import os
import sqlite3
from pathlib import Path

DB_PATH = os.environ.get("DB_PATH", "/data/whattodo.db")
SCHEMA_VERSION = 3

DEFAULT_CATEGORIES = [
    ("Work", "#2563eb"),
    ("Life", "#16a34a"),
    ("Personal", "#9333ea"),
    ("YouTube", "#dc2626"),
]

SCHEMA = """
CREATE TABLE IF NOT EXISTS meta (
    key   TEXT PRIMARY KEY,
    value TEXT NOT NULL
);
CREATE TABLE IF NOT EXISTS categories (
    id       INTEGER PRIMARY KEY,
    name     TEXT NOT NULL UNIQUE COLLATE NOCASE,
    color    TEXT NOT NULL DEFAULT '#6b7280',
    position INTEGER NOT NULL DEFAULT 0
);
CREATE TABLE IF NOT EXISTS projects (
    id          INTEGER PRIMARY KEY,
    name        TEXT NOT NULL,
    notes       TEXT NOT NULL DEFAULT '',
    category_id INTEGER REFERENCES categories(id) ON DELETE SET NULL,
    due_date    TEXT,
    done        INTEGER NOT NULL DEFAULT 0,
    done_at     TEXT,
    created_at  TEXT NOT NULL,
    updated_at  TEXT NOT NULL
);
CREATE TABLE IF NOT EXISTS tasks (
    id             INTEGER PRIMARY KEY,
    title          TEXT NOT NULL,
    notes          TEXT NOT NULL DEFAULT '',
    category_id    INTEGER REFERENCES categories(id) ON DELETE SET NULL,
    project_id     INTEGER REFERENCES projects(id) ON DELETE SET NULL,
    priority       INTEGER NOT NULL DEFAULT 0,
    due_date       TEXT,
    planned_date   TEXT,
    start_time     TEXT,
    end_time       TEXT,
    tags          TEXT NOT NULL DEFAULT '[]',
    recurrence     TEXT NOT NULL DEFAULT 'none',
    recur_interval INTEGER NOT NULL DEFAULT 1,
    done           INTEGER NOT NULL DEFAULT 0,
    done_at        TEXT,
    created_at     TEXT NOT NULL,
    updated_at     TEXT NOT NULL
);
CREATE TABLE IF NOT EXISTS subtasks (
    id       INTEGER PRIMARY KEY,
    task_id  INTEGER NOT NULL REFERENCES tasks(id) ON DELETE CASCADE,
    title    TEXT NOT NULL,
    done     INTEGER NOT NULL DEFAULT 0,
    position INTEGER NOT NULL DEFAULT 0
);
CREATE INDEX IF NOT EXISTS idx_subtasks_task ON subtasks(task_id);
"""


def connect() -> sqlite3.Connection:
    # FastAPI may open a request's connection and run its endpoint on different threads;
    # each connection is still used by only one request at a time.
    conn = sqlite3.connect(DB_PATH, check_same_thread=False)
    conn.row_factory = sqlite3.Row
    conn.execute("PRAGMA foreign_keys = ON")
    return conn


def init() -> None:
    Path(DB_PATH).parent.mkdir(parents=True, exist_ok=True)
    conn = connect()
    try:
        conn.execute("PRAGMA journal_mode = WAL")
        conn.executescript(SCHEMA)
        row = conn.execute("SELECT value FROM meta WHERE key = 'schema_version'").fetchone()
        if row is not None and int(row["value"]) < SCHEMA_VERSION:
            migrate(conn, int(row["value"]))
        elif row is None:
            # Fresh database: seed default categories.
            with conn:
                for i, (name, color) in enumerate(DEFAULT_CATEGORIES):
                    conn.execute(
                        "INSERT INTO categories (name, color, position) VALUES (?, ?, ?)",
                        (name, color, i),
                    )
                conn.execute(
                    "INSERT INTO meta (key, value) VALUES ('schema_version', ?)",
                    (str(SCHEMA_VERSION),),
                )
    finally:
        conn.close()


def migrate(conn: sqlite3.Connection, version: int) -> None:
    # Keep a copy of the database as it was before migrating, next to it.
    backup = sqlite3.connect(f"{DB_PATH}.before-v{SCHEMA_VERSION}.bak")
    try:
        conn.backup(backup)
    finally:
        backup.close()
    with conn:
        if version < 2:
            conn.execute("ALTER TABLE tasks ADD COLUMN start_time TEXT")
            conn.execute("ALTER TABLE tasks ADD COLUMN end_time TEXT")
        if version < 3:
            # The projects table itself is created by SCHEMA before migrating.
            conn.execute("ALTER TABLE tasks ADD COLUMN planned_date TEXT")
            conn.execute(
                "ALTER TABLE tasks ADD COLUMN project_id INTEGER REFERENCES projects(id) ON DELETE SET NULL"
            )
        conn.execute(
            "UPDATE meta SET value = ? WHERE key = 'schema_version'", (str(SCHEMA_VERSION),)
        )