feat(pygal): implement sankey-basic

plots/sankey-basic/implementations/python/pygal.py

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+""" anyplot.ai
+sankey-basic: Basic Sankey Diagram
+Library: pygal 3.1.0 | Python 3.13.13
+Quality: 85/100 | Created: 2026-04-30
+"""
+
+import os
+import sys
+
+
+# Pop script dir so this file (pygal.py) doesn't shadow the installed pygal package
+_script_dir = sys.path.pop(0)
+import cairosvg  # noqa: E402
+from pygal.style import Style  # noqa: E402
+
+
+sys.path.insert(0, _script_dir)
+
+# Theme tokens
+THEME = os.getenv("ANYPLOT_THEME", "light")
+PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
+INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
+INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
+INK_MUTED = "#6B6A63" if THEME == "light" else "#A8A79F"
+
+OKABE_ITO = ("#009E73", "#D55E00", "#0072B2", "#CC79A7", "#E69F00", "#56B4E9", "#F0E442")
+
+# pygal Style is the single source of truth for all visual properties
+chart_style = Style(
+    background=PAGE_BG,
+    plot_background=PAGE_BG,
+    foreground=INK,
+    foreground_strong=INK,
+    foreground_subtle=INK_MUTED,
+    colors=OKABE_ITO,
+    title_font_size=48,
+    label_font_size=38,
+    value_font_size=28,
+    font_family="sans-serif",
+)
+
+# Read all visual tokens from the Style object — single source of truth
+BG = chart_style.background
+FG = chart_style.foreground
+FG_SUBTLE = chart_style.foreground_subtle
+PALETTE = chart_style.colors
+TITLE_SIZE = chart_style.title_font_size
+LABEL_SIZE = chart_style.label_font_size
+VALUE_SIZE = chart_style.value_font_size
+FONT = chart_style.font_family
+
+# Canvas
+WIDTH = 4800
+HEIGHT = 2700
+MARGIN_L = 400
+MARGIN_R = 440
+MARGIN_T = 220
+MARGIN_B = 130
+NODE_W = 52
+NODE_GAP = 40
+
+# Dominant flows get higher opacity to direct attention to key pathways
+ALPHA_DOMINANT = 0.72
+ALPHA_DEFAULT = 0.38
+DOMINANT_THRESHOLD = 20  # TWh
+
+# Data — energy flow in TWh (sources → end-use sectors)
+node_labels = [
+    "Coal",
+    "Natural Gas",
+    "Nuclear",
+    "Renewables",
+    "Residential",
+    "Commercial",
+    "Industrial",
+    "Transportation",
+]
+N_SRC = 4  # first 4 are sources; rest are targets
+
+flows = [
+    (0, 4, 5),  # Coal → Residential
+    (0, 5, 8),  # Coal → Commercial
+    (0, 6, 25),  # Coal → Industrial  ← dominant
+    (1, 4, 22),  # Gas → Residential   ← dominant
+    (1, 5, 18),  # Gas → Commercial
+    (1, 6, 15),  # Gas → Industrial
+    (1, 7, 3),  # Gas → Transportation
+    (2, 4, 12),  # Nuclear → Residential
+    (2, 5, 10),  # Nuclear → Commercial
+    (2, 6, 8),  # Nuclear → Industrial
+    (3, 4, 8),  # Renewables → Residential
+    (3, 5, 6),  # Renewables → Commercial
+    (3, 6, 5),  # Renewables → Industrial
+    (3, 7, 4),  # Renewables → Transportation
+]
+
+# Compute per-node totals
+node_total = [0] * len(node_labels)
+for src, tgt, val in flows:
+    node_total[src] += val
+    node_total[tgt] += val
+
+# Layout: vertical scale so the taller column fills available height
+avail_h = HEIGHT - MARGIN_T - MARGIN_B
+n_src_gaps = N_SRC - 1
+n_tgt_gaps = len(node_labels) - N_SRC - 1
+scale = (avail_h - max(n_src_gaps, n_tgt_gaps) * NODE_GAP) / sum(node_total[:N_SRC])
+
+# Node y positions
+node_x = []
+node_y0 = []
+node_y1 = []
+
+# Source nodes (left column)
+src_block_h = sum(node_total[i] * scale for i in range(N_SRC)) + n_src_gaps * NODE_GAP
+y = MARGIN_T + (avail_h - src_block_h) / 2
+for i in range(N_SRC):
+    h = node_total[i] * scale
+    node_x.append(MARGIN_L)
+    node_y0.append(y)
+    node_y1.append(y + h)
+    y += h + NODE_GAP
+
+# Target nodes (right column)
+tgt_indices = list(range(N_SRC, len(node_labels)))
+tgt_block_h = sum(node_total[i] * scale for i in tgt_indices) + n_tgt_gaps * NODE_GAP
+y = MARGIN_T + (avail_h - tgt_block_h) / 2
+for i in tgt_indices:
+    h = node_total[i] * scale
+    node_x.append(WIDTH - MARGIN_R - NODE_W)
+    node_y0.append(y)
+    node_y1.append(y + h)
+    y += h + NODE_GAP
+
+# Link paths (cubic bezier ribbons)
+src_cursor = list(node_y0[:N_SRC])
+tgt_cursor = list(node_y0[N_SRC:])
+link_data = []
+for src, tgt, val in flows:
+    h = val * scale
+    x1 = node_x[src] + NODE_W
+    y1t = src_cursor[src]
+    y1b = y1t + h
+    src_cursor[src] += h
+
+    tgt_local = tgt - N_SRC
+    x2 = node_x[tgt]
+    y2t = tgt_cursor[tgt_local]
+    y2b = y2t + h
+    tgt_cursor[tgt_local] += h
+
+    cx = (x1 + x2) / 2
+    path = (
+        f"M {x1:.1f},{y1t:.1f} "
+        f"C {cx:.1f},{y1t:.1f} {cx:.1f},{y2t:.1f} {x2:.1f},{y2t:.1f} "
+        f"L {x2:.1f},{y2b:.1f} "
+        f"C {cx:.1f},{y2b:.1f} {cx:.1f},{y1b:.1f} {x1:.1f},{y1b:.1f} Z"
+    )
+    c = PALETTE[src]  # color drawn from Style object palette
+    r, g, b = int(c[1:3], 16), int(c[3:5], 16), int(c[5:7], 16)
+    alpha = ALPHA_DOMINANT if val >= DOMINANT_THRESHOLD else ALPHA_DEFAULT
+    dominant = val >= DOMINANT_THRESHOLD
+    # Ribbon midpoint for annotation placement
+    ribbon_mid_y = (y1t + y1b + y2t + y2b) / 4
+    link_data.append((f"rgba({r},{g},{b},{alpha})", path, dominant, cx, ribbon_mid_y, val))
+
+
+# Build SVG string
+parts = [
+    f'<svg xmlns="http://www.w3.org/2000/svg" width="{WIDTH}" height="{HEIGHT}" viewBox="0 0 {WIDTH} {HEIGHT}">',
+    f'<rect width="{WIDTH}" height="{HEIGHT}" fill="{BG}"/>',
+    # Title — font size from chart_style.title_font_size
+    f'<text x="{WIDTH // 2}" y="{MARGIN_T // 2}" text-anchor="middle" '
+    f'dominant-baseline="middle" font-family="{FONT}" font-size="{TITLE_SIZE}" '
+    f'font-weight="600" fill="{FG}">'
+    f"Energy Distribution · sankey-basic · pygal · anyplot.ai</text>",
+    '<g id="links">',
+]
+
+# Non-dominant flows drawn first (background layer)
+for fill, path, dominant, _cx, _ribbon_mid_y, _val in link_data:
+    if not dominant:
+        parts.append(f'<path d="{path}" fill="{fill}" stroke="none"/>')
+
+# Dominant flows drawn on top with annotation showing their magnitude
+for fill, path, dominant, cx, ribbon_mid_y, val in link_data:
+    if dominant:
+        parts.append(f'<path d="{path}" fill="{fill}" stroke="none"/>')
+        parts.append(
+            f'<text x="{cx:.1f}" y="{ribbon_mid_y:.1f}" text-anchor="middle" '
+            f'dominant-baseline="middle" font-family="{FONT}" font-size="{VALUE_SIZE}" '
+            f'font-weight="700" fill="{FG}" opacity="0.80">{val} TWh</text>'
+        )
+
+parts.append("</g>")
+
+# Nodes
+parts.append('<g id="nodes">')
+for i in range(len(node_labels)):
+    color = PALETTE[i] if i < N_SRC else INK_SOFT
+    x = node_x[i]
+    y0 = node_y0[i]
+    h = node_y1[i] - node_y0[i]
+    parts.append(f'<rect x="{x:.1f}" y="{y0:.1f}" width="{NODE_W}" height="{h:.1f}" fill="{color}" rx="5"/>')
+parts.append("</g>")
+
+# Labels — font sizes from chart_style.label_font_size / chart_style.value_font_size
+parts.append('<g id="labels">')
+for i in range(len(node_labels)):
+    y_mid = (node_y0[i] + node_y1[i]) / 2
+    label = node_labels[i]
+    val_str = f"{node_total[i]} TWh"
+    if i < N_SRC:
+        tx = node_x[i] - 24
+        anchor = "end"
+    else:
+        tx = node_x[i] + NODE_W + 24
+        anchor = "start"
+    parts.append(
+        f'<text x="{tx:.1f}" y="{y_mid - 22:.1f}" text-anchor="{anchor}" '
+        f'dominant-baseline="middle" font-family="{FONT}" font-size="{LABEL_SIZE}" '
+        f'font-weight="500" fill="{FG}">{label}</text>'
+    )
+    parts.append(
+        f'<text x="{tx:.1f}" y="{y_mid + 26:.1f}" text-anchor="{anchor}" '
+        f'dominant-baseline="middle" font-family="{FONT}" font-size="{VALUE_SIZE}" '
+        f'fill="{FG_SUBTLE}">{val_str}</text>'
+    )
+parts.append("</g>")
+parts.append("</svg>")
+
+svg_content = "\n".join(parts)
+
+# Save HTML (pygal-style interactive output)
+html_content = (
+    f'<!DOCTYPE html><html><head><meta charset="utf-8">'
+    f"<title>sankey-basic · pygal · anyplot.ai</title>"
+    f"<style>body{{margin:0;background:{BG}}}</style></head>"
+    f"<body>{svg_content}</body></html>"
+)
+with open(f"plot-{THEME}.html", "w", encoding="utf-8") as fh:
+    fh.write(html_content)
+
+# Save PNG via cairosvg (same pipeline pygal.render_to_png uses internally)
+cairosvg.svg2png(bytestring=svg_content.encode("utf-8"), write_to=f"plot-{THEME}.png")