"""
Rename rules: each rule transforms a filename (stem + extension) and returns a new name.
Rules are applied in sequence; extension can be changed by a rule that includes it.
"""
import csv
import re
from abc import ABC, abstractmethod
from dataclasses import dataclass, field
from pathlib import Path
from typing import List, Optional


@dataclass
class Rule(ABC):
    enabled: bool = True

    @abstractmethod
    def apply(
        self,
        stem: str,
        ext: str,
        index: int,
        total: int,
        original_name: Optional[str] = None,
    ) -> tuple[str, str]:
        """Return (new_stem, new_ext). Index is 0-based. original_name is the filename at pipeline start (for CSV lookup)."""
        pass

    def _split_name(self, name: str) -> tuple[str, str]:
        if "." in name and not name.startswith("."):
            idx = name.rfind(".")
            return name[:idx], name[idx:]
        return name, ""


# --- Text rules ---

@dataclass
class ReplaceRule(Rule):
    find: str = ""
    replace: str = ""
    case_sensitive: bool = False
    whole_word: bool = False

    def apply(
        self,
        stem: str,
        ext: str,
        index: int,
        total: int,
        original_name: Optional[str] = None,
    ) -> tuple[str, str]:
        if not self.find:
            return stem, ext
        flags = 0 if self.case_sensitive else re.IGNORECASE
        if self.whole_word:
            pattern = r"\b" + re.escape(self.find) + r"\b"
        else:
            pattern = re.escape(self.find)
        new_stem = re.sub(pattern, self.replace, stem, flags=flags)
        return new_stem, ext


@dataclass
class RegexRule(Rule):
    pattern: str = ""
    replacement: str = ""

    def apply(
        self,
        stem: str,
        ext: str,
        index: int,
        total: int,
        original_name: Optional[str] = None,
    ) -> tuple[str, str]:
        if not self.pattern:
            return stem, ext
        try:
            new_stem = re.sub(self.pattern, self.replacement, stem)
        except re.error:
            return stem, ext
        return new_stem, ext


@dataclass
class InsertRule(Rule):
    text: str = ""
    position: int = 0  # 0 = start, -1 = end, or character index

    def apply(
        self,
        stem: str,
        ext: str,
        index: int,
        total: int,
        original_name: Optional[str] = None,
    ) -> tuple[str, str]:
        if not self.text:
            return stem, ext
        if self.position <= 0:
            return self.text + stem, ext  # start
        if self.position >= len(stem) or self.position == -1:
            return stem + self.text, ext  # end
        return stem[: self.position] + self.text + stem[self.position :], ext


@dataclass
class RemoveRule(Rule):
    remove_type: str = "chars"  # chars, digits, first_n, last_n, from_start, from_end
    value: str = ""  # chars to remove, or n for first_n/last_n
    from_start: str = ""
    from_end: str = ""

    def apply(
        self,
        stem: str,
        ext: str,
        index: int,
        total: int,
        original_name: Optional[str] = None,
    ) -> tuple[str, str]:
        if self.remove_type == "chars" and self.value:
            return stem.replace(self.value, ""), ext
        if self.remove_type == "digits":
            return re.sub(r"\d+", "", stem), ext
        if self.remove_type == "first_n":
            try:
                n = int(self.value)
                return stem[n:], ext
            except ValueError:
                return stem, ext
        if self.remove_type == "last_n":
            try:
                n = int(self.value)
                return stem[:-n] if n > 0 else stem, ext
            except ValueError:
                return stem, ext
        if self.remove_type == "from_start" and self.from_start:
            idx = stem.find(self.from_start)
            if idx >= 0:
                return stem[idx + len(self.from_start) :], ext
        if self.remove_type == "from_end" and self.from_end:
            idx = stem.rfind(self.from_end)
            if idx >= 0:
                return stem[:idx], ext
        return stem, ext


@dataclass
class CaseRule(Rule):
    case_type: str = "title"  # upper, lower, title, sentence

    def apply(
        self,
        stem: str,
        ext: str,
        index: int,
        total: int,
        original_name: Optional[str] = None,
    ) -> tuple[str, str]:
        if self.case_type == "upper":
            return stem.upper(), ext
        if self.case_type == "lower":
            return stem.lower(), ext
        if self.case_type == "title":
            return stem.title(), ext
        if self.case_type == "sentence":
            if stem:
                return stem[0].upper() + stem[1:].lower(), ext
            return stem, ext
        return stem, ext


@dataclass
class NumberingRule(Rule):
    start: int = 1
    step: int = 1
    padding: int = 2  # zero-pad width
    where: str = "prefix"  # prefix, suffix, insert_at
    insert_at: int = 0
    separator: str = " "

    def apply(
        self,
        stem: str,
        ext: str,
        index: int,
        total: int,
        original_name: Optional[str] = None,
    ) -> tuple[str, str]:
        num = self.start + index * self.step
        num_str = str(num).zfill(max(1, self.padding))
        if self.where == "prefix":
            return f"{num_str}{self.separator}{stem}", ext
        if self.where == "suffix":
            return f"{stem}{self.separator}{num_str}", ext
        if self.where == "insert_at":
            pos = max(0, min(self.insert_at, len(stem)))
            return stem[:pos] + num_str + self.separator + stem[pos:], ext
        return stem, ext


# Episode renumber: match SxxExx or similar, replace episode number only, keep title
@dataclass
class EpisodeRenumberRule(Rule):
    start: int = 1
    step: int = 1
    padding: int = 2
    # Pattern: group 1 = prefix (e.g. "S01E"), group 2 = episode digits, group 3 = rest (title)
    pattern: str = r"(.*?[Ss]\d+[Ee])(\d+)(.*)"

    def apply(
        self,
        stem: str,
        ext: str,
        index: int,
        total: int,
        original_name: Optional[str] = None,
    ) -> tuple[str, str]:
        try:
            m = re.match(self.pattern, stem)
        except re.error:
            return stem, ext
        if not m:
            return stem, ext
        prefix, _old_ep, rest = m.group(1), m.group(2), m.group(3)
        ep_num = self.start + index * self.step
        ep_str = str(ep_num).zfill(max(1, self.padding))
        new_stem = f"{prefix}{ep_str}{rest}"
        return new_stem, ext


@dataclass
class PrefixSuffixRule(Rule):
    prefix: str = ""
    suffix: str = ""

    def apply(
        self,
        stem: str,
        ext: str,
        index: int,
        total: int,
        original_name: Optional[str] = None,
    ) -> tuple[str, str]:
        return (self.prefix + stem + self.suffix), ext


@dataclass
class CsvMappingRule(Rule):
    """Rename using a CSV with columns 'Original Name' and 'Target Name'. Lookup by original filename (as on disk)."""
    csv_path: str = ""
    _mapping: dict = field(default_factory=dict, repr=False)  # original_name -> target_name, loaded on first use

    def _load_mapping(self) -> dict:
        if getattr(self, "_mapping_loaded", False):
            return self._mapping
        self._mapping = {}
        path = Path(self.csv_path)
        if not path.is_file():
            setattr(self, "_mapping_loaded", True)
            return self._mapping
        try:
            with open(path, newline="", encoding="utf-8") as f:
                reader = csv.DictReader(f)
                if not reader.fieldnames:
                    setattr(self, "_mapping_loaded", True)
                    return self._mapping
                # Normalize header: strip spaces, accept "Original Name" and "Target Name"
                orig_key = next((k for k in reader.fieldnames if k.strip().lower() == "original name"), None)
                target_key = next((k for k in reader.fieldnames if k.strip().lower() == "target name"), None)
                if orig_key is None or target_key is None:
                    setattr(self, "_mapping_loaded", True)
                    return self._mapping
                for row in reader:
                    orig = row.get(orig_key, "").strip()
                    target = row.get(target_key, "").strip()
                    if orig:
                        self._mapping[orig] = target
        except (OSError, csv.Error):
            pass
        setattr(self, "_mapping_loaded", True)
        return self._mapping

    def apply(
        self,
        stem: str,
        ext: str,
        index: int,
        total: int,
        original_name: Optional[str] = None,
    ) -> tuple[str, str]:
        if not self.csv_path or original_name is None:
            return stem, ext
        mapping = self._load_mapping()
        target = mapping.get(original_name)
        if target is None:
            return stem, ext
        return self._split_name(target)