/**
 * Serializable, store-agnostic aura state and transitions.
 *
 * The combat store owns the aura array. Every operation in this module returns
 * new state, making the transitions safe to use from Zustand setters and easy
 * to replay in tests.
 */

export type CombatEntityId = string;
export type AuraDisposition = "buff" | "debuff";
export type AuraStackBehavior = "refresh" | "replace" | "add";
export type DispelCategory = "magic" | "curse" | "poison" | "disease" | "enrage";
export type AuraModifierOperation = "flat" | "percent";
export type DamageSchool =
  | "physical"
  | "holy"
  | "fire"
  | "nature"
  | "frost"
  | "shadow"
  | "arcane";
export type AttackKind = "melee" | "ranged" | "spell";

export type ProcTrigger =
  | "hit"
  | "crit"
  | "damage-taken"
  | "dodge"
  | "parry"
  | "block"
  | "cast"
  | "heal"
  | "periodic"
  | "kill";

export type AuraModifier =
  | {
      readonly kind: "stat";
      readonly stat: string;
      readonly operation: AuraModifierOperation;
      readonly value: number;
      readonly perStack?: boolean;
    }
  | {
      readonly kind: "resource";
      readonly resource: string;
      readonly property: "maximum" | "regeneration" | "cost" | "generation";
      readonly operation: AuraModifierOperation;
      readonly value: number;
      readonly perStack?: boolean;
    }
  | {
      readonly kind: "damage";
      readonly direction: "dealt" | "taken";
      readonly school?: DamageSchool;
      readonly attackKind?: AttackKind;
      readonly operation: AuraModifierOperation;
      readonly value: number;
      readonly perStack?: boolean;
    }
  | {
      readonly kind: "healing";
      readonly direction: "done" | "taken";
      readonly operation: AuraModifierOperation;
      readonly value: number;
      readonly perStack?: boolean;
    };

export interface AuraAbsorbDefinition {
  readonly id: string;
  readonly amount: number;
  /** Number of matching attacks this absorb fully negates instead of consuming a point pool. */
  readonly hitCharges?: number;
  /** Omit to absorb all damage schools. */
  readonly school?: DamageSchool;
  /** Optional school set for absorbs such as Anti-Magic Shell. */
  readonly schools?: readonly DamageSchool[];
  /** Fraction of each incoming packet this absorb can consume; defaults to 1. */
  readonly fraction?: number;
  /** Defaults to true, granting `amount` of capacity for each aura stack. */
  readonly perStack?: boolean;
}

export interface AuraAbsorbState {
  readonly id: string;
  readonly school?: DamageSchool;
  readonly schools?: readonly DamageSchool[];
  readonly fraction?: number;
  readonly remaining: number;
  readonly remainingHits?: number;
}

export type AuraProcAction =
  | {
      readonly kind: "apply-aura";
      readonly auraId: string;
      readonly target: "aura-source" | "aura-target" | "event-other";
    }
  | {
      readonly kind: "resource";
      readonly resource: string;
      readonly amount: number;
      readonly target: "aura-source" | "aura-target" | "event-other";
    }
  | {
      readonly kind: "damage";
      readonly amount: number;
      readonly school: DamageSchool;
      readonly target: "aura-source" | "aura-target" | "event-other";
    }
  | {
      readonly kind: "heal";
      readonly amount: number;
      readonly target: "aura-source" | "aura-target" | "event-other";
    }
  | {
      /** Escape hatch for a named combat-store transition with custom data. */
      readonly kind: "custom";
      readonly id: string;
      readonly data?: Readonly<Record<string, string | number | boolean>>;
    };

export interface AuraProcDefinition {
  readonly id: string;
  readonly triggers: ProcTrigger | readonly ProcTrigger[];
  /** Limit attack-triggered procs to the listed landed attack types. */
  readonly attackKinds?: readonly AttackKind[];
  /** Probability from 0 through 1. */
  readonly chance: number;
  readonly internalCooldownMs?: number;
  /** Successful activations before exhaustion. Omit for unlimited charges. */
  readonly charges?: number;
  readonly action: AuraProcAction;
}

export interface AuraProcState {
  readonly procId: string;
  readonly readyAt: number;
  /** Null means the proc has unlimited charges. */
  readonly remainingCharges: number | null;
}

export interface AuraDefinition {
  readonly id: string;
  readonly name: string;
  /** Player-facing explanation shown by aura tooltips. */
  readonly description?: string;
  readonly disposition: AuraDisposition;
  /** Spell artwork used by every generic aura HUD surface. */
  readonly icon?: string;
  /** Keep a mechanically active aura out of the generic HUD strip when another widget owns its display. */
  readonly hideFromAuraStrip?: boolean;
  /** Null means the aura persists until explicitly removed. */
  readonly durationMs: number | null;
  readonly maxStacks?: number;
  /** Initial stack count for charged buffs such as Inner Fire. */
  readonly initialStacks?: number;
  readonly stackBehavior?: AuraStackBehavior;
  /** Defaults to true. False makes applications from all sources share one aura. */
  readonly uniqueBySource?: boolean;
  /** A target can have only one aura from an exclusive stance/form/seal/etc. group. */
  readonly exclusiveGroup?: string;
  /** Explicit non-numeric gameplay state such as stealth, tracking, flight, or water walking. */
  readonly utilityTags?: readonly string[];
  /** Enemy control mechanics ignored while this aura is active. */
  readonly controlImmunities?: readonly ("confuse" | "fear" | "sleep" | "root" | "slow" | "stun" | "silence")[];
  /** Chance from 0 through 1 to reflect an incoming spell. */
  readonly reflectSpellChance?: number;
  /** Portion of incoming target damage transferred to the aura source. */
  readonly redirectDamagePercent?: number;
  /** Shared source-max-health cap for Paladin Divine Sacrifice redirection. */
  readonly redirectDamageCapPercent?: number;
  readonly dispelCategory?: DispelCategory;
  readonly dispelPriority?: number;
  readonly modifiers?: readonly AuraModifier[];
  readonly absorbs?: readonly AuraAbsorbDefinition[];
  readonly procs?: readonly AuraProcDefinition[];
}

export interface ActiveAura {
  readonly instanceId: string;
  readonly definition: AuraDefinition;
  readonly sourceId: CombatEntityId;
  readonly targetId: CombatEntityId;
  readonly appliedAt: number;
  readonly expiresAt: number | null;
  readonly stacks: number;
  readonly absorbs: readonly AuraAbsorbState[];
  readonly procStates: readonly AuraProcState[];
  /** Cumulative redirected damage for an aura that owns a shared redirect cap. */
  readonly redirectedDamage?: number;
  /** Number of Fire critical hits landed during the current Combustion buff. */
  readonly combustionCriticalHits?: number;
}

export interface ApplyAuraRequest {
  readonly definition: AuraDefinition;
  readonly sourceId: CombatEntityId;
  readonly targetId: CombatEntityId;
  readonly now: number;
  readonly stacks?: number;
}

export interface AuraApplicationResult {
  readonly auras: readonly ActiveAura[];
  readonly aura: ActiveAura;
  readonly replaced?: ActiveAura;
}

export interface ExpireAurasResult {
  readonly active: readonly ActiveAura[];
  readonly expired: readonly ActiveAura[];
}

export interface DispelRequest {
  /** Friendly dispels remove debuffs; hostile dispels purge buffs. */
  readonly relationship: "friendly" | "hostile";
  readonly categories: readonly DispelCategory[];
  readonly maxCount?: number;
}

export interface DispelResult {
  readonly auras: readonly ActiveAura[];
  readonly removed: readonly ActiveAura[];
}

export interface AbsorbDamageRequest {
  readonly targetId: CombatEntityId;
  readonly amount: number;
  readonly school: DamageSchool;
  readonly now: number;
  readonly countsAsAttack?: boolean;
}

export interface AbsorbConsumption {
  readonly auraInstanceId: string;
  readonly absorbId: string;
  readonly amount: number;
}

export interface AbsorbDamageResult {
  readonly auras: readonly ActiveAura[];
  readonly absorbed: number;
  readonly remainingDamage: number;
  readonly consumptions: readonly AbsorbConsumption[];
}

export interface ProcEvent {
  readonly trigger: ProcTrigger;
  /** Entity whose auras should react to this event. */
  readonly subjectId: CombatEntityId;
  readonly otherId?: CombatEntityId;
  readonly abilityId?: string;
  readonly amount?: number;
  readonly school?: DamageSchool;
  readonly attackKind?: AttackKind;
}

export interface ProcRollContext {
  readonly aura: ActiveAura;
  readonly proc: AuraProcDefinition;
  readonly event: ProcEvent;
}

export type ProcRoll = (context: ProcRollContext) => number;

export interface TriggeredAuraProc {
  readonly auraInstanceId: string;
  readonly auraId: string;
  readonly procId: string;
  readonly sourceId: CombatEntityId;
  readonly targetId: CombatEntityId;
  readonly event: ProcEvent;
  readonly action: AuraProcAction;
}

export interface EvaluateAuraProcsResult {
  readonly auras: readonly ActiveAura[];
  readonly triggered: readonly TriggeredAuraProc[];
}

const nonNegative = (value: number): number => Math.max(0, Number.isFinite(value) ? value : 0);

function boundedPositiveInteger(value: number | undefined, fallback: number): number {
  if (value === undefined || !Number.isFinite(value)) return fallback;
  return Math.max(1, Math.floor(value));
}

function auraIdentity(
  definition: AuraDefinition,
  sourceId: CombatEntityId,
  targetId: CombatEntityId,
): string {
  return definition.uniqueBySource === false
    ? `${targetId}:${definition.id}`
    : `${targetId}:${definition.id}:${sourceId}`;
}

function expiresAt(definition: AuraDefinition, now: number): number | null {
  return definition.durationMs === null ? null : now + nonNegative(definition.durationMs);
}

function newAbsorbStates(definition: AuraDefinition, stacks: number): readonly AuraAbsorbState[] {
  return (definition.absorbs ?? []).map((absorb) => ({
    id: absorb.id,
    school: absorb.school,
    schools: absorb.schools,
    fraction: absorb.fraction,
    remaining: nonNegative(absorb.amount) * (absorb.perStack === false ? 1 : stacks),
    ...(absorb.hitCharges === undefined
      ? {}
      : { remainingHits: Math.max(0, Math.floor(nonNegative(absorb.hitCharges))) }),
  }));
}

function newProcStates(definition: AuraDefinition): readonly AuraProcState[] {
  return (definition.procs ?? []).map((proc) => ({
    procId: proc.id,
    readyAt: 0,
    remainingCharges:
      proc.charges === undefined ? null : Math.max(0, Math.floor(nonNegative(proc.charges))),
  }));
}

function makeAura(request: ApplyAuraRequest, stacks: number): ActiveAura {
  const { definition, sourceId, targetId, now } = request;
  return {
    instanceId: auraIdentity(definition, sourceId, targetId),
    definition,
    sourceId,
    targetId,
    appliedAt: now,
    expiresAt: expiresAt(definition, now),
    stacks,
    absorbs: newAbsorbStates(definition, stacks),
    procStates: newProcStates(definition),
    ...(definition.redirectDamageCapPercent === undefined ? {} : { redirectedDamage: 0 }),
  };
}

/** Apply, refresh, replace, or add stacks without mutating existing store state. */
export function applyAura(
  current: readonly ActiveAura[],
  request: ApplyAuraRequest,
): AuraApplicationResult {
  const { definition } = request;
  const maxStacks = boundedPositiveInteger(definition.maxStacks, 1);
  const requestedStacks = Math.min(maxStacks, boundedPositiveInteger(request.stacks ?? definition.initialStacks, 1));
  const instanceId = auraIdentity(definition, request.sourceId, request.targetId);
  // Mage armors have several DBC effects that coexist until another armor
  // replaces them. Other exclusive groups retain their single-aura behavior.
  const exclusiveSpellName = definition.name.replace(/, Aura \d+\)$/, ")");
  const exclusive = definition.exclusiveGroup
    ? current.filter((aura) => (
        aura.targetId === request.targetId
        && aura.definition.exclusiveGroup === definition.exclusiveGroup
        && aura.instanceId !== instanceId
        && (definition.exclusiveGroup !== "mage:armor"
          || aura.definition.name.replace(/, Aura \d+\)$/, ")") !== exclusiveSpellName)
      ))
    : [];
  const exclusiveIds = new Set(exclusive.map((aura) => aura.instanceId));
  const base = exclusiveIds.size > 0
    ? current.filter((aura) => !exclusiveIds.has(aura.instanceId))
    : current;
  const existingIndex = base.findIndex((aura) => aura.instanceId === instanceId);

  if (existingIndex < 0) {
    const aura = makeAura(request, requestedStacks);
    return { auras: [...base, aura], aura, ...(exclusive[0] ? { replaced: exclusive[0] } : {}) };
  }

  const existing = base[existingIndex];
  const behavior = definition.stackBehavior ?? "refresh";
  const stacks = behavior === "add"
    ? Math.min(maxStacks, existing.stacks + requestedStacks)
    : behavior === "replace"
      ? requestedStacks
      : existing.stacks;

  const replacement = makeAura(request, stacks);
  const aura = behavior === "refresh"
    ? {
        ...replacement,
        stacks,
        // Refreshing duration does not reset an already-used proc charge or ICD.
        procStates: existing.procStates,
      }
    : replacement;
  const auras = [...base];
  auras[existingIndex] = aura;
  return { auras, aura, replaced: existing };
}

/** Remove timed auras whose expiry is at or before `now`. */
export function expireAuras(current: readonly ActiveAura[], now: number): ExpireAurasResult {
  const active: ActiveAura[] = [];
  const expired: ActiveAura[] = [];
  for (const aura of current) {
    (aura.expiresAt !== null && aura.expiresAt <= now ? expired : active).push(aura);
  }
  return { active, expired };
}

/**
 * Friendly dispels remove matching debuffs; hostile dispels remove matching
 * buffs. Higher dispelPriority is selected first, then the oldest application.
 */
export function dispelAuras(current: readonly ActiveAura[], request: DispelRequest): DispelResult {
  const wantedDisposition: AuraDisposition = request.relationship === "friendly" ? "debuff" : "buff";
  const categories = new Set(request.categories);
  const maxCount = Math.max(0, Math.floor(request.maxCount ?? 1));
  const candidates = current
    .filter((aura) =>
      aura.definition.disposition === wantedDisposition &&
      aura.definition.dispelCategory !== undefined &&
      categories.has(aura.definition.dispelCategory))
    .sort((left, right) =>
      (right.definition.dispelPriority ?? 0) - (left.definition.dispelPriority ?? 0) ||
      left.appliedAt - right.appliedAt ||
      left.instanceId.localeCompare(right.instanceId))
    .slice(0, maxCount);
  const removedIds = new Set(candidates.map((aura) => aura.instanceId));
  return {
    auras: current.filter((aura) => !removedIds.has(aura.instanceId)),
    removed: candidates,
  };
}

function modifierStackMultiplier(modifier: AuraModifier, aura: ActiveAura): number {
  return modifier.perStack === false ? 1 : aura.stacks;
}

function resolveModifiedValue(
  base: number,
  current: readonly ActiveAura[],
  matches: (modifier: AuraModifier) => boolean,
): number {
  let flat = 0;
  let percent = 0;
  for (const aura of current) {
    for (const modifier of aura.definition.modifiers ?? []) {
      if (!matches(modifier)) continue;
      const value = modifier.value * modifierStackMultiplier(modifier, aura);
      if (modifier.operation === "flat") flat += value;
      else percent += value;
    }
  }
  return Math.max(0, (base + flat) * (1 + percent));
}

export function resolveStatValue(
  base: number,
  current: readonly ActiveAura[],
  stat: string,
): number {
  return resolveModifiedValue(base, current, (modifier) =>
    modifier.kind === "stat" && modifier.stat === stat);
}

export function resolveResourceValue(
  base: number,
  current: readonly ActiveAura[],
  resource: string,
  property: Extract<AuraModifier, { kind: "resource" }>["property"],
): number {
  return resolveModifiedValue(base, current, (modifier) =>
    modifier.kind === "resource" &&
    modifier.resource === resource &&
    modifier.property === property);
}

export interface DamageModifierContext {
  readonly direction: "dealt" | "taken";
  readonly school: DamageSchool;
  readonly attackKind: AttackKind;
}

export function resolveDamageValue(
  base: number,
  current: readonly ActiveAura[],
  context: DamageModifierContext,
): number {
  return resolveModifiedValue(base, current, (modifier) =>
    modifier.kind === "damage" &&
    modifier.direction === context.direction &&
    (modifier.school === undefined || modifier.school === context.school) &&
    (modifier.attackKind === undefined || modifier.attackKind === context.attackKind));
}

export function resolveHealingValue(
  base: number,
  current: readonly ActiveAura[],
  direction: "done" | "taken",
): number {
  return resolveModifiedValue(base, current, (modifier) =>
    modifier.kind === "healing" && modifier.direction === direction);
}

/** Consume matching absorbs in expiry/application order and return updated auras. */
export function absorbDamage(
  current: readonly ActiveAura[],
  request: AbsorbDamageRequest,
): AbsorbDamageResult {
  let remainingDamage = nonNegative(request.amount);
  const consumptions: AbsorbConsumption[] = [];
  const order = current
    .filter((aura) =>
      aura.targetId === request.targetId &&
      (aura.expiresAt === null || aura.expiresAt > request.now))
    .sort((left, right) =>
      (left.expiresAt ?? Number.POSITIVE_INFINITY) - (right.expiresAt ?? Number.POSITIVE_INFINITY) ||
      left.appliedAt - right.appliedAt)
    .map((aura) => aura.instanceId);
  const next = [...current];

  for (const auraId of order) {
    if (remainingDamage <= 0) break;
    const index = next.findIndex((aura) => aura.instanceId === auraId);
    if (index < 0) continue;
    const aura = next[index];
    const absorbs = aura.absorbs.map((absorb) => {
      if (remainingDamage <= 0
        || (absorb.school !== undefined && absorb.school !== request.school)
        || (absorb.schools !== undefined && !absorb.schools.includes(request.school))) {
        return absorb;
      }
      const packetFraction = Math.max(0, Math.min(1, absorb.fraction ?? 1));
      const isChargedAttackAbsorb = absorb.remainingHits !== undefined
        && request.countsAsAttack === true
        && absorb.remainingHits > 0;
      if (absorb.remainingHits !== undefined && !isChargedAttackAbsorb) return absorb;
      const amount = isChargedAttackAbsorb
        ? remainingDamage * packetFraction
        : Math.min(absorb.remaining, remainingDamage * packetFraction);
      remainingDamage -= amount;
      if (amount > 0) {
        consumptions.push({ auraInstanceId: aura.instanceId, absorbId: absorb.id, amount });
      }
      return {
        ...absorb,
        remaining: absorb.remaining - amount,
        ...(isChargedAttackAbsorb ? { remainingHits: absorb.remainingHits! - 1 } : {}),
      };
    });
    next[index] = { ...aura, absorbs };
  }
  return {
    auras: next,
    absorbed: nonNegative(request.amount) - remainingDamage,
    remainingDamage,
    consumptions,
  };
}

function procHasTrigger(proc: AuraProcDefinition, trigger: ProcTrigger): boolean {
  return (Array.isArray(proc.triggers) ? proc.triggers : [proc.triggers]).includes(trigger);
}

/** Evaluate and update all eligible proc states for one combat event. */
export function evaluateAuraProcs(
  current: readonly ActiveAura[],
  event: ProcEvent,
  now: number,
  roll: ProcRoll = () => Math.random(),
): EvaluateAuraProcsResult {
  const triggered: TriggeredAuraProc[] = [];
  const auras = current.map((aura) => {
    if (
      aura.targetId !== event.subjectId ||
      (aura.expiresAt !== null && aura.expiresAt <= now) ||
      !aura.definition.procs?.length
    ) {
      return aura;
    }

    let changed = false;
    const procStates = aura.procStates.map((state) => {
      const proc = aura.definition.procs?.find((candidate) => candidate.id === state.procId);
      if (
        proc === undefined ||
        !procHasTrigger(proc, event.trigger) ||
        (proc.attackKinds !== undefined
          && (event.attackKind === undefined || !proc.attackKinds.includes(event.attackKind))) ||
        state.readyAt > now ||
        state.remainingCharges === 0
      ) {
        return state;
      }

      const chance = Math.min(1, Math.max(0, proc.chance));
      const rolled = roll({ aura, proc, event });
      if (!Number.isFinite(rolled) || rolled < 0 || rolled >= chance) return state;

      changed = true;
      const nextCharges = state.remainingCharges === null
        ? null
        : Math.max(0, state.remainingCharges - 1);
      triggered.push({
        auraInstanceId: aura.instanceId,
        auraId: aura.definition.id,
        procId: proc.id,
        sourceId: aura.sourceId,
        targetId: aura.targetId,
        event,
        action: proc.action,
      });
      return {
        procId: state.procId,
        readyAt: now + nonNegative(proc.internalCooldownMs ?? 0),
        remainingCharges: nextCharges,
      };
    });
    return changed ? { ...aura, procStates } : aura;
  });
  return { auras, triggered };
}