backend/compiler.py

import os
import json
import re
from google import genai
from google.genai import types

COMPILER_SYSTEM_PROMPT = """
You are a deterministic Manim script generator for a text-to-educational-animation engine.

Your job:
Convert the user prompt into a single clean Manim Community Edition Python script.

The script will be executed automatically by a backend system, so the structure must be strict.

────────────────────────────

ABSOLUTE REQUIREMENTS

────────────────────────────

Always output ONLY Python code.

No markdown
No explanations
No comments
No triple quotes
NEVER include self.add_sound() calls
NEVER include audio or sound methods

Exactly 1 Scene class:

class GenScene(Scene):


Never use any other scene name.

Imports:

from manim import *


No LaTeX
Never use:
MathTex
Tex
Matrix
TexTemplate

Use only:
Text("expression or label")


────────────────────────────

ASCII RULES (CRITICAL)

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1. NEVER output Unicode mathematical characters or subscript/superscript glyphs.
   ❌ Do not use: ² ₁ ₓ α β γ θ π σ → ∞ × ÷
   ✔️ Instead use ONLY plain ASCII text:
   "x^2" instead of "x²"
   "x_1" instead of "x₁"
   "pi" instead of "π"
   "velocity" instead of "→v"

2. The script must be compatible with Windows console and UTF-8 only.
   - No special glyphs, emoji, arrows, smart quotes, curly quotes, or accents.

────────────────────────────

VISUAL RULES (CRITICAL)

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1. NEVER allow visuals to go outside the video frame.
   - Keep all objects centered or inside safe boundaries.
   - Do not let squares, shapes, or arrows clip off-screen.
   - Standard frame is [-7, 7] horizontally and [-4, 4] vertically. Keep well within this.

2. MANDATORY SPACING - No overlapping elements.
   - Use FadeOut() to CLEAR previous content before showing new content
   - Minimum buffer between objects: buff=0.5 (NEVER less than 0.4)
   - Use screen zones:
     * TOP zone (y=3 to y=2): For titles/headers
     * MIDDLE zone (y=1 to y=-1): For main content
     * BOTTOM zone (y=-2 to y=-3): For explanations/labels
   - ALWAYS clear screen between major steps using self.play(FadeOut(VGroup(*self.mobjects)))
   - Position text with .to_edge(UP/DOWN) or .shift(UP*2 / DOWN*2) to avoid center crowding

3. Visual accuracy FIRST.
   - Show geometry clearly.
   - Avoid rotating or stretching objects unnecessarily.
   - Avoid random effects.
   - Use scale(0.7) for text if needed to prevent overflow

────────────────────────────

ANIMATION RULES

────────────────────────────

1. Timing for audio synchronization:
   - Each narration step gets approximately 3-4 seconds of animation
   - Use run_time=1.0 for Write() and Create()
   - Use run_time=0.8 for FadeIn/FadeOut
   - Add self.wait(1.5) between major steps for narration
   - TOTAL scene duration should be 12-20 seconds

2. Only use these animations:
   Create
   FadeIn
   FadeOut
   Write
   Transform
   MoveTo
   Scale
   Rotate

3. No 3D, no camera zoom, no cinematic effects, no physics.

4. STRUCTURE each step clearly:
   - Clear previous content with FadeOut
   - Show new title/concept
   - Display visual elements one by one
   - Add wait time for narration
   - Transition to next step

────────────────────────────

STRUCTURE & PACING

────────────────────────────

1. Follow step-by-step logic:
   - Introduce main idea
   - Draw objects (one-by-one, not overlapping)
   - Highlight key components
   - Explain or show the formula visually
   - Conclude cleanly

2. Keep total runtime 12–18 seconds.
   - Use self.wait(1) or self.wait(2) to pace the video.

────────────────────────────

OUTPUT FORMAT EXAMPLE

────────────────────────────

from manim import *

class GenScene(Scene):
    def construct(self):
        # 1. Introduce
        title = Text("Concept Name").scale(0.8).to_edge(UP)
        self.play(Write(title), run_time=1)
        self.wait(0.5)

        # 2. Draw Objects
        box = Square(side_length=2, color=BLUE)
        self.play(Create(box), run_time=1)
        self.wait(0.5)

        # 3. Label (No overlap)
        label = Text("Side = 2").next_to(box, DOWN, buff=0.5)
        self.play(Write(label), run_time=1)
        self.wait(1)

        # 4. Conclude
        self.play(FadeOut(box), FadeOut(label), run_time=1)
        self.wait(1)

────────────────────────────

FINAL OUTPUT RULE

────────────────────────────

➡️ Return ONLY Python code.
➡️ No formatting, no text, no explanations.
➡️ Only 1 Scene class named GenScene.
"""

async def generate_manim_code(outline: dict, step_audio_paths=None):
    outline_str = json.dumps(outline, indent=2)
    api_key = os.environ.get("GEMINI_API_KEY")
    if not api_key:
        raise ValueError("GEMINI_API_KEY not found in environment variables.")
    
    client = genai.Client(api_key=api_key)
    prompt = f"{COMPILER_SYSTEM_PROMPT}\n\nINPUT OUTLINE:\n{outline_str}\n\nPYTHON CODE:"
    
    try:
        response = client.models.generate_content(
            model='gemini-2.5-flash',
            contents=prompt
        )
        code = response.text.strip()
        # Cleanup markdown if present
        if code.startswith("```python"):
            code = code[9:]
        elif code.startswith("```"):
            code = code[3:]
        if code.endswith("```"):
            code = code[:-3]
        # --- POST-PROCESSING SANITIZATION ---
        if "MathTex" in code or "Tex(" in code:
            print("WARNING: Model used LaTeX despite instructions. Sanitizing code...")
            code = code.replace("MathTex", "Text")
            code = code.replace("Tex(", "Text(")
            replacements = {
                r"^\\circ": " degrees", r"\\circ": " degrees", "°": " degrees",
                r"\\theta": "theta", "θ": "theta",
                r"\\pi": "pi", "π": "pi",
                r"\\alpha": "alpha", "α": "alpha",
                r"\\beta": "beta", "β": "beta",
                r"\\gamma": "gamma", "γ": "gamma",
                r"\\sigma": "sigma", "σ": "sigma",
                r"\\Delta": "Delta", "Δ": "Delta",
                r"\\times": "x", "×": "x",
                r"\\cdot": "*", "·": "*",
                r"\\div": "/", "÷": "/",
                r"\\pm": "+/-", "±": "+/-",
                r"\\approx": "~", "≈": "~",
                r"\\neq": "!=", "≠": "!=",
                r"\\le": "<=", "≤": "<=",
                r"\\ge": ">=", "≥": ">=",
                r"\\infty": "infinity", "∞": "infinity",
                r"\\Rightarrow": "->", "⇒": "->",
                r"\\rightarrow": "->", "→": "->",
                r"\\leftarrow": "<-", "←": "<-",
                "²": "^2", "³": "^3", "₁": "_1", "₂": "_2", "ₓ": "_x",
                r"\\\\": "\n", # Double backslash to newline
                "–": "-", # En dash to hyphen
                "—": "-", # Em dash to hyphen
                "’": "'", # Smart quotes
                "“": '"',
                "”": '"',
            }
            for pattern, replacement in replacements.items():
                code = code.replace(pattern, replacement)
        # Remove any model-generated self.add_sound calls and self.wait calls
        lines = code.split('\n')
        code = '\n'.join([line for line in lines if "self.add_sound" not in line and not line.strip().startswith("self.wait(")])
        
        # Fix .center usage (replace .center with .get_center() only when used as an argument)
        code = re.sub(r'([\w\)\]]+)\.center(\s*\))', r'\1.get_center()\2', code)
        code = re.sub(r'class\s+\w+\(Scene\):', 'class GenScene(Scene):', code)
        
        # Fix VGroup(*self.mobjects) -> Group(*self.mobjects)
        # VGroup can only contain VMobjects, but self.mobjects may contain Groups
        code = re.sub(r'VGroup\(\*self\.mobjects\)', r'Group(*self.mobjects)', code)

        # DISABLE audio insertion - it causes syntax errors
        # Audio feature is disabled to prevent malformed code
        
        # Validate Python syntax
        try:
            compile(code, '<string>', 'exec')
            print("✓ Generated code validated successfully")
        except SyntaxError as se:
            print(f"⚠ Syntax error in generated code: {se}")
            print(f"  Line {se.lineno}: {se.text}")
            # Try to fix by removing problematic lines
            lines = code.split('\n')
            fixed_lines = []
            error_line = se.lineno - 1 if se.lineno else -1
            
            for i, line in enumerate(lines):
                skip = False
                if i == error_line or "self.add_sound" in line or (line.strip().startswith("self.wait(") and "self.play" not in lines[i-1] if i > 0 else False):
                    print(f"  ✗ Removing problematic line {i+1}: {line.strip()}")
                    skip = True
                if not skip:
                    fixed_lines.append(line)
            
            code = '\n'.join(fixed_lines)
            # Try compiling again
            try:
                compile(code, '<string>', 'exec')
                print("✓ Fixed syntax errors")
            except SyntaxError as se2:
                print(f"⚠ Still has syntax errors: {se2}")

        return code
    except Exception as e:
        print(f"Error generating code with Gemini: {e}")
        raise e