import uuid

from fastapi import HTTPException, status
from jinja2 import Environment, TemplateSyntaxError, select_autoescape
from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from app.models.pdf_template import PdfTemplate

_jinja_env = Environment(autoescape=select_autoescape(["html"]))


def validate_jinja2(html: str) -> tuple[bool, str]:
    """Validate Jinja2 template syntax. Returns (is_valid, error_message)."""
    try:
        _jinja_env.parse(html)
        return True, ""
    except TemplateSyntaxError as e:
        return False, f"Template syntax error at line {e.lineno}: {e.message}"


async def list_templates(db: AsyncSession, active_only: bool = True, locale: str | None = None) -> list[PdfTemplate]:
    stmt = select(PdfTemplate)
    if active_only:
        stmt = stmt.where(PdfTemplate.is_active == True)  # noqa: E712
    if locale:
        stmt = stmt.where(PdfTemplate.locale == locale)
    stmt = stmt.order_by(PdfTemplate.is_default.desc(), PdfTemplate.name, PdfTemplate.locale)
    result = await db.execute(stmt)
    return list(result.scalars().all())


async def get_template(db: AsyncSession, template_id: uuid.UUID) -> PdfTemplate:
    result = await db.execute(select(PdfTemplate).where(PdfTemplate.id == template_id))
    template = result.scalar_one_or_none()
    if not template:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Template not found")
    return template


async def get_default_template(db: AsyncSession, locale: str = "en") -> PdfTemplate | None:
    result = await db.execute(
        select(PdfTemplate).where(
            PdfTemplate.is_default == True,  # noqa: E712
            PdfTemplate.locale == locale,
        )
    )
    tmpl = result.scalar_one_or_none()
    if not tmpl:
        # Fallback to any default
        result = await db.execute(
            select(PdfTemplate).where(PdfTemplate.is_default == True)  # noqa: E712
        )
        tmpl = result.scalars().first()
    return tmpl


async def create_template(db: AsyncSession, **kwargs) -> PdfTemplate:
    html = kwargs.get("html_content", "")
    valid, error = validate_jinja2(html)
    if not valid:
        raise HTTPException(status_code=status.HTTP_422_UNPROCESSABLE_ENTITY, detail=error)

    template = PdfTemplate(**kwargs)
    db.add(template)
    await db.flush()
    return template


async def update_template(db: AsyncSession, template_id: uuid.UUID, **kwargs) -> PdfTemplate:
    template = await get_template(db, template_id)

    if "html_content" in kwargs and kwargs["html_content"] is not None:
        valid, error = validate_jinja2(kwargs["html_content"])
        if not valid:
            raise HTTPException(status_code=status.HTTP_422_UNPROCESSABLE_ENTITY, detail=error)

    for key, value in kwargs.items():
        if value is not None:
            setattr(template, key, value)
    await db.flush()
    return template


async def delete_template(db: AsyncSession, template_id: uuid.UUID) -> None:
    template = await get_template(db, template_id)
    if template.is_default:
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="Cannot delete the default template",
        )
    await db.delete(template)


async def render_preview(html_content: str) -> str:
    """Render template with sample data for preview."""
    valid, error = validate_jinja2(html_content)
    if not valid:
        raise HTTPException(status_code=status.HTTP_422_UNPROCESSABLE_ENTITY, detail=error)

    template = _jinja_env.from_string(html_content)
    return template.render(
        title="Sample Report",
        user_name="John Doe",
        generated_at="2026-03-19 12:00 UTC",
        memories=[
            {"category": "health", "title": "Annual Checkup", "content": "Last checkup was in January 2026. All results normal.", "importance": "medium"},
            {"category": "finance", "title": "Tax Deadline", "content": "Filing deadline: April 15, 2026", "importance": "high"},
        ],
        documents=[
            {"original_filename": "report_2026.pdf", "doc_type": "report", "excerpt": "This is a sample document excerpt showing how document content appears in the report..."},
        ],
        ai_summary="This is a sample AI-generated summary of the user's data.",
    )