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I
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export function diff(a: string, b: string, { colors = false, context = 3 } = {}): string {
const hunks = [] as string[]
const { lines } = patience(tokenize(a), tokenize(b))
for (let after = -1; (after < lines.length) && (!Number.isNaN(after));) {
const { next, patch } = _diff(lines, { after, colors, context })
hunks.push(patch)
after = next
}
const patch = hunks.join("").replace(/\n?\n$/, "")
return patch ? `--- a\n+++ b\n${patch}` : ""
}
function _diff(lines: line[], { after = -1, colors = false, context = 0 }: { after?: number; context?: number; colors?: boolean }): { next: number; patch: string } {
const k = lines.findIndex(({ a, b, token }, i) => ((a < 0) || (b < 0)) && (!token) && (i > after))
if (k < 0) {
return { next: NaN, patch: "" }
}
const patch = [lines[k]]
for (const delta of [-1, 1]) {
let contextual = context
for (let i = k; (i >= 0) && (i < lines.length); i += delta) {
if (i === k) {
continue
}
if ((delta < 0) && (lines[i].token === "!\n")) {
break
}
if ((lines[i].a < 0) || (lines[i].b < 0) || ((contextual > 0) && (lines[i].a >= 0) && (lines[i].b >= 0))) {
switch (true) {
case delta < 0:
patch.unshift(lines[i])
break
case delta > 0:
patch.push(lines[i])
break
}
}
if ((lines[i].a < 0) || (lines[i].b < 0)) {
contextual = context
}
if ((lines[i].a >= 0) && (lines[i].b >= 0)) {
contextual--
if ((delta > 0) && (!lines.slice(i + 1, i + 1 + context + 1).every(({ a, b }) => (a >= 0) && (b >= 0)))) {
contextual = context
}
if (contextual <= 0) {
break
}
}
}
}
let a = (patch.find(({ a, token }) => (a >= 0) && (!token))?.a ?? -1) + 1
let b = (patch.find(({ b, token }) => (b >= 0) && (!token))?.b ?? -1) + 1
const A = patch.filter(({ a, token }) => (a >= 0) && (!token)).length
const B = patch.filter(({ b, token }) => (b >= 0) && (!token)).length
if (context <= 1) {
switch (true) {
case A > 0:
b = a - 1
break
case B > 0:
a = b
break
}
}
return {
next: lines.indexOf(patch.findLast(({ a, b, token }) => ((a < 0) || (b < 0)) && (!token))!),
patch: [
{ line: `@@ -${a}${(A !== 1) || (a === 0) ? `,${A}` : ""} +${b}${(B !== 1) || (b === 0) ? `,${B}` : ""} @@\n`, a: NaN, b: NaN },
...patch,
].map(({ line, a, b, token }) => {
switch (true) {
case token === "!\n":
return "\\ No newline at end of file\n"
case a < 0:
return colors ? `\x1b[32m+${line}\x1b[0m` : `+${line}`
case b < 0:
return colors ? `\x1b[31m-${line}\x1b[0m` : `-${line}`
case Number.isNaN(a) && Number.isNaN(b):
return colors ? `\x1b[36m${line}\x1b[0m` : line
default:
return line === "\n" ? line : ` ${line}`
}
}).join(""),
}
}
export function tokenize(text: string): string[] {
text += "\n"
return [...text.matchAll(/.*(?:\r?\n)/g)].map(([token]) => token.replace(/\r\n$/, "\n")).filter((token) => token)
}
function unique({ lines }: operand, i: number, j: number) {
const occurrences = new Map<string, { index: number; count: number }>()
for (; i <= j; i++) {
const line = lines[i]
if (occurrences.has(line)) {
const entry = occurrences.get(line)!
entry.count++
entry.index = i
continue
}
occurrences.set(line, { index: i, count: 1 })
}
return new Map<string, number>([...occurrences].filter(([_, { count }]) => count === 1).map(([key, { index }]) => [key, index]))
}
function common(A: operand, B: operand, Ai: number, Aj: number, Bi: number, Bj: number) {
const a = unique(A, Ai, Aj)
const b = unique(B, Bi, Bj)
return new Map<string, position>([...a].filter(([line]) => b.has(line)).map(([line, index]) => [line, { a: index, b: b.get(line)! }]))
}
function lcs(ab: ReturnType<typeof common>) {
const lcs = [] as Array<position & { previous?: position }>
const subsequences = [] as Array<typeof lcs>
for (const [_, v] of ab) {
let i = 0
while (subsequences.at(i)?.at(-1)?.b! < v.b) {
i++
}
subsequences[i] ??= []
subsequences[i].push({ ...v, previous: (i > 0 ? subsequences.at(i - 1)?.at(-1) : undefined) })
}
if (subsequences.length) {
lcs.push(subsequences.at(-1)!.at(-1)!)
while (lcs.at(-1)!.previous) {
lcs.push(lcs.at(-1)!.previous!)
}
}
return lcs.reverse()
}
function register(result: result, A: operand, B: operand, a: number, b: number) {
const line = { line: 0 <= a ? A.lines[a] : B.lines[b], a, b } as line
switch (true) {
case b < 0:
result.deleted++
break
case a < 0:
result.added++
break
}
result.lines.push(line)
}
function submatch(result: result, A: operand, B: operand, Ai: number, Aj: number, Bi: number, Bj: number) {
while ((Ai <= Aj) && (Bi <= Bj) && (A.lines[Ai] === B.lines[Bi])) {
register(result, A, B, Ai++, Bi++)
}
const Tj = Aj
while ((Ai <= Aj) && (Bi <= Bj) && (A.lines[Aj] === B.lines[Bj])) {
Aj--
Bj--
}
const ab = common(A, B, Ai, Aj, Bi, Bj)
if (ab.size) {
recurse(result, A, B, Ai, Aj, Bi, Bj, ab)
} else {
while (Ai <= Aj) {
register(result, A, B, Ai++, -1)
}
while (Bi <= Bj) {
register(result, A, B, -1, Bi++)
}
}
while (Aj < Tj) {
register(result, A, B, ++Aj, ++Bj)
}
}
function recurse(result: result, A: operand, B: operand, Ai: number, Aj: number, Bi: number, Bj: number, ab?: ReturnType<typeof common>) {
const x = lcs(ab ?? common(A, B, Ai, Aj, Bi, Bj))
if (!x.length) {
submatch(result, A, B, Ai, Aj, Bi, Bj)
return
}
if ((Ai < x[0].a) || (Bi < x[0].b)) {
submatch(result, A, B, Ai, x[0].a - 1, Bi, x[0].b - 1)
}
let i = 0
for (; i < x.length - 1; i++) {
submatch(result, A, B, x[i].a, x[i + 1].a - 1, x[i].b, x[i + 1].b - 1)
}
if (+(x[i].a <= Aj) | +(x[i].b <= Bj)) {
submatch(result, A, B, x[i].a, Aj, x[i].b, Bj)
}
}
function postprocess(result: result) {
const la = result.lines.findLast(({ a }) => a >= 0)!
const lb = result.lines.findLast(({ b }) => b >= 0)!
if ((la.line !== "\n") && (lb.line !== "\n")) {
if (la !== lb) {
result.lines.splice(result.lines.indexOf(la) + 1, 0, { line: "", a: la.a + 1, b: -1, token: "!\n" })
result.lines.splice(result.lines.indexOf(lb) + 1, 0, { line: "", a: -1, b: lb.b + 1, token: "!\n" })
}
else if (la === lb) {
result.lines.splice(result.lines.indexOf(la) + 1, 0, { line: "", a: la.a + 1, b: lb.b + 1, token: "!\n" })
}
} else {
if ((lb.line === "\n") && (lb.b >= 0) && (lb.a < 0)) {
result.lines.splice(result.lines.indexOf(la), 1, { ...la, b: -1 }, { line: "", a: la.a + 1, b: -1, token: "!\n" }, ...((la.a >= 0) && (la.b >= 0) ? [{ ...la, b: la.a, a: -1 }] : []))
result.lines.splice(result.lines.indexOf(lb), 1)
}
if ((la.line === "\n") && (la.a >= 0) && (la.b < 0)) {
result.lines.splice(result.lines.indexOf(lb), 1, ...((lb.a >= 0) && (lb.b >= 0) ? [{ ...lb, a: lb.b, b: -1 }] : []), { ...lb, a: -1 }, { line: "", a: -1, b: lb.b + 1, token: "!\n" })
result.lines.splice(result.lines.indexOf(la), 1)
}
if ((la === lb) && (la.line === "\n")) {
la.token = "\n"
}
}
}
function patience(a: string[], b: string[]) {
const A = { lines: a } as operand
const B = { lines: b } as operand
const result = { lines: [], added: 0, deleted: 0 } as result
recurse(result, A, B, 0, A.lines.length - 1, 0, B.lines.length - 1)
postprocess(result)
return result
}
type result = {
lines: line[]
added: number
deleted: number
}
type line = { line: string; token?: string } & position
type position = { a: number; b: number }
type operand = { lines: string[] }
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