#include <X11/Xlib.h>
#include <X11/Xatom.h>
#include <X11/Xutil.h>
#include <cairo.h>
#include <cairo-xlib.h>
#include <pango/pangocairo.h>

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

#define M_PI 3.14159265358979323846

typedef struct Vec2 {
    double x, y;
} Vec2;

typedef struct RGB {
    double r, g, b;
} RGB;

typedef struct uui_row {
    Vec2 starting_position, position, spacing, element_size;
    bool is_vertical;
} uui_row_t;

typedef struct uui_context {
    int hot_id, active_id;
    Vec2 mouse_pos;
    bool mouse1_down;
    cairo_t *cr;
} uui_context_t;

typedef enum {
    TEXT_CENTER_ALIGN,
    TEXT_CENTER_ALIGN_LEFT,
} TextCenterAlign;

typedef struct uui_text_style {
    RGB text_color;
    PangoFontDescription *font_description;
    TextCenterAlign center_align;
} uui_text_style_t;

typedef struct uui_button_style {
    RGB normal_color, hot_color, active_color;
    double border_radius;
    int do_fill;
    uui_text_style_t *text_style;
} uui_button_style_t;

Vec2 vec2(double x, double y) {
    return (Vec2) {
        x, y
    };
}

RGB rgb(double r, double g, double b) {
    return (RGB) {
        r, g, b
    };
}

bool uui_collide_point_rect(Vec2 pos, Vec2 size, Vec2 point) {
    return point.x >= pos.x && pos.x + size.x >= point.x &&
        point.y >= pos.y && pos.y + size.y >= point.y;
}

void panic(int exit_code, const char *error) {
    fputs(error, stderr);
    exit(exit_code);
}

cairo_surface_t *create_x11_surface(int x, int y) {
    Display *dsp;
    Drawable da;
    int screen;
    cairo_surface_t *sfc;

    if ((dsp = XOpenDisplay(NULL)) == NULL)
        panic(1, "Failed to open display");

    screen = DefaultScreen(dsp);
    da = XCreateSimpleWindow(dsp, DefaultRootWindow(dsp), 0, 0, x, y, 0, 0, 0);
    XSelectInput(dsp, da, ButtonPressMask | ButtonReleaseMask | KeyPressMask | PointerMotionMask);
    XMapWindow(dsp, da);

    sfc = cairo_xlib_surface_create(dsp, da, DefaultVisual(dsp, screen), x, y);
    cairo_xlib_surface_set_size(sfc, x, y);

    return sfc;
}

void destroy_x11_surface(cairo_surface_t *sfc) {
    Display *dsp = cairo_xlib_surface_get_display(sfc);
    cairo_surface_destroy(sfc);
    XCloseDisplay(dsp);
}

void uui_handle_event(uui_context_t *uc, XEvent *e) {
    char keybuf[8];
    KeySym key;

    switch (e->type) {
        case ButtonPress:
            if (e->xbutton.button == Button1)
                uc->mouse1_down = true;
            break;
        case ButtonRelease:
            if (e->xbutton.button == Button1)
                uc->mouse1_down = false;
            break;
        case KeyPress:
            XLookupString(&e->xkey, keybuf, sizeof(keybuf), &key, NULL);
            break;
        case MotionNotify:
            uc->mouse_pos.x = e->xmotion.x;
            uc->mouse_pos.y = e->xmotion.y;
            break;
    }
}

void uui_draw_rect(cairo_t *cr, Vec2 pos, Vec2 size, double border_radius)
{
    double x = pos.x;
    double y = pos.y;
    double width = size.x;
    double height = size.y;
    if (border_radius > 0) {
        double aspect = 1.0;
        double corner_radius = border_radius;
        double radius = corner_radius / aspect;
        double degrees = M_PI / 180.0;

        cairo_new_sub_path(cr);
        cairo_arc(cr, x + width - radius, y + radius, radius, -90 * degrees, 0 * degrees);
        cairo_arc(cr, x + width - radius, y + height - radius, radius, 0 * degrees, 90 * degrees);
        cairo_arc(cr, x + radius, y + height - radius, radius, 90 * degrees, 180 * degrees);
        cairo_arc(cr, x + radius, y + radius, radius, 180 * degrees, 270 * degrees);
        cairo_close_path(cr);
    } else {
        cairo_rectangle(cr, x, y, width, height);
    }
}

void uui_draw_text(cairo_t *cr, PangoFontDescription *desc, Vec2 pos, const char *text) {
    PangoLayout *layout = pango_cairo_create_layout(cr);
    pango_layout_set_font_description(layout, desc);
    pango_layout_set_text(layout, text, -1);
    cairo_move_to(cr, pos.x, pos.y);
    pango_cairo_show_layout(cr, layout);
    g_object_unref(layout);
}

void uui_draw_centered_text(cairo_t *cr, PangoFontDescription *desc, TextCenterAlign align, Vec2 rect_pos, Vec2 rect_size, const char *text) {
    PangoLayout *layout = pango_cairo_create_layout(cr);
    int font_width;
    int font_height;

    pango_layout_set_font_description(layout, desc);
    pango_layout_set_text(layout, text, -1);
    pango_layout_get_pixel_size(layout, &font_width, &font_height);

    double x = rect_pos.x + ((rect_size.x - font_width) / 2);
    double y = rect_pos.y + ((rect_size.y - font_height) / 2);
    
    if (align == TEXT_CENTER_ALIGN_LEFT) {
        // center the text only horizontally and add a hardcoded padding to the x position
        // TODO: unhardcode the padding
        x = rect_pos.x + 4;
    }

    cairo_move_to(cr, x, y);
    pango_cairo_show_layout(cr, layout);
    g_object_unref(layout);
}

bool uui_do_click_region(uui_context_t *uc, Vec2 pos, Vec2 size, int id) {
    if (id != -1) {
        /* if the element is hot (hovered) and mouse button 1 is down, it's clicked */
        if (uc->hot_id == id && uc->mouse1_down) {
            /* this function only ever returns true once - when the click happens (unless id == -1, in which case it's checked each time, see below) */
            if (uc->active_id == id) {
                return false;
            }
            uc->active_id = id;
            return true;
        } else {
            uc->active_id = -1;
            return false;
        }
    } else {
        /* if the user provided -1 as an id, we will do the check independently of the hot/active system */
        return uc->mouse1_down && uui_collide_point_rect(pos, size, uc->mouse_pos);
    }
}

bool uui_do_hover_region(uui_context_t *uc, Vec2 pos, Vec2 size, int id) {
    if (id != -1) {
        if (uui_collide_point_rect(pos, size, uc->mouse_pos)) {
            uc->hot_id = id;
            return true;
        } else {
            uc->hot_id = -1;
            return false;
        }
    } else {
        /* if the user provided -1 as an id, we will do the check independently of the hot/active system */
        return uui_collide_point_rect(pos, size, uc->mouse_pos);
    }
}

void uui_do_text(uui_context_t *uc, uui_text_style_t *style, Vec2 pos, const char *text) {
    cairo_save(uc->cr);

    cairo_set_source_rgb(uc->cr, style->text_color.r, style->text_color.g, style->text_color.b);
    uui_draw_text(uc->cr, style->font_description, pos, text);
    cairo_fill(uc->cr);

    cairo_restore(uc->cr);
}

void uui_do_centered_text(uui_context_t *uc, uui_text_style_t *style, Vec2 pos, Vec2 size, const char *text) {
    cairo_save(uc->cr);

    cairo_set_source_rgb(uc->cr, style->text_color.r, style->text_color.g, style->text_color.b);
    uui_draw_centered_text(uc->cr, style->font_description, style->center_align, pos, size, text);
    cairo_fill(uc->cr);

    cairo_restore(uc->cr);
}

bool uui_do_button(uui_context_t *uc, uui_button_style_t *style, Vec2 pos, Vec2 size, const char *text, int id) {
    bool clicked = false;

    cairo_save(uc->cr);

    if (uui_do_hover_region(uc, pos, size, id)) {
        cairo_set_source_rgb(uc->cr, style->hot_color.r, style->hot_color.g, style->hot_color.b);
        if (uui_do_click_region(uc, pos, size, id)) {
            cairo_set_source_rgb(uc->cr, style->active_color.r, style->active_color.g, style->active_color.b);
            clicked = true;
        }
    } else {
        cairo_set_source_rgb(uc->cr, style->normal_color.r, style->normal_color.g, style->normal_color.b);
    }

    uui_draw_rect(uc->cr, pos, size, style->border_radius);

    if (style->do_fill) {
        cairo_fill(uc->cr);
    } else {
        cairo_stroke(uc->cr);
    }

    if (text != NULL) {
        uui_do_centered_text(uc, style->text_style, pos, size, text);
    }

    cairo_restore(uc->cr);

    return clicked;
}

uui_context_t *uui_context_create(cairo_t *cr) {
    uui_context_t *uc = malloc(sizeof(uui_context_t));
    uc->mouse_pos = vec2(0, 0);
    uc->mouse1_down = false;
    uc->cr = cr;
    return uc;
}

void uui_context_destroy(uui_context_t *uc) {
    free(uc);
}

void uui_row_start(uui_row_t *row) {
    row->position = row->starting_position;
}

void uui_row_advance(uui_row_t *row, Vec2 add) {
    /* advance the position, respecting the spacing, regardless of direction */
    row->position.x += add.x + row->spacing.x;
    row->position.y += add.y + row->spacing.y;
}

void uui_row_element(uui_row_t *row) {
    /* increment position based on element size */
    /* the spacing is added regardless of the direction */
    if (row->is_vertical) { 
        row->position.y += row->element_size.y;
    } else {
        row->position.x += row->element_size.x;
    }
    row->position.x += row->spacing.x;
    row->position.y += row->spacing.y;
}

int main(void) {
    cairo_surface_t *sfc = create_x11_surface(800, 600);
    cairo_t *cr = cairo_create(sfc);
    PangoFontDescription *font_description = pango_font_description_new();
    uui_context_t *uc = uui_context_create(cr);
    uui_button_style_t button_style;
    uui_text_style_t text_style;
    uui_row_t row;

    XEvent e;

    pango_font_description_set_family(font_description, "sans-serif");
    pango_font_description_set_weight(font_description, PANGO_WEIGHT_NORMAL);
    pango_font_description_set_absolute_size(font_description, 16 * PANGO_SCALE);

    button_style.border_radius = 8;
    button_style.do_fill = 1;
    button_style.normal_color = rgb(1.0, 0.0, 0.0);
    button_style.hot_color = rgb(0.0, 1.0, 0.0);
    button_style.active_color = rgb(0.0, 0.0, 1.0);
    button_style.text_style = &text_style;

    text_style.text_color = rgb(1.0, 1.0, 1.0);
    text_style.font_description = font_description;
    text_style.center_align = TEXT_CENTER_ALIGN_LEFT; 

    row.starting_position = vec2(20.0, 20.0);
    row.position = vec2(0.0, 0.0);
    row.spacing = vec2(20.0, 0.0);
    row.element_size = vec2(100.0, 30.0);
    row.is_vertical = false;

    int selected_tab = 0;

    for (;;) {
        XNextEvent(cairo_xlib_surface_get_display(sfc), &e);
        uui_handle_event(uc, &e);

        cairo_set_source_rgb(cr, 0.0, 0.0, 0.0);
        cairo_paint(cr);

        uui_row_start(&row);
        if (uui_do_button(uc, &button_style, row.position, row.element_size, "one", 0)) {
            selected_tab = 0;
        }
        uui_row_element(&row);
        if (uui_do_button(uc, &button_style, row.position, row.element_size, "two", 1)) {
            selected_tab = 1;
        }
        uui_row_element(&row);
        if (uui_do_button(uc, &button_style, row.position, row.element_size, "three", 2)) {
            selected_tab = 2;
        }
        uui_row_element(&row);
        if (uui_do_button(uc, &button_style, row.position, row.element_size, "four", 3)) {
            selected_tab = 3;
        }
        uui_row_element(&row);

        char *text = "no tab selected";

        switch (selected_tab) {
            case 0:
                text = "tab 1";
                break;
            case 1:
                text = "tab 2";
                break;
            case 2:
                text = "tab 3";
                break;
            case 3:
                text = "tab 4";
                break;
        }

        uui_do_text(uc, &text_style, row.position, text);
    }

    pango_font_description_free(font_description);
    cairo_destroy(cr);
    destroy_x11_surface(sfc);
    uui_context_destroy(uc);
    return 0;
}