import {
	getCurveHandlesForNormalizedCubicBezier,
	getEditableScalarChannels,
	getEasingModeForKind,
	getNormalizedCubicBezierForScalarSegment,
	getScalarKeyframeContext,
	updateScalarKeyframeCurve,
} from "@/animation";
import type {
	AnimationPath,
	ElementAnimations,
	NormalizedCubicBezier,
	ScalarCurveKeyframePatch,
	ScalarGraphKeyframeContext,
	SelectedKeyframeRef,
} from "@/animation/types";
import type { SceneTracks, TimelineElement } from "@/timeline";

const GRAPH_LINEAR_CURVE: NormalizedCubicBezier = [0, 0, 1, 1];
const FLAT_VALUE_EPSILON = 1e-6;
const LINEAR_CURVE_EPSILON = 1e-6;

export type GraphEditorUnavailableReason =
	| "no-keyframe-selected"
	| "multiple-keyframes-selected"
	| "selected-keyframes-span-multiple-elements"
	| "selected-keyframes-are-not-adjacent"
	| "selected-properties-have-no-shared-component"
	| "selected-element-missing"
	| "selected-element-has-no-animations"
	| "selected-keyframe-has-no-scalar-channel"
	| "selected-keyframe-missing-on-channel"
	| "selected-keyframe-has-no-next-segment"
	| "selected-segment-is-hold"
	| "selected-segment-is-flat";

export interface GraphEditorComponentOption {
	key: string;
	label: string;
}

interface GraphEditorPropertyOption {
	key: string;
	label: string;
	context: ScalarGraphKeyframeContext;
	allContexts: ScalarGraphKeyframeContext[];
}

export interface GraphEditorResolvedSegment {
	propertyPath: SelectedKeyframeRef["propertyPath"];
	keyframeId: string;
	context: ScalarGraphKeyframeContext;
	allContexts: ScalarGraphKeyframeContext[];
	cubicBezier: NormalizedCubicBezier;
	referenceSpanValue: number;
}

interface GraphEditorBaseSelectionState {
	componentOptions: GraphEditorComponentOption[];
	activeComponentKey: string | null;
	message: string;
}

export interface GraphEditorUnavailableState
	extends GraphEditorBaseSelectionState {
	status: "unavailable";
	reason: GraphEditorUnavailableReason;
}

export interface GraphEditorReadyState extends GraphEditorBaseSelectionState {
	status: "ready";
	trackId: string;
	elementId: string;
	element: TimelineElement;
	segments: GraphEditorResolvedSegment[];
	cubicBezier: NormalizedCubicBezier;
}

export type GraphEditorSelectionState =
	| GraphEditorUnavailableState
	| GraphEditorReadyState;

export interface GraphEditorCurvePatch {
	keyframeId: string;
	patch: ScalarCurveKeyframePatch;
}

function createUnavailableState({
	reason,
	message,
	componentOptions = [],
	activeComponentKey = null,
}: {
	reason: GraphEditorUnavailableReason;
	message: string;
	componentOptions?: GraphEditorComponentOption[];
	activeComponentKey?: string | null;
}): GraphEditorUnavailableState {
	return {
		status: "unavailable",
		reason,
		message,
		componentOptions,
		activeComponentKey,
	};
}

function findElementByKeyframe({
	tracks,
	keyframe,
}: {
	tracks: SceneTracks;
	keyframe: SelectedKeyframeRef;
}): { element: TimelineElement; trackId: string; elementId: string } | null {
	for (const track of [...tracks.overlay, tracks.main, ...tracks.audio]) {
		if (track.id !== keyframe.trackId) {
			continue;
		}

		const element = track.elements.find(
			(trackElement) => trackElement.id === keyframe.elementId,
		);
		if (!element) {
			return null;
		}

		return {
			element,
			trackId: track.id,
			elementId: element.id,
		};
	}

	return null;
}

function findKeyframeTime({
	animations,
	propertyPath,
	keyframeId,
}: {
	animations: ElementAnimations;
	propertyPath: AnimationPath;
	keyframeId: string;
}): number | null {
	const binding = animations.bindings[propertyPath];
	if (!binding) return null;

	for (const component of binding.components) {
		const channel = animations.channels[component.channelId];
		if (channel?.kind !== "scalar") continue;
		const key = channel.keys.find((k) => k.id === keyframeId);
		if (key !== undefined) return key.time;
	}

	return null;
}

function groupSelectedKeyframesByProperty({
	selectedKeyframes,
}: {
	selectedKeyframes: SelectedKeyframeRef[];
}) {
	const groups = new Map<
		string,
		{
			trackId: string;
			elementId: string;
			propertyPath: SelectedKeyframeRef["propertyPath"];
			keyframes: SelectedKeyframeRef[];
		}
	>();

	for (const keyframe of selectedKeyframes) {
		const groupKey = `${keyframe.trackId}:${keyframe.elementId}:${keyframe.propertyPath}`;
		const existingGroup = groups.get(groupKey);
		if (existingGroup) {
			existingGroup.keyframes.push(keyframe);
			continue;
		}

		groups.set(groupKey, {
			trackId: keyframe.trackId,
			elementId: keyframe.elementId,
			propertyPath: keyframe.propertyPath,
			keyframes: [keyframe],
		});
	}

	return [...groups.values()];
}

function getComponentLabel({ componentKey }: { componentKey: string }): string {
	switch (componentKey) {
		case "value":
			return "Value";
		default:
			return componentKey.toUpperCase();
	}
}

/**
 * Returns the absolute value span of the nearest non-flat adjacent segment,
 * used as the Y-axis scale when editing a flat segment in the graph editor.
 * Falls back to 1.0 if all surrounding segments are also flat.
 */
function getReferenceSpanValue({
	context,
}: {
	context: ScalarGraphKeyframeContext;
}): number {
	const sorted = [...context.channel.keys].sort((a, b) => a.time - b.time);
	const leftIndex = sorted.findIndex((k) => k.id === context.keyframe.id);
	const rightIndex = context.nextKey
		? sorted.findIndex((k) => k.id === context.nextKey?.id)
		: -1;

	for (let i = leftIndex - 1; i >= 0; i--) {
		const span = Math.abs(sorted[i + 1].value - sorted[i].value);
		if (span > FLAT_VALUE_EPSILON) return span;
	}

	if (rightIndex !== -1) {
		for (let i = rightIndex; i < sorted.length - 1; i++) {
			const span = Math.abs(sorted[i + 1].value - sorted[i].value);
			if (span > FLAT_VALUE_EPSILON) return span;
		}
	}

	return 1.0;
}

interface GraphEditorPropertySelection {
	propertyPath: SelectedKeyframeRef["propertyPath"];
	keyframeId: string;
	secondaryKeyframeId: string | null;
	options: GraphEditorPropertyOption[];
}

function resolvePropertySelection({
	element,
	propertyKeyframes,
}: {
	element: TimelineElement;
	propertyKeyframes: ReturnType<
		typeof groupSelectedKeyframesByProperty
	>[number];
}):
	| GraphEditorPropertySelection
	| {
			reason: GraphEditorUnavailableReason;
			message: string;
	  } {
	if (propertyKeyframes.keyframes.length > 2) {
		return {
			reason: "multiple-keyframes-selected",
			message: "Select at most two adjacent keyframes per property.",
		};
	}

	if (!element.animations) {
		return {
			reason: "selected-element-has-no-animations",
			message: "The selected keyframe has no editable graph.",
		};
	}

	const scalarResult = getEditableScalarChannels({
		animations: element.animations,
		propertyPath: propertyKeyframes.propertyPath,
	});
	if (!scalarResult || scalarResult.channels.length === 0) {
		return {
			reason: "selected-keyframe-has-no-scalar-channel",
			message: "The selected keyframe has no editable graph channel.",
		};
	}

	const primaryKeyframe = propertyKeyframes.keyframes[0];
	let resolvedKeyframeId = primaryKeyframe.keyframeId;
	let secondaryKeyframeId =
		propertyKeyframes.keyframes.length === 2
			? propertyKeyframes.keyframes[1].keyframeId
			: null;

	if (secondaryKeyframeId !== null) {
		const time1 = findKeyframeTime({
			animations: element.animations,
			propertyPath: propertyKeyframes.propertyPath,
			keyframeId: primaryKeyframe.keyframeId,
		});
		const time2 = findKeyframeTime({
			animations: element.animations,
			propertyPath: propertyKeyframes.propertyPath,
			keyframeId: secondaryKeyframeId,
		});
		if (time2 !== null && (time1 === null || time2 < time1)) {
			resolvedKeyframeId = secondaryKeyframeId;
			secondaryKeyframeId = primaryKeyframe.keyframeId;
		}
	}

	const { binding: resolvedBinding, channels: scalarChannels } = scalarResult;
	const easingMode = getEasingModeForKind(resolvedBinding.kind);
	const contexts = scalarChannels.flatMap((channel) => {
		const context = getScalarKeyframeContext({
			animations: element.animations,
			propertyPath: propertyKeyframes.propertyPath,
			componentKey: channel.componentKey,
			keyframeId: resolvedKeyframeId,
		});
		if (!context) {
			return [];
		}

		return [
			{
				context,
				option: {
					key: channel.componentKey,
					label: getComponentLabel({ componentKey: channel.componentKey }),
				},
			},
		];
	});

	if (contexts.length === 0) {
		return {
			reason: "selected-keyframe-missing-on-channel",
			message: "The selected keyframe is not editable as a graph segment.",
		};
	}

	// For shared-easing bindings (e.g. color), all components always use the same
	// curve. Collapse them to a single "value" option so the key is compatible with
	// single-component scalar bindings (e.g. opacity), enabling mixed selections.
	const options =
		easingMode === "shared"
			? [
					{
						key: "value",
						label: "Curve",
						context: contexts[0].context,
						allContexts: contexts.map(({ context }) => context),
					},
				]
			: contexts.map(({ context, option }) => ({
					key: option.key,
					label: option.label,
					context,
					allContexts: [context],
				}));

	return {
		propertyPath: propertyKeyframes.propertyPath,
		keyframeId: resolvedKeyframeId,
		secondaryKeyframeId,
		options,
	};
}

function isLinearCurve({
	cubicBezier,
}: {
	cubicBezier: NormalizedCubicBezier;
}): boolean {
	return (
		Math.abs(cubicBezier[0]) <= LINEAR_CURVE_EPSILON &&
		Math.abs(cubicBezier[1]) <= LINEAR_CURVE_EPSILON &&
		Math.abs(cubicBezier[2] - 1) <= LINEAR_CURVE_EPSILON &&
		Math.abs(cubicBezier[3] - 1) <= LINEAR_CURVE_EPSILON
	);
}

function resolveSegmentForOption({
	propertySelection,
	componentKey,
}: {
	propertySelection: GraphEditorPropertySelection;
	componentKey: string;
}):
	| {
			segment: GraphEditorResolvedSegment;
	  }
	| {
			reason: GraphEditorUnavailableReason;
			message: string;
	  } {
	const option = propertySelection.options.find(
		(propertyOption) => propertyOption.key === componentKey,
	);
	if (!option) {
		return {
			reason: "selected-properties-have-no-shared-component",
			message: "Selected properties do not share a graph-editable channel.",
		};
	}

	if (!option.context.nextKey) {
		return {
			reason: "selected-keyframe-has-no-next-segment",
			message: "Select a keyframe that has an outgoing segment.",
		};
	}

	if (
		propertySelection.secondaryKeyframeId !== null &&
		option.context.nextKey.id !== propertySelection.secondaryKeyframeId
	) {
		return {
			reason: "selected-keyframes-are-not-adjacent",
			message: "Selected keyframes must be adjacent on each property.",
		};
	}

	if (option.context.keyframe.segmentToNext === "step") {
		return {
			reason: "selected-segment-is-hold",
			message: "Hold segments have a fixed value - easing has no effect here.",
		};
	}

	const referenceSpanValue = getReferenceSpanValue({ context: option.context });
	const cubicBezier =
		option.context.keyframe.segmentToNext === "linear"
			? GRAPH_LINEAR_CURVE
			: getNormalizedCubicBezierForScalarSegment({
					leftKey: option.context.keyframe,
					rightKey: option.context.nextKey,
					referenceSpanValue,
				});
	if (!cubicBezier) {
		return {
			reason: "selected-segment-is-flat",
			message:
				"Cannot edit a segment where both keyframes are at the same time.",
		};
	}

	return {
		segment: {
			propertyPath: propertySelection.propertyPath,
			keyframeId: propertySelection.keyframeId,
			context: option.context,
			allContexts: option.allContexts,
			cubicBezier,
			referenceSpanValue,
		},
	};
}

export function resolveGraphEditorSelectionState({
	tracks,
	selectedKeyframes,
	preferredComponentKey,
}: {
	tracks: SceneTracks;
	selectedKeyframes: SelectedKeyframeRef[];
	preferredComponentKey?: string | null;
}): GraphEditorSelectionState {
	if (selectedKeyframes.length === 0) {
		return createUnavailableState({
			reason: "no-keyframe-selected",
			message: "Select a keyframe to edit its curve.",
		});
	}

	const propertyKeyframes = groupSelectedKeyframesByProperty({
		selectedKeyframes,
	});
	const primaryKeyframe = propertyKeyframes[0]?.keyframes[0];
	if (!primaryKeyframe) {
		return createUnavailableState({
			reason: "no-keyframe-selected",
			message: "Select a keyframe to edit its curve.",
		});
	}

	const selectedElement = findElementByKeyframe({
		tracks,
		keyframe: primaryKeyframe,
	});
	if (!selectedElement) {
		return createUnavailableState({
			reason: "selected-element-missing",
			message: "The selected keyframe could not be resolved.",
		});
	}

	const spansMultipleElements = propertyKeyframes.some(
		(propertySelection) =>
			propertySelection.trackId !== selectedElement.trackId ||
			propertySelection.elementId !== selectedElement.elementId,
	);
	if (spansMultipleElements) {
		return createUnavailableState({
			reason: "selected-keyframes-span-multiple-elements",
			message: "Selected keyframes must be on the same element.",
		});
	}

	const propertySelections = propertyKeyframes.map((propertySelection) =>
		resolvePropertySelection({
			element: selectedElement.element,
			propertyKeyframes: propertySelection,
		}),
	);
	const unavailablePropertySelection = propertySelections.find(
		(propertySelection) => "reason" in propertySelection,
	);
	if (
		unavailablePropertySelection &&
		"reason" in unavailablePropertySelection
	) {
		return createUnavailableState({
			reason: unavailablePropertySelection.reason,
			message: unavailablePropertySelection.message,
		});
	}

	const resolvedPropertySelections = propertySelections.filter(
		(propertySelection): propertySelection is GraphEditorPropertySelection =>
			!("reason" in propertySelection),
	);
	const sharedComponentOptions =
		resolvedPropertySelections[0]?.options.filter((componentOption) =>
			resolvedPropertySelections.every((propertySelection) =>
				propertySelection.options.some(
					(option) => option.key === componentOption.key,
				),
			),
		) ?? [];
	const componentOptions = sharedComponentOptions.map(({ key, label }) => ({
		key,
		label,
	}));
	if (componentOptions.length === 0) {
		return createUnavailableState({
			reason: "selected-properties-have-no-shared-component",
			message: "Selected properties do not share a graph-editable channel.",
		});
	}

	// Try each component option in preference order (preferred first, then the rest)
	// and stop at the first key where every property resolves to a valid segment.
	// This single pass both selects the active key and produces the segment list.
	const candidateKeys = [
		...(preferredComponentKey &&
		componentOptions.some((option) => option.key === preferredComponentKey)
			? [preferredComponentKey]
			: []),
		...componentOptions
			.filter((option) => option.key !== preferredComponentKey)
			.map((option) => option.key),
	];

	let activeComponentKey = componentOptions[0].key;
	let segmentResults: ReturnType<typeof resolveSegmentForOption>[] = [];

	for (const candidateKey of candidateKeys) {
		const results = resolvedPropertySelections.map((propertySelection) =>
			resolveSegmentForOption({
				propertySelection,
				componentKey: candidateKey,
			}),
		);
		activeComponentKey = candidateKey;
		segmentResults = results;
		if (results.every((result) => "segment" in result)) {
			break;
		}
	}

	const unavailableSegment = segmentResults.find(
		(result) => !("segment" in result),
	);
	if (unavailableSegment && !("segment" in unavailableSegment)) {
		return createUnavailableState({
			reason: unavailableSegment.reason,
			message: unavailableSegment.message,
			componentOptions,
			activeComponentKey,
		});
	}

	const segments = segmentResults.flatMap((result) =>
		"segment" in result ? [result.segment] : [],
	);
	const primarySegment = segments[0];
	if (!primarySegment) {
		return createUnavailableState({
			reason: "selected-keyframe-missing-on-channel",
			message: "The selected keyframe is not editable as a graph segment.",
			componentOptions,
			activeComponentKey,
		});
	}

	return {
		status: "ready",
		message:
			segments.length === 1
				? "Edit graph"
				: `Edit graph for ${segments.length} properties`,
		componentOptions,
		activeComponentKey,
		trackId: selectedElement.trackId,
		elementId: selectedElement.elementId,
		element: selectedElement.element,
		segments,
		cubicBezier: primarySegment.cubicBezier,
	};
}

export function buildGraphEditorCurvePatches({
	context,
	cubicBezier,
	referenceSpanValue,
}: {
	context: ScalarGraphKeyframeContext;
	cubicBezier: NormalizedCubicBezier;
	referenceSpanValue: number;
}): GraphEditorCurvePatch[] | null {
	if (!context.nextKey) {
		return null;
	}

	if (isLinearCurve({ cubicBezier })) {
		return [
			{
				keyframeId: context.keyframe.id,
				patch: {
					segmentToNext: "linear",
					rightHandle: null,
				},
			},
			{
				keyframeId: context.nextKey.id,
				patch: {
					leftHandle: null,
				},
			},
		];
	}

	const handles = getCurveHandlesForNormalizedCubicBezier({
		leftKey: context.keyframe,
		rightKey: context.nextKey,
		cubicBezier,
		referenceSpanValue,
	});
	if (!handles) {
		return null;
	}

	return [
		{
			keyframeId: context.keyframe.id,
			patch: {
				segmentToNext: "bezier",
				rightHandle: handles.rightHandle,
			},
		},
		{
			keyframeId: context.nextKey.id,
			patch: {
				leftHandle: handles.leftHandle,
			},
		},
	];
}

export function applyGraphEditorCurvePreview({
	animations,
	context,
	cubicBezier,
	referenceSpanValue,
}: {
	animations: ElementAnimations | undefined;
	context: ScalarGraphKeyframeContext;
	cubicBezier: NormalizedCubicBezier;
	referenceSpanValue: number;
}): ElementAnimations | undefined {
	const patches = buildGraphEditorCurvePatches({
		context,
		cubicBezier,
		referenceSpanValue,
	});
	if (!patches) {
		return animations;
	}

	return patches.reduce<ElementAnimations | undefined>(
		(nextAnimations, { keyframeId, patch }) =>
			updateScalarKeyframeCurve({
				animations: nextAnimations,
				propertyPath: context.propertyPath,
				componentKey: context.componentKey,
				keyframeId,
				patch,
			}),
		animations,
	);
}