#include <ui.h>

#include "uiLibrary.h"
#include "widget/table.h"
#include "widget/widget.h"

#include <cassert.h>
#include <cstring.h>

static const uiPixel uiBlack = {40, 40, 40, 255};
static const uiPixel uiWhite = {255, 255, 255, 255};
static const uiPixel uiPink  = {128, 0, 128, 255};

/// Render state.
///
/// Render functions are allowed to manipulate the state internally (e.g., the
/// subsurface), but must leave the state intact before returning, except, of
/// course, for the rendered pixels.
///
/// We store a subsurface separate from the surface so that we can always check
/// whether a given coordinate is within the bounds of the physical surface.
typedef struct RenderState {
  uiSurface surface;    /// Surface of pixels on which the UI is rendered.
  uiRect    subsurface; /// Subregion where the current UI widget is rendered.
  uiPoint   pen;        /// Current pen position relative to subsurface.
} RenderState;

static void RenderWidget(RenderState* state, const uiWidget* widget);

/// Push a new subsurface onto which subsequent UI widgets are rendered.
void PushSubsurface(
    RenderState* state, int width, int height, uiRect* original_subsurface,
    uiPoint* original_pen) {
  assert(state);
  assert(original_subsurface);
  assert(original_pen);

  *original_subsurface = state->subsurface;
  *original_pen        = state->pen;

  state->subsurface.x      = state->subsurface.x + state->pen.x;
  state->subsurface.width  = width;
  state->subsurface.height = height;
  state->pen.x             = 0;
}

/// Restore the previous subsurface.
void PopSubsurface(
    RenderState* state, const uiRect* original_subsurface,
    const uiPoint* original_pen) {
  assert(state);
  assert(original_subsurface);
  assert(original_pen);

  state->subsurface = *original_subsurface;
  state->pen        = *original_pen;
}

/// Check whether pen + (w,h) is within the surface and subsurface.
static bool PenInSurface(const RenderState* state, int w, int h) {
  assert(state);

  // Surface.
  const bool in_surface =
      ((state->subsurface.x + state->pen.x + w) < state->surface.width) &&
      ((state->subsurface.y + state->pen.y + h) < state->surface.height);

  // Subsurface.
  const bool in_subsurface = ((state->pen.x + w) < state->subsurface.width) &&
                             ((state->pen.y + h) < state->subsurface.height);

  return in_surface && in_subsurface;
}

/// Get the pixel at (x,y).
static uiPixel* SurfaceXy(uiSurface* surface, int x, int y) {
  assert(surface);
  assert(x >= 0);
  assert(y >= 0);
  assert(x < surface->width);
  assert(y < surface->height);
  return surface->pixels + (surface->width * y) + x;
}

/// Get the pixel at pen + (x,y).
static uiPixel* PixelXy(RenderState* state, int x, int y) {
  assert(state);
  return SurfaceXy(
      &state->surface, state->subsurface.x + state->pen.x + x,
      state->subsurface.y + state->pen.y + y);
}

/// Fill a rectangle with a constant colour.
static void FillRect(const uiRect* rect, uiPixel colour, RenderState* state) {
  assert(rect);
  assert(state);
  assert(rect->width <= state->subsurface.width);
  assert(rect->height <= state->subsurface.height);

  for (int y = rect->y; y < rect->y + rect->height; ++y) {
    uiPixel* pixel = PixelXy(state, rect->x, y);
    for (int x = rect->x; x < rect->x + rect->width; ++x) {
      *pixel++ = colour;
    }
  }
}

/// Render a glyph.
/// The glyph is clamped to the surface's bounds.
static void RenderGlyph(
    const FontAtlas* atlas, unsigned char c, RenderState* state) {
  assert(atlas);
  assert(state);
  assert(atlas->header.glyph_width <= state->subsurface.width);
  assert(atlas->header.glyph_height <= state->subsurface.height);

  const int glyph_width  = atlas->header.glyph_width;
  const int glyph_height = atlas->header.glyph_height;

  const unsigned char* glyph = FontGetGlyph(atlas, c);

  for (int y = 0; (y < atlas->header.glyph_height) &&
                  PenInSurface(state, glyph_width - 1, glyph_height - 1);
       ++y) {
    for (int x = 0; (x < atlas->header.glyph_width) &&
                    PenInSurface(state, glyph_width - 1, glyph_height - 1);
         ++x, ++glyph) {
      uiPixel* pixel = PixelXy(state, x, y);
      if (*glyph > 0) {
        pixel->r = *glyph;
        pixel->g = *glyph;
        pixel->b = *glyph;
        pixel->a = 255;
      }
    }
  }
}

/// Render text.
static void RenderText(const char* text, size_t length, RenderState* state) {
  assert(text);
  assert(state);

  const FontAtlas* atlas = g_ui.font;

  const int glyph_width  = atlas->header.glyph_width;
  const int glyph_height = atlas->header.glyph_height;

  // Save the x-pen so that we can restore it after rendering the text.
  const int x0 = state->pen.x;

  // Truncate the text rendering if it exceeds the subsurface's width or height.
  const char* c = text;
  for (size_t i = 0;
       (i < length) && PenInSurface(state, glyph_width - 1, glyph_height - 1);
       ++i, ++c, state->pen.x += glyph_width) {
    RenderGlyph(atlas, *c, state);
  }

  state->pen.x = x0;
}

/// Render a frame.
static void RenderFrame(const uiFrame* frame, RenderState* state) {
  assert(frame);

  FillRect(&frame->widget.rect, uiBlack, state);
}

/// Render a label.
static void RenderLabel(const uiLabel* label, RenderState* state) {
  assert(label);
  assert(state);

  RenderText(string_data(label->text), string_length(label->text), state);
}

/// Render a table.
static void RenderTable(const uiTable* table, RenderState* state) {
  assert(table);
  assert(state);

  const int x0 = state->pen.x;
  const int y0 = state->pen.y;

  uiRect  original_subsurface = {0};
  uiPoint original_pen        = {0};

  int col_widths_sum = 0;

  // Render header.
  if (table->header) {
    for (int col = 0; col < table->cols; ++col) {
      // Crop the column contents to the column width so that one column does
      // not spill into the next.
      PushSubsurface(
          state, table->widths[col], state->subsurface.height,
          &original_subsurface, &original_pen);

      const uiCell* cell = &table->header[col];
      RenderWidget(state, cell->child);

      // Reset the original subsurface and pen for subsequent columns.
      PopSubsurface(state, &original_subsurface, &original_pen);

      // Keep track of the sum of column widths to later render the scroll bar.
      col_widths_sum += table->widths[col];

      // Next column.
      state->pen.x += table->widths[col];
    }
  }
  state->pen.x = x0;
  state->pen.y += g_ui.font->header.glyph_height;

  // Render rows.
  for (int row = table->offset;
       (row < table->rows) && PenInSurface(state, 0, 0); ++row) {
    for (int col = 0; (col < table->cols) && PenInSurface(state, 0, 0); ++col) {
      // Crop the column contents to the column width so that one column does
      // not spill into the next.
      PushSubsurface(
          state, table->widths[col], state->subsurface.height,
          &original_subsurface, &original_pen);

      state->subsurface.x     = state->subsurface.x + state->pen.x;
      state->subsurface.width = table->widths[col];
      state->pen.x            = 0;

      const uiCell* cell = GetCell(table, row, col);
      RenderWidget(state, cell->child);

      // Reset the original subsurface and pen for subsequent columns.
      PopSubsurface(state, &original_subsurface, &original_pen);

      // Next column.
      state->pen.x += table->widths[col];
    }
    state->pen.x = x0;
    state->pen.y += g_ui.font->header.glyph_height;
  }
  state->pen.y = y0;

  // Render scrollbar.
  if (table->flags.vertical_overflow) {
    state->pen.x = col_widths_sum;

    const int y_start = (int)((double)table->offset / (double)table->rows *
                              (double)table->height);

    const int height = (int)((double)table->num_visible_rows /
                             (double)table->rows * (double)table->height);

    FillRect(
        &(uiRect){.y = y_start, .width = ScrollBarWidth, .height = height},
        uiPink, state);

    state->pen.x = x0;
  }
}

/// Render a widget.
static void RenderWidget(RenderState* state, const uiWidget* widget) {
  assert(state);
  assert(widget);

  // Render this widget.
  switch (widget->type) {
  case uiTypeButton:
    break;
  case uiTypeFrame:
    RenderFrame((const uiFrame*)widget, state);
    break;
  case uiTypeLabel:
    RenderLabel((const uiLabel*)widget, state);
    break;
  case uiTypeTable:
    RenderTable((const uiTable*)widget, state);
    break;
  case uiTypeMax:
    TRAP();
    break;
  }

  // Render children.
  list_foreach(widget->children, child, { RenderWidget(state, child); });
}

void uiRender(const uiFrame* frame, uiSurface* surface) {
  assert(frame);
  assert(surface);

  RenderWidget(
      &(RenderState){
          .surface = *surface,
          .subsurface =
              (uiRect){
                       .x      = 0,
                       .y      = 0,
                       .width  = surface->width,
                       .height = surface->height},
          .pen = {.x = 0, .y = 0},
  },
      (const uiWidget*)frame);
}