const builtin = @import("builtin");
const std = @import("std");

const value = @import("value.zig");

const seq = value.seq;

const Value = value.Value;

/// A "heap value" that could be a Value or object header.
pub const Hval = union {
    value: Value,
    seq_header: seq.Header,
};

var _debugAlloc = switch (builtin.mode) {
    .Debug => std.heap.DebugAllocator(.{}).init,
    else => undefined,
};
const alloc = switch (builtin.mode) {
    .Debug => _debugAlloc.allocator(),
    else => std.heap.smp_allocator,
};

// Cons cells

var cons_pool = std.heap.MemoryPool([2]Value).init(alloc);

pub fn cons(v1: Value, v2: Value) *[2]Value {
    const mem = cons_pool.create() catch @panic("OOM");
    mem[0] = v1;
    mem[1] = v2;
    return mem;
}

// Interned strings

var istr_pool = std.hash_map.StringHashMap(void).init(alloc);

pub fn intern(header: seq.Header, str: []const u8) *seq.Header {
    const hs = @sizeOf(seq.Header);
    const size = str.len + hs;
    const copy = alloc.alloc(u8, size) catch @panic("OOM");
    const header_bytes: [hs]u8 = @bitCast(header);
    @memcpy(copy[0..hs], &header_bytes);
    @memcpy(copy[hs..size], str);
    const entry = istr_pool.getOrPutValue(copy, {}) catch @panic("OOM");
    return @ptrCast(entry.key_ptr);
}

pub fn istrHeader(ptr: *Hval) *seq.Header {
    const entry_key: *[]u8 = @ptrCast(ptr);
    return @alignCast(@ptrCast(entry_key.ptr));
}