1 files changed, 279 insertions, 0 deletions
diff --git a/app/converter/cover.py b/app/converter/cover.py
new file mode 100644
index 0000000..b2d3cb5
--- /dev/null
+++ b/app/converter/cover.py
@@ -0,0 +1,279 @@
+"""Book cover generation: stdlib-only PNG with gradient + title text.
+
+Covers are a vertical gradient between two random light colors with the
+book title rendered on top in white with a black outline and a drop
+shadow, using an embedded 5x7 bitmap font. No third-party image libraries
+are required: PNG scanlines are packed and compressed with zlib/struct
+directly.
+"""
+
+import logging
+import random
+import struct
+import zlib
+from colorsys import hsv_to_rgb
+from pathlib import Path
+from typing import List, Optional, Tuple
+
+logger = logging.getLogger(__name__)
+
+COVER_WIDTH = 600
+COVER_HEIGHT = 900
+
+# 5x7 bitmap font for ASCII 32..126. Each glyph is 7 rows of 5 bits
+# (MSB left), encoded as ints for compactness.
+_FONT = {
+    " ": [0, 0, 0, 0, 0, 0, 0],
+    "!": [0x04, 0x04, 0x04, 0x04, 0x04, 0x00, 0x04],
+    '"': [0x0A, 0x0A, 0x00, 0x00, 0x00, 0x00, 0x00],
+    "#": [0x0A, 0x0A, 0x1F, 0x0A, 0x1F, 0x0A, 0x0A],
+    "$": [0x04, 0x0F, 0x14, 0x0E, 0x05, 0x1E, 0x04],
+    "%": [0x18, 0x19, 0x02, 0x04, 0x08, 0x13, 0x03],
+    "&": [0x08, 0x14, 0x14, 0x08, 0x15, 0x12, 0x0D],
+    "'": [0x04, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00],
+    "(": [0x02, 0x04, 0x08, 0x08, 0x08, 0x04, 0x02],
+    ")": [0x08, 0x04, 0x02, 0x02, 0x02, 0x04, 0x08],
+    "*": [0x00, 0x04, 0x15, 0x0E, 0x15, 0x04, 0x00],
+    "+": [0x00, 0x04, 0x04, 0x1F, 0x04, 0x04, 0x00],
+    ",": [0x00, 0x00, 0x00, 0x00, 0x04, 0x04, 0x08],
+    "-": [0x00, 0x00, 0x00, 0x1F, 0x00, 0x00, 0x00],
+    ".": [0x00, 0x00, 0x00, 0x00, 0x00, 0x0C, 0x0C],
+    "/": [0x00, 0x01, 0x02, 0x04, 0x08, 0x10, 0x00],
+    "0": [0x0E, 0x11, 0x13, 0x15, 0x19, 0x11, 0x0E],
+    "1": [0x04, 0x0C, 0x04, 0x04, 0x04, 0x04, 0x0E],
+    "2": [0x0E, 0x11, 0x01, 0x02, 0x04, 0x08, 0x1F],
+    "3": [0x1F, 0x02, 0x04, 0x02, 0x01, 0x11, 0x0E],
+    "4": [0x02, 0x06, 0x0A, 0x12, 0x1F, 0x02, 0x02],
+    "5": [0x1F, 0x10, 0x1E, 0x01, 0x01, 0x11, 0x0E],
+    "6": [0x06, 0x08, 0x10, 0x1E, 0x11, 0x11, 0x0E],
+    "7": [0x1F, 0x01, 0x02, 0x04, 0x08, 0x08, 0x08],
+    "8": [0x0E, 0x11, 0x11, 0x0E, 0x11, 0x11, 0x0E],
+    "9": [0x0E, 0x11, 0x11, 0x0F, 0x01, 0x02, 0x0C],
+    ":": [0x00, 0x0C, 0x0C, 0x00, 0x0C, 0x0C, 0x00],
+    ";": [0x00, 0x0C, 0x0C, 0x00, 0x0C, 0x04, 0x08],
+    "<": [0x02, 0x04, 0x08, 0x10, 0x08, 0x04, 0x02],
+    "=": [0x00, 0x00, 0x1F, 0x00, 0x1F, 0x00, 0x00],
+    ">": [0x08, 0x04, 0x02, 0x01, 0x02, 0x04, 0x08],
+    "?": [0x0E, 0x11, 0x01, 0x02, 0x04, 0x00, 0x04],
+    "@": [0x0E, 0x11, 0x17, 0x15, 0x17, 0x10, 0x0E],
+    "A": [0x0E, 0x11, 0x11, 0x1F, 0x11, 0x11, 0x11],
+    "B": [0x1E, 0x11, 0x11, 0x1E, 0x11, 0x11, 0x1E],
+    "C": [0x0E, 0x11, 0x10, 0x10, 0x10, 0x11, 0x0E],
+    "D": [0x1C, 0x12, 0x11, 0x11, 0x11, 0x12, 0x1C],
+    "E": [0x1F, 0x10, 0x10, 0x1E, 0x10, 0x10, 0x1F],
+    "F": [0x1F, 0x10, 0x10, 0x1E, 0x10, 0x10, 0x10],
+    "G": [0x0E, 0x11, 0x10, 0x17, 0x11, 0x11, 0x0F],
+    "H": [0x11, 0x11, 0x11, 0x1F, 0x11, 0x11, 0x11],
+    "I": [0x0E, 0x04, 0x04, 0x04, 0x04, 0x04, 0x0E],
+    "J": [0x01, 0x01, 0x01, 0x01, 0x01, 0x11, 0x0E],
+    "K": [0x11, 0x12, 0x14, 0x18, 0x14, 0x12, 0x11],
+    "L": [0x10, 0x10, 0x10, 0x10, 0x10, 0x10, 0x1F],
+    "M": [0x11, 0x1B, 0x15, 0x15, 0x11, 0x11, 0x11],
+    "N": [0x11, 0x19, 0x15, 0x13, 0x11, 0x11, 0x11],
+    "O": [0x0E, 0x11, 0x11, 0x11, 0x11, 0x11, 0x0E],
+    "P": [0x1E, 0x11, 0x11, 0x1E, 0x10, 0x10, 0x10],
+    "Q": [0x0E, 0x11, 0x11, 0x11, 0x15, 0x12, 0x0D],
+    "R": [0x1E, 0x11, 0x11, 0x1E, 0x14, 0x12, 0x11],
+    "S": [0x0F, 0x10, 0x10, 0x0E, 0x01, 0x01, 0x1E],
+    "T": [0x1F, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04],
+    "U": [0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x0E],
+    "V": [0x11, 0x11, 0x11, 0x11, 0x11, 0x0A, 0x04],
+    "W": [0x11, 0x11, 0x11, 0x15, 0x15, 0x15, 0x0A],
+    "X": [0x11, 0x11, 0x0A, 0x04, 0x0A, 0x11, 0x11],
+    "Y": [0x11, 0x11, 0x0A, 0x04, 0x04, 0x04, 0x04],
+    "Z": [0x1F, 0x01, 0x02, 0x04, 0x08, 0x10, 0x1F],
+    "[": [0x0E, 0x08, 0x08, 0x08, 0x08, 0x08, 0x0E],
+    "\\": [0x00, 0x10, 0x08, 0x04, 0x02, 0x01, 0x00],
+    "]": [0x0E, 0x02, 0x02, 0x02, 0x02, 0x02, 0x0E],
+    "^": [0x04, 0x0A, 0x11, 0x00, 0x00, 0x00, 0x00],
+    "_": [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x1F],
+    "`": [0x08, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00],
+    "a": [0x00, 0x00, 0x0E, 0x01, 0x0F, 0x11, 0x0F],
+    "b": [0x10, 0x10, 0x1E, 0x11, 0x11, 0x11, 0x1E],
+    "c": [0x00, 0x00, 0x0F, 0x10, 0x10, 0x10, 0x0F],
+    "d": [0x01, 0x01, 0x0F, 0x11, 0x11, 0x11, 0x0F],
+    "e": [0x00, 0x00, 0x0E, 0x11, 0x1F, 0x10, 0x0E],
+    "f": [0x06, 0x08, 0x1E, 0x08, 0x08, 0x08, 0x08],
+    "g": [0x00, 0x0F, 0x11, 0x11, 0x0F, 0x01, 0x1E],
+    "h": [0x10, 0x10, 0x1E, 0x11, 0x11, 0x11, 0x11],
+    "i": [0x04, 0x00, 0x0C, 0x04, 0x04, 0x04, 0x0E],
+    "j": [0x02, 0x00, 0x06, 0x02, 0x02, 0x12, 0x0C],
+    "k": [0x10, 0x10, 0x12, 0x14, 0x18, 0x14, 0x12],
+    "l": [0x0C, 0x04, 0x04, 0x04, 0x04, 0x04, 0x0E],
+    "m": [0x00, 0x00, 0x1A, 0x15, 0x15, 0x15, 0x15],
+    "n": [0x00, 0x00, 0x1E, 0x11, 0x11, 0x11, 0x11],
+    "o": [0x00, 0x00, 0x0E, 0x11, 0x11, 0x11, 0x0E],
+    "p": [0x00, 0x00, 0x1E, 0x11, 0x11, 0x1E, 0x10],
+    "q": [0x00, 0x00, 0x0F, 0x11, 0x11, 0x0F, 0x01],
+    "r": [0x00, 0x00, 0x16, 0x09, 0x08, 0x08, 0x08],
+    "s": [0x00, 0x00, 0x0F, 0x10, 0x0E, 0x01, 0x1E],
+    "t": [0x08, 0x08, 0x1E, 0x08, 0x08, 0x08, 0x06],
+    "u": [0x00, 0x00, 0x11, 0x11, 0x11, 0x13, 0x0D],
+    "v": [0x00, 0x00, 0x11, 0x11, 0x11, 0x0A, 0x04],
+    "w": [0x00, 0x00, 0x11, 0x15, 0x15, 0x15, 0x0A],
+    "x": [0x00, 0x00, 0x11, 0x0A, 0x04, 0x0A, 0x11],
+    "y": [0x00, 0x00, 0x11, 0x11, 0x0F, 0x01, 0x1E],
+    "z": [0x00, 0x00, 0x1F, 0x02, 0x04, 0x08, 0x1F],
+    "{": [0x06, 0x08, 0x08, 0x04, 0x08, 0x08, 0x06],
+    "|": [0x04, 0x04, 0x04, 0x04, 0x04, 0x04, 0x04],
+    "}": [0x0C, 0x02, 0x02, 0x04, 0x02, 0x02, 0x0C],
+    "~": [0x00, 0x00, 0x08, 0x15, 0x02, 0x00, 0x00],
+}
+
+_GLYPH_WIDTH = 5
+_GLYPH_HEIGHT = 7
+_TEXT_SCALE = 6  # render each font pixel as a 6x6 block
+_TEXT_MARGIN = 60  # horizontal padding when wrapping
+_TEXT_COLOR = (255, 255, 255)
+_STROKE_COLOR = (0, 0, 0)
+_STROKE_WIDTH = 3  # outline thickness in pixels
+_SHADOW_OFFSET = 4  # drop shadow shift in pixels (down-right)
+_SHADOW_DARKEN = 0.55  # shadow keeps 55% of the background color
+
+
+def _random_light_color(rng: random.Random) -> Tuple[int, int, int]:
+    """A random pastel: any hue, low saturation, high value."""
+    hue = rng.random()
+    saturation = rng.uniform(0.25, 0.55)
+    value = rng.uniform(0.82, 0.95)
+    r, g, b = hsv_to_rgb(hue, saturation, value)
+    return int(r * 255), int(g * 255), int(b * 255)
+
+
+def _lerp(a: int, b: int, t: float) -> int:
+    return int(round(a + (b - a) * t))
+
+
+def _text_width(text: str) -> int:
+    """Pixel width of ``text`` at the rendered scale (spaces count too)."""
+    if not text:
+        return 0
+    return (len(text) * (_GLYPH_WIDTH + 1) - 1) * _TEXT_SCALE
+
+
+def _wrap_title(title: str, max_width: int) -> List[str]:
+    """Word-wrap ``title`` into lines that fit ``max_width`` pixels."""
+    words = title.split()
+    if not words:
+        return []
+    lines: List[str] = []
+    current = ""
+    for word in words:
+        candidate = f"{current} {word}".strip()
+        if _text_width(candidate) <= max_width or not current:
+            current = candidate
+        else:
+            lines.append(current)
+            current = word
+    if current:
+        lines.append(current)
+    return lines
+
+
+def _set_pixel(pixels: List[List[Tuple[int, int, int]]], x: int, y: int,
+               color: Tuple[int, int, int], darken: Optional[float] = None) -> None:
+    """Set one pixel: solid ``color``, or darken the existing pixel by ``darken``."""
+    if not 0 <= y < len(pixels):
+        return
+    if not 0 <= x < len(pixels[y]):
+        return
+    if darken is None:
+        pixels[y][x] = color
+    else:
+        r, g, b = pixels[y][x]
+        pixels[y][x] = (int(r * darken), int(g * darken), int(b * darken))
+
+
+def _render_line(pixels: List[List[Tuple[int, int, int]]], text: str, x0: int, y0: int,
+                 color: Tuple[int, int, int] = (0, 0, 0),
+                 darken: Optional[float] = None) -> None:
+    """Blit one line of bitmap text onto the pixel grid in place.
+
+    With ``darken``, each glyph pixel darkens whatever is underneath it
+    instead of painting a solid color (used for the drop shadow, which
+    stays tinted by the gradient behind it).
+    """
+    for char_index, char in enumerate(text):
+        glyph = _FONT.get(char)
+        if glyph is None:
+            continue
+        x_off = x0 + char_index * (_GLYPH_WIDTH + 1) * _TEXT_SCALE
+        for gy, bits in enumerate(glyph):
+            for gx in range(_GLYPH_WIDTH):
+                if not bits & (1 << (_GLYPH_WIDTH - 1 - gx)):
+                    continue
+                for dy in range(_TEXT_SCALE):
+                    for dx in range(_TEXT_SCALE):
+                        _set_pixel(pixels,
+                                   x_off + gx * _TEXT_SCALE + dx,
+                                   y0 + gy * _TEXT_SCALE + dy,
+                                   color, darken)
+
+
+def _encode_png(width: int, height: int, pixels: List[List[Tuple[int, int, int]]]) -> bytes:
+    """Encode an RGB pixel grid as a PNG using only the stdlib."""
+    def chunk(chunk_type: bytes, data: bytes) -> bytes:
+        payload = chunk_type + data
+        return (struct.pack(">I", len(data)) + payload
+                + struct.pack(">I", zlib.crc32(payload) & 0xFFFFFFFF))
+
+    raw = b"".join(
+        b"\x00" + bytes(channel for pixel in scanline for channel in pixel)
+        for scanline in pixels
+    )
+    ihdr = struct.pack(">IIBBBBB", width, height, 8, 2, 0, 0, 0)  # 8-bit RGB
+    return (b"\x89PNG\r\n\x1a\n"
+            + chunk(b"IHDR", ihdr)
+            + chunk(b"IDAT", zlib.compress(raw, 9))
+            + chunk(b"IEND", b""))
+
+
+def generate_cover(title: str, path: Path, width: int = COVER_WIDTH,
+                   height: int = COVER_HEIGHT, seed: Optional[int] = None) -> Optional[Path]:
+    """Write a gradient cover PNG with ``title`` centered on it.
+
+    ``seed`` makes the gradient reproducible (used by tests). Returns the
+    path on success, or None when the PNG cannot be written (the audiobook
+    still gets tags, just without cover art).
+    """
+    rng = random.Random(seed)
+    top_color = _random_light_color(rng)
+    bottom_color = _random_light_color(rng)
+
+    pixels = []
+    for y in range(height):
+        t = y / max(1, height - 1)
+        color = (_lerp(top_color[0], bottom_color[0], t),
+                 _lerp(top_color[1], bottom_color[1], t),
+                 _lerp(top_color[2], bottom_color[2], t))
+        pixels.append([color] * width)
+
+    lines = _wrap_title((title or "").strip(), width - 2 * _TEXT_MARGIN)
+    if lines:
+        line_height = _GLYPH_HEIGHT * _TEXT_SCALE + _TEXT_SCALE * 3
+        total_height = len(lines) * line_height
+        y_start = max(0, (height - total_height) // 2)
+        for line_index, line in enumerate(lines):
+            x0 = (width - _text_width(line)) // 2
+            y0 = y_start + line_index * line_height
+            # Paint order: drop shadow (the outlined glyph's full silhouette
+            # — glyph dilated by the stroke width — shifted down-right and
+            # darkened, tinted by the gradient underneath), then the black
+            # outline traced around the glyph, then the solid white text.
+            for dx in range(-_STROKE_WIDTH, _STROKE_WIDTH + 1):
+                for dy in range(-_STROKE_WIDTH, _STROKE_WIDTH + 1):
+                    _render_line(pixels, line, x0 + dx + _SHADOW_OFFSET,
+                                 y0 + dy + _SHADOW_OFFSET, darken=_SHADOW_DARKEN)
+            for dx in range(-_STROKE_WIDTH, _STROKE_WIDTH + 1):
+                for dy in range(-_STROKE_WIDTH, _STROKE_WIDTH + 1):
+                    _render_line(pixels, line, x0 + dx, y0 + dy,
+                                 color=_STROKE_COLOR)
+            _render_line(pixels, line, x0, y0, color=_TEXT_COLOR)
+
+    try:
+        path.write_bytes(_encode_png(width, height, pixels))
+    except OSError as exc:
+        logger.warning("Could not write cover image %s: %s", path, exc)
+        return None
+    logger.info("Generated cover: %s (gradient %s -> %s)", path, top_color, bottom_color)
+    return path