import type { PromptBuffer } from "./buffer.js";
import { segmentPromptText } from "./segmentation.js";

export type ReadlineMode = "vi-insert" | "vi-command" | "vi-replace";

export type ReadlineState = {
  readonly mode: ReadlineMode;
  readonly buffer: PromptBuffer;
};

export function initialReadlineState(buffer: PromptBuffer): ReadlineState {
  return { mode: "vi-insert", buffer };
}

/** Match Readline's command-mode cursor placement after leaving insertion. */
export function enterViAppendMode(state: ReadlineState): ReadlineState {
  const line = state.buffer.lines[state.buffer.cursor.line];
  const current =
    line === undefined
      ? undefined
      : segmentPromptText(line, state.buffer.pasteMarkerIds).find(
          (segment) => segment.start === state.buffer.cursor.column,
        );
  return {
    mode: "vi-insert",
    buffer: {
      ...state.buffer,
      cursor: {
        line: state.buffer.cursor.line,
        column: current?.end ?? state.buffer.cursor.column,
      },
    },
  };
}

export function enterViCommandMode(state: ReadlineState): ReadlineState {
  const line = state.buffer.lines[state.buffer.cursor.line];
  if (line === undefined || state.buffer.cursor.column === 0) {
    return { ...state, mode: "vi-command" };
  }

  const priorSegment = segmentPromptText(line, state.buffer.pasteMarkerIds)
    .filter((segment) => segment.end <= state.buffer.cursor.column)
    .at(-1);
  return {
    mode: "vi-command",
    buffer: {
      ...state.buffer,
      cursor: {
        line: state.buffer.cursor.line,
        column: priorSegment?.start ?? 0,
      },
    },
  };
}