import type { Hunk } from './types'

// Pure helpers turning -U0 hunks into per-line change marks for the head view.
// Pure additions → "added"; replaced ranges → "modified"; pure deletions → a
// marker on the line after which content was removed.

export type LineMark = 'added' | 'modified' | 'deleted'

export function lineMarks(hunks: Hunk[], lineCount: number): Map<number, LineMark> {
  const marks = new Map<number, LineMark>()
  for (const h of hunks) {
    if (h.newLines === 0) {
      // Deleted after line newStart (0 = top of file).
      marks.set(Math.min(Math.max(h.newStart, 1), lineCount), 'deleted')
      continue
    }
    const kind: LineMark = h.oldLines === 0 ? 'added' : 'modified'
    for (let l = h.newStart; l < h.newStart + h.newLines && l <= lineCount; l++) marks.set(l, kind)
  }
  return marks
}

/** 1-based first line of each hunk, for next/previous-change navigation. */
export function hunkAnchors(hunks: Hunk[]): number[] {
  return hunks.map((h) => Math.max(h.newStart, 1))
}

/** Where a base line is in the head view: in a hunk's removed lines, or the head line it became. */
export type BaseLinePlace = { removed: Hunk } | { headLine: number }

/**
 * Places a 1-based base line against -U0 hunks: the hunk whose removed lines
 * hold it, or, for a line the change kept, its head line number (0: above
 * line 1).
 */
export function baseLinePlace(hunks: Hunk[], line: number): BaseLinePlace {
  let delta = 0
  for (const h of [...hunks].sort((a, b) => a.oldStart - b.oldStart)) {
    if (h.oldLines > 0 && h.oldStart <= line && line < h.oldStart + h.oldLines) return { removed: h }
    // Before the line: removed lines ending above it, or lines added after an earlier base line.
    const before = h.oldLines > 0 ? h.oldStart + h.oldLines - 1 < line : h.oldStart < line
    if (before) delta += h.newLines - h.oldLines
  }
  return { headLine: Math.max(0, line + delta) }
}

/** Whether base lines overlap lines the change removed (or replaced). */
export const inRemoved = (hunks: Hunk[], lines: readonly [number, number]): boolean =>
  hunks.some((h) => h.oldLines > 0 && h.oldStart <= lines[1] && h.oldStart + h.oldLines - 1 >= lines[0])