#!/usr/bin/env python3
"""Write umtool/report-to-video/face-metrics.mjs: the advance of every character
IBM Plex Sans maps, at the weights the rail / ledger / scroll / chart SVG text
draws (400 and 700, wdth 100), measured from the VENDORED variable font.

fit() and wrapPx() in render-cards.mjs measure a branded run with this table, so
a column set in Plex Sans is truncated by what the run is, not by an average
(see "Why a table, not an average" in the README). The font itself is read and
never written: Plex carries a Reserved Font Name, so it ships unmodified.

  python3 umtool/report-to-video/fonts/gen-face-metrics.py            # rewrite the module
  python3 umtool/report-to-video/fonts/gen-face-metrics.py --stdout   # print it (the parity test)

Needs fontTools (pip install fonttools). The module records the fontTools
version it was generated with; the parity test skips under another one, because
the instancer's rounding of variation deltas is fontTools's, not the font's.
"""
import hashlib
import json
import os
import sys

import fontTools
from fontTools.ttLib import TTFont
from fontTools.varLib import instancer

HERE = os.path.dirname(os.path.abspath(__file__))
FONT = "IBMPlexSans[wdth,wght].ttf"
OUT = os.path.join(os.path.dirname(HERE), "face-metrics.mjs")
WEIGHTS = (400, 700)
WDTH = 100


def runs(cps):
    """Contiguous [first, last] codepoint ranges, in order."""
    out = []
    for cp in cps:
        if out and cp == out[-1][1] + 1:
            out[-1][1] = cp
        else:
            out.append([cp, cp])
    return out


def wrap(values, indent="      ", width=100):
    lines, line = [], ""
    for v in values:
        s = f"{v},"
        if line and len(indent) + len(line) + 1 + len(s) > width:
            lines.append(indent + line)
            line = s
        else:
            line = f"{line} {s}" if line else s
    if line:
        lines.append(indent + line)
    return "\n".join(lines)


def build():
    path = os.path.join(HERE, FONT)
    raw = open(path, "rb").read()
    sha = hashlib.sha256(raw).hexdigest()
    base = TTFont(path)
    upm = base["head"].unitsPerEm
    cps = sorted(base.getBestCmap())
    adv = {}
    for w in WEIGHTS:
        inst = instancer.instantiateVariableFont(TTFont(path), {"wght": w, "wdth": WDTH})
        cmap = inst.getBestCmap()
        hmtx = inst["hmtx"].metrics
        adv[w] = [hmtx[cmap[cp]][0] for cp in cps]

    parts = [
        "// GENERATED by umtool/report-to-video/fonts/gen-face-metrics.py -- do not edit; re-run it.",
        "//",
        f"// The advance, in font units, of every character {FONT} maps, at the",
        f"// weights the rail / ledger / scroll / chart SVG text draws (wght {' and '.join(map(str, WEIGHTS))},",
        f"// wdth {WDTH}): what fit() and wrapPx() measure a branded run by. svg-faces.mjs reads it.",
        "export const IBM_PLEX_SANS_METRICS = {",
        f"  font: {json.dumps(FONT)},",
        f"  sha256: {json.dumps(sha)},",
        f"  fontTools: {json.dumps(fontTools.version)},",
        f"  unitsPerEm: {upm},",
        f"  wdth: {WDTH},",
        "  // [first, last] codepoint ranges; the advances below follow them in order.",
        "  ranges: [",
        wrap([f"[{a}, {b}]" for a, b in runs(cps)], indent="    "),
        "  ],",
        "  advances: {",
    ]
    for w in WEIGHTS:
        parts.append(f"    {w}: [")
        parts.append(wrap(adv[w]))
        parts.append("    ],")
    parts += ["  },", "};", ""]
    return "\n".join(parts)


if __name__ == "__main__":
    text = build()
    if "--stdout" in sys.argv[1:]:
        sys.stdout.write(text)
    else:
        with open(OUT, "w") as f:
            f.write(text)
        print(f"wrote {os.path.relpath(OUT)}")