// Hunk diffs for the DSH diff card ({path, oldText, newText} per hunk, 3 lines of context).
// Each hunk also carries `oldStart`/`newStart` (1-based file lines of its first row) and `rows`
// ([op, text] with op '=', '-', '+') so a client can draw a line-number gutter.
import { lineMap } from './store.js'
import { splitLines } from './text.js'

export function hunkDiffs(path, before, after, context = 3) {
  const a = splitLines(before).lines
  const b = splitLines(after).lines
  const map = lineMap(a, b)
  // Walk both sides, emitting ops: '=' common, '-' removed, '+' added.
  const ops = [] // [op, text, oldLine|null, newLine|null]
  let i = 1; let j = 1
  const pairs = [...map.entries()].sort((x, y) => x[0] - y[0])
  for (const [ai, bj] of pairs) {
    while (i < ai) { ops.push(['-', a[i - 1], i, null]); i++ }
    while (j < bj) { ops.push(['+', b[j - 1], null, j]); j++ }
    ops.push(['=', a[i - 1], i, j]); i++; j++
  }
  while (i <= a.length) { ops.push(['-', a[i - 1], i, null]); i++ }
  while (j <= b.length) { ops.push(['+', b[j - 1], null, j]); j++ }
  const changed = ops.map((o, k) => (o[0] !== '=' ? k : -1)).filter((k) => k >= 0)
  if (!changed.length) return []
  const spans = []
  for (const k of changed) {
    const s = Math.max(0, k - context); const e = Math.min(ops.length - 1, k + context)
    const last = spans.at(-1)
    if (last && s <= last[1] + 1) last[1] = Math.max(last[1], e)
    else spans.push([s, e])
  }
  return spans.map(([s, e]) => {
    const oldL = []; const newL = []; const rows = []
    let oldStart = null; let newStart = null
    for (let k = s; k <= e; k++) {
      const [op, text, ol, nl] = ops[k]
      if (op !== '+') { oldL.push(text); oldStart ??= ol }
      if (op !== '-') { newL.push(text); newStart ??= nl }
      rows.push([op, text])
    }
    // A pure insertion/deletion side has no line of its own: anchor it next to its neighbour.
    oldStart ??= Math.max(1, (ops.slice(0, s).findLast((o) => o[2] !== null)?.[2] ?? 0) + 1)
    newStart ??= Math.max(1, (ops.slice(0, s).findLast((o) => o[3] !== null)?.[3] ?? 0) + 1)
    return { path, oldText: oldL.length ? oldL.join('\n') : null, newText: newL.join('\n'), oldStart, newStart, rows }
  })
}