// modules for managing loading dynamic libraries
//

const ModuleInterface = struct {
    startup: *const fn (*anyopaque, ?*anyopaque) callconv(.C) bool = undefined,
    shutdown: *const fn () callconv(.C) void = undefined,
};

pub const ModuleLoaderArgs = extern struct {
    firstLoad: bool,
    engine: *core.Engine,
    nameRegistry: *p2.NameRegistry,
    packerFS: *core.PackerFS,
    // luaState: *anyopaque,
    // luaAllocator: *anyopaque,
    debugDrawInterface: *debug.DebugDrawInterface,
};

pub const LoadedModule = struct {
    baseModulePath: []const u8,
    moduleName: []const u8,
    stagedPaths: std.ArrayListUnmanaged([]u8) = .{},
    loaded: std.ArrayListUnmanaged(ModuleInterface) = .{},
    activePath: ?[]const u8 = null,
    stagingCount: u32 = 0,
    lastLoad: i64 = 0,
    lastModification: i64 = 0,

    pdbPath: ?[]const u8 = null,

    startOnLoad: bool = true,
    started: bool = false,
    initialLoad: bool = true,
    autoLoad: bool = true,
    loadNextFrame: bool = false,

    pub fn getInterface(self: @This()) ?ModuleInterface {
        return self.loaded.getLastOrNull();
    }

    pub fn stageModule(self: *@This(), allocator: std.mem.Allocator) !void {
        //const stagingDirectory = ".modulecache/<name>/0/";
        const stagingDirectoryPath = try std.fmt.allocPrint(allocator, ".modulecache/{d}/{s}/{d}", .{
            core.getSessionStamp(),
            self.moduleName,
            self.stagedPaths.items.len,
        });
        defer allocator.free(stagingDirectoryPath);

        try std.fs.cwd().makePath(stagingDirectoryPath);

        const stagedPath = try std.fmt.allocPrint(allocator, "{s}/{s}", .{
            stagingDirectoryPath,
            try p2.sharedLibNameAlloc(allocator, self.moduleName),
        });

        try std.fs.cwd().copyFile(self.baseModulePath, std.fs.cwd(), stagedPath, .{});

        if (self.pdbPath) |pdbPath| {
            const stagedPdbPath = try std.fmt.allocPrint(allocator, "{s}/{s}.pdb", .{ stagingDirectoryPath, self.moduleName });
            try std.fs.cwd().copyFile(pdbPath, std.fs.cwd(), stagedPdbPath, .{});
        }

        self.stagedPaths.append(allocator, stagedPath) catch unreachable;
    }

    pub fn loadStagedModule(self: *@This(), allocator: std.mem.Allocator) !void {
        const stagedPath = self.stagedPaths.getLast();
        var lib = try std.DynLib.open(stagedPath);
        var mod = ModuleInterface{};
        mod.startup = lib.lookup(@TypeOf(mod.startup), "startup") orelse return error.BadModule;
        mod.shutdown = lib.lookup(@TypeOf(mod.shutdown), "shutdown") orelse return error.BadModule;

        try self.loaded.append(allocator, mod);
    }

    pub fn load(self: *@This(), allocator: std.mem.Allocator) !void {
        core.engine_log("[ModuleLoader] loading module: ", .{});
        self.lastLoad = std.time.microTimestamp();

        try self.stageModule(allocator);
        try self.loadStagedModule(allocator);
    }

    // logic for testing if we should stage and load
    //
    // 1. modification check time > last load time
    // 2. current time > modification check time + debounce
    pub fn maybeStageAndLoad(self: *@This(), allocator: std.mem.Allocator) !bool {
        var shouldLoad: bool = false;

        if (self.lastModification > self.lastLoad) {
            const currentTime = std.time.microTimestamp();

            // give 100ms for debouncing
            if (currentTime > self.lastModification + 50_000) {
                shouldLoad = true;
            }
        }

        if (self.initialLoad) {
            self.initialLoad = false;
            shouldLoad = true;
        }

        if (shouldLoad and (self.autoLoad or self.loadNextFrame)) {
            self.loadNextFrame = false;
            try self.load(allocator);
            return true;
        }

        return false;
    }
};

fn dllChangedCallback(pathChanged: []const u8, ctx: ?*anyopaque) void {
    const loaded: *LoadedModule = @ptrCast(@alignCast(ctx.?));
    loaded.lastModification = std.time.microTimestamp();

    core.engine_log("{s} change detected", .{pathChanged});
}

pub const ModuleLoader = struct {
    backingAllocator: std.mem.Allocator,
    arena: std.heap.ArenaAllocator,
    loadedModules: std.ArrayListUnmanaged(*LoadedModule) = .{},
    watchInitialized: bool = false,

    pub var NeonObjectTable = core.EngineObjectVTable.from(@This(), "core.ModuleLoader");
    pub fn create(allocator: std.mem.Allocator) !*@This() {
        const self = try allocator.create(@This());

        self.* = .{
            .backingAllocator = allocator,
            .arena = std.heap.ArenaAllocator.init(allocator),
        };

        return self;
    }

    pub fn addModule(self: *@This(), moduleName: []const u8) !void {
        // modules are always looked for under zig-out/modules
        if (core.BuildOption("static_build")) {
            core.engine_log("[ModuleLoader]: skipping dynamic load, hot loading is not available", .{});
            return;
        }

        core.engine_log("[ModuleLoader]: adding module to watch '{s}'", .{moduleName});
        const libFileName = try p2.sharedLibNameAlloc(self.arena.allocator(), moduleName);
        const loaded = try self.arena.allocator().create(LoadedModule);

        if (self.watchInitialized == false) {
            core.fs().watchPath("zig-out/modules/");
            self.watchInitialized = true;
        }

        loaded.* = LoadedModule{
            .baseModulePath = try std.fmt.allocPrint(self.arena.allocator(), "zig-out/modules/{s}", .{libFileName}),
            .moduleName = moduleName,
            .lastModification = std.time.microTimestamp(),
        };

        if (@import("builtin").os.tag == .windows) {
            loaded.pdbPath = try std.fmt.allocPrint(self.arena.allocator(), "zig-out/modules/{s}.pdb", .{libFileName[0 .. libFileName.len - 4]});
        }

        try core.fs().addFileChangedCallback(libFileName, dllChangedCallback, loaded);

        try self.loadedModules.append(self.arena.allocator(), loaded);
    }

    pub fn activateModuleVersion(self: *@This(), mod: *LoadedModule, index: usize) void {
        mod.autoLoad = false; // once we load a specific version we don't want to autoload anymore
        //
        if (index < mod.loaded.items.len) {
            var a = self.backingAllocator;
            var args = getModuleLoaderArgs(false);
            if (mod.loaded.items[index].startup(&a, &args)) {
                core.engine_log("module startup done", .{});
            }
        }
    }

    pub fn tick(self: *@This(), dt: f64) void {
        _ = dt;
        for (self.loadedModules.items) |loaded| {
            const didLoad = loaded.maybeStageAndLoad(self.arena.allocator()) catch |err| {
                core.engine_log("unable to load module error: {any}", .{err});
                if (@errorReturnTrace()) |trace| {
                    std.debug.dumpStackTrace(trace.*);
                }
                continue;
            };

            if (didLoad) {
                const i = loaded.getInterface();

                if (i) |interface| {
                    if (loaded.startOnLoad) {
                        if (!loaded.started) {
                            var a = self.backingAllocator;
                            var args = getModuleLoaderArgs(loaded.loaded.items.len == 1);
                            if (interface.startup(&a, &args)) {
                                core.engine_log("[ModuleLoader] module startup done", .{});
                            }
                        }
                    }
                }
            }
        }
    }

    pub fn destroy(self: *@This()) void {
        // std.fs.cwd().deleteTree(".modulecache") catch {};
        self.arena.deinit();
        self.backingAllocator.destroy(self);
    }
};

pub fn getModuleLoaderArgs(first: bool) ModuleLoaderArgs {
    return .{
        .firstLoad = first,
        .engine = core.getEngine(),
        .nameRegistry = core.names.gRegistry,
        .packerFS = core.fs(),
        // .luaState = @ptrCast(core.script.gLuaState.l),
        // .luaAllocator = &core.script.gLuaAllocator,
        .debugDrawInterface = debug.gDebugDrawInterface.?,
    };
}

const std = @import("std");
const core = @import("../core.zig");
const p2 = @import("p2");
const debug = @import("../debug_draw.zig");