#!/usr/bin/env python3
"""
Generate a top-to-bottom linear gradient PNG from three hex colors.

Matches: linear-gradient(#2a1a5e, #8b4789, #f4a261)

Usage:
    python gradient_to_png.py --width 1920 --height 1080 --out bg.png
"""

import argparse
from PIL import Image

def hex_to_rgb(h: str):
    """Convert #rrggbb or rrggbb to (r,g,b)."""
    h = h.strip()
    if h.startswith("#"):
        h = h[1:]
    if len(h) != 6:
        raise ValueError("Hex color must be 6 hex digits, got: " + h)
    return tuple(int(h[i:i+2], 16) for i in (0, 2, 4))

def lerp(a: int, b: int, t: float) -> int:
    """Linear interpolation between integers a and b, t in [0,1]."""
    return int(round(a + (b - a) * t))

def mix_color(c1, c2, t: float):
    """Interpolate between two RGB colors (tuple of 3 ints)."""
    return (lerp(c1[0], c2[0], t),
            lerp(c1[1], c2[1], t),
            lerp(c1[2], c2[2], t))

def make_three_stop_vertical_gradient(width: int, height: int, hex1: str, hex2: str, hex3: str) -> Image.Image:
    """
    Create a Pillow Image with a vertical gradient going through three colors evenly:
      - color1 at top (0%)
      - color2 at 50%
      - color3 at bottom (100%)
    This mirrors `linear-gradient(color1, color2, color3)` in CSS with no explicit stops.
    """
    c1 = hex_to_rgb(hex1)
    c2 = hex_to_rgb(hex2)
    c3 = hex_to_rgb(hex3)

    img = Image.new("RGB", (width, height))
    pixels = img.load()

    # For each row compute color:
    for y in range(height):
        t = y / float(max(1, height - 1))  # 0.0..1.0
        if t <= 0.5:
            # interpolate between c1 and c2 (0.0..0.5 -> 0.0..1.0)
            local_t = t / 0.5
            color = mix_color(c1, c2, local_t)
        else:
            # interpolate between c2 and c3 (0.5..1.0 -> 0.0..1.0)
            local_t = (t - 0.5) / 0.5
            color = mix_color(c2, c3, local_t)

        # fill the row with the computed color
        for x in range(width):
            pixels[x, y] = color

    return img

def main():
    parser = argparse.ArgumentParser(description="Render a 3-stop vertical CSS-like gradient to PNG")
    parser.add_argument("--width", "-W", type=int, default=1920, help="Output image width in pixels")
    parser.add_argument("--height", "-H", type=int, default=1080, help="Output image height in pixels")
    parser.add_argument("--out", "-o", default="gradient.png", help="Output PNG filename")
    parser.add_argument("--c1", default="#2a1a5e", help="Top color (hex)")
    parser.add_argument("--c2", default="#8b4789", help="Middle color (hex)")
    parser.add_argument("--c3", default="#f4a261", help="Bottom color (hex)")
    args = parser.parse_args()

    img = make_three_stop_vertical_gradient(args.width, args.height, args.c1, args.c2, args.c3)
    img.save(args.out, "PNG")
    print(f"Saved {args.out} ({args.width}x{args.height})")

if __name__ == "__main__":
    main()