$fn = 64;

// --- Parameters ---
width = 160;          // Total width of the stand
back_height = 160;    // Height of the back support
shelf_depth = 40;     // Depth of the ledge holding the book
lip_height = 20;      // Height of the front lip to keep pages open
thickness = 4;        // Wall thickness
tilt = 25;            // Angle (in degrees) tilted back from vertical
base_y = -25;         // Leg extension downwards to form the flat base

// --- Modules ---

// 2D Profile of the resting tray (backrest, shelf, and lip)
module tray_profile() {
    rotate([0, 0, -tilt]) {
        // Backrest
        square([thickness, back_height]);
        // Shelf
        translate([-shelf_depth + thickness, 0]) square([shelf_depth, thickness]);
        // Lip
        translate([-shelf_depth + thickness, 0]) square([thickness, lip_height]);
    }
}

// 2D Profile of the solid support legs
module leg_profile() {
    // Calculate key outer points of the tray after rotation to attach the legs perfectly
    // Rotation formula: x' = x*cos(a) - y*sin(a), y' = x*sin(a) + y*cos(a)
    
    // Point slightly down from the top of the backrest
    P_top = [
        thickness*cos(-tilt) - (back_height-30)*sin(-tilt),
        thickness*sin(-tilt) + (back_height-30)*cos(-tilt)
    ];
    // Bottom corner where backrest meets shelf
    P_corner = [
        thickness*cos(-tilt),
        thickness*sin(-tilt)
    ];
    // Bottom outer corner of the front lip
    P_front = [
        (-shelf_depth + thickness)*cos(-tilt),
        (-shelf_depth + thickness)*sin(-tilt)
    ];

    polygon([
        P_top,
        [P_top[0], base_y],   // Drop down to base from back
        [P_front[0], base_y], // Flat base across to the front
        P_front,
        P_corner              // Hug the bottom of the tray
    ]);
}

// Combined 2D profile for the leg sections
module full_profile() {
    union() {
        tray_profile();
        leg_profile();
    }
}

// Complete 3D Stand
module rulebook_stand() {
    union() {
        // Left leg
        translate([0, 0, 0])
            rotate([90, 0, 90])
                linear_extrude(thickness)
                    full_profile();

        // Right leg
        translate([width - thickness, 0, 0])
            rotate([90, 0, 90])
                linear_extrude(thickness)
                    full_profile();

        // Center leg
        translate([(width - thickness)/2, 0, 0])
            rotate([90, 0, 90])
                linear_extrude(thickness)
                    full_profile();

        // Main tray (spans the entire width)
        translate([0, 0, 0])
            rotate([90, 0, 90])
                linear_extrude(width)
                    tray_profile();
    }
}

// Center the stand on the build plate and lift so the base rests perfectly on Z=0
translate([-width/2, 0, -base_y])
    rulebook_stand();