"""
Parametric Edit Operations Engine

Executes edit operations on palette tensors with pointer-based addressing.
Operations preserve scope balance and support region-relative indexing.

Key Features:
- Parametric actions with arguments
- Pointer arithmetic (region-relative → absolute)
- Scope balance verification
- Macro pattern transformations
- Stateless execution (pure functions)
"""

import torch
from dataclasses import dataclass
from typing import Tuple, Optional, List
from enum import IntEnum

# Import RegionMetadata from scope_pooler
from .scope_pooler import RegionMetadata


class OpCode(IntEnum):
    """Operation codes for edit actions"""
    # Control (0-99)
    NO_OP = 0
    MOVE_NEXT = 1
    FOCUS_PARENT = 2

    # Atomic edits (150-199)
    DELETE_RANGE = 150
    INSERT_TOKEN = 151
    REPLACE_TOKEN = 152
    SWAP_TOKENS = 153

    # Macro transforms (300-349)
    PY_FOR_TO_JS_FOR = 300
    SYNC_TO_ASYNC = 301
    ADD_TRY_EXCEPT = 302

    # Control flow
    DONE = 499


@dataclass
class EditAction:
    """
    Parametric edit operation with arguments

    Fields:
        op_id: Operation code from OpCode enum
        region_id: Which semantic region to operate on [0, R)
        i_start: Token index within region (relative addressing)
        i_end: End token index (for range operations, -1 if unused)
        payload_idx: Palette index to insert/replace (0-4095)
        confidence: Model confidence in [0, 1]

    Invariants:
        - 0 <= region_id < num_regions
        - 0 <= i_start < region_length
        - i_end >= i_start or i_end == -1
        - 0 <= payload_idx < 4096
        - 0 <= confidence <= 1
    """
    op_id: int
    region_id: int
    i_start: int
    i_end: int
    payload_idx: int
    confidence: float = 1.0

    def __post_init__(self):
        """Validate invariants"""
        assert self.op_id >= 0, f"Invalid op_id: {self.op_id}"
        assert self.region_id >= 0, f"Invalid region_id: {self.region_id}"
        assert self.i_start >= 0, f"Invalid i_start: {self.i_start}"
        assert self.i_end >= -1, f"Invalid i_end: {self.i_end}"
        if self.i_end != -1:
            assert self.i_end >= self.i_start, f"i_end ({self.i_end}) < i_start ({self.i_start})"
        assert 0 <= self.payload_idx < 4096, f"Invalid payload_idx: {self.payload_idx}"
        assert 0 <= self.confidence <= 1, f"Invalid confidence: {self.confidence}"


# Custom exceptions
class EditError(Exception):
    """Base class for edit errors"""
    pass


class ScopeBalanceError(EditError):
    """Operation would break scope balance"""
    pass


class InvalidPointerError(EditError):
    """Pointer out of bounds"""
    pass


class RegionNotFoundError(EditError):
    """region_id invalid"""
    pass


class PatternNotFoundError(EditError):
    """Macro pattern not found in region"""
    pass


class PaletteEditOps:
    """
    Stateless edit operation executor

    All methods are pure functions (no internal state).
    Thread-safe and deterministic.

    Constants:
        START_OF_SCOPE: 0
        END_OF_SCOPE: 1
        NOOP: 2
    """

    # Palette constants
    START_OF_SCOPE = 0
    END_OF_SCOPE = 1
    NOOP = 2

    # Macro pattern definitions
    MACRO_PATTERNS = {
        OpCode.PY_FOR_TO_JS_FOR: {
            'pattern': [20, 220, 220],  # for x in collection
            'target': [20, 201, 220],   # for(let x of collection)
            'name': 'Python for → JavaScript for'
        },
    }

    @staticmethod
    def apply(
        palette_img: torch.Tensor,  # (H, W)
        action: EditAction,
        metadata: RegionMetadata
    ) -> Tuple[torch.Tensor, bool]:
        """
        Apply edit action to palette

        Args:
            palette_img: (H, W) palette indices
            action: Edit action with parameters
            metadata: Region metadata from ScopePooler

        Returns:
            new_palette: (H, W) modified palette
            success: bool - whether operation succeeded

        Guarantees:
            - Original palette unchanged (pure function)
            - If success=False, new_palette == palette_img
            - Scope balance preserved on success

        Failure cases:
            - Invalid region_id
            - Invalid pointer indices
            - Scope imbalance after edit
        """
        # Validate inputs
        if action.region_id >= len(metadata.starts):
            return palette_img, False

        # Create working copy
        palette = palette_img.clone()

        try:
            # Pre-check balance
            if not PaletteEditOps.verify_scope_balance(palette):
                raise ScopeBalanceError("Input palette has unbalanced scopes")

            # Dispatch to operation
            if action.op_id == OpCode.NO_OP:
                new_palette = palette

            elif action.op_id == OpCode.DELETE_RANGE:
                new_palette = PaletteEditOps.delete_range(
                    palette, action.region_id, action.i_start, action.i_end, metadata
                )

            elif action.op_id == OpCode.INSERT_TOKEN:
                new_palette = PaletteEditOps.insert_token(
                    palette, action.region_id, action.i_start, action.payload_idx, metadata
                )

            elif action.op_id == OpCode.REPLACE_TOKEN:
                new_palette = PaletteEditOps.replace_token(
                    palette, action.region_id, action.i_start, action.payload_idx, metadata
                )

            elif action.op_id == OpCode.SWAP_TOKENS:
                new_palette = PaletteEditOps.swap_tokens(
                    palette, action.region_id, action.i_start, action.i_end, metadata
                )

            elif action.op_id in PaletteEditOps.MACRO_PATTERNS:
                new_palette = PaletteEditOps.macro_transform(
                    palette, action.op_id, action.region_id, metadata
                )

            else:
                # Unknown operation
                return palette_img, False

            # Post-check balance
            if not PaletteEditOps.verify_scope_balance(new_palette):
                raise ScopeBalanceError("Operation broke scope balance")

            return new_palette, True

        except EditError as e:
            # Operation failed - return original
            return palette_img, False

    @staticmethod
    def delete_range(
        palette: torch.Tensor,
        region_id: int,
        i_start: int,
        i_end: int,
        metadata: RegionMetadata
    ) -> torch.Tensor:
        """
        Delete tokens in range [i_start, i_end] within region

        Algorithm:
            1. Convert region-relative indices to absolute (h,w)
            2. Create mask for tokens to delete
            3. Check if deleting scope markers
            4. Shift remaining tokens left
            5. Pad with NOOP at end

        Returns:
            Modified palette

        Raises:
            InvalidPointerError: If indices out of bounds
            ScopeBalanceError: If would break balance
        """
        H, W = palette.shape
        region_mask = metadata.masks[region_id]  # (H, W)

        # Get region positions in flattened order (content tokens only)
        positions = PaletteEditOps._get_region_positions(region_mask, W, palette)

        # Validate indices
        if i_start < 0 or i_start >= len(positions):
            raise InvalidPointerError(f"i_start={i_start} out of bounds (region size={len(positions)})")
        if i_end < i_start or i_end >= len(positions):
            raise InvalidPointerError(f"i_end={i_end} out of bounds")

        # Convert to absolute positions
        abs_positions = [positions[i] for i in range(i_start, i_end + 1)]

        # Check if deleting scope markers
        palette_flat = palette.flatten()
        for pos in abs_positions:
            if palette_flat[pos] in [PaletteEditOps.START_OF_SCOPE, PaletteEditOps.END_OF_SCOPE]:
                # For now, disallow deleting scope markers
                # TODO: Implement smart deletion (delete matching pairs)
                raise ScopeBalanceError("Cannot delete scope markers")

        # Create deletion mask
        delete_mask = torch.zeros(H * W, dtype=torch.bool)
        for pos in abs_positions:
            delete_mask[pos] = True

        # Shift tokens left
        new_palette_flat = palette_flat[~delete_mask]

        # Pad with NOOP
        pad_size = H * W - len(new_palette_flat)
        if pad_size > 0:
            padding = torch.full((pad_size,), PaletteEditOps.NOOP, dtype=palette.dtype)
            new_palette_flat = torch.cat([new_palette_flat, padding])

        return new_palette_flat.view(H, W)

    @staticmethod
    def insert_token(
        palette: torch.Tensor,
        region_id: int,
        i_start: int,
        payload_idx: int,
        metadata: RegionMetadata
    ) -> torch.Tensor:
        """
        Insert token at position i_start within region

        Algorithm:
            1. Convert to absolute position
            2. Check if inserting scope marker (requires pair)
            3. Shift tokens right from position
            4. Insert payload
            5. Handle overflow

        Returns:
            Modified palette

        Raises:
            InvalidPointerError: If index out of bounds
            ScopeBalanceError: If inserting unpaired scope marker
        """
        H, W = palette.shape
        region_mask = metadata.masks[region_id]
        positions = PaletteEditOps._get_region_positions(region_mask, W, palette)

        # Validate index
        if i_start < 0 or i_start > len(positions):  # Allow insertion at end
            raise InvalidPointerError(f"i_start={i_start} out of bounds")

        # Get absolute position
        if i_start < len(positions):
            abs_pos = positions[i_start]
        else:
            # Insert at end of region
            abs_pos = positions[-1] + 1 if positions else 0

        # Check for scope marker insertion
        if payload_idx == PaletteEditOps.START_OF_SCOPE:
            # TODO: Also insert matching END
            raise ScopeBalanceError("Cannot insert unpaired START_OF_SCOPE")
        if payload_idx == PaletteEditOps.END_OF_SCOPE:
            raise ScopeBalanceError("Cannot insert unpaired END_OF_SCOPE")

        # Flatten and insert
        palette_flat = palette.flatten()

        # Create new palette with extra space
        new_palette_flat = torch.zeros(H * W, dtype=palette.dtype)

        # Copy before insertion point
        new_palette_flat[:abs_pos] = palette_flat[:abs_pos]

        # Insert payload
        new_palette_flat[abs_pos] = payload_idx

        # Copy after insertion point (shifted right)
        if abs_pos < H * W - 1:
            new_palette_flat[abs_pos + 1:] = palette_flat[abs_pos:H*W-1]

        return new_palette_flat.view(H, W)

    @staticmethod
    def replace_token(
        palette: torch.Tensor,
        region_id: int,
        i_start: int,
        payload_idx: int,
        metadata: RegionMetadata
    ) -> torch.Tensor:
        """
        Replace token at i_start with payload_idx

        Simplest operation: direct assignment
        Restriction: Cannot replace scope markers with non-markers

        Returns:
            Modified palette

        Raises:
            InvalidPointerError: If index out of bounds
            ScopeBalanceError: If replacing scope marker with non-marker
        """
        H, W = palette.shape
        region_mask = metadata.masks[region_id]
        positions = PaletteEditOps._get_region_positions(region_mask, W, palette)

        # Validate index
        if i_start < 0 or i_start >= len(positions):
            raise InvalidPointerError(f"i_start={i_start} out of bounds")

        abs_pos = positions[i_start]
        h, w = abs_pos // W, abs_pos % W

        # Check scope marker replacement
        old_value = palette[h, w].item()
        is_old_scope = old_value in [PaletteEditOps.START_OF_SCOPE, PaletteEditOps.END_OF_SCOPE]
        is_new_scope = payload_idx in [PaletteEditOps.START_OF_SCOPE, PaletteEditOps.END_OF_SCOPE]

        if is_old_scope and not is_new_scope:
            raise ScopeBalanceError("Cannot replace scope marker with non-marker")
        if is_old_scope and is_new_scope and old_value != payload_idx:
            raise ScopeBalanceError("Cannot replace START with END or vice versa")

        # Direct replacement
        new_palette = palette.clone()
        new_palette[h, w] = payload_idx
        return new_palette

    @staticmethod
    def swap_tokens(
        palette: torch.Tensor,
        region_id: int,
        i_start: int,
        i_end: int,
        metadata: RegionMetadata
    ) -> torch.Tensor:
        """
        Swap tokens at i_start and i_end

        Restriction: Cannot swap START ↔ END (would break structure)

        Returns:
            Modified palette

        Raises:
            InvalidPointerError: If indices out of bounds
            ScopeBalanceError: If swapping START ↔ END
        """
        H, W = palette.shape
        region_mask = metadata.masks[region_id]
        positions = PaletteEditOps._get_region_positions(region_mask, W, palette)

        # Validate indices
        if i_start < 0 or i_start >= len(positions):
            raise InvalidPointerError(f"i_start={i_start} out of bounds")
        if i_end < 0 or i_end >= len(positions):
            raise InvalidPointerError(f"i_end={i_end} out of bounds")

        abs_pos1 = positions[i_start]
        abs_pos2 = positions[i_end]

        h1, w1 = abs_pos1 // W, abs_pos1 % W
        h2, w2 = abs_pos2 // W, abs_pos2 % W

        # Check scope marker swap
        val1, val2 = palette[h1, w1].item(), palette[h2, w2].item()

        if (val1 == PaletteEditOps.START_OF_SCOPE and val2 == PaletteEditOps.END_OF_SCOPE) or \
           (val1 == PaletteEditOps.END_OF_SCOPE and val2 == PaletteEditOps.START_OF_SCOPE):
            raise ScopeBalanceError("Cannot swap START ↔ END")

        # Swap
        new_palette = palette.clone()
        new_palette[h1, w1], new_palette[h2, w2] = palette[h2, w2], palette[h1, w1]
        return new_palette

    @staticmethod
    def macro_transform(
        palette: torch.Tensor,
        op_id: int,
        region_id: int,
        metadata: RegionMetadata
    ) -> torch.Tensor:
        """
        Apply macro pattern transformation

        Searches for pattern in region and replaces with target.

        Returns:
            Modified palette

        Raises:
            PatternNotFoundError: If pattern not found in region
        """
        if op_id not in PaletteEditOps.MACRO_PATTERNS:
            raise EditError(f"Unknown macro operation: {op_id}")

        macro = PaletteEditOps.MACRO_PATTERNS[op_id]
        pattern = macro['pattern']
        target = macro['target']

        # Extract region tokens
        region_mask = metadata.masks[region_id]
        positions = PaletteEditOps._get_region_positions(region_mask, palette.shape[1], palette)

        palette_flat = palette.flatten()
        region_tokens = [palette_flat[pos].item() for pos in positions]

        # Pattern matching (sliding window)
        pattern_len = len(pattern)
        found = False

        for i in range(len(region_tokens) - pattern_len + 1):
            window = region_tokens[i:i + pattern_len]
            if window == pattern:
                # Match found - apply transformation
                for j, target_token in enumerate(target):
                    abs_pos = positions[i + j]
                    h, w = abs_pos // palette.shape[1], abs_pos % palette.shape[1]
                    palette[h, w] = target_token
                found = True
                break  # Apply once per region

        if not found:
            raise PatternNotFoundError(f"Pattern {pattern} not found in region {region_id}")

        return palette

    @staticmethod
    def verify_scope_balance(palette: torch.Tensor) -> bool:
        """
        Check if START_OF_SCOPE == END_OF_SCOPE count

        Returns:
            True if balanced, False otherwise
        """
        num_starts = (palette == PaletteEditOps.START_OF_SCOPE).sum().item()
        num_ends = (palette == PaletteEditOps.END_OF_SCOPE).sum().item()
        return num_starts == num_ends

    @staticmethod
    def _get_region_positions(mask: torch.Tensor, W: int, palette: torch.Tensor = None) -> List[int]:
        """
        Get flattened positions of region in scan order (content tokens only, excluding scope markers)

        Args:
            mask: (H, W) boolean mask
            W: width
            palette: (H, W) palette tensor (optional, used to filter scope markers)

        Returns:
            List of flattened indices where mask is True and token is not a scope marker, sorted
        """
        positions = mask.nonzero(as_tuple=False)  # (N, 2) of (h, w)
        flat_positions = (positions[:, 0] * W + positions[:, 1]).tolist()

        # If palette provided, filter out scope markers
        if palette is not None:
            filtered_positions = []
            for pos in flat_positions:
                h, w = pos // W, pos % W
                token = palette[h, w].item()
                if token not in [PaletteEditOps.START_OF_SCOPE, PaletteEditOps.END_OF_SCOPE]:
                    filtered_positions.append(pos)
            return sorted(filtered_positions)

        return sorted(flat_positions)