app.py

import hashlib
import json
import textwrap
import gradio as gr

# ----------------------------
# Helpers
# ----------------------------

def canonicalize(text: str) -> str:
    """
    Canonicalize input so the demo behaves consistently.
    - Strips trailing spaces per line
    - Normalizes newlines
    """
    if text is None:
        return ""
    lines = [ln.rstrip() for ln in text.splitlines()]
    return "\n".join(lines).strip()

def fingerprint(text: str) -> str:
    """
    Returns a SHA-256 fingerprint of the canonicalized text.
    This is presented as a 'digital fingerprint' (no crypto jargon).
    """
    c = canonicalize(text)
    h = hashlib.sha256(c.encode("utf-8")).hexdigest()
    return f"sha256:{h}"

def compare(original: str, edited: str):
    o = canonicalize(original)
    e = canonicalize(edited)

    if not o:
        return "", "", "Add an original text to generate a fingerprint."

    fp_o = fingerprint(o)
    fp_e = fingerprint(e)

    if not edited.strip():
        status = "Edit the right side and watch what happens to verification."
    elif fp_o == fp_e:
        status = "✅ MATCH — the text is unchanged (verification passes)."
    else:
        status = "❌ TAMPER DETECTED — the fingerprint changed (verification fails)."

    return fp_o, fp_e, status


# ----------------------------
# Default demo content (safe + generic)
# ----------------------------

DEFAULT_RECEIPT = textwrap.dedent("""
RECEIPT (DEMO)

Type: Agreement Summary
Created: 2025-12-14
Parties: [REDACTED] ↔ [REDACTED]

Statement:
"Service will be delivered by Friday. Payment due upon delivery."

Notes:
This is an educational demo. It certifies integrity (unchanged text), not truth.
""").strip()


# ----------------------------
# UI
# ----------------------------

with gr.Blocks(title="Test It Yourself — Verification Demo") as demo:
    gr.Markdown(
        """
# Test It Yourself

This is a simple educational demo:

- The left side is the **original** text.
- The right side is the **edited** text.
- The system generates a **digital fingerprint** for each.
- Change anything on the right → the fingerprint changes → verification fails.

**No accounts. No trust required.**
        """.strip()
    )

    with gr.Row():
        original = gr.Textbox(
            label="Original (demo text)",
            value=DEFAULT_RECEIPT,
            lines=14
        )
        edited = gr.Textbox(
            label="Edited (try changing one word)",
            value=DEFAULT_RECEIPT,
            lines=14
        )

    with gr.Row():
        fp_original = gr.Textbox(label="Original fingerprint", interactive=False)
        fp_edited = gr.Textbox(label="Edited fingerprint", interactive=False)

    status = gr.Markdown()

    gr.Button("Compare / Verify").click(
        compare,
        inputs=[original, edited],
        outputs=[fp_original, fp_edited, status]
    )

    gr.Markdown(
        """
---

### What this demo is (and isn’t)

- **This demo shows integrity:** whether text changed.
- **It does not prove truth:** it can’t verify whether the statement is real.
- Production-grade verification systems enforce durability and refusal behavior beyond this demo.
        """.strip()
    )

demo.launch()