"""Transições entre clipes vizinhos.

Extraído de writer.py — ver fcpxml/writer/__init__.py para o conjunto.
"""

import xml.etree.ElementTree as ET

from ..models import (
    TimeValue,
)
from .helpers import FCP_EFFECTS


class TransitionsMixin:
    """Transições entre clipes vizinhos."""

    # TRANSITION OPERATIONS
    # ========================================================================

    def add_transition(
        self,
        clip_id: str,
        position: str = 'end',
        transition_type: str = 'cross-dissolve',
        duration: str = '00:00:00:15'
    ) -> ET.Element:
        """
        Add a transition to a clip.

        Args:
            clip_id: Target clip
            position: 'start', 'end', or 'both'
            transition_type: Type of transition
            duration: Transition duration

        Returns:
            Created transition element(s)
        """
        spine, clip, clip_index = self._require_spine_clip(clip_id)

        trans_duration = self._parse_time(duration)

        # Effect name and FCP built-in effect UID lookup via registry
        effect_name, effect_uid = FCP_EFFECTS.get(
            transition_type,
            FCP_EFFECTS['cross-dissolve']
        )

        # Ensure effect resource exists in <resources>
        effect_ref_id = None
        if effect_uid:
            root = self.tree.getroot()
            resources = root.find('.//resources')
            if resources is not None:
                for eff in resources.findall('effect'):
                    if eff.get('uid') == effect_uid:
                        effect_ref_id = eff.get('id')
                        break
                if effect_ref_id is None:
                    effect_ref_id = self._unique_resource_id(resources, 'r_dissolve')
                    eff_el = ET.SubElement(resources, 'effect')
                    eff_el.set('id', effect_ref_id)
                    eff_el.set('name', effect_name)
                    eff_el.set('uid', effect_uid)

        transitions_added = []

        _, clip_dur, clip_offset = self._get_clip_times(clip)
        half_dur = trans_duration * 0.5

        if position in ('end', 'both'):
            end_offset = clip_offset + clip_dur - half_dur
            transition = self._make_transition_element(
                effect_name, end_offset, trans_duration, effect_ref_id
            )
            spine.insert(clip_index + 1, transition)
            transitions_added.append(transition)

        if position in ('start', 'both'):
            start_offset = clip_offset - half_dur
            if start_offset < TimeValue.zero():
                raise ValueError(
                    f"Transition at start would produce negative offset "
                    f"({start_offset.to_seconds():.3f}s) for clip '{clip_id}'"
                )
            transition = self._make_transition_element(
                effect_name, start_offset, trans_duration, effect_ref_id
            )
            spine.insert(clip_index, transition)
            transitions_added.append(transition)

        return transitions_added[0] if len(transitions_added) == 1 else transitions_added

    # ========================================================================