import os
from fastapi import FastAPI
from fastapi.responses import HTMLResponse

app = FastAPI()

def generate_substitution_cipher(flag):
    substitution_rules = []
    for i, char in enumerate(flag):
        position = i + 1  # 1-based index
        if char.isalpha():
            if char.isupper():
                substitution_rules.append(f"the {position}th flag is '{char}', upper.\n")
            else:  # char is lowercase
                substitution_rules.append(f"the {position}th flag is '{char}', lower.\n")
        else:
            substitution_rules.append(f"the {position}th flag is '{char}', character.\n")

    substitution_dict = {
        'a': 'x', 'b': 'y', 'c': 'z', 'd': 'a', 'e': 'b', 'f': 'c', 'g': 'd',
        'h': 'e', 'i': 'f', 'j': 'g', 'k': 'h', 'l': 'i', 'm': 'j', 'n': 'k',
        'o': 'l', 'p': 'm', 'q': 'n', 'r': 'o', 's': 'p', 't': 'q', 'u': 'r',
        'v': 's', 'w': 't', 'x': 'u', 'y': 'v', 'z': 'w',
        'A': 'X', 'B': 'Y', 'C': 'Z', 'D': 'A', 'E': 'B', 'F': 'C', 'G': 'D',
        'H': 'E', 'I': 'F', 'J': 'G', 'K': 'H', 'L': 'I', 'M': 'J', 'N': 'K',
        'O': 'L', 'P': 'M', 'Q': 'N', 'R': 'O', 'S': 'P', 'T': 'Q', 'U': 'R',
        'V': 'S', 'W': 'T', 'X': 'U', 'Y': 'V', 'Z': 'W',
        ' ': ' '  # 保持空格不变
    }
    
    substitution_rules.append("The quick brown fox jumps a lazy dog.")
    encrypted_rules = []
    for rule in substitution_rules:
        for char in rule:
            if char in substitution_dict:
                encrypted_rules.append(substitution_dict[char])
            else:
                encrypted_rules.append(char)

    return ''.join(encrypted_rules)

@app.get("/", response_class=HTMLResponse)
async def read_root():
    flag = os.getenv("GZCTF_FLAG", "Woodpecker{test-Flag_0}")
    cipher_text = generate_substitution_cipher(flag)
    return f"<h1>下面的密文有Flag哦（PS：单表替换）：</h1><p>{cipher_text}</p>"

if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, host="0.0.0.0", port=8000)