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use libc::size_t;
use std::mem;

use constant::{FL_USHIFT, FL_USER_1, FL_USER_3, FL_USER_4};
use types::{c_long, InternalValue, RBasic, Value};

extern "C" {
    pub fn rb_ary_concat(array: Value, other_array: Value) -> Value;
    pub fn rb_ary_dup(array: Value) -> Value;
    pub fn rb_ary_entry(array: Value, offset: c_long) -> Value;
    pub fn rb_ary_join(array: Value, separator: Value) -> Value;
    pub fn rb_ary_new() -> Value;
    pub fn rb_ary_new_capa(capacity: c_long) -> Value;
    pub fn rb_ary_pop(array: Value) -> Value;
    pub fn rb_ary_push(array: Value, item: Value) -> Value;
    pub fn rb_ary_reverse(array: Value) -> Value;
    pub fn rb_ary_shift(array: Value) -> Value;
    pub fn rb_ary_sort_bang(array: Value) -> Value;
    pub fn rb_ary_sort(array: Value) -> Value;
    pub fn rb_ary_store(array: Value, index: c_long, item: Value) -> Value;
    pub fn rb_ary_to_s(array: Value) -> Value;
    pub fn rb_ary_unshift(array: Value, item: Value) -> Value;
}

#[repr(C)]
enum RArrayEmbed {
    Flag = FL_USER_1,
    LenMask = FL_USER_4 | FL_USER_3,
    LenShift = FL_USHIFT + 3,
}

#[repr(C)]
struct RArrayAs {
    heap: RArrayHeap,
}

#[repr(C)]
struct RArrayHeap {
    len: c_long,
    // Really, this is a union but value is the largest item.
    value: InternalValue,
    ptr: InternalValue,
}

#[repr(C)]
struct RArray {
    basic: RBasic,
    as_: RArrayAs,
}

pub unsafe fn rb_ary_len(value: Value) -> c_long {
    let rarray: *const RArray = mem::transmute(value.value);
    let flags = (*rarray).basic.flags;

    if flags & (RArrayEmbed::Flag as size_t) == 0 {
        (*rarray).as_.heap.len
    } else {
        ((flags as i64 >> RArrayEmbed::LenShift as i64) &
         (RArrayEmbed::LenMask as i64 >> RArrayEmbed::LenShift as i64)) as c_long
    }
}