#!/usr/bin/env python3
"""
Generate a VLW font file compatible with LovyanGFX / M5GFX.

VLW format (all big-endian int32), verified against lgfx_fonts.cpp:
  Header (6 x int32):
    [0] glyph_count
    [1] vlw_encoder_version (write 8, matches Processing default)
    [2] font_size (points)
    [3] reserved / discard
    [4] ascent
    [5] descent

  Per glyph (7 x int32), at offset 24:
    [0] codepoint
    [1] height
    [2] width
    [3] xAdvance
    [4] dY  (y delta from baseline: ascent_px - bitmap_top)
    [5] gdX (x delta from cursor:   bitmap_left / lsb)
    [6] reserved (0)

  Bitmaps (at offset 24 + gCount*28):
    width * height bytes each, 1 byte per pixel (0=off, 255=on)
"""

import struct
import math
import freetype

FONT_PATH = "/usr/share/fonts/Unifont/Unifont.ttf"
SIZE_PT   = 24
DPI       = 96
GLYPHS    = "ʘ⌐■★()>_<Ox "
OUT       = "unifont24.vlw"
OUT_H     = "../src/unifont24_vlw.h"

face = freetype.Face(FONT_PATH)
face.set_char_size(SIZE_PT * 64, 0, DPI, 0)

metrics_face = face.size
ascent_px  = math.ceil(metrics_face.ascender  / 64)
descent_px = math.ceil(-metrics_face.descender / 64)  # positive

glyphs_data = []  # (codepoint, height, width, xAdvance, dY, gdX, pixels)

for ch in GLYPHS:
    cp = ord(ch)
    # Grayscale render — gives 1 byte per pixel output
    face.load_char(cp, freetype.FT_LOAD_RENDER)
    slot   = face.glyph
    bitmap = slot.bitmap

    w      = bitmap.width
    h      = bitmap.rows
    gdX    = slot.bitmap_left              # x offset from cursor
    dY     = slot.bitmap_top               # y delta from baseline (above baseline = positive)
    xAdv   = math.ceil(slot.advance.x / 64)

    # Grayscale pitch may be wider than width — trim to width bytes per row
    # FreeType renders top-to-bottom in FT_PIXEL_MODE_GRAY — no reversal needed
    pitch  = bitmap.pitch
    raw    = bytes(bitmap.buffer)
    pixels = bytearray()
    for row in range(h):
        pixels += raw[row * pitch: row * pitch + w]

    glyphs_data.append((cp, h, w, xAdv, dY, gdX, bytes(pixels)))
    print(f"  U+{cp:04X} '{ch}'  adv={xAdv}  {w}x{h}  gdX={gdX} dY={dY}")

# MUST be sorted ascending by codepoint — getUnicodeIndex uses lower_bound
glyphs_data.sort(key=lambda g: g[0])

with open(OUT, "wb") as f:
    # Header — 6 int32s
    f.write(struct.pack(">iiiiii",
        len(glyphs_data),  # [0] glyph count
        8,                 # [1] vlw encoder version
        SIZE_PT,           # [2] font size in points
        0,                 # [3] reserved
        ascent_px,         # [4] ascent
        descent_px,        # [5] descent
    ))
    # Glyph records
    for cp, h, w, xAdv, dY, gdX, _ in glyphs_data:
        f.write(struct.pack(">iiiiiii", cp, h, w, xAdv, dY, gdX, 0))
    # Bitmaps (1 byte per pixel)
    for _, _, _, _, _, _, pixels in glyphs_data:
        f.write(pixels)

print(f"\nWrote '{OUT}'  ({len(glyphs_data)} glyphs, size={SIZE_PT}pt @ {DPI}dpi)")
print(f"Ascent={ascent_px}  Descent={descent_px}")

# C header for embedding in firmware flash
vlw_bytes = open(OUT, "rb").read()
with open(OUT_H, "w") as h_file:
    h_file.write("#pragma once\n")
    h_file.write("#include <stdint.h>\n\n")
    h_file.write(f"// Auto-generated by gen_vlw.py — {len(glyphs_data)} glyphs, {SIZE_PT}pt\n")
    h_file.write(f"// Usage: M5.Display.loadFont(unifont24_vlw);\n\n")
    h_file.write(f"static const uint8_t unifont24_vlw[] = {{\n")
    for i, b in enumerate(vlw_bytes):
        if i % 16 == 0:
            h_file.write("  ")
        h_file.write(f"0x{b:02X},")
        if i % 16 == 15:
            h_file.write("\n")
        else:
            h_file.write(" ")
    h_file.write("\n};\n")

print(f"Wrote '{OUT_H}'  ({len(vlw_bytes)} bytes)")