const std = @import("std");
const builtin = @import("builtin");
const dvui = @import("dvui");
const Document = @import("models/Document.zig");
const RenderEngine = @import("render/RenderEngine.zig").RenderEngine;
const ImageRect = @import("models/basic_models.zig").ImageRect;
const Point2 = @import("models/basic_models.zig").Point2;
const Color = dvui.Color;

const Canvas = @This();

allocator: std.mem.Allocator,
document: *Document,
render_engine: RenderEngine,
texture: ?dvui.Texture = null,
pos: dvui.Point = dvui.Point{ .x = 400, .y = 400 },
scroll: dvui.ScrollInfo = .{
    .vertical = .auto,
    .horizontal = .auto,
},
native_scaling: bool = true,
redraw_throttle_ms: u32 = 50,
_visible_rect: ?ImageRect = null,
_zoom: f32 = 1,
_redraw_pending: bool = false,
_last_redraw_time_ms: i64 = 0,
cursor_document_point: ?Point2 = null,

pub fn init(allocator: std.mem.Allocator, document: *Document, engine: RenderEngine) Canvas {
    return .{
        .allocator = allocator,
        .document = document,
        .render_engine = engine,
    };
}

pub fn deinit(self: *Canvas) void {
    if (self.texture) |texture| {
        dvui.Texture.destroyLater(texture);
        self.texture = null;
    }
}

pub fn redrawExample(self: *Canvas) !void {
    const full = self.getZoomedImageSize();

    const vis: ImageRect = self._visible_rect orelse ImageRect{ .x = 0, .y = 0, .w = 0, .h = 0 };

    if (vis.w == 0 or vis.h == 0) {
        if (self.texture) |tex| {
            dvui.Texture.destroyLater(tex);
            self.texture = null;
        }
        return;
    }

    const new_texture = self.render_engine.example(.{ .w = full.w, .h = full.h }, vis) catch null;

    if (new_texture) |tex| {
        if (self.texture) |old_tex| {
            dvui.Texture.destroyLater(old_tex);
        }

        self.texture = tex;
    }
    self._last_redraw_time_ms = std.time.milliTimestamp();
}

pub fn exampleReset(self: *Canvas) !void {
    self.render_engine.exampleReset();
    try self.redrawExample();
}

pub fn setZoom(self: *Canvas, value: f32) void {
    self._zoom = @max(value, 0.01);
}

pub fn addZoom(self: *Canvas, value: f32) void {
    self._zoom += value;
    self._zoom = @max(self._zoom, 0.01);
}

pub fn requestRedraw(self: *Canvas) void {
    self._redraw_pending = true;
}

pub fn processPendingRedraw(self: *Canvas) !void {
    if (!self._redraw_pending) return;
    if (self.redraw_throttle_ms == 0) {
        self._redraw_pending = false;
        try self.redrawExample();
        return;
    }
    const now_ms = std.time.milliTimestamp();
    const elapsed: i64 = if (self._last_redraw_time_ms == 0) self.redraw_throttle_ms else now_ms - self._last_redraw_time_ms;
    if (elapsed < @as(i64, @intCast(self.redraw_throttle_ms))) return;
    self._redraw_pending = false;
    try self.redrawExample();
}

pub fn getZoomedImageSize(self: Canvas) ImageRect {
    const doc = self.document;
    return .{
        .x = @intFromFloat(self.pos.x),
        .y = @intFromFloat(self.pos.y),
        .w = @intFromFloat(doc.size.width * self._zoom),
        .h = @intFromFloat(doc.size.height * self._zoom),
    };
}

pub fn contentPointToDocument(self: Canvas, content_point: dvui.Point, natural_scale: f32) ?Point2 {
    const img = self.getZoomedImageSize();
    const left_n = @as(f32, @floatFromInt(img.x)) / natural_scale;
    const top_n = @as(f32, @floatFromInt(img.y)) / natural_scale;
    const right_n = @as(f32, @floatFromInt(img.x + img.w)) / natural_scale;
    const bottom_n = @as(f32, @floatFromInt(img.y + img.h)) / natural_scale;

    if (content_point.x < left_n or content_point.x >= right_n or
        content_point.y < top_n or content_point.y >= bottom_n)
        return null;

    const px_x = content_point.x * natural_scale - @as(f32, @floatFromInt(img.x));
    const px_y = content_point.y * natural_scale - @as(f32, @floatFromInt(img.y));
    return Point2{
        .x = px_x / self._zoom,
        .y = px_y / self._zoom,
    };
}

pub fn updateVisibleImageRect(self: *Canvas, viewport: dvui.Rect, scroll_offset: dvui.Point) bool {
    const next = computeVisibleImageRect(self.*, viewport, scroll_offset);
    var changed = false;
    if (self._visible_rect) |vis| {
        changed |= next.x != vis.x or next.y != vis.y or next.w != vis.w or next.h != vis.h;
    }
    self._visible_rect = next;
    if (changed) {
        std.debug.print("Visible Image Rect: {{ x: {}, y: {}, w: {}, h: {} }}\n", .{ next.x, next.y, next.w, next.h });
    }
    if (changed or self.texture == null) {
        return true;
    }
    return false;
}

fn computeVisibleImageRect(self: Canvas, viewport: dvui.Rect, scroll_offset: dvui.Point) ImageRect {
    const image_rect = self.getZoomedImageSize();

    const img_w: u32 = image_rect.w;
    const img_h: u32 = image_rect.h;

    const vis_w: u32 = @min(@as(u32, @intFromFloat(viewport.w)), img_w);
    const vis_h: u32 = @min(@as(u32, @intFromFloat(viewport.h)), img_h);

    const raw_x: i64 = @intFromFloat(scroll_offset.x - @as(f32, @floatFromInt(image_rect.x)));
    const raw_y: i64 = @intFromFloat(scroll_offset.y - @as(f32, @floatFromInt(image_rect.y)));

    const vis_x: u32 = @intCast(std.math.clamp(raw_x, 0, @as(i64, img_w) - @as(i64, vis_w)));
    const vis_y: u32 = @intCast(std.math.clamp(raw_y, 0, @as(i64, img_h) - @as(i64, vis_h)));

    return ImageRect{
        .x = vis_x,
        .y = vis_y,
        .w = vis_w,
        .h = vis_h,
    };
}