"""AI Script Builder service — generates scripts from natural language descriptions."""
import logging
import re
from datetime import datetime, timezone
from typing import Optional
from uuid import UUID

from sqlalchemy import select, func, text
from sqlalchemy.exc import IntegrityError
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import selectinload

from app.core.ai_provider import get_ai_provider
from app.core.config import settings
from app.models.script_builder_session import ScriptBuilderSession, ScriptBuilderMessage
from app.schemas.script_builder import (
    ScriptBuilderMessageResponse,
    ScriptBuilderSessionDetail,
    ScriptBuilderSessionSummary,
)

logger = logging.getLogger(__name__)

MAX_MESSAGES_PER_SESSION = 30

LANGUAGE_PROMPTS = {
    "powershell": """\
You are an expert PowerShell script writer for MSP (Managed Service Provider) environments.

## Script Standards
- Use Advanced Functions with CmdletBinding and param() blocks
- Include comment-based help (.SYNOPSIS, .DESCRIPTION, .PARAMETER, .EXAMPLE)
- Use try/catch/finally for error handling
- Use Write-Verbose for diagnostic output, Write-Error for failures
- Support pipeline input where appropriate
- Use approved PowerShell verbs (Get-, Set-, New-, Remove-, etc.)
- Import required modules at the top (e.g., Import-Module ActiveDirectory)
- Use [Parameter(Mandatory=$true)] for required params
- Default to UTF-8 output for exports

## Security
- Never hardcode credentials — use Get-Credential or SecureString params
- Use -WhatIf and -Confirm support via SupportsShouldProcess
- Validate input with ValidateSet, ValidatePattern, ValidateRange
""",
    "bash": """\
You are an expert Bash script writer for Linux/macOS system administration.

## Script Standards
- Start with #!/bin/bash
- Use set -euo pipefail for safety
- Parse arguments with getopts or positional parameters
- Include a usage() function for --help
- Use functions for logical grouping
- Quote all variable expansions ("$var" not $var)
- Use [[ ]] for conditionals (not [ ])
- Add comments explaining non-obvious logic
- Use lowercase_with_underscores for variable names
- Exit with meaningful exit codes (0=success, 1=general error, 2=usage error)

## Security
- Never store passwords in scripts — use environment variables or prompts
- Validate all user inputs
- Use mktemp for temporary files
""",
    "python": """\
You are an expert Python script writer for IT automation and system administration.

## Script Standards
- Use Python 3.10+ syntax
- Add type hints to all function signatures
- Use argparse for CLI argument parsing
- Include if __name__ == "__main__": guard
- Use logging module (not print) for diagnostic output
- Use docstrings for functions and modules
- Use pathlib.Path instead of os.path
- Handle exceptions with specific exception types
- Use f-strings for string formatting
- Follow PEP 8 naming conventions

## Security
- Never hardcode secrets — use environment variables or config files
- Validate and sanitize all user inputs
- Use subprocess.run() with shell=False (never shell=True with user input)
""",
}

SYSTEM_PROMPT_TEMPLATE = """\
{language_prompt}

## Response Format
Respond conversationally. When generating a script:
1. Briefly explain what the script does and any assumptions
2. Include the complete script in a single fenced code block with the language tag
3. Suggest a filename (e.g., `Get-LinkedGPOs.ps1`)

When the user asks for modifications, generate the COMPLETE updated script (not a diff).

## Context
The user is an MSP engineer using ResolutionFlow. They need scripts for managing client infrastructure.
Keep scripts practical, production-ready, and well-documented.\
"""


def _extract_script_from_response(content: str, language: str) -> tuple[str | None, str | None]:
    """Extract code block and filename from AI response.

    Returns (script, filename) tuple.
    """
    # Map language to code fence tags
    lang_tags = {
        "powershell": ["powershell", "ps1", "pwsh"],
        "bash": ["bash", "sh", "shell"],
        "python": ["python", "py", "python3"],
    }
    tags = lang_tags.get(language, [language])

    # Try each language-specific tag, then fall back to generic fence
    script = None
    for tag in tags:
        pattern = rf"```{tag}\s*\n(.*?)```"
        match = re.search(pattern, content, re.DOTALL | re.IGNORECASE)
        if match:
            script = match.group(1).strip()
            break
    else:
        # Try generic code fence
        pattern = r"```\s*\n(.*?)```"
        match = re.search(pattern, content, re.DOTALL)
        script = match.group(1).strip() if match else None

    # Extract filename suggestion
    filename = None
    ext_map = {"powershell": ".ps1", "bash": ".sh", "python": ".py"}
    ext = ext_map.get(language, ".txt")
    filename_pattern = rf"`([A-Za-z0-9_\-]+{re.escape(ext)})`"
    fname_match = re.search(filename_pattern, content)
    if fname_match:
        filename = fname_match.group(1)

    return script, filename


async def create_session(
    db: AsyncSession,
    user_id: UUID,
    account_id: UUID,
    team_id: UUID | None,
    language: str,
    initial_prompt: str | None = None,
    origin: str = "standalone",
    ai_session_id: UUID | None = None,
) -> ScriptBuilderSession:
    """Create a new Script Builder session."""
    session = ScriptBuilderSession(
        user_id=user_id,
        account_id=account_id,
        team_id=team_id,
        language=language,
        origin=origin,
        ai_session_id=ai_session_id,
    )
    db.add(session)
    await db.flush()

    # If initial prompt provided (e.g., from FlowPilot), send first message
    if initial_prompt:
        await send_message(db, session, initial_prompt)

    return session


async def send_message(
    db: AsyncSession,
    session: ScriptBuilderSession,
    user_content: str,
) -> ScriptBuilderMessageResponse:
    """Send a user message and get AI response with generated script."""
    # Acquire per-session advisory lock to prevent concurrent message count races.
    # Two simultaneous sends to the same session would otherwise both read the same
    # count, both pass the limit check, and both insert — exceeding the cap.
    session_lock_key = hash(str(session.id)) % (2**62)
    await db.execute(text("SELECT pg_advisory_xact_lock(:key)"), {"key": session_lock_key})

    # Count existing messages for the session
    msg_count_result = await db.execute(
        select(func.count(ScriptBuilderMessage.id)).where(
            ScriptBuilderMessage.session_id == session.id,
            ScriptBuilderMessage.role == "user",
        )
    )
    user_msg_count = msg_count_result.scalar_one()

    if user_msg_count >= MAX_MESSAGES_PER_SESSION:
        raise ValueError(f"Session has reached the maximum of {MAX_MESSAGES_PER_SESSION} messages.")

    now = datetime.now(timezone.utc)

    # Create user message record
    user_msg = ScriptBuilderMessage(
        session_id=session.id,
        role="user",
        content=user_content,
        created_at=now,
    )
    db.add(user_msg)
    await db.flush()

    # Build system prompt
    language_prompt = LANGUAGE_PROMPTS.get(session.language, LANGUAGE_PROMPTS["powershell"])
    system_prompt = SYSTEM_PROMPT_TEMPLATE.format(language_prompt=language_prompt)

    # Build conversation for AI — get last 20 messages for context window
    recent_result = await db.execute(
        select(ScriptBuilderMessage)
        .where(ScriptBuilderMessage.session_id == session.id)
        .order_by(ScriptBuilderMessage.created_at.desc())
        .limit(20)
    )
    recent_msgs = list(reversed(recent_result.scalars().all()))
    ai_messages = [{"role": m.role, "content": m.content} for m in recent_msgs]

    # Call AI
    model = settings.get_model_for_action("script_build")
    provider = get_ai_provider(model=model)
    ai_text, input_tokens, output_tokens = await provider.generate_text(
        system_prompt=[
            {"type": "text", "text": system_prompt},
            # cacheable: SYSTEM_PROMPT_TEMPLATE with a per-session language
            # substitution. Two sessions on the same language share a cache
            # entry; different languages cache independently. Conversation
            # history (ai_messages) is NOT cached at this layer — if that
            # becomes a cost driver, route script_builder through the chat
            # wrapper (0.4) which handles history caching.
        ],
        messages=ai_messages,
        max_tokens=8192,
    )

    # Extract script from response
    script, filename = _extract_script_from_response(ai_text, session.language)
    line_count = len(script.splitlines()) if script else None

    # Create assistant message record
    assistant_msg = ScriptBuilderMessage(
        session_id=session.id,
        role="assistant",
        content=ai_text,
        script=script,
        script_filename=filename,
        line_count=line_count,
        input_tokens=input_tokens,
        output_tokens=output_tokens,
        created_at=datetime.now(timezone.utc),
    )
    db.add(assistant_msg)

    # Update session denormalized fields
    if script:
        session.latest_script = script
        session.latest_script_filename = filename
    if not session.title:
        # Auto-generate title from first user message (truncate)
        first_user = user_content[:100]
        session.title = first_user if len(user_content) <= 100 else first_user + "..."
    session.updated_at = datetime.now(timezone.utc)

    await db.flush()

    return ScriptBuilderMessageResponse(
        role="assistant",
        content=ai_text,
        script=script,
        script_filename=filename,
        line_count=line_count,
        timestamp=datetime.now(timezone.utc),
    )


async def get_session(
    db: AsyncSession,
    session_id: UUID,
    user_id: UUID,
) -> ScriptBuilderSession | None:
    """Get a session by ID, ensuring the user owns it."""
    result = await db.execute(
        select(ScriptBuilderSession)
        .options(selectinload(ScriptBuilderSession.message_records))
        .where(
            ScriptBuilderSession.id == session_id,
            ScriptBuilderSession.user_id == user_id,
        )
    )
    return result.scalar_one_or_none()


async def list_sessions(
    db: AsyncSession,
    user_id: UUID,
    limit: int = 20,
    offset: int = 0,
    *,
    include_inline: bool = False,
) -> list[ScriptBuilderSession]:
    """List user's builder sessions ordered by updated_at desc.

    By default (include_inline=False) excludes pilot_inline sessions so the
    /script-builder dashboard only shows standalone sessions.
    """
    stmt = (
        select(ScriptBuilderSession)
        .where(ScriptBuilderSession.user_id == user_id)
    )
    if not include_inline:
        stmt = stmt.where(ScriptBuilderSession.origin == "standalone")
    stmt = stmt.order_by(ScriptBuilderSession.updated_at.desc()).limit(limit).offset(offset)
    result = await db.execute(stmt)
    return list(result.scalars().all())


async def delete_session(
    db: AsyncSession,
    session_id: UUID,
    user_id: UUID,
) -> bool:
    """Delete a builder session. Returns True if deleted."""
    session = await get_session(db, session_id, user_id)
    if not session:
        return False
    await db.delete(session)
    await db.flush()
    return True


async def count_user_sessions(
    db: AsyncSession,
    user_id: UUID,
    *,
    include_inline: bool = False,
) -> int:
    """Count active builder sessions for a user.

    By default (include_inline=False) excludes pilot_inline sessions so they
    don't consume slots against the MAX_SESSIONS_PER_USER cap.
    """
    stmt = select(func.count(ScriptBuilderSession.id)).where(
        ScriptBuilderSession.user_id == user_id
    )
    if not include_inline:
        stmt = stmt.where(ScriptBuilderSession.origin == "standalone")
    result = await db.execute(stmt)
    return result.scalar_one()


async def save_to_library(
    db: AsyncSession,
    session: ScriptBuilderSession,
    name: str,
    description: str | None,
    category_id: UUID | None,
    share_with_team: bool,
    user_id: UUID,
    account_id: UUID,
    team_id: UUID | None,
    script_body: str | None = None,
    parameters_schema: dict | None = None,
) -> "ScriptTemplate":
    """Save the latest generated script to the Script Library as a ScriptTemplate."""
    import uuid as uuid_mod
    from app.models.script_template import ScriptTemplate, ScriptCategory

    if not session.latest_script:
        raise ValueError("No script has been generated in this session yet")

    # Resolve category: use provided, or find "AI Generated" default
    resolved_category_id = category_id
    if not resolved_category_id:
        result = await db.execute(
            select(ScriptCategory.id).where(ScriptCategory.slug == "ai-generated")
        )
        default_cat = result.scalar_one_or_none()
        if not default_cat:
            raise ValueError("Default 'AI Generated' category not found. Run migrations.")
        resolved_category_id = default_cat

    # Generate slug. Use a UUID suffix on first attempt to prevent concurrent
    # saves with the same name from hitting the unique constraint on slug.
    base_slug = name.lower().replace(" ", "-").replace("_", "-")[:80]
    base_slug = re.sub(r"[^a-z0-9\-]", "", base_slug)

    # Check if the base slug is already taken; if not, use it clean (no suffix).
    # If taken, or if the insert races with a concurrent request, retry with a
    # fresh UUID suffix. The unique constraint on script_templates.slug is the
    # authoritative guard — the application check just avoids unnecessary retries.
    existing = await db.execute(
        select(ScriptTemplate.id).where(ScriptTemplate.slug == base_slug)
    )
    slug = base_slug if not existing.scalar_one_or_none() else f"{base_slug}-{uuid_mod.uuid4().hex[:6]}"

    for attempt in range(3):
        template = ScriptTemplate(
            id=uuid_mod.uuid4(),
            category_id=resolved_category_id,
            created_by=user_id,
            account_id=account_id,
            team_id=team_id if share_with_team else None,
            name=name,
            slug=slug,
            description=description,
            script_body=script_body or session.latest_script,
            parameters_schema=parameters_schema or {"parameters": []},
            default_values={},
            validation_rules={},
            tags=[session.language, "ai-generated"],
            complexity="intermediate",
            is_verified=False,
            is_active=True,
            version=1,
            usage_count=0,
        )
        db.add(template)
        try:
            await db.flush()
            return template
        except IntegrityError as exc:
            if "uq_script_templates_slug" not in str(exc.orig) or attempt == 2:
                raise
            await db.rollback()
            slug = f"{base_slug}-{uuid_mod.uuid4().hex[:8]}"

    raise RuntimeError("Failed to generate a unique slug after 3 attempts")