw = std.Io.File.stderr().writer(io, &err_buf);
    try errw.interface.writeAll("facts: stdin: " ++ message ++ "\n");
    try errw.interface.flush();
}

fn printStdinLine(io: std.Io, writer: *std.Io.Writer, raw: []const u8) !bool {
    if (raw.len == 0) return true;
    const ok = try printFact(io, writer, raw);
    try writer.flush();
    return ok;
}

fn readStdinLines(io: std.Io, writer: *std.Io.Writer) !bool {
    var had_error = false;
    var read_buf: [8192]u8 = undefined;
    var line_buf: [std.Io.Dir.max_path_bytes]u8 = undefined;
    var line_len: usize = 0;
    var dropping_long_line = false;

    while (true) {
        const n = try std.posix.read(std.posix.STDIN_FILENO, &read_buf);
        if (n == 0) break;
        for (read_buf[0..n]) |byte| {
            if (byte == '\n') {
                if (!dropping_long_line) {
                    if (!try printStdinLine(io, writer, line_buf[0..line_len])) had_error = true;
                }
                line_len = 0;
                dropping_long_line = false;
                continue;
            }
            if (dropping_long_line) continue;
            if (line_len == line_buf.len) {
                try printStdinError(io, "input path exceeds max path length");
                had_error = true;
                line_len = 0;
                dropping_long_line = true;
                continue;
            }
            line_buf[line_len] = byte;
            line_len += 1;
        }
    }

    if (!dropping_long_line and line_len != 0) {
        if (!try printStdinLine(io, writer, line_buf[0..line_len])) had_error = true;
    }
    return had_error;
}

pub fn main(init: std.process.Init) !void {
    const allocator = init.gpa;

    var help_args = try std.process.Args.Iterator.initAllocator(init.minimal.args, allocator);
    defer help_args.deinit();
    _ = help_args.skip();
    while (help_args.next()) |arg| {
        if (isHelp(arg)) {
            try usage(std.Io.File.stdout(), init.io);
            return;
        }
    }

    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);
    try out.interface.writeAll("path\tkind\tsize\tmode\tmtime_ns\n");

    var saw_arg = false;
    var had_error = false;
    while (args.next()) |arg| {
        saw_arg = true;
        if (!try printFact(init.io, &out.interface, arg)) had_error = true;
    }
    if (!saw_arg) {
        try out.interface.flush();
        had_error = readStdinLines(init.io, &out.interface) catch |err| die(init.io, "facts: stdin: {s}\n", .{@errorName(err)});
    }
    try out.interface.flush();
    if (had_error) std.process.exit(1);
}