import json
import re
from pathlib import Path
from typing import Any, Dict, List, Optional, Tuple


ROLE_HEADERS = {"# system", "# user", "# assistant"}
JSON_SCHEMA_HEADER = "# JSON schema"


def fill_template_file(template_path: str, data: Dict[str, Any]) -> Tuple[List[Dict[str, str]], Optional[Dict[str, Any]]]:
    """
    Reads a DAS-style prompt template and returns:
      1. chat messages: [{"role": "...", "content": "..."}]
      2. response_format: dict | None

    Supported template features:
    - role headers:
        # system
        # user
        # assistant

    - placeholders:
        [key]
        {{key}}

    - loop sections:
        # start field_name
        ...
        # end field_name

      where data[field_name] is a list[dict]

    - nested loops inside loops

    - optional JSON schema block:
        # JSON schema
        { ... valid JSON ... }
    """
    raw_text = Path(template_path).read_text(encoding="utf-8")

    prompt_text, schema_text = _split_prompt_and_schema(raw_text)

    expanded_prompt = _expand_template(prompt_text, data)
    messages = _parse_role_markdown(expanded_prompt)

    response_format = None
    if schema_text:
        schema_payload = json.loads(schema_text)
        response_format = _schema_to_response_format(schema_payload)

    return messages, response_format


def _split_prompt_and_schema(text: str) -> Tuple[str, Optional[str]]:
    if JSON_SCHEMA_HEADER not in text:
        return text, None

    prompt_part, schema_part = text.split(JSON_SCHEMA_HEADER, 1)
    schema_text = schema_part.strip()

    if not schema_text:
        return prompt_part, None

    return prompt_part.rstrip(), schema_text


def _schema_to_response_format(schema_payload: Dict[str, Any]) -> Dict[str, Any]:
    """
    Expects DAS-style schema payload, e.g.
    {
      "name": "decoded_das",
      "schema": {...},
      "strict": true
    }
    """
    if "name" not in schema_payload or "schema" not in schema_payload:
        raise ValueError("JSON schema block must contain at least 'name' and 'schema' keys.")

    return {
        "type": "json_schema",
        "json_schema": {
            "name": schema_payload["name"],
            "schema": schema_payload["schema"],
            "strict": schema_payload.get("strict", True),
        },
    }


def _expand_template(text: str, data: Dict[str, Any]) -> str:
    lines = text.splitlines()
    expanded_lines, _ = _process_block(lines, 0, data)
    expanded_text = "\n".join(expanded_lines)
    expanded_text = _replace_placeholders(expanded_text, data)
    return expanded_text.strip()


def _process_block(lines: List[str], start_idx: int, context: Dict[str, Any]) -> Tuple[List[str], int]:
    """
    Recursively processes lines until the end of the block or a matching # end ...
    """
    output: List[str] = []
    i = start_idx

    while i < len(lines):
        stripped = lines[i].strip()

        if stripped.startswith("# end "):
            return output, i

        if stripped.startswith("# start "):
            field_name = stripped.replace("# start ", "", 1).strip()
            block_lines, end_idx = _collect_loop_block(lines, i + 1, field_name)

            loop_value = _resolve_key(field_name, context)
            if loop_value is None:
                loop_value = []
            if not isinstance(loop_value, list):
                raise ValueError(f"Loop field '{field_name}' must be a list, got {type(loop_value).__name__}.")

            for idx, item in enumerate(loop_value, start=1):
                child_context = dict(context)

                if isinstance(item, dict):
                    child_context.update(item)
                else:
                    child_context[field_name] = item

                child_context["$index"] = idx
                child_context[field_name] = item

                expanded_child, _ = _process_block(block_lines, 0, child_context)
                output.extend(expanded_child)

            i = end_idx + 1
            continue

        output.append(_replace_placeholders(lines[i], context))
        i += 1

    return output, i


def _collect_loop_block(lines: List[str], start_idx: int, field_name: str) -> Tuple[List[str], int]:
    """
    Collects lines until the matching # end field_name, respecting nested loops.
    Returns (block_lines, end_index).
    """
    block: List[str] = []
    depth = 1
    i = start_idx

    while i < len(lines):
        stripped = lines[i].strip()

        if stripped.startswith("# start "):
            nested_name = stripped.replace("# start ", "", 1).strip()
            if nested_name == field_name:
                depth += 1
            block.append(lines[i])
            i += 1
            continue

        if stripped.startswith("# end "):
            end_name = stripped.replace("# end ", "", 1).strip()
            if end_name == field_name:
                depth -= 1
                if depth == 0:
                    return block, i
            block.append(lines[i])
            i += 1
            continue

        block.append(lines[i])
        i += 1

    raise ValueError(f"Missing matching '# end {field_name}' in template.")


def _parse_role_markdown(text: str) -> List[Dict[str, str]]:
    messages: List[Dict[str, str]] = []
    current_role: Optional[str] = None
    buffer: List[str] = []

    for line in text.splitlines():
        stripped = line.strip()

        if stripped in ROLE_HEADERS:
            if current_role is not None:
                content = _clean_content("\n".join(buffer))
                messages.append({"role": current_role, "content": content})

            current_role = stripped.replace("# ", "")
            buffer = []
            continue

        buffer.append(line)

    if current_role is not None:
        content = _clean_content("\n".join(buffer))
        messages.append({"role": current_role, "content": content})

    if not messages:
        raise ValueError(
            "Template must contain at least one role header: '# system', '# user', or '# assistant'."
        )

    return messages


def _clean_content(text: str) -> str:
    lines = text.splitlines()

    while lines and not lines[0].strip():
        lines.pop(0)
    while lines and not lines[-1].strip():
        lines.pop()

    if not lines:
        return ""

    min_indent = None
    for line in lines:
        if not line.strip():
            continue
        indent = len(line) - len(line.lstrip(" "))
        if min_indent is None or indent < min_indent:
            min_indent = indent

    min_indent = min_indent or 0
    cleaned = "\n".join(line[min_indent:] if len(line) >= min_indent else line for line in lines)
    return cleaned.strip()


def _replace_placeholders(text: str, context: Dict[str, Any]) -> str:
    """
    Supports both:
      [key]
      {{key}}
    including dotted keys:
      [speaker.name]
      {{speaker.name}}
    and special loop index:
      [$index]
      {{$index}}
    """

    def square_repl(match: re.Match) -> str:
        key = match.group(1).strip()
        value = _resolve_key(key, context)
        return _stringify(value)

    def brace_repl(match: re.Match) -> str:
        key = match.group(1).strip()
        value = _resolve_key(key, context)
        return _stringify(value)

    text = re.sub(r"\[([^\[\]]+)\]", square_repl, text)
    text = re.sub(r"\{\{([^{}]+)\}\}", brace_repl, text)
    return text


def _resolve_key(key: str, context: Dict[str, Any]) -> Any:
    if key in context:
        return context[key]

    if "." not in key:
        return ""

    current: Any = context
    for part in key.split("."):
        part = part.strip()
        if isinstance(current, dict) and part in current:
            current = current[part]
        else:
            return ""

    return current


def _stringify(value: Any) -> str:
    if value is None:
        return ""
    if isinstance(value, str):
        return value
    if isinstance(value, (int, float, bool)):
        return str(value)
    if isinstance(value, list):
        return ", ".join(_stringify(v) for v in value)
    if isinstance(value, dict):
        return json.dumps(value, ensure_ascii=False)
    return str(value)