//! Top-level module
// SPDX-FileCopyrightText: 2024-2025 Nguyễn Gia Phong
// SPDX-License-Identifier: GPL-3.0-or-later

const ArgsTuple = std.meta.ArgsTuple;
const HashMap = std.AutoHashMapUnmanaged;
const Type = std.builtin.Type;
const assert = std.debug.assert;
const builtin = @import("builtin");
const c = @cImport(@cInclude("janet.h"));
const c_allocator = std.heap.c_allocator;
const eql = std.mem.eql;
const expectEqualDeep = std.testing.expectEqualDeep;
const toLower = std.ascii.toLower;
const std = @import("std");

pub const IgnoredDecl = struct {
    type: type,
    decl: []const u8,
};
const ignored_decls = if (builtin.is_test) [_]IgnoredDecl{
} else @import("root").zsanett_ignored_decls;
comptime {
    assert(@typeInfo(@TypeOf(ignored_decls)).array.child == IgnoredDecl);
}

pub const Environment = @import("Environment.zig");
test {
    _ = Environment;
}

/// Associative list of Zig and wrapped Janet functions.
var fn_map: HashMap(*const anyopaque, c.JanetCFunction) = undefined;

/// Initializes global Janet state, that is thread local.
pub fn init() void {
    _ = c.janet_init(); // always 0
    fn_map = .empty;
}

/// Frees resources managed by Janet.
pub fn deinit() void {
    fn_map.deinit(c_allocator);
    c.janet_deinit();
}

/// Janet environment Table.
pub const Table = c.JanetTable;

/// Janet value structure.
pub const Value = c.Janet;

/// Creates a Janet keyword in kebab-case.
fn keyword(comptime name: [:0]const u8) Value {
    var n: usize = 0;
    var kebab: [name.len * 2]u8 = undefined;
    for (name) |char| {
        switch (char) {
            'A'...'Z' => {
                if (n > 0) {
                    kebab[n] = '-';
                    n += 1;
                }
                kebab[n] = toLower(char);
            },
            '_' => kebab[n] = '-',
            else => kebab[n] = char,
        }
        n += 1;
    }
    kebab[n] = 0;
    return c.janet_keywordv(&kebab, @as(i32, @intCast(n)));
}

/// Gets function argument.
fn getArg(comptime T: type, argv: [*c]Value, n: i32) !T {
    return switch (@typeInfo(T)) {
        .bool => c.janet_getboolean(argv, n) != 0,
        .int => |int| @intCast(switch (int.signedness) {
            .signed => switch (int.bits) {
                0...16 => c.janet_getinteger16,
                17...32 => c.janet_getinteger,
                else => c.janet_getinteger64,
            },
            .unsigned => if (T != usize) switch (int.bits) {
                0...16 => c.janet_getuinteger16,
                17...32 => c.janet_getuinteger,
                else => c.janet_getuinteger64,
            } else c.janet_getsize,
        }(argv, n)),
        .float => @floatCast(c.janet_getnumber(argv, n)),
        else => unwrap(T, argv[@intCast(n)]),
    };
}

/// Wraps native type in Janet value.
pub fn wrap(x: anytype) !Value {
    const T = @TypeOf(x);
    return switch (@typeInfo(T)) {
        .void => c.janet_wrap_nil(),
        .bool => c.janet_wrap_boolean(@intFromBool(x)),
        .int => c.janet_wrap_integer(@intCast(x)),
        .comptime_int => c.janet_wrap_integer(x),
        .float => c.janet_wrap_number(@floatCast(x)),
        .comptime_float  => c.janet_wrap_number(x),
        .enum_literal => keyword(@tagName(x)),
        .array => |info| y: {
            var tuple: [info.len]Value = undefined;
            for (x, &tuple) |src, *dest|
                dest.* = try wrap(src);
            break :y c.janet_wrap_tuple(c.janet_tuple_n(&tuple, tuple.len));
        },
        .@"enum" => switch (x) {
            inline else => |tag| keyword(@tagName(tag)),
        },
        .error_set => switch (x) {
            inline else => |err| keyword("error/" ++ @errorName(err)),
        },
        .error_union => try wrap(x catch |err| err),
        .@"fn" => |info| y: {
            assert(!info.is_generic);
            const entry = try fn_map.getOrPut(c_allocator, &x);
            if (entry.found_existing)
                break :y c.janet_wrap_cfunction(entry.value_ptr.*);
            const n = info.params.len;
            const y = struct {
                fn cfun(argc: i32, argv: [*c]Value) callconv(.C) Value {
                    c.janet_fixarity(argc, n);
                    var args: ArgsTuple(@TypeOf(x)) = undefined;
                    inline for (&args, info.params, 0..) |*arg, param, i| {
                        const P = param.type.?;
                        arg.* = getArg(P, argv, i) catch |err|
                            return wrap(err) catch unreachable;
                    }
                    return wrap(@call(.auto, x, args)) catch |err|
                        (wrap(err) catch unreachable);
                }
            }.cfun;
            entry.value_ptr.* = y;
            break :y c.janet_wrap_cfunction(y);
        },
        .optional => try wrap(x orelse {}),
        .pointer => |info| switch (info.size) {
            .one, .many, .c => c.janet_wrap_pointer(@constCast(@ptrCast(x))),
            .slice => y: {
                const len: i32 = @intCast(x.len * @sizeOf(info.child));
                if (info.is_const) {
                    const string = c.janet_string(@ptrCast(x.ptr), len);
                    break :y c.janet_wrap_string(string);
                } else {
                    const memory: *anyopaque = @ptrCast(x.ptr);
                    const buffer = c.janet_pointer_buffer_unsafe(memory,
                                                                 len, len);
                    break :y c.janet_wrap_buffer(buffer);
                }
            },
        },
        .@"struct" => |info| y: {
            const cfuns = fns: {
                var count: usize = 0;
                var cfuns: [info.decls.len]struct { Value, Value } = undefined;
                inline for (info.decls) |decl_info| {
                    if (comptime for (ignored_decls) |ignored| {
                        if (ignored.type == T and eql(u8, ignored.decl,
                                                      decl_info.name))
                            break true;
                    } else false)
                        continue;
                    const decl = @field(T, decl_info.name);
                    switch (@typeInfo(@TypeOf(decl))) {
                        .@"fn" => |fn_info| if (!fn_info.is_generic) {
                            cfuns[count] = .{
                                keyword(decl_info.name),
                                try wrap(decl),
                            };
                            count += 1;
                        },
                        else => {},
                    }
                }
                break :fns cfuns[0..count];
            };
            const count = cfuns.len + info.fields.len;
            const kv = c.janet_struct_begin(@intCast(count));
            for (cfuns) |cfun| {
                const k, const v = cfun;
                c.janet_struct_put(kv, k, v);
            }
            inline for (info.fields) |field| {
                const k = keyword(field.name);
                const v = @field(x, field.name);
                c.janet_struct_put(kv, k, try wrap(v));
            }
            break :y c.janet_wrap_struct(c.janet_struct_end(kv));
        },
        .@"union" => |info| if (info.tag_type != null) switch (x) {
            inline else => |v, tag| c.janet_wrap_tuple(y: {
                const k = keyword(@tagName(tag));
                const tuple = [_]Value{ k, try wrap(v) };
                break :y c.janet_tuple_n(&tuple, tuple.len);
            }),
        } else @compileError("can't wrap untagged union"),
        .vector => |info| try wrap(@as([info.len]info.child, x)),
        else => @compileError(@typeName(@TypeOf(x))),
    };
}

/// Unwraps Janet value to a tuple head.
fn tupleHead(x: Value) *const c.JanetTupleHead {
    return c.janet_tuple_head(c.janet_unwrap_tuple(x));
}

/// Accesses Janet tuple data type-safely.
fn tupleData(len: comptime_int,
             head: *const c.JanetTupleHead) *const [len]Value {
    assert(head.length == len);
    return @ptrCast(head.data());
}

/// Compares given Janet values for equality.
fn equal(x: Value, y: Value) bool {
    return c.janet_equals(x, y) != 0;
}

/// Checks for Janet nil.
fn isNil(x: Value) bool {
    return c.janet_checktype(x, c.JANET_NIL) != 0;
}

/// Unwraps to native type.
pub fn unwrap(comptime T: type, x: Value) !T {
    return switch (@typeInfo(T)) {
        .void => {},
        .bool => c.janet_unwrap_boolean(x) != 0,
        .int => @intCast(c.janet_unwrap_integer(x)),
        .float => @floatCast(c.janet_unwrap_number(x)),
        inline .array, .vector => |info| y: {
            const head = tupleHead(x);
            var array: [info.len]info.child = undefined;
            for (tupleData(info.len, head).*, &array) |src, *dest|
                dest.* = try unwrap(info.child, src);
            break :y array;
        },
        .@"enum" => |info| inline for (info.fields) |field| {
            if (equal(keyword(field.name), x))
                break @field(T, field.name);
        } else error.NoCorrespodingEnum,
        .@"fn" => y: {
            var iterator = fn_map.iterator();
            while (iterator.next()) |entry|
                if (entry.value_ptr.* == c.janet_unwrap_cfunction(x))
                    break :y entry.key_ptr.*;
            break :y error.UnknownFunction;
        },
        .optional => |info| if (isNil(x)) null else unwrap(info.child, x),
        .pointer => |info| switch (info.size) {
            .one, .many, .c => @alignCast(@ptrCast(c.janet_unwrap_pointer(x))),
            .slice => slice: {
                const ptr = if (info.is_const)
                    c.janet_unwrap_string(x)
                else
                    c.janet_unwrap_buffer(x).*.data;
                comptime var many_info = info;
                many_info.size = .many;
                const Many = @Type(Type{ .pointer = many_info });
                const many: Many = @alignCast(@ptrCast(ptr));
                const size = if (info.is_const)
                    c.janet_string_length(ptr)
                else
                    c.janet_unwrap_buffer(x).*.count;
                const len = @divExact(size, @sizeOf(info.child));
                break :slice if (info.sentinel()) |sentinel|
                    many[0..@intCast(len):sentinel]
                else
                    many[0..@intCast(len)];
            },
        },
        .@"struct" => |info| y: {
            const src = c.janet_unwrap_struct(x);
            var dest: T = undefined;
            inline for (info.fields) |field| {
                const k = keyword(field.name);
                const v = c.janet_struct_get(src, k);
                @field(dest, field.name) = if (isNil(v))
                    field.defaultValue() orelse return error.MissingStructField
                else
                    try unwrap(field.type, v);
            }
            break :y dest;
        },
        .@"union" => |info| if (info.tag_type != null) y: {
            const head = tupleHead(x);
            const k, const v = tupleData(2, head).*;
            inline for (info.fields) |field| {
                if (equal(keyword(field.name), k))
                    break :y @unionInit(T, field.name,
                                            try unwrap(field.type, v));
            } else break :y error.UnionTagNotFound;
        } else @compileError("can't wrap untagged union"),
        else => @compileError(@typeName(T)),
    };
}

test "isomorphism" {
    init();
    defer deinit();
    const Immutable = struct {
        nothing: void = {},
        boolean: bool = true,
        integer: u16 = 42069,
        float: f64 = 420.69,
        enumeration: enum { this, that } = .that,
        array: [3]u64 = .{ 1, 4, 2 },
        string: [:0]const u8 = "foobar",
        c_string: [*c]const u8 = "baz",
        slice: []const i32 = &.{ 8, 1, 4 },
        tagged_union: union(enum) {
            integer: i32,
            float: f32,
        } = .{ .integer = 123456789 },
        vector: @Vector(3, u4) = .{ 5, 6, 7 },

        pub fn sum(i: @This()) f64 {
            return @as(f64, @floatFromInt(i.integer)) + i.float;
        }
    };
    const i = Immutable{};
    try expectEqualDeep(i, try unwrap(Immutable, try wrap(i)));
    const sum = try unwrap(@TypeOf(&Immutable.sum), try wrap(Immutable.sum));
    try expectEqualDeep(i.sum(), sum(i));

    var array: [2]bool = undefined;
    const buffer: []bool = &array;
    buffer[0] = false;
    buffer[1] = true;
    try expectEqualDeep(buffer, try unwrap(@TypeOf(buffer), try wrap(buffer)));
}