Gantt Chart Generator

Business Case

Problem Statement

Schedule visualization challenges:

• Complex task dependencies
• Progress tracking
• Critical path visibility
• Multi-level WBS display

Solution

Generate interactive Gantt charts from schedule data with dependency visualization, progress tracking, and export capabilities.

Technical Implementation

python
import pandas as pd
from typing import Dict, Any, List, Optional
from dataclasses import dataclass, field
from datetime import date, timedelta
from enum import Enum


class TaskStatus(Enum):
    NOT_STARTED = "not_started"
    IN_PROGRESS = "in_progress"
    COMPLETED = "completed"
    DELAYED = "delayed"
    ON_HOLD = "on_hold"


class DependencyType(Enum):
    FS = "finish_to_start"
    SS = "start_to_start"
    FF = "finish_to_finish"
    SF = "start_to_finish"


@dataclass
class Task:
    task_id: str
    name: str
    start_date: date
    end_date: date
    wbs_code: str = ""
    progress: float = 0  # 0-100
    status: TaskStatus = TaskStatus.NOT_STARTED
    assignee: str = ""
    level: int = 0
    is_milestone: bool = False
    is_summary: bool = False
    parent_id: str = ""


@dataclass
class Dependency:
    predecessor_id: str
    successor_id: str
    dep_type: DependencyType = DependencyType.FS
    lag: int = 0


class GanttChartGenerator:
    """Generate Gantt charts for construction scheduling."""

    def __init__(self, project_name: str):
        self.project_name = project_name
        self.tasks: Dict[str, Task] = {}
        self.dependencies: List[Dependency] = []

    def add_task(self, task: Task):
        """Add task to chart."""
        self.tasks[task.task_id] = task

    def add_dependency(self, predecessor_id: str, successor_id: str,
                       dep_type: DependencyType = DependencyType.FS,
                       lag: int = 0):
        """Add dependency between tasks."""
        self.dependencies.append(Dependency(
            predecessor_id=predecessor_id,
            successor_id=successor_id,
            dep_type=dep_type,
            lag=lag
        ))

    def import_from_df(self, df: pd.DataFrame):
        """Import tasks from DataFrame."""

        for _, row in df.iterrows():
            task = Task(
                task_id=str(row['task_id']),
                name=row['name'],
                start_date=pd.to_datetime(row['start_date']).date(),
                end_date=pd.to_datetime(row['end_date']).date(),
                wbs_code=str(row.get('wbs_code', '')),
                progress=float(row.get('progress', 0)),
                level=int(row.get('level', 0)),
                is_milestone=bool(row.get('is_milestone', False)),
                is_summary=bool(row.get('is_summary', False)),
                parent_id=str(row.get('parent_id', ''))
            )
            self.add_task(task)

    def get_project_range(self) -> tuple:
        """Get project date range."""

        if not self.tasks:
            return (date.today(), date.today())

        min_date = min(t.start_date for t in self.tasks.values())
        max_date = max(t.end_date for t in self.tasks.values())
        return (min_date, max_date)

    def get_duration(self, task_id: str) -> int:
        """Get task duration in days."""

        task = self.tasks.get(task_id)
        if task:
            return (task.end_date - task.start_date).days + 1
        return 0

    def generate_text_gantt(self, width: int = 60) -> str:
        """Generate text-based Gantt chart."""

        if not self.tasks:
            return "No tasks"

        lines = []
        start, end = self.get_project_range()
        total_days = (end - start).days + 1
        scale = width / total_days if total_days > 0 else 1

        # Header
        lines.append(f"Project: {self.project_name}")
        lines.append(f"Period: {start} to {end}")
        lines.append("-" * (40 + width))

        # Tasks
        for task in sorted(self.tasks.values(), key=lambda t: (t.level, t.start_date)):
            indent = "  " * task.level
            name = f"{indent}{task.name}"[:35].ljust(35)

            # Bar position
            bar_start = int((task.start_date - start).days * scale)
            bar_length = max(1, int(self.get_duration(task.task_id) * scale))

            # Progress bar
            progress_length = int(bar_length * task.progress / 100)
            bar = " " * bar_start
            bar += "█" * progress_length
            bar += "░" * (bar_length - progress_length)
            bar = bar[:width].ljust(width)

            status_char = "◆" if task.is_milestone else "│"
            lines.append(f"{name} {status_char}{bar}│ {task.progress:.0f}%")

        return "\n".join(lines)

    def generate_mermaid_gantt(self) -> str:
        """Generate Mermaid Gantt diagram."""

        lines = [
            "gantt",
            f"    title {self.project_name}",
            "    dateFormat YYYY-MM-DD",
            ""
        ]

        # Group by WBS prefix
        sections = {}
        for task in self.tasks.values():
            section = task.wbs_code.split('.')[0] if task.wbs_code else "Tasks"
            if section not in sections:
                sections[section] = []
            sections[section].append(task)

        for section, tasks in sections.items():
            lines.append(f"    section {section}")
            for task in sorted(tasks, key=lambda t: t.start_date):
                duration = self.get_duration(task.task_id)
                status = ""
                if task.status == TaskStatus.COMPLETED:
                    status = "done, "
                elif task.status == TaskStatus.IN_PROGRESS:
                    status = "active, "

                if task.is_milestone:
                    lines.append(f"    {task.name} :milestone, {task.start_date}, 0d")
                else:
                    lines.append(f"    {task.name} :{status}{task.task_id}, {task.start_date}, {duration}d")

        return "\n".join(lines)

    def generate_html_gantt(self) -> str:
        """Generate HTML/CSS Gantt chart."""

        start, end = self.get_project_range()
        total_days = (end - start).days + 1

        html = f"""
<!DOCTYPE html>
<html>
<head>
    <title>Gantt Chart - {self.project_name}</title>
    <style>
        .gantt {{ font-family: Arial, sans-serif; }}
        .task {{ display: flex; margin: 2px 0; height: 25px; align-items: center; }}
        .task-name {{ width: 200px; padding-right: 10px; font-size: 12px; }}
        .task-bar {{ position: relative; height: 20px; background: #e0e0e0; flex: 1; }}
        .bar {{ position: absolute; height: 100%; }}
        .bar-fill {{ background: #4CAF50; }}
        .bar-progress {{ background: #2196F3; }}
        .milestone {{ width: 10px; height: 10px; background: #FF5722; transform: rotate(45deg); margin-left: 10px; }}
    </style>
</head>
<body>
    <div class="gantt">
        <h2>{self.project_name}</h2>
        <p>{start} - {end}</p>
"""

        for task in sorted(self.tasks.values(), key=lambda t: (t.level, t.start_date)):
            left = ((task.start_date - start).days / total_days) * 100
            width = (self.get_duration(task.task_id) / total_days) * 100
            progress_width = width * task.progress / 100

            indent = "&nbsp;" * (task.level * 4)

            if task.is_milestone:
                html += f'<div class="task"><div class="task-name">{indent}{task.name}</div><div class="task-bar"><div class="milestone" style="left:{left}%"></div></div></div>\n'
            else:
                html += f'''<div class="task">
    <div class="task-name">{indent}{task.name}</div>
    <div class="task-bar">
        <div class="bar bar-fill" style="left:{left}%; width:{width}%"></div>
        <div class="bar bar-progress" style="left:{left}%; width:{progress_width}%"></div>
    </div>
</div>\n'''

        html += "</div></body></html>"
        return html

    def get_critical_path(self) -> List[str]:
        """Identify critical path tasks (simplified)."""

        if not self.dependencies:
            return [t.task_id for t in sorted(self.tasks.values(), key=lambda x: x.end_date)[-5:]]

        # Find tasks with no slack (simplified approach)
        critical = []
        _, project_end = self.get_project_range()

        for task in self.tasks.values():
            if task.end_date == project_end:
                critical.append(task.task_id)
                # Trace predecessors
                for dep in self.dependencies:
                    if dep.successor_id == task.task_id:
                        critical.append(dep.predecessor_id)

        return list(set(critical))

    def export_to_excel(self, output_path: str) -> str:
        """Export Gantt data to Excel."""

        with pd.ExcelWriter(output_path, engine='openpyxl') as writer:
            # Tasks
            tasks_df = pd.DataFrame([{
                'ID': t.task_id,
                'WBS': t.wbs_code,
                'Name': t.name,
                'Start': t.start_date,
                'End': t.end_date,
                'Duration': self.get_duration(t.task_id),
                'Progress': t.progress,
                'Status': t.status.value,
                'Level': t.level
            } for t in self.tasks.values()])
            tasks_df.to_excel(writer, sheet_name='Tasks', index=False)

            # Dependencies
            deps_df = pd.DataFrame([{
                'Predecessor': d.predecessor_id,
                'Successor': d.successor_id,
                'Type': d.dep_type.value,
                'Lag': d.lag
            } for d in self.dependencies])
            deps_df.to_excel(writer, sheet_name='Dependencies', index=False)

        return output_path

Quick Start

python
from datetime import date, timedelta

# Create Gantt chart
gantt = GanttChartGenerator("Office Building A")

# Add tasks
gantt.add_task(Task("T1", "Foundation", date(2024, 6, 1), date(2024, 6, 30), "01", progress=100))
gantt.add_task(Task("T2", "Structure", date(2024, 7, 1), date(2024, 9, 30), "02", progress=60))
gantt.add_task(Task("T3", "MEP Rough-in", date(2024, 8, 1), date(2024, 10, 31), "03", progress=30))
gantt.add_task(Task("M1", "Topping Out", date(2024, 9, 30), date(2024, 9, 30), is_milestone=True))

# Add dependencies
gantt.add_dependency("T1", "T2")
gantt.add_dependency("T2", "T3")

# Generate text Gantt
print(gantt.generate_text_gantt())

Common Use Cases

1. Mermaid Diagram

python
mermaid = gantt.generate_mermaid_gantt()
print(mermaid)  # Copy to Mermaid editor

2. HTML Export

python
html = gantt.generate_html_gantt()
with open("gantt.html", "w") as f:
    f.write(html)

3. Critical Path

python
critical = gantt.get_critical_path()
print(f"Critical tasks: {critical}")

Resources

• DDC Book: Chapter 3.3 - 4D Scheduling and BIM
• Website: https://datadrivenconstruction.io