// strings — operations over str ({ptr,len}). Hare port; see
// ref/hare/strings/.
//
// Documented divergences from Hare:
//
//   - `concat(a, b)` is 2-arg. Hare ships `concat(strs: str...)`
//     (ref/hare/strings/concat.ha:5). Blocks on task #16 (cstage
//     variadic-pack drops .len of multi-field element type). Cite
//     reverts on fix.
//   - `trim` / `ltrim` / `rtrim` take a single rune. Hare's are
//     `(exclude: rune...)` (ref/hare/strings/trim.ha:54). Same
//     blocker as concat. Hare's no-rune branch (strip whitespace)
//     is also dropped — depends on a rune set.
//   - `contains` is non-variadic. Hare's is
//     `contains(haystack, needles: (str | rune)...)`
//     (ref/hare/strings/contains.ha:9). Same blocker.
//   - `byteindex` / `rbyteindex` rune arms encode via
//     `utf8.encoderune`; the legacy impls scanned for `r: u8` (an
//     undocumented ASCII-only restriction that silently dropped
//     to the wrong byte for U+80..U+7FF and higher).
//   - `dup(s: str) str` — Hare returns `(str | nomem)`. ww's
//     `os.alloc` aborts on OOM (no `nomem` type), so we return plain
//     `str`. Empty input returns `{nil, 0}`; Hare returns the static
//     empty string — same observable result.
//   - `iterator` is flattened (`offs`, `src`, `reverse` fields).
//     Hare uses anonymous-embedded `utf8::decoder`
//     (ref/hare/strings/iter.ha:6-9); ww has no anonymous-embed
//     syntax, so `next`/`prev` copy `offs`/`src` into a local
//     `utf8.decoder` for the call, then write `offs` back.
//   - Hare's private `move()` helper dispatches on a `forward: bool`
//     using a function-pointer `let fun = if (forward) &utf8::next
//     else &utf8::prev`. ww has no fn-pointers in scope yet, so the
//     dispatch is a branch on `forward` selecting the call site.
//   - `slice` deferred — Hare's `fromutf8_unsafe(utf8::slice(begin,
//     end))` (ref/hare/strings/iter.ha:76) hits wwstage fnretlookup
//     same-name cross-module phantom return-ABI fixup (task #34).
//     Lands once #34 clears.

package strings;

import bytes;
import encoding.utf8;
import os;

// toutf8 — borrowed []u8 view of `s`. ref/hare/strings/utf8.ha:29.
// `cap` equals `len`; the slice does not own a separate allocation.
export fn toutf8(s: str) []u8 = {
	let r: []u8;
	r.ptr = s.ptr;
	r.len = s.len;
	r.cap = s.len;
	return r;
};

// fromutf8_unsafe — borrowed str view of `in`. Does not validate.
// ref/hare/strings/utf8.ha:10.
export fn fromutf8_unsafe(in: []u8) str = {
	let r: str;
	r.ptr = in.ptr;
	r.len = in.len;
	return r;
};

// compare — three-way bytewise codepoint-order comparison.
// ref/hare/strings/compare.ha:12.
export fn compare(a: str, b: str) i32 = {
	let n: i32 = a.len;
	if (b.len < n) { n = b.len; };
	let i: i32 = 0;
	for (i < n) {
		if (a[i] != b[i]) { return (a[i]: i32) - (b[i]: i32); };
		i += 1;
	};
	return a.len - b.len;
};

// dup — allocate a fresh copy of `s`. Caller releases with
// `os.free(r.ptr, r.len: u64)`. ref/hare/strings/dup.ha:7.
export fn dup(s: str) str = {
	let r: str;
	r.ptr = nil;
	r.len = 0;
	if (s.len == 0) { return r; };
	let buf: *u8 = os.alloc(s.len: u64): *u8;
	let i: i32 = 0;
	for (i < s.len) { buf[i] = s[i]; i += 1; };
	r.ptr = buf;
	r.len = s.len;
	return r;
};

// freeall — release each element + the slice header. The natural
// disposer for any `[]str` of dup'd elements (e.g. shlex.split).
// ref/hare/strings/dup.ha:38.
//
// Empty elements (`{nil, 0}` from a zero-length dup) are skipped:
// os.free on a nil pointer at len 0 tickles the rt_free guard. The
// slice header itself is freed at `cap * 16` (one str = 16B); a
// never-grown slice (cap == 0) skips the header free.
export fn freeall(s: []str) void = {
	let i: i32 = 0;
	for (i < s.len) {
		if (s[i].len > 0) {
			os.free(s[i].ptr: *void, s[i].len: u64);
		};
		i += 1;
	};
	if (s.cap > 0) {
		os.free(s.ptr: *void, (s.cap: u64) * 16u64);
	};
};

// concat — fresh allocation containing `a` then `b`. Caller releases
// with `os.free(r.ptr, r.len: u64)`. ref/hare/strings/concat.ha:5
// (subset: Hare's `(strs: str...)` blocks on task #16).
export fn concat(a: str, b: str) str = {
	let total: i32 = a.len + b.len;
	let buf: *u8 = os.alloc(total: u64): *u8;
	let i: i32 = 0;
	for (i < a.len) { buf[i] = a[i]; i += 1; };
	let j: i32 = 0;
	for (j < b.len) { buf[a.len + j] = b[j]; j += 1; };
	let r: str;
	r.ptr = buf;
	r.len = total;
	return r;
};

// sub — borrowed `s[start..end]`. ref/hare/strings/sub.ha:30 is
// rune-wise; this ww form is byte-wise (no rune iterator yet, planned
// for commit 2). Clamps out-of-range silently where Hare aborts —
// retained for the existing getopt caller; will graduate when the
// rune-wise form lands.
export fn sub(s: str, start: i32, end: i32) str = {
	let lo: i32 = start;
	let hi: i32 = end;
	if (lo < 0)     { lo = 0; };
	if (hi > s.len) { hi = s.len; };
	if (hi < lo)    { hi = lo; };
	let r: str;
	r.ptr = s.ptr + (lo: u64);
	r.len = hi - lo;
	return r;
};

// runebytes — encode `r` into caller's `scratch` (must hold 4 bytes)
// and return the borrowed slice trimmed to the encoded length. Hare
// inlines the same shape at ref/hare/strings/index.ha:132.
fn runebytes(scratch: []u8, r: rune) []u8 = {
	let n: i32 = utf8.encoderune(scratch, r);
	let s: []u8;
	s.ptr = scratch.ptr;
	s.len = n;
	s.cap = n;
	return s;
};

// hasprefix — true iff `in` begins with `prefix`.
// ref/hare/strings/suffix.ha:8.
export fn hasprefix(in: str, prefix: (str | rune)) bool = {
	let scratch: [4]u8;
	let p: []u8 = match (prefix) {
	case let s: str  => yield toutf8(s);
	case let r: rune => yield runebytes(scratch[0:4], r);
	};
	return bytes.hasprefix(toutf8(in), p);
};

// hassuffix — true iff `in` ends with `suff`.
// ref/hare/strings/suffix.ha:26.
export fn hassuffix(in: str, suff: (str | rune)) bool = {
	let scratch: [4]u8;
	let s: []u8 = match (suff) {
	case let v: str  => yield toutf8(v);
	case let r: rune => yield runebytes(scratch[0:4], r);
	};
	return bytes.hassuffix(toutf8(in), s);
};

// byteindex — byte-wise offset of `needle` in `haystack`, or void if
// absent. ref/hare/strings/index.ha:127. Rune arm encodes via
// utf8.encoderune (Hare passes the encoded slice straight to
// bytes::index).
export fn byteindex(haystack: str, needle: (str | rune)) (i32 | void) = {
	let scratch: [4]u8;
	let n: []u8 = match (needle) {
	case let s: str  => yield toutf8(s);
	case let r: rune => yield runebytes(scratch[0:4], r);
	};
	return bytes.index(toutf8(haystack), n);
};

// rbyteindex — byte-wise offset of the last `needle` in `haystack`.
// ref/hare/strings/index.ha:138.
export fn rbyteindex(haystack: str, needle: (str | rune)) (i32 | void) = {
	let scratch: [4]u8;
	let n: []u8 = match (needle) {
	case let s: str  => yield toutf8(s);
	case let r: rune => yield runebytes(scratch[0:4], r);
	};
	return bytes.rindex(toutf8(haystack), n);
};

// contains — true iff `needle` occurs in `haystack`.
// ref/hare/strings/contains.ha:9 (subset: Hare's variadic form
// `(needles: (str | rune)...)` blocks on task #16).
export fn contains(haystack: str, needle: (str | rune)) bool = {
	match (byteindex(haystack, needle)) {
	case let i: i32 => return true;
	case void       => return false;
	};
	return false;
};

// trimprefix — `s` with `prefix` stripped from the front, or `s`
// unchanged if it doesn't start with `prefix`. Borrowed view.
// ref/hare/strings/trim.ha:60.
export fn trimprefix(input: str, prefix: str) str = {
	if (!hasprefix(input, prefix)) { return input; };
	let r: str;
	r.ptr = input.ptr + (prefix.len: u64);
	r.len = input.len - prefix.len;
	return r;
};

// trimsuffix — symmetric. ref/hare/strings/trim.ha:69.
export fn trimsuffix(input: str, suffix: str) str = {
	if (!hassuffix(input, suffix)) { return input; };
	let r: str;
	r.ptr = input.ptr;
	r.len = input.len - suffix.len;
	return r;
};

// ltrim — strip occurrences of `exclude` (encoded as UTF-8) from the
// front. Borrowed view. ref/hare/strings/trim.ha:11 (subset: single
// rune; Hare's `(trim: rune...)` blocks on task #16). The no-rune
// strip-whitespace branch is omitted for the same reason.
export fn ltrim(input: str, exclude: rune) str = {
	let scratch: [4]u8;
	let pat: []u8 = runebytes(scratch[0:4], exclude);
	let i: i32 = 0;
	for (i + pat.len <= input.len) {
		let j: i32 = 0;
		let ok: bool = true;
		for (j < pat.len) {
			if (input[i + j] != pat[j]) { ok = false; j = pat.len; }
			else { j += 1; };
		};
		if (!ok) { break; };
		i += pat.len;
	};
	let r: str;
	r.ptr = input.ptr + (i: u64);
	r.len = input.len - i;
	return r;
};

// rtrim — strip occurrences of `exclude` from the end. Borrowed view.
// ref/hare/strings/trim.ha:32 (same subset note).
export fn rtrim(input: str, exclude: rune) str = {
	let scratch: [4]u8;
	let pat: []u8 = runebytes(scratch[0:4], exclude);
	let n: i32 = input.len;
	for (n >= pat.len) {
		let off: i32 = n - pat.len;
		let j: i32 = 0;
		let ok: bool = true;
		for (j < pat.len) {
			if (input[off + j] != pat[j]) { ok = false; j = pat.len; }
			else { j += 1; };
		};
		if (!ok) { break; };
		n -= pat.len;
	};
	let r: str;
	r.ptr = input.ptr;
	r.len = n;
	return r;
};

// trim — strip from both ends. ref/hare/strings/trim.ha:54.
export fn trim(input: str, exclude: rune) str = {
	return ltrim(rtrim(input, exclude), exclude);
};

// iterator — UTF-8 rune cursor over a `str`. Layout flattens Hare's
// anonymous-embedded `utf8::decoder` (ref/hare/strings/iter.ha:6-9) to
// explicit fields. `reverse` selects walk direction: forward iterators
// (`iter`) advance through utf8.next; reverse iterators (`riter`) advance
// through utf8.prev. May be copied to save state.
export type iterator = struct {
	offs:    i32,
	src:     []u8,
	reverse: bool,
};

// iter — initialize a forward iterator at the start of `src`.
// ref/hare/strings/iter.ha:24.
export fn iter(src: str) iterator = {
	let r: iterator;
	r.src = toutf8(src);
	r.offs = 0;
	r.reverse = false;
	return r;
};

// riter — initialize a reverse iterator at the end of `src`. `next`
// on a reverse iterator walks back through the string.
// ref/hare/strings/iter.ha:32.
export fn riter(src: str) iterator = {
	let r: iterator;
	r.src = toutf8(src);
	r.offs = src.len;
	r.reverse = true;
	return r;
};

// move — private dispatch shared by next/prev. `forward` selects
// utf8.next vs utf8.prev. Aborts on more/invalid per Hare's
// ref/hare/strings/iter.ha:51-58 ("Invalid UTF-8 string (this should
// not happen)"). Hare picks the utf8 function via a fn-pointer; ww
// branches on `forward` at each call site instead.
fn move(forward: bool, it: *iterator) (rune | utf8.done) = {
	let d: utf8.decoder;
	d.src = it.src;
	d.offs = it.offs;
	if (forward) {
		match (utf8.next(&d)) {
		case let r: rune          => { it.offs = d.offs; return r; };
		case let dn: utf8.done    => return dn;
		case let m:  utf8.more    => abort("strings.move: invalid UTF-8");
		case let e:  utf8.invalid => abort("strings.move: invalid UTF-8");
		};
	} else {
		match (utf8.prev(&d)) {
		case let r: rune          => { it.offs = d.offs; return r; };
		case let dn: utf8.done    => return dn;
		case let m:  utf8.more    => abort("strings.move: invalid UTF-8");
		case let e:  utf8.invalid => abort("strings.move: invalid UTF-8");
		};
	};
};

// next — advance the iterator one rune. Forward iterators step
// through utf8.next; reverse iterators (riter) step backward through
// utf8.prev. Returns utf8.done at end-of-walk. ref/hare/strings/iter.ha:45.
export fn next(it: *iterator) (rune | utf8.done) = {
	return move(!it.reverse, it);
};

// prev — step back one rune. Dual to next: on a forward iterator
// this walks utf8.prev; on a reverse iterator (riter) it walks
// utf8.next. ref/hare/strings/iter.ha:49.
export fn prev(it: *iterator) (rune | utf8.done) = {
	return move(it.reverse, it);
};

// iterstr — borrowed view of the bytes remaining in the iterator's
// walk direction. Forward iter: bytes from offs to end; reverse iter:
// bytes from start to offs. ref/hare/strings/iter.ha:63.
export fn iterstr(it: *iterator) str = {
	let r: []u8;
	if (it.reverse) {
		r = it.src[0:it.offs];
	} else {
		r = it.src[it.offs:it.src.len];
	};
	return fromutf8_unsafe(r);
};

// strings.slice deferred — Hare's delegation form
// `fromutf8_unsafe(utf8::slice(begin, end))` (ref/hare/strings/iter.ha:76)
// triggers wwstage fnretlookup same-name cross-module phantom return-ABI
// fixup (task #34, Class A wwstage UNDER, sub-bug of #4e). Inlining the
// body would diverge from Hare at API level (rule 9). Land after #34.

// position — byte-wise offset of the iterator in its source.
// ref/hare/strings/iter.ha:82.
export fn position(it: *iterator) i32 = {
	return it.offs;
};