//! Runtime Object, whose memory is managed through the virtual machine's
//! garbage collector.
//!
//! This structure is the base object type that is embedded into subtypes.
//! Each subtype has a `.create` method to allocate a new object.
const std = @import("std");
const Story = @import("../Story.zig");
const Object = @This();

tag: Tag,
is_marked: bool = false,
node: std.SinglyLinkedList.Node = .{},

pub const Tag = enum {
    string,
    code,
    knot,

    pub fn tagBytes(tag: Tag) []const u8 {
        return switch (tag) {
            .string => "String",
            .code => "Code",
            .knot => "Knot",
        };
    }

    pub fn ObjectType(comptime tag: Tag) type {
        return switch (tag) {
            .string => Object.String,
            .code => Object.Code,
            .knot => Object.Knot,
        };
    }
};

pub fn eql(lhs: *Object, rhs: *Object) bool {
    if (lhs.tag != rhs.tag) return false;
    return switch (lhs.tag) {
        .string => blk: {
            const lhs_object: *Object.String = @ptrCast(lhs);
            const rhs_object: *Object.String = @ptrCast(rhs);
            break :blk std.mem.eql(u8, lhs_object.toSlice(), rhs_object.toSlice());
        },
        .code => |_| false,
        .knot => |_| false,
    };
}

pub fn destroy(obj: *Object, story: *Story) void {
    inline for (comptime std.meta.fields(Tag)) |field| {
        const tag = @field(Tag, field.name);
        if (obj.tag == tag) {
            const typed_obj: *Tag.ObjectType(tag) = @alignCast(@fieldParentPtr("base", obj));
            typed_obj.destroy(story);
            return;
        }
    }
    unreachable;
}

pub const String = struct {
    base: Object,
    hash: u32, // TODO: Not implemented.
    length: usize, // TODO: This could probably be u32.
    bytes: [*]const u8,

    const Type = Object.String;

    pub const Options = struct {
        bytes: []const u8,
    };

    pub fn create(story: *Story, options: Options) error{OutOfMemory}!*Object.String {
        const gpa = story.allocator;
        const alloc_len = @sizeOf(Type) + options.bytes.len + 1;
        const raw = try gpa.alignedAlloc(u8, .of(Type), alloc_len);
        const object: *Type = @ptrCast(raw);

        object.* = .{
            .base = .{ .tag = .string },
            .hash = 0,
            .length = options.bytes.len,
            .bytes = undefined,
        };

        // Point bytes slice to the memory *after* the struct
        const buf = raw[@sizeOf(Type)..][0 .. options.bytes.len + 1];
        object.bytes = buf.ptr;
        @memcpy(buf[0..options.bytes.len], options.bytes);
        buf[options.bytes.len] = 0;

        story.gc_objects.prepend(&object.base.node);
        return object;
    }

    pub fn destroy(obj: *String, story: *Story) void {
        const gpa = story.allocator;
        const alloc_len = @sizeOf(Type) + obj.length + 1;
        const base: [*]align(@alignOf(Type)) u8 = @ptrCast(obj);
        gpa.free(base[0..alloc_len]);
    }

    pub fn toSlice(obj: *const Object.String) []const u8 {
        return obj.bytes[0..obj.length];
    }

    pub fn fromValue(story: *Story, value: Story.Value) !*Object.String {
        const print_buffer_len = 64;
        var print_buffer: [print_buffer_len]u8 = undefined;
        switch (value) {
            .nil, .bool, .int, .float => {
                const bytes = try std.fmt.bufPrint(&print_buffer, "{f}", .{value});
                return .create(story, .{ .bytes = bytes });
            },
            .object => |object| switch (object.tag) {
                .string => return @ptrCast(object),
                else => return error.TypeError,
            },
        }
    }

    pub fn concat(story: *Story, lhs: *String, rhs: *String) !*Object.String {
        const gpa = story.allocator;
        const length = lhs.length + rhs.length;
        const bytes = try gpa.alloc(u8, length + 1);
        defer gpa.free(bytes);

        @memcpy(bytes[0..lhs.length], lhs.bytes[0..lhs.length]);
        @memcpy(bytes[lhs.length..], rhs.bytes[0..rhs.length]);
        //ink_gc_disown(story, INK_OBJ(lhs));
        //ink_gc_disown(story, INK_OBJ(rhs));
        return .create(story, .{ .bytes = bytes });
    }
};

/// Immutable object type for code chunks.
pub const Code = struct {
    base: Object,
    /// Number of arguments.
    args_count: u32,
    /// Number of local variables.
    locals_count: u32,
    /// Stack size required to load.
    stack_size: u32,
    /// Table of global constant indexes.
    constants: []const u8,
    /// Raw compiled bytecode.
    bytecode: []const u8,

    pub const Options = struct {
        args_count: u32,
        locals_count: u32,
        stack_size: u32,
        constants: []const u8,
        code_bytes: []const u8,
    };

    const Type = Code;

    pub fn create(story: *Story, options: Options) error{OutOfMemory}!*Object.Code {
        const gpa = story.allocator;
        const raw = try gpa.alignedAlloc(u8, .of(Type), @sizeOf(Type));
        const obj: *Type = @ptrCast(raw);

        obj.* = .{
            .base = .{ .tag = .code },
            .args_count = options.args_count,
            .locals_count = options.locals_count,
            .stack_size = options.stack_size,
            .constants = options.constants,
            .bytecode = options.code_bytes,
        };

        story.gc_objects.prepend(&obj.base.node);
        return obj;
    }

    pub fn destroy(obj: *Code, story: *Story) void {
        const gpa = story.allocator;
        gpa.free(obj.constants);
        gpa.free(obj.bytecode);

        const base: [*]align(@alignOf(Type)) u8 = @ptrCast(obj);
        gpa.free(base[0..@sizeOf(Type)]);
    }
};

pub const Knot = struct {
    base: Object,
    /// Pointer to the name of the knot.
    name: *Object.String,
    /// Pointer to the code object for the knot.
    code: *Object.Code,
    members: std.StringHashMapUnmanaged(*Object) = .empty,

    pub const Options = struct {
        name: []const u8,
        code: *Object.Code,
    };

    const Type = Knot;

    pub fn create(story: *Story, options: Options) error{OutOfMemory}!*Object.Knot {
        const gpa = story.allocator;
        const raw = try gpa.alignedAlloc(u8, .of(Type), @sizeOf(Type));
        const obj: *Type = @ptrCast(raw);

        obj.* = .{
            .base = .{ .tag = .knot },
            .name = try .create(story, .{
                .bytes = options.name,
            }),
            .code = options.code,
            .members = .empty,
        };

        story.gc_objects.prepend(&obj.base.node);
        return obj;
    }

    pub fn destroy(obj: *Knot, story: *Story) void {
        const gpa = story.allocator;
        obj.members.deinit(gpa);

        const alloc_len = @sizeOf(Type);
        const base: [*]align(@alignOf(Type)) u8 = @ptrCast(obj);
        gpa.free(base[0..alloc_len]);
    }
};