file_insert_content.lua

-- MCP Tool: file_insert_content
-- Insert content at specific line number(s) in a file
-- Supports batch insertions with automatic offset calculation
-- Entry kind: function.lua

local json = require("json")
local projects = require("projects")

--- Split content into lines preserving structure
local function split_lines(content)
    local lines = {}
    local pos = 1
    while pos <= #content do
        local nl = string.find(content, "\n", pos, true)
        if nl then
            table.insert(lines, string.sub(content, pos, nl - 1))
            pos = nl + 1
        else
            table.insert(lines, string.sub(content, pos))
            pos = #content + 1
        end
    end
    return lines
end

--- Split insertion content into lines
local function split_insert_content(content)
    local lines = split_lines(content)
    -- If content ends with \n, remove trailing empty
    if #content > 0 and string.sub(content, -1) == "\n" and #lines > 0 and lines[#lines] == "" then
        table.remove(lines)
    end
    return lines
end

local function call(arguments)
    local vol, err = projects.resolve(arguments.project)
    if err then
        return "Error: " .. err
    end

    local path = arguments.path
    if not path or path == "" then
        return "Error: path is required"
    end

    local insertions = arguments.insertions
    if not insertions or #insertions == 0 then
        return "Error: insertions is required — must provide at least one insertion"
    end

    -- Read current content
    local content, read_err = vol:readfile(path)
    if read_err then
        return "Error reading file: " .. tostring(read_err)
    end

    local lines = split_lines(content)
    local has_trailing_newline = #content > 0 and string.sub(content, -1) == "\n"
    local position = arguments.position or "after"

    -- Validate insertions
    for i, ins in ipairs(insertions) do
        if not ins.line then
            return string.format("Error: insertion #%d missing 'line' field", i)
        end
        if not ins.content then
            return string.format("Error: insertion #%d missing 'content' field", i)
        end
    end

    -- Sort insertions by line number descending
    -- This ensures earlier insertions don't shift line numbers for later ones
    local sorted = {}
    for i, ins in ipairs(insertions) do
        table.insert(sorted, {index = i, line = ins.line, content = ins.content})
    end
    table.sort(sorted, function(a, b) return a.line > b.line end)

    local total_inserted = 0

    for _, ins in ipairs(sorted) do
        local line_num = ins.line
        local new_lines = split_insert_content(ins.content)

        local insert_at
        if line_num == -1 then
            -- End of file
            insert_at = #lines + 1
        elseif position == "before" then
            insert_at = math.max(1, line_num)
        else -- "after"
            insert_at = math.min(#lines + 1, line_num + 1)
        end

        -- Insert lines in reverse order at the same position
        for j = #new_lines, 1, -1 do
            table.insert(lines, insert_at, new_lines[j])
        end
        total_inserted = total_inserted + #new_lines
    end

    -- Reassemble content
    local new_content = table.concat(lines, "\n")
    if has_trailing_newline then
        new_content = new_content .. "\n"
    end

    local _, write_err = vol:writefile(path, new_content)
    if write_err then
        return "Error writing file: " .. tostring(write_err)
    end

    return string.format(
        "Successfully inserted %d line%s at %d location%s in '%s'",
        total_inserted, total_inserted == 1 and "" or "s",
        #insertions, #insertions == 1 and "" or "s",
        path
    )
end

return { call = call }