nvim/lua/git/diff.lua

local log = require("log")
local repo = require("git.repo")

local M = {}

---@param buf integer
---@param worktree string
---@param path string
local function attach_index_writer(buf, worktree, path)
    vim.api.nvim_create_autocmd("BufWriteCmd", {
        buffer = buf,
        callback = function()
            local body = table.concat(
                vim.api.nvim_buf_get_lines(buf, 0, -1, false),
                "\n"
            ) .. "\n"
            local hash = vim.system(
                { "git", "hash-object", "-w", "--stdin" },
                { cwd = worktree, stdin = body, text = true }
            ):wait()
            if hash.code ~= 0 then
                log.error("git hash-object failed: %s", hash.stderr or "")
                return
            end
            local sha = vim.trim(hash.stdout or "")
            local mode = vim.b[buf].git_index_mode
            if not mode then
                mode = "100644"
                local ls = vim.system(
                    { "git", "ls-files", "-s", "--", path },
                    { cwd = worktree, text = true }
                ):wait()
                if ls.code == 0 and ls.stdout then
                    local m = ls.stdout:match("^(%d+)")
                    if m then
                        mode = m
                    end
                end
                vim.b[buf].git_index_mode = mode
            end
            local upd = vim.system({
                "git",
                "update-index",
                "--cacheinfo",
                mode .. "," .. sha .. "," .. path,
            }, { cwd = worktree, text = true }):wait()
            if upd.code ~= 0 then
                log.error("git update-index failed: %s", upd.stderr or "")
                return
            end
            vim.bo[buf].modified = false
        end,
    })
end

---@param worktree string
---@param revspec string  anything `git show` accepts (e.g. `HEAD:foo`, `:foo`, blob SHA)
---@return string[]
local function read_show(worktree, revspec)
    local result = vim.system(
        { "git", "show", revspec },
        { cwd = worktree, text = true }
    )
        :wait()
    local content = result.code == 0 and (result.stdout or "") or ""
    local lines = vim.split(content, "\n", { plain = true, trimempty = false })
    if #lines > 0 and lines[#lines] == "" then
        table.remove(lines)
    end
    return lines
end

---@param worktree string
---@param ref string '' for index, 'HEAD' or a sha for committed refs
---@param path string
---@param is_index boolean? true to hook :w to update the git index
---@return integer
function M.git_show_buf(worktree, ref, path, is_index)
    local lines = read_show(worktree, ref .. ":" .. path)
    local buf = vim.api.nvim_create_buf(false, true)
    vim.api.nvim_buf_set_lines(buf, 0, -1, false, lines)
    vim.bo[buf].buftype = is_index and "acwrite" or "nofile"
    vim.bo[buf].bufhidden = "wipe"
    vim.bo[buf].swapfile = false
    if is_index then
        attach_index_writer(buf, worktree, path)
    else
        vim.bo[buf].modifiable = false
    end
    vim.bo[buf].modified = false
    return buf
end

---@param worktree string
---@param blob string  the blob SHA (full or abbreviated)
---@return integer
function M.git_show_blob(worktree, blob)
    local lines = read_show(worktree, blob)
    local buf = vim.api.nvim_create_buf(false, true)
    vim.api.nvim_buf_set_lines(buf, 0, -1, false, lines)
    vim.bo[buf].buftype = "nofile"
    vim.bo[buf].bufhidden = "wipe"
    vim.bo[buf].swapfile = false
    vim.bo[buf].modifiable = false
    vim.bo[buf].modified = false
    return buf
end

---@return integer
function M.empty_buf()
    local buf = vim.api.nvim_create_buf(false, true)
    vim.bo[buf].buftype = "nofile"
    vim.bo[buf].bufhidden = "wipe"
    vim.bo[buf].swapfile = false
    vim.bo[buf].modifiable = false
    vim.bo[buf].modified = false
    return buf
end

---@param abs_path string
---@return integer
function M.load_file_buf(abs_path)
    local buf = vim.fn.bufadd(abs_path)
    vim.fn.bufload(buf)
    return buf
end

---@param buf integer
---@param name string
local function set_buf_name_and_filetype(buf, name)
    pcall(vim.api.nvim_buf_set_name, buf, name)
    local ft = vim.filetype.match({ buf = buf })
    if ft then
        vim.bo[buf].filetype = ft
    end
end

---@class ow.Git.SplitOpts
---@field ref string '' for index, 'HEAD' for HEAD
---@field vertical boolean

---@param opts ow.Git.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)
    if cur_path == "" then
        log.warning("no file in current buffer")
        return
    end
    local _, worktree = repo.resolve(cur_path)
    if not worktree then
        log.warning("not in a git repository")
        return
    end
    local rel = vim.fs.relpath(worktree, cur_path)
    if not rel then
        log.warning("file is outside the worktree")
        return
    end

    local is_index = opts.ref == ""
    local other = M.git_show_buf(worktree, opts.ref, rel, is_index)
    local label = is_index and "index" or opts.ref
    set_buf_name_and_filetype(other, "git://" .. label .. "/" .. rel)

    local split_cmd = opts.vertical and "leftabove vertical sbuffer "
        or "leftabove sbuffer "
    vim.cmd(split_cmd .. other)
    vim.cmd("diffthis")
    vim.cmd("wincmd p")
    vim.cmd("diffthis")
end

return M