diffview.nvim/lua/diffview/diff.lua at main · lexmiin/diffview.nvim · GitHub

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--[[

An implementation of Myers' diff algorithm

Derived from: https://github.com/Swatinem/diff

]]

local oop = require("diffview.oop")

local M = {}

---@enum EditToken

local EditToken = oop.enum({

NOOP = 1,

DELETE = 2,

INSERT = 3,

REPLACE = 4,

})

---@class Diff : diffview.Object

---@operator call : Diff

---@field a any[]

---@field b any[]

---@field moda boolean[]

---@field modb boolean[]

---@field up table<integer, integer>

---@field down table<integer, integer>

---@field eql_fn function

local Diff = oop.create_class("Diff")

---Diff constructor.

---@param a any[]

---@param b any[]

---@param eql_fn function|nil

function Diff:init(a, b, eql_fn)

self.a = a

self.b = b

self.moda = {}

self.modb = {}

self.up = {}

self.down = {}

self.eql_fn = eql_fn or function(aa, bb)

return aa == bb

end

for i = 1, #a do

self.moda[i] = false

end

for i = 1, #b do

self.modb[i] = false

end

self:lcs(1, #self.a + 1, 1, #self.b + 1)

end

---@return EditToken[]

function Diff:create_edit_script()

local astart = 1

local bstart = 1

local aend = #self.moda

local bend = #self.modb

local script = {}

while astart <= aend or bstart <= bend do

if astart <= aend and bstart <= bend then

if not self.moda[astart] and not self.modb[bstart] then

table.insert(script, EditToken.NOOP)

astart = astart + 1

bstart = bstart + 1

goto continue

elseif self.moda[astart] and self.modb[bstart] then

table.insert(script, EditToken.REPLACE)

astart = astart + 1

bstart = bstart + 1

goto continue

end

if astart <= aend and (bstart > bend or self.moda[astart]) then

table.insert(script, EditToken.DELETE)

astart = astart + 1

end

if bstart <= bend and (astart > aend or self.modb[bstart]) then

table.insert(script, EditToken.INSERT)

bstart = bstart + 1

end

::continue::

end

return script

end

---@private

---@param astart integer

---@param aend integer

---@param bstart integer

---@param bend integer

function Diff:lcs(astart, aend, bstart, bend)

-- separate common head

while astart < aend and bstart < bend and self.eql_fn(self.a[astart], self.b[bstart]) do

astart = astart + 1

bstart = bstart + 1

end

-- separate common tail

while astart < aend and bstart < bend and self.eql_fn(self.a[aend - 1], self.b[bend - 1]) do

aend = aend - 1

bend = bend - 1

end

if astart == aend then

-- only insertions

while bstart < bend do

self.modb[bstart] = true

bstart = bstart + 1

end

elseif bend == bstart then

-- only deletions

while astart < aend do

self.moda[astart] = true

astart = astart + 1

end

else

local snake = self:snake(astart, aend, bstart, bend)

self:lcs(astart, snake.x, bstart, snake.y)

self:lcs(snake.u, aend, snake.v, bend)

end

---@class Diff.Snake

---@field x integer

---@field y integer

---@field u integer

---@field v integer

---@private

---@param astart integer

---@param aend integer

---@param bstart integer

---@param bend integer

---@return Diff.Snake

function Diff:snake(astart, aend, bstart, bend)

local N = aend - astart

local MM = bend - bstart

local kdown = astart - bstart

local kup = aend - bend

local delta = N - MM

local deltaOdd = delta % 2 ~= 0

self.down[kdown + 1] = astart

self.up[kup - 1] = aend

local Dmax = (N + MM) / 2 + 1

for D = 0, Dmax do

local x, y

-- Forward path

for k = kdown - D, kdown + D, 2 do

if k == kdown - D then

x = self.down[k + 1] -- down

else

x = self.down[k - 1] + 1 -- right

if k < kdown + D and self.down[k + 1] >= x then

x = self.down[k + 1] -- down

end

y = x - k

while x < aend and y < bend and self.eql_fn(self.a[x], self.b[y]) do

x = x + 1

y = y + 1 -- diagonal

end

self.down[k] = x

if deltaOdd and kup - D < k and k < kup + D and self.up[k] <= self.down[k] then

return {

x = self.down[k],

y = self.down[k] - k,

u = self.up[k],

v = self.up[k] - k,

}

end

-- Reverse path

for k = kup - D, kup + D, 2 do

if k == kup + D then

x = self.up[k - 1] -- up

else

x = self.up[k + 1] - 1 -- left

if k > kup - D and self.up[k - 1] < x then

x = self.up[k - 1] -- up

end

y = x - k

while x > astart and y > bstart and self.eql_fn(self.a[x - 1], self.b[y - 1]) do

x = x - 1

y = y - 1 -- diagonal

end

self.up[k] = x

if not deltaOdd and kdown - D <= k and k <= kdown + D and self.up[k] <= self.down[k] then

return {

x = self.down[k],

y = self.down[k] - k,

u = self.up[k],

v = self.up[k] - k,

}

end

error("Unexpected state!")

end

M.EditToken = EditToken

M.Diff = Diff

return M

diffview.nvim/lua/diffview/diff.lua at main · lexmiin/diffview.nvim · GitHub

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