import "@ffi/c"
import "@std/mem"
import "@std/io"
import "@std/arraylist"

PathError :: enum { invalid_path, path_failed, directory_failed, source_too_large }
Error :: alias mem.AllocError | PathError | io.OpenError | io.CloseError | io.ReadError

@hide:file
terminated proc(allocator mem.Allocator, text []u8) []mut u8 ! (mem.AllocError | PathError) {
    if (text.len == 0 or text.len == maxval!(usize)) return .invalid_path
    for (text) |byte| if (byte == 0) return .invalid_path
    bytes :: try mem.alloc(u8, allocator, text.len + 1)
    memcopy!(bytes[..text.len], text)
    bytes[text.len] = 0
    return bytes
}

@hide:file
copy proc(allocator mem.Allocator, text []u8) []mut u8 ! mem.AllocError {
    bytes :: try mem.alloc(u8, allocator, text.len)
    memcopy!(bytes, text)
    return bytes
}

#! caller owns the canonical absolute path; release it with mem.free using `allocator`.
canonical proc(allocator mem.Allocator, path []u8) []mut u8 ! Error {
    input :: try terminated(allocator, path)
    defer mem.free(allocator, input)
    # Darwin realpath requires a PATH_MAX-sized caller buffer (including its terminator).
    buffer [1024]mut u8 := undefined
    if (c.realpath(ptrcast!(input.ptr), ptrcast!(buffer[..].ptr)) == null) {
        if (c.__error()?^ == c.ENOMEM) return .out_of_memory
        return .path_failed
    }
    length := usize(0)
    while (length < buffer.len and buffer[length] != 0) length += 1
    if (length == buffer.len) return .path_failed
    return try copy(allocator, buffer[..length])
}

@hide:file
mode proc(allocator mem.Allocator, path []u8) c_ushort ! Error {
    input :: try terminated(allocator, path)
    defer mem.free(allocator, input)
    result [1]mut c.Stat := undefined
    if (c.stat(ptrcast!(input.ptr), result[..].ptr) == 0)
        return result[0].st_mode

    error :: c.__error()?^
    if (error == c.ENOMEM) return .out_of_memory
    if (error == c.ENOENT or error == c.ENOTDIR) return 0

    return .path_failed
}

is_directory proc(allocator mem.Allocator, path []u8) bool ! Error {
    return ((try mode(allocator, path)) & c_ushort(61440)) == 16384
}

#! returns an owned canonical package directory for either a file or directory input.
directory proc(allocator mem.Allocator, path []u8) []mut u8 ! Error {
    resolved :: try canonical(allocator, path)
    errdefer mem.free(allocator, resolved)
    if (try is_directory(allocator, resolved)) return resolved

    end := resolved.len
    while (end > 1 and resolved[end - 1] != '/') end -= 1
    parent_text :: if (end == 1) resolved[..1] else resolved[..end - 1]
    parent :: try copy(allocator, parent_text)
    mem.free(allocator, resolved)

    return parent
}

@hide:file
join proc(allocator mem.Allocator, base, name []u8) []mut u8 ! mem.AllocError {
    separator :: if (base.len == 1 and base[0] == '/') usize(0) else usize(1)
    if (base.len > maxval!(usize) - separator or name.len > maxval!(usize) - base.len - separator)
        return .out_of_memory

    bytes :: try mem.alloc(u8, allocator, base.len + separator + name.len)
    memcopy!(bytes[..base.len], base)

    if (separator != 0) bytes[base.len] = '/'
    memcopy!(bytes[base.len + separator..], name)

    return bytes
}

@hide:file
exists proc(allocator mem.Allocator, base, name []u8) bool ! Error {
    path :: try join(allocator, base, name)
    defer mem.free(allocator, path)
    input :: try terminated(allocator, path)
    defer mem.free(allocator, input)
    if (c.access(ptrcast!(input.ptr), 0) == 0) return true

    error :: c.__error()?^
    if (error == c.ENOENT or error == c.ENOTDIR) return false

    return .path_failed
}

#! finds the nearest ancestor build.hon/build.bro, otherwise uses the supplied directory.
project_root proc(allocator mem.Allocator, package_dir []u8) []mut u8 ! Error {
    end := package_dir.len
    while true {
        base :: package_dir[..end]
        if (try exists(allocator, base, "build.hon") or try exists(allocator, base, "build.bro"))
            return try copy(allocator, base)

        if (end == 1) break

        while (end > 1 and package_dir[end - 1] != '/') end -= 1
        if (end > 1) end -= 1
    }
    return try copy(allocator, package_dir)
}

#! relative imports start at the importing package; @ imports start at the project root.
resolve proc(allocator mem.Allocator, root_dir, package_dir, import_path []u8) []mut u8 ! Error {
    if (import_path.len == 0 or import_path[0] == '/') return .invalid_path
    for (import_path) |byte| if (byte == 0) return .invalid_path
    base := package_dir
    path := import_path
    if (path[0] == '@') {
        base = root_dir
        path = path[1..]
        if (path.len == 0 or path[0] == '/') return .invalid_path
    }
    joined :: try join(allocator, base, path)
    defer mem.free(allocator, joined)
    return try canonical(allocator, joined)
}

@hide:file
ends_with proc(text, suffix []u8) bool {
    return text.len >= suffix.len and mem.eql(text[text.len - suffix.len..], suffix)
}

@hide:file
before proc(left, right []u8) bool {
    count :: if (left.len < right.len) left.len else right.len
    for 0..count |index| {
        if (left[index] != right[index]) return left[index] < right[index]
    }
    return left.len < right.len
}

#! lists production sources in bytewise order; caller frees every path and the list.
files proc(allocator mem.Allocator, package_dir []u8) arraylist.ArrayList([]u8) ! Error {
    input :: try terminated(allocator, package_dir)
    defer mem.free(allocator, input)
    opened :: c.opendir(ptrcast!(input.ptr))
    if (opened == null) {
        if (c.__error()?^ == c.ENOMEM) return .out_of_memory
        return .directory_failed
    }
    handle :: opened?
    closing := false
    defer { if (!closing) _ = c.closedir(handle) }
    result := arraylist.init([]u8, allocator)
    errdefer {
        for (result.items) |path| mem.free(allocator, path)
        arraylist.deinit(&result)
    }
    while true {
        c.__error()?^ = 0
        next :: c.readdir(handle)
        if (next == null) {
            if (c.__error()?^ != 0) return .directory_failed
            break
        }
        entry :: next?
        # DT_REG, DT_LNK and DT_UNKNOWN; never open directories, sockets or FIFOs as sources.
        if (entry.d_type != 8 and entry.d_type != 10 and entry.d_type != 0) continue
        length :: usize(entry.d_namlen)
        if (length >= 1024) return .directory_failed
        pointer *u8 :: ptrcast!(entry.d_name[..].ptr)
        name :: pointer[..length]
        if ((!ends_with(name, ".hon") and !ends_with(name, ".bro"))
            or ends_with(name, ".test.hon") or ends_with(name, ".test.bro")) continue
        path :: try join(allocator, package_dir, name)
        errdefer mem.free(allocator, path)
        if (entry.d_type != 8 and ((try mode(allocator, path)) & c_ushort(61440)) != 32768) {
            mem.free(allocator, path)
            continue
        }
        try arraylist.append(&result, path)
    }
    closing = true
    if (c.closedir(handle) != 0) return .directory_failed
    # in-place heapsort: deterministic O(n log n), no additional allocation.
    count := result.items.len
    start :: divtrunc!(count, 2)
    for (0..start) |i| sift(result.items, start - i - 1, count)
    while (count > 1) {
        count -= 1
        temporary :: result.items[0]
        result.items[0] = result.items[count]
        result.items[count] = temporary
        sift(result.items, 0, count)
    }
    return result
}

@hide:file
sift proc(items []mut []u8, start, count usize) void {
    root := start
    while (root < divtrunc!(count, 2)) {
        child := root * 2 + 1
        if (child + 1 < count and before(items[child], items[child + 1])) child += 1
        if (!before(items[root], items[child])) break
        temporary :: items[root]
        items[root] = items[child]
        items[child] = temporary
        root = child
    }
}

#! reads through the supplied IO provider; returned bytes belong to the caller.
read_source proc(allocator mem.Allocator, runtime io.Io, path []u8) arraylist.ArrayList(u8) ! Error {
    # source input must be a regular file, not a FIFO/device that can block before reading.
    if (((try mode(allocator, path)) & c_ushort(61440)) != 32768) return .open_failed
    input :: try terminated(allocator, path)
    defer mem.free(allocator, input)
    file :: try io.open(runtime, input.ptr[..path.len;0], .read_only)
    closing := false
    defer { if (!closing) io.close(file) catch |_| {} }
    bytes := io.read_all(allocator, io.reader(file), usize(maxval!(u32))) catch |err| {
        match err {
            .limit_exceeded: return .source_too_large
            else: return err
        }
    }
    errdefer arraylist.deinit(&bytes)
    closing = true
    try io.close(file)
    return bytes
}