import { and, desc, eq, max } from "drizzle-orm";
import type { ProjectRevisionSource } from "../../domain/ports/project-revision.store.js";
import type { AppDatabase } from "../database-context.js";
import { projectHistoryStackEntries } from "../schema/project-history-stack-entries.js";

export interface ApplyProjectHistoryTransitionInput {
  projectId: string;
  source: ProjectRevisionSource;
  recordedChangeSetId: string;
  targetChangeSetId?: string;
}

export function applyProjectHistoryTransition(
  database: AppDatabase,
  input: ApplyProjectHistoryTransitionInput
) {
  if (input.source === "user" || input.source === "restore") {
    database
      .delete(projectHistoryStackEntries)
      .where(
        and(
          eq(projectHistoryStackEntries.projectId, input.projectId),
          eq(projectHistoryStackEntries.stack, "redo")
        )
      )
      .run();
    push(
      database,
      input.projectId,
      input.recordedChangeSetId,
      "undo"
    );
    return;
  }

  if (input.source === "undo" || input.source === "redo") {
    if (!input.targetChangeSetId) {
      throw new Error(
        `${input.source} requires a target change set.`
      );
    }
    const sourceStack = input.source;
    const targetStack = input.source === "undo" ? "redo" : "undo";
    const top = database
      .select({
        changeSetId: projectHistoryStackEntries.changeSetId,
      })
      .from(projectHistoryStackEntries)
      .where(
        and(
          eq(projectHistoryStackEntries.projectId, input.projectId),
          eq(projectHistoryStackEntries.stack, sourceStack)
        )
      )
      .orderBy(desc(projectHistoryStackEntries.position))
      .limit(1)
      .get();
    if (!top || top.changeSetId !== input.targetChangeSetId) {
      throw new Error(
        `${input.source} target is not the top ${sourceStack} command.`
      );
    }

    const nextPosition = getNextPosition(
      database,
      input.projectId,
      targetStack
    );
    const moved = database
      .update(projectHistoryStackEntries)
      .set({ stack: targetStack, position: nextPosition })
      .where(
        and(
          eq(projectHistoryStackEntries.projectId, input.projectId),
          eq(
            projectHistoryStackEntries.changeSetId,
            input.targetChangeSetId
          )
        )
      )
      .run();
    if (moved.changes !== 1) {
      throw new Error("Project history stack changed during transition.");
    }
  }
}

function push(
  database: AppDatabase,
  projectId: string,
  changeSetId: string,
  stack: "undo" | "redo"
) {
  database
    .insert(projectHistoryStackEntries)
    .values({
      projectId,
      changeSetId,
      stack,
      position: getNextPosition(database, projectId, stack),
    })
    .run();
}

function getNextPosition(
  database: AppDatabase,
  projectId: string,
  stack: "undo" | "redo"
) {
  const current = database
    .select({ position: max(projectHistoryStackEntries.position) })
    .from(projectHistoryStackEntries)
    .where(
      and(
        eq(projectHistoryStackEntries.projectId, projectId),
        eq(projectHistoryStackEntries.stack, stack)
      )
    )
    .get();
  return (current?.position ?? 0) + 1;
}