"""Evidence-owned deterministic chunking for canonical corpus documents."""

import hashlib
import json
import re
from dataclasses import asdict, dataclass

from tht.evidence.corpus.models import CanonicalChunk, CanonicalDocument


@dataclass(frozen=True, slots=True)
class ChunkPolicy:
    version: str
    max_chars: int

    def __post_init__(self) -> None:
        if not self.version:
            raise ValueError("chunk policy version must not be empty")
        if self.max_chars <= 0:
            raise ValueError("max_chars must be greater than zero")


def _hash(text: str) -> str:
    return hashlib.sha256(text.encode("utf-8")).hexdigest()


def _contents(content: str, maximum: int) -> list[str]:
    result: list[str] = []
    start = 0
    while start < len(content):
        end = min(start + maximum, len(content))
        if end < len(content):
            boundaries = list(re.finditer(r"\s+", content[start:end]))
            if boundaries:
                end = start + boundaries[-1].end()
        result.append(content[start:end])
        start = end
    return result


def _policy_fingerprint(policy: ChunkPolicy) -> str:
    serialized = json.dumps(asdict(policy), ensure_ascii=False, sort_keys=True, separators=(",", ":"))
    return f"sha256:{_hash(serialized)}"


def chunk(document: CanonicalDocument, policy: ChunkPolicy) -> list[CanonicalChunk]:
    """Split canonical text with stable character-count boundaries and identifiers."""
    chunks: list[CanonicalChunk] = []
    policy_fingerprint = _policy_fingerprint(policy)
    for ordinal, content in enumerate(_contents(document.content, policy.max_chars)):
        chunk_hash = f"sha256:{_hash(content)}"
        identifier = _hash(
            ":".join(
                (
                    document.document_id,
                    document.content_hash,
                    policy_fingerprint,
                    str(ordinal),
                    chunk_hash,
                )
            )
        )
        chunks.append(
            CanonicalChunk(
                chunk_id=f"chunk:{identifier}",
                document_id=document.document_id,
                ordinal=ordinal,
                content=content,
                content_hash=chunk_hash,
                source_uri=document.source_uri,
                pipeline_version=document.pipeline_version,
                metadata={
                    "chunk_policy": {
                        "version": policy.version,
                        "max_chars": policy.max_chars,
                        "fingerprint": policy_fingerprint,
                    },
                    "document": document.model_dump(mode="json")["metadata"],
                    "source_fingerprint": document.source_fingerprint,
                    "title": document.title,
                },
            )
        )
    return chunks