#!/usr/bin/env python3

import os
import sys
import io
import secrets
import sqlite3
import zstandard
from datetime import datetime
from urllib.parse import parse_qs
from pathlib import Path
from dataclasses import dataclass
from typing import Optional, Dict, List, Any
from boto3.session import Session
from botocore.client import Config
from botocore.handlers import set_list_objects_encoding_type_url
from pygments import highlight
from pygments.lexers import guess_lexer, get_lexer_by_name
from pygments.formatters import HtmlFormatter


@dataclass
class Environment:
    request_method: str
    content_length: int
    path: Optional[str]
    parameters: Dict[str, List[str]]
    content_length_max_bytes: int
    access_key: str
    secret_key: str
    endpoint: str
    region: str
    bucket: str
    signature_version: str
    key_length: int
    site: str
    dict: Path
    db_path: Path

    def __init__(self, environment: Dict[str, str]):
        self.request_method = environment["REQUEST_METHOD"]
        self.content_length = int(environment["CONTENT_LENGTH"])

        try:
            self.path = environment["PATH_INFO"]
        except KeyError:
            self.path = None

        try:
            query_string = environment["QUERY_STRING"]
            self.parameters = parse_qs(query_string)
        except KeyError:
            self.parameters = {}

        self.content_length_max_bytes = int(
            environment["PASTE_CONTENT_LENGTH_MAX_BYTES"]
        )
        self.access_key = environment["PASTE_ACCESS_KEY"]
        self.secret_key = environment["PASTE_SECRET_KEY"]
        self.endpoint = environment["PASTE_ENDPOINT"]
        self.region = environment["PASTE_REGION"]
        self.bucket = environment["PASTE_BUCKET_NAME"]
        self.signature_version = environment["PASTE_SIGNATURE_VERSION"]
        self.db_path = Path(environment["PASTE_DB"])
        self.key_length = int(environment["PASTE_KEY_LENGTH"])
        self.site = environment["PASTE_SITE"]
        self.dict = Path(environment["PASTE_DICT"])
        self.storage_max_bytes = int(environment["PASTE_STORAGE_MAX_BYTES"])


def connect_to_s3(
    endpoint: str,
    region: str,
    signature_version: str,
    access_key: str,
    secret_key: str,
):
    session = Session(
        aws_access_key_id=access_key,
        aws_secret_access_key=secret_key,
        region_name=region,
    )

    session.events.unregister(
        "before-parameter-build.s3.ListObjects", set_list_objects_encoding_type_url
    )

    return session.resource(
        "s3",
        endpoint_url=endpoint,
        config=Config(signature_version=signature_version),
    )


def key_in_db(cursor: sqlite3.Cursor, key: str) -> bool:
    results = cursor.execute("select * from pastes where pastes.key=?", (key,))
    return results.fetchone() is not None


def get_syntax_from_db(cursor: sqlite3.Cursor, key: str) -> Optional[str]:
    results = cursor.execute(
        "select pastes.syntax from pastes where pastes.key=?", (key,)
    )
    return results.fetchone()


def get_storage_use(cursor: sqlite3.Cursor) -> Optional[int]:
    results = cursor.execute("select sum(pastes.size) from pastes")

    if (row := results.fetchone()) is not None:
        return row[0]
    else:
        return None


def delete_oldest_paste(cursor: sqlite3.Cursor) -> Optional[str]:
    results = cursor.execute(
        "select pastes.key from pastes order by pastes.datetime limit 1"
    )

    if (row := results.fetchone()) is not None:
        key = row[0]

        cursor.execute("delete from pastes where pastes.key=?", (key,))

        return key
    else:
        return None


def generate_key(words: List[str], length: int) -> str:
    choices = []
    for _ in range(length):
        choices.append(secrets.choice(words))

    return "-".join(word for word in choices).lower()


def pygmentize(content: str, syntax: Optional[str]) -> str:
    if syntax is not None:
        try:
            lexer = get_lexer_by_name(syntax)
        except Exception as e:
            print(e, file=sys.stderr)
            lexer = guess_lexer(content)
    else:
        lexer = guess_lexer(content)

    formatter = HtmlFormatter(full=True, cssclass="source")

    return highlight(content, lexer, formatter)


def main():
    try:
        environment = Environment({key: val for key, val in os.environ.items()})
    except Exception as e:
        print("Status: 500\r\n")
        print(f"failed to load environment: {e}", file=sys.stderr)
        return

    if environment.request_method not in ["GET", "POST"]:
        print("Status: 400\r\n")
        print(f"unsupported request method: {environment.request_method}")
        return

    try:
        words = environment.dict.read_text().split("\n")
    except Exception as e:
        print("Status: 500\r\n")
        print(f"failed to load dictonary: {e}", file=sys.stderr)
        return

    try:
        s3 = connect_to_s3(
            environment.endpoint,
            environment.region,
            environment.signature_version,
            environment.access_key,
            environment.secret_key,
        )
    except Exception as e:
        print("Status: 500\r\n")
        print(f"failed to connect to s3: {e}", file=sys.stderr)
        return

    try:
        bucket = s3.Bucket(environment.bucket)
    except Exception as e:
        print("Status: 500\r\n")
        print(f"failed to connect to bucket: {e}", file=sys.stderr)
        return

    try:
        connection = sqlite3.connect(environment.db_path)
        cursor = connection.cursor()
    except Exception as e:
        print("Status: 500\r\n")
        print(f"failed to connect to database: {e}")
        return

    match environment.request_method:
        case "POST" if (
            environment.content_length > environment.content_length_max_bytes
        ):
            print("Status: 400\r\n")
            print(
                f"content length exceeded maximum length of {environment.content_length_max_bytes}"
            )
            return

        case "POST":
            # delete pastes to make size for new one
            while (
                (storage_use := get_storage_use(cursor)) is not None
                and storage_use + environment.content_length
                > environment.storage_max_bytes
            ):
                match delete_oldest_paste(cursor):
                    case str(key):
                        try:
                            s3.Object(environment.bucket, key).delete()
                        except Exception as e:
                            print("Status: 500\r\n")
                            print(
                                f"failed to delete object: {key}: {e}", file=sys.stderr
                            )
                            return

                        try:
                            connection.commit()
                            print(
                                f"rotated {key} out to make room for new paste",
                                file=sys.stderr,
                            )
                        except Exception as e:
                            print("Status: 500\r\n")
                            print(f"failed to commit to database: {e}", file=sys.stderr)
                            return
                    case None:
                        break

            try:
                syntax = environment.parameters["syntax"][0]
            except KeyError:
                syntax = None
            except IndexError:
                syntax = None
            except Exception as e:
                print("Status: 500\r\n")
                print(f'failed to load query parameter "syntax": {e}', file=sys.stderr)
                return

            try:
                key = generate_key(words, environment.key_length)
                while key_in_db(cursor, key):
                    key = generate_key(words, environment.key_length)
            except Exception as e:
                print("Status: 500\r\n")
                print(f"failed to query database: {e}", file=sys.stderr)
                return

            content = sys.stdin.buffer.read(environment.content_length)

            try:
                content.decode()
            except Exception as e:
                print("Status: 400\r\n")
                print(f"failed to decode content: {e}")
                return

            compressed = zstandard.compress(content)
            buffer = io.BytesIO(compressed)

            try:
                cursor.execute(
                    "insert into pastes values (?, ?, ?, ?)",
                    (
                        key,
                        len(compressed),
                        datetime.now().isoformat(),
                        syntax,
                    ),
                )
            except Exception as e:
                print("Status: 500\r\n")
                print(f"failed to insert into database: {e}", file=sys.stderr)
                return

            try:
                bucket.upload_fileobj(buffer, key)
            except Exception as e:
                print("Status: 500\r\n")
                print(f"failed to upload paste: {e}", file=sys.stderr)
                return

            try:
                connection.commit()
            except Exception as e:
                print("Status: 500\r\n")
                print(f"failed to commit to db: {e}")
                return

            print("Status: 200\r\n")
            print(f"{environment.site}/{key}")
            return

        case "GET" if environment.path is None:
            print("Status: 400\r\n")
            print("please provide a key to fetch")
            return

        case "GET":
            # strip leading / from path
            key = environment.path[1:]

            try:
                exists = key_in_db(cursor, key)
            except Exception as e:
                print("Status: 500\r\n")
                print(f"failed to query db: {e}")
                return

            if not exists:
                print("Status: 404\r\n")
                return

            buffer = io.BytesIO()

            try:
                bucket.download_fileobj(key, buffer)
            except Exception as e:
                print("Status: 500\r\n")
                print(f"failed to download from bucket: {e}")
                return

            buffer.seek(0)

            decompressed = zstandard.decompress(buffer.read())
            content = decompressed.decode()

            try:
                syntax = environment.parameters["syntax"][0]
            except KeyError:
                try:
                    syntax = get_syntax_from_db(cursor, key)
                except Exception as e:
                    print("Status: 500\r\n")
                    print(f"failed to query database: {e}")
                    return

            try:
                if environment.parameters["raw"]:
                    raw = True
                else:
                    raw = False
            except KeyError:
                raw = False

            if raw:
                print("Status: 200\r\n")
                print(content)
                return
            else:
                highlighted = pygmentize(content, syntax)
                print("Status: 200\r\n")
                print(highlighted)
                return


main()