// Console I/O layer of flibc — `puts` and a comptime-format `printf`
// on top of the unified write_fd ABI. Both build their output into a
// stack-resident 256-byte buffer, then emit it to fd 1 (stdout) in a
// single length-carrying syscall. Output longer than 255 bytes is
// silently truncated; the demo programs ship are well below that bound.
//
// Format spec is a deliberate subset of C printf:
//   %%       — literal '%'
//   %s       — null-terminated string ([*:0]const u8)
//   %d / %i  — signed decimal (any int that fits in i64)
//   %u       — unsigned decimal (any int that fits in u64)
//   %x       — lowercase hex (any int that fits in u64)
//   %c       — single byte
// Width / precision / padding are not supported — this is demoware-
// grade by design; richer formatting belongs to future fsh /
// coreutils work once a real userland exercises it.

use "syscalls" as sys

const BUF_LEN usize = 256

/// puts — write a null-terminated string followed by a newline. Mirrors
/// the C library shape (line-buffered, sentinel-terminated input).
pub fn puts(s [*:0]u8) void {
    var buf [BUF_LEN]u8 = undefined
    var pos usize = 0
    // Same BUF_LEN-1 truncation bound printf enforces: copy the input,
    // append the newline, then flush `pos` bytes in one syscall.
    buf_put_zstr(&buf, &pos, s)
    buf_put_byte(&buf, &pos, '\n')
    _ = sys.write_fd(1, &buf, pos)
}

/// printf(fmt, .{args...}) — format and emit. The format string is
/// walked at comptime so the dispatch on each spec resolves to a
/// straight call into the matching `buf_put_*` helper at codegen time;
/// no runtime parser, no jump table.
///
/// Output longer than BUF_LEN-1 (255 bytes) is silently truncated.
/// This matches the demo-grade scope of flibc; production code
/// requiring large prints should use a more robust IO layer.
pub fn printf(comptime fmt []u8, args anytype) void {
    var buf [BUF_LEN]u8 = undefined
    var pos usize = 0

    // Scale evaluation quota linearly with format string length; the
    // + 1000 covers the comptime walker's fixed per-spec overhead.
    #setEvalBranchQuota(8 * fmt.len + 1000)
    comptime var i usize = 0
    comptime var arg_idx usize = 0
    inline while i < fmt.len {
        const c = fmt[i]
        if c == '%' && i + 1 < fmt.len {
            const spec = fmt[i + 1]
            if spec == '%' {
                buf_put_byte(&buf, &pos, '%')
            } else {
                emit_spec(&buf, &pos, spec, args[arg_idx])
                arg_idx += 1
            }
            i += 2
        } else {
            buf_put_byte(&buf, &pos, c)
            i += 1
        }
    }

    const len = if (pos < BUF_LEN) pos else BUF_LEN - 1
    _ = sys.write_fd(1, &buf, len)
}

// Dispatch a single arg-consuming spec. Inline so each call site is
// resolved at the printf comptime walk — `spec` is comptime and only
// the matching arm contributes to runtime code generation. Wrapping
// the args[arg_idx] read in a separate inline fn (rather than a
// switch inside printf) keeps the comptime tuple index away from
// arg-less specs (`%%`, literals): if no arg-consuming spec runs in a
// given iteration, args is never indexed at all.
inline fn emit_spec(buf *mut [BUF_LEN]u8, pos *mut usize, comptime spec u8, arg anytype) void {
    switch spec {
        's' => buf_put_zstr(buf, pos, arg),
        'd', 'i' => buf_put_signed(buf, pos, #intCast(arg)),
        'u' => buf_put_unsigned(buf, pos, #intCast(arg)),
        'x' => buf_put_hex(buf, pos, #intCast(arg)),
        'c' => buf_put_byte(buf, pos, #intCast(arg)),
        else => #compileError("flibc.printf: unsupported %" ++ &[_]u8{spec}),
    }
}

// Saturating byte append — silently drops overflow past BUF_LEN-1 so
// the trailing slot stays free for the '\0' that printf writes before
// flushing. Truncating-on-overflow matches the demo-grade scope; the
// alternative (a syscall-per-flush mid-format) would push complexity
// disproportionate to the use case.
fn buf_put_byte(buf *mut [BUF_LEN]u8, pos *mut usize, c u8) void {
    if pos.* < BUF_LEN - 1 {
        buf[pos.*] = c
        pos.* += 1
    }
}

fn buf_put_zstr(buf *mut [BUF_LEN]u8, pos *mut usize, s [*:0]u8) void {
    var k usize = 0
    while s[k] != 0 {
        buf_put_byte(buf, pos, s[k])
        k += 1
    }
}

fn buf_put_signed(buf *mut [BUF_LEN]u8, pos *mut usize, val i64) void {
    if val < 0 {
        buf_put_byte(buf, pos, '-')
        // i64.min would overflow `-val`; bitcast to u64 to recover the
        // magnitude in two's complement (-i64.min == i64.min reinterpret).
        // Branchless and avoids the IntegerOverflow runtime check.
        const mag u64 = #bitCast(-(val +% 1))
        buf_put_unsigned(buf, pos, mag + 1)
    } else {
        buf_put_unsigned(buf, pos, #intCast(val))
    }
}

fn buf_put_unsigned(buf *mut [BUF_LEN]u8, pos *mut usize, val u64) void {
    if val == 0 {
        buf_put_byte(buf, pos, '0')
        return
    }
    // u64.max is 20 decimal digits; 20 + slack rounds to the nearest
    // power-of-two stack slot.
    var tmp [20]u8 = undefined
    var n usize = 0
    var v = val
    while v > 0 {
        tmp[n] = #intCast('0' + (v % 10))
        n += 1
        v /= 10
    }
    while n > 0 {
        n -= 1
        buf_put_byte(buf, pos, tmp[n])
    }
}

fn buf_put_hex(buf *mut [BUF_LEN]u8, pos *mut usize, val u64) void {
    if val == 0 {
        buf_put_byte(buf, pos, '0')
        return
    }
    const digits = "0123456789abcdef"
    var tmp [16]u8 = undefined
    var n usize = 0
    var v = val
    while v > 0 {
        tmp[n] = digits[#as(usize, #intCast(v & 0xf))]
        n += 1
        v >>= 4
    }
    while n > 0 {
        n -= 1
        buf_put_byte(buf, pos, tmp[n])
    }
}