import "@std/mem"
import "@std/io"
import "@std/fs"
import "@std/arraylist"

SourceError :: enum { source_too_large }

Error :: alias fs.Error
    | SourceError
    | io.OpenError
    | io.CloseError
    | io.ReadError

@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
}

#! 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 fs.canonical(allocator, path)
    errdefer mem.free(allocator, resolved)
    if (try fs.kind(allocator, resolved) == .directory) 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
}

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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
}

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exists proc(allocator mem.Allocator, base, name []u8) bool ! Error {
    path :: try join(allocator, base, name)
    defer mem.free(allocator, path)
    return try fs.exists(allocator, path)
}

#! 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 fs.canonical(allocator, joined)
}

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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 {
    handle := try fs.open_directory(allocator, package_dir)
    closing := false
    defer { if (!closing) fs.close_directory(&handle) catch |_| {} }
    result := arraylist.init([]u8, allocator)
    errdefer {
        for (result.items) |path| mem.free(allocator, path)
        arraylist.deinit(&result)
    }
    while (try fs.next(&handle)) |entry| {
        if (
            entry.kind != .file
            and entry.kind != .link
            and entry.kind != .unknown
        ) continue
        name :: entry.name
        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.kind != .file and try fs.kind(allocator, path) != .file) {
            mem.free(allocator, path)
            continue
        }
        try arraylist.append(&result, path)
    }
    closing = true
    try fs.close_directory(&handle)
    # 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
}

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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
    }
}

#! the compiler limits source size to its u32 span address space; storage remains caller-owned.
read_source proc(allocator mem.Allocator, runtime io.Io, path []u8) arraylist.ArrayList(u8) ! Error {
    return fs.read_file(allocator, runtime, path, usize(maxval!(u32))) catch |err| {
        match err {
            .limit_exceeded: return .source_too_large
            else: return err
        }
    }
}