nvim/lua/git/diff.lua

local Revision = require("git.revision")
local repo = require("git.repo")
local util = require("git.util")

local M = {}

---@class ow.Git.Diff.Side
---@field buf integer
---@field name string?

---@class ow.Git.Diff.Pair
---@field left ow.Git.Diff.Side
---@field right ow.Git.Diff.Side

---@param win integer
---@param enabled boolean
function M.set_diff(win, enabled)
    vim.api.nvim_win_call(win, function()
        vim.cmd(enabled and "diffthis" or "diffoff")
    end)
end

---@param left integer
---@param right integer
---@param vertical boolean
function M.open(left, right, vertical)
    local left_name = vim.api.nvim_buf_get_name(left)
    vim.cmd.normal({ "m'", bang = true })
    vim.api.nvim_set_current_buf(right)
    vim.cmd.diffsplit({
        args = { left_name },
        mods = { split = "aboveleft", vertical = vertical, keepjumps = true },
        magic = { file = false },
    })
end

---@param left_win integer
---@param right_win integer
---@param pair ow.Git.Diff.Pair
function M.update_pair(left_win, right_win, pair)
    M.set_diff(left_win, false)
    M.set_diff(right_win, false)
    vim.api.nvim_win_set_buf(left_win, pair.left.buf)
    vim.api.nvim_win_set_buf(right_win, pair.right.buf)
    for _, side in ipairs({ pair.left, pair.right }) do
        if side.name then
            util.set_buf_name(side.buf, side.name)
        end
    end
    M.set_diff(left_win, true)
    M.set_diff(right_win, true)
    vim.api.nvim_win_set_cursor(left_win, { 1, 0 })
    vim.api.nvim_win_set_cursor(right_win, { 1, 0 })
    vim.cmd.syncbind()
end

---@param buf_a integer
---@param buf_b integer
---@param a_left boolean
---@param vertical boolean
local function place_pair(buf_a, buf_b, a_left, vertical)
    if a_left then
        M.open(buf_a, buf_b, vertical)
    else
        M.open(buf_b, buf_a, vertical)
    end
end

---@param opts ow.Git.Diff.SplitOpts
---@param buf integer
---@param rev ow.Git.Revision
local function uri_split(opts, buf, rev)
    local r = repo.resolve(buf)
    if not r then
        util.error("git URI buffer has no worktree")
        return
    end
    if not rev.path then
        util.error("git URI has no path, cannot diff against worktree")
        return
    end
    local object = require("git.object")

    if opts.rev and opts.rev:find(":", 1, true) then
        local content = util.exec(
            { "git", "cat-file", "-p", opts.rev },
            { cwd = r.worktree, silent = true }
        )
        if not content then
            util.error("invalid rev: %s", opts.rev)
            return
        end
        place_pair(
            buf,
            object.buf_for(r, Revision.parse(opts.rev), content),
            false,
            opts.vertical
        )
        return
    end

    if not opts.rev then
        local worktree_path = vim.fs.joinpath(r.worktree, rev.path)
        if not vim.uv.fs_stat(worktree_path) then
            util.error("worktree file does not exist: %s", rev.path)
            return
        end
        local worktree_buf = vim.fn.bufadd(worktree_path)
        vim.fn.bufload(worktree_buf)
        place_pair(buf, worktree_buf, true, opts.vertical)
        return
    end

    if rev.stage == 1 then
        util.error("gD on merge base is ambiguous, use :Gdiffsplit <rev>")
        return
    end

    local mapping = {
        [2] = { Revision.new({ stage = 3, path = rev.path }), true },
        [3] = { Revision.new({ stage = 2, path = rev.path }), false },
        [0] = { Revision.new({ base = "HEAD", path = rev.path }), false },
    }
    local m = mapping[rev.stage]
        or { Revision.new({ stage = 0, path = rev.path }), true }
    local other_rev, left = m[1], m[2]
    local content = util.exec(
        { "git", "cat-file", "-p", other_rev:format() },
        { cwd = r.worktree, silent = true }
    )
    if not content then
        util.error("invalid rev: %s", other_rev:format())
        return
    end
    place_pair(buf, object.buf_for(r, other_rev, content), left, opts.vertical)
end

---@class ow.Git.Diff.SplitOpts
---@field rev string?
---@field vertical boolean

---@param opts ow.Git.Diff.SplitOpts
function M.split(opts)
    local cur_buf = vim.api.nvim_get_current_buf()
    local cur_path = vim.api.nvim_buf_get_name(cur_buf)

    local cur_rev = require("git.object").parse_uri(cur_path)
    if cur_rev then
        return uri_split(opts, cur_buf, cur_rev)
    end

    if cur_path == "" then
        util.error("no file in current buffer")
        return
    end
    if vim.bo[cur_buf].buftype ~= "" then
        util.error("cannot diff this buffer (not a worktree file)")
        return
    end
    cur_path = vim.fn.resolve(cur_path)
    local r = repo.resolve(cur_path)
    if not r then
        util.error("not in a git repository")
        return
    end
    local rel = vim.fs.relpath(r.worktree, cur_path)

    local rev
    if not opts.rev then
        rev = Revision.new({ stage = 0, path = rel })
    elseif opts.rev:find(":", 1, true) then
        rev = Revision.parse(opts.rev)
    else
        rev = Revision.new({ base = opts.rev, path = rel })
    end
    local content = util.exec(
        { "git", "cat-file", "-p", rev:format() },
        { cwd = r.worktree, silent = true }
    )
    if not content then
        util.error("invalid rev: %s", rev:format())
        return
    end
    local buf = require("git.object").buf_for(r, rev, content)
    place_pair(buf, cur_buf, true, opts.vertical)
end

return M