feat(altair): implement icicle-basic (#2517)

## Implementation: `icicle-basic` - altair

Implements the **altair** version of `icicle-basic`.

**File:** `plots/icicle-basic/implementations/altair.py`

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20585400003)*

---------

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Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/icicle-basic/implementations/altair.py

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+""" pyplots.ai
+icicle-basic: Basic Icicle Chart
+Library: altair 6.0.0 | Python 3.13.11
+Quality: 91/100 | Created: 2025-12-30
+"""
+
+import altair as alt
+import pandas as pd
+
+
+# Data: File system hierarchy with sizes (in MB)
+# Structure designed with balanced folder sizes for better visibility
+data = [
+    # Root
+    {"name": "root", "parent": None, "value": 0},
+    # Level 1: Main folders
+    {"name": "Documents", "parent": "root", "value": 0},
+    {"name": "Media", "parent": "root", "value": 0},
+    {"name": "Projects", "parent": "root", "value": 0},
+    # Level 2: Documents subfolders
+    {"name": "Reports", "parent": "Documents", "value": 0},
+    {"name": "Presentations", "parent": "Documents", "value": 0},
+    # Level 2: Media subfolders
+    {"name": "Images", "parent": "Media", "value": 0},
+    {"name": "Videos", "parent": "Media", "value": 0},
+    # Level 2: Projects subfolders
+    {"name": "WebApp", "parent": "Projects", "value": 0},
+    {"name": "DataScience", "parent": "Projects", "value": 0},
+    # Level 3: Leaf nodes with sizes balanced for better visual representation
+    {"name": "Q1_Report.pdf", "parent": "Reports", "value": 120},
+    {"name": "Q2_Report.pdf", "parent": "Reports", "value": 95},
+    {"name": "Annual_Review.pdf", "parent": "Reports", "value": 150},
+    {"name": "Sales_Deck.pptx", "parent": "Presentations", "value": 85},
+    {"name": "Strategy.pptx", "parent": "Presentations", "value": 110},
+    {"name": "photo_album.jpg", "parent": "Images", "value": 180},
+    {"name": "banner.png", "parent": "Images", "value": 75},
+    {"name": "tutorial.mp4", "parent": "Videos", "value": 350},
+    {"name": "demo.mp4", "parent": "Videos", "value": 280},
+    {"name": "frontend.js", "parent": "WebApp", "value": 65},
+    {"name": "backend.py", "parent": "WebApp", "value": 120},
+    {"name": "styles.css", "parent": "WebApp", "value": 45},
+    {"name": "analysis.ipynb", "parent": "DataScience", "value": 95},
+    {"name": "model.pkl", "parent": "DataScience", "value": 180},
+]
+
+df = pd.DataFrame(data)
+
+# Build tree structure using iterative approach (KISS - no helper functions)
+name_to_idx = {row["name"]: i for i, row in enumerate(data)}
+children = {row["name"]: [] for row in data}
+for row in data:
+    if row["parent"]:
+        children[row["parent"]].append(row["name"])
+
+# Calculate levels (depth) iteratively
+levels = {"root": 0}
+queue = ["root"]
+while queue:
+    current = queue.pop(0)
+    for child in children[current]:
+        levels[child] = levels[current] + 1
+        queue.append(child)
+
+for row in data:
+    row["level"] = levels[row["name"]]
+
+# Calculate cumulative values bottom-up (leaf to root)
+max_level = max(levels.values())
+for level in range(max_level, -1, -1):
+    for row in data:
+        if row["level"] == level:
+            if children[row["name"]]:
+                row["total_value"] = sum(data[name_to_idx[c]]["total_value"] for c in children[row["name"]])
+            else:
+                row["total_value"] = row["value"]
+
+# Calculate x positions iteratively (horizontal placement based on value)
+positions = {"root": (0, 1)}
+queue = ["root"]
+while queue:
+    current = queue.pop(0)
+    x_start, x_end = positions[current]
+    child_list = children[current]
+    if child_list:
+        total = sum(data[name_to_idx[c]]["total_value"] for c in child_list)
+        if total > 0:
+            current_x = x_start
+            for child in child_list:
+                child_val = data[name_to_idx[child]]["total_value"]
+                child_width = (x_end - x_start) * child_val / total
+                positions[child] = (current_x, current_x + child_width)
+                current_x += child_width
+                queue.append(child)
+
+for row in data:
+    row["x_start"], row["x_end"] = positions[row["name"]]
+
+# Prepare data for Altair rectangles
+rect_data = []
+for row in data:
+    if row["total_value"] > 0:
+        rect_data.append(
+            {
+                "name": row["name"],
+                "x_start": row["x_start"],
+                "x_end": row["x_end"],
+                "y_start": row["level"],
+                "y_end": row["level"] + 1,
+                "level": row["level"],
+                "value": row["total_value"],
+                "parent": row["parent"] if row["parent"] else "None",
+            }
+        )
+
+rect_df = pd.DataFrame(rect_data)
+
+# Color scale with stronger contrast between adjacent levels
+# Using distinct hues for better visual separation
+level_colors = ["#1a5276", "#f39c12", "#27ae60", "#8e44ad", "#e74c3c"]
+
+# Create icicle chart with mark_rect
+chart = (
+    alt.Chart(rect_df)
+    .mark_rect(stroke="white", strokeWidth=2)
+    .encode(
+        x=alt.X("x_start:Q", axis=None, scale=alt.Scale(domain=[0, 1])),
+        x2=alt.X2("x_end:Q"),
+        y=alt.Y(
+            "y_start:Q",
+            axis=alt.Axis(
+                title="Hierarchy Level",
+                labelFontSize=18,
+                titleFontSize=22,
+                values=list(range(max_level + 2)),
+                format="d",
+            ),
+            scale=alt.Scale(domain=[0, max_level + 1]),
+        ),
+        y2=alt.Y2("y_end:Q"),
+        color=alt.Color(
+            "level:O",
+            scale=alt.Scale(domain=list(range(max_level + 1)), range=level_colors),
+            legend=alt.Legend(title="Level", labelFontSize=16, titleFontSize=18, orient="right"),
+        ),
+        tooltip=["name:N", "value:Q", "parent:N", "level:O"],
+    )
+)
+
+# Add text labels for larger rectangles
+text = (
+    alt.Chart(rect_df)
+    .mark_text(fontSize=14, color="white", fontWeight="bold", align="center")
+    .encode(
+        x=alt.X("x_mid:Q", scale=alt.Scale(domain=[0, 1])),
+        y=alt.Y("y_mid:Q", scale=alt.Scale(domain=[0, max_level + 1])),
+        text=alt.Text("label:N"),
+    )
+    .transform_calculate(
+        x_mid="(datum.x_start + datum.x_end) / 2",
+        y_mid="(datum.y_start + datum.y_end) / 2",
+        width="datum.x_end - datum.x_start",
+        label="datum.width > 0.05 ? datum.name : ''",
+    )
+)
+
+# Combine chart and text
+icicle = (
+    (chart + text)
+    .properties(width=1600, height=900, title="icicle-basic · altair · pyplots.ai")
+    .configure_title(fontSize=28, anchor="middle")
+    .configure_view(strokeWidth=0)
+)
+
+# Save as PNG and HTML
+icicle.save("plot.png", scale_factor=3.0)
+icicle.save("plot.html")

plots/icicle-basic/metadata/altair.yaml

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+library: altair
+specification_id: icicle-basic
+created: '2025-12-30T00:03:43Z'
+updated: '2025-12-30T00:22:46Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20585400003
+issue: 0
+python_version: 3.13.11
+library_version: 6.0.0
+preview_url: https://storage.googleapis.com/pyplots-images/plots/icicle-basic/altair/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/icicle-basic/altair/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/icicle-basic/altair/plot.html
+quality_score: 91
+review:
+  strengths:
+  - Excellent hierarchical visualization with clear parent-child relationships visible
+    through spatial adjacency
+  - Smart label hiding for narrow rectangles prevents text overlap
+  - Good use of Altair declarative syntax with mark_rect and transform_calculate
+  - Interactive tooltips enhance usability
+  - File system example matches specification suggested application perfectly
+  - Clean code structure following KISS principles with iterative tree building
+  weaknesses:
+  - Color palette uses only blue hues which may reduce accessibility for some colorblind
+    users; consider using more distinct hues across levels
+  - Some leaf nodes appear very narrow making the hierarchy harder to read in that
+    section