#!/usr/bin/env python3
import json
import math
import sys
from datetime import datetime, timedelta
from pathlib import Path


COLORS = [
    "#ebedf0",
    "#9be9a8",
    "#40c463",
    "#30a14e",
    "#216e39",
]

CELL = 12
GAP = 2
RECT = CELL - GAP
LEFT_PAD = 30
TOP_PAD = 20
RIGHT_PAD = 10
BOTTOM_PAD = 10
FONT_FAMILY = "-apple-system,BlinkMacSystemFont,Segoe UI,Helvetica,Arial,sans-serif"
LABEL_COLOR = "#57606a"


def load_heatmap(path):
    with path.open() as handle:
        return json.load(handle)


def date_range(start, end):
    current = start
    while current <= end:
        yield current
        current += timedelta(days=1)


def previous_sunday(day):
    return day - timedelta(days=(day.weekday() + 1) % 7)


def next_saturday(day):
    return day + timedelta(days=(5 - day.weekday()) % 7)


def intensity(count, max_count):
    if count <= 0 or max_count <= 0:
        return 0
    return max(1, min(4, math.ceil((count / max_count) * 4)))


def weekday_row(day):
    return (day.weekday() + 1) % 7


def month_labels(grid_start, visible_start, grid_end):
    labels = []
    total_weeks = ((grid_end - grid_start).days // 7) + 1

    for week in range(total_weeks):
        week_start = grid_start + timedelta(days=week * 7)
        week_label = None

        for offset in range(7):
            day = week_start + timedelta(days=offset)
            if day < visible_start:
                continue

            if week == 0 and week_label is None:
                week_label = day.strftime("%b")

            if day.day == 1:
                week_label = day.strftime("%b")
                break

        if week_label is not None:
            if not labels or labels[-1][1] != week_label:
                labels.append((week, week_label))

    return labels


def build_rect(day, start, counts, max_count):
    date_str = day.isoformat()
    count = counts.get(date_str, 0)
    level = intensity(count, max_count)
    x = LEFT_PAD + (((day - start).days // 7) * CELL)
    y = TOP_PAD + (weekday_row(day) * CELL)

    commit_label = "commit" if count == 1 else "commits"

    return (
        f'<rect x="{x}" y="{y}" width="{RECT}" height="{RECT}" rx="2" ry="2" '
        f'fill="{COLORS[level]}">'
        f"<title>{date_str}: {count} {commit_label}</title>"
        "</rect>"
    )


def generate_svg(data):
    counts = {entry["date"]: entry["count"] for entry in data["days"]}
    max_count = data["max_daily_commits"]

    start = datetime.strptime(data["from_date"], "%Y-%m-%d").date()
    end = datetime.strptime(data["to_date"], "%Y-%m-%d").date()
    aligned_start = previous_sunday(start)
    aligned_end = next_saturday(end)
    weeks = ((aligned_end - aligned_start).days // 7) + 1

    width = LEFT_PAD + (weeks * CELL) + RIGHT_PAD
    height = TOP_PAD + (7 * CELL) + BOTTOM_PAD

    svg = [
        f'<svg width="{width}" height="{height}" viewBox="0 0 {width} {height}" '
        'xmlns="http://www.w3.org/2000/svg" role="img" aria-label="Commit activity heatmap">',
        '<style>',
        f'text {{ font: 10px {FONT_FAMILY}; fill: {LABEL_COLOR}; }}',
        '</style>',
    ]

    for week, label in month_labels(aligned_start, start, aligned_end):
        x = LEFT_PAD + (week * CELL)
        svg.append(f'<text x="{x}" y="10">{label}</text>')

    for label, row in (("Mon", 1), ("Wed", 3), ("Fri", 5)):
        y = TOP_PAD + (row * CELL) + 8
        svg.append(f'<text x="0" y="{y}">{label}</text>')

    for day in date_range(aligned_start, aligned_end):
        svg.append(build_rect(day, aligned_start, counts, max_count))

    svg.append("</svg>")
    return "\n".join(svg) + "\n"


def main():
    if len(sys.argv) not in {2, 3}:
        print(
            "Usage: generate_heatmap_svg.py <heatmap.json> [output.svg]",
            file=sys.stderr,
        )
        return 1

    input_path = Path(sys.argv[1])
    output = generate_svg(load_heatmap(input_path))

    if len(sys.argv) == 3:
        output_path = Path(sys.argv[2])
        output_path.parent.mkdir(parents=True, exist_ok=True)
        output_path.write_text(output)
    else:
        sys.stdout.write(output)

    return 0


if __name__ == "__main__":
    raise SystemExit(main())