local string_sub = string.sub
local string_len = string.len

-- ammo damage modifiers are static values that increase with research
-- modifier is multiplied by base damage and then added to damage, so a negative value will reduce base damage and a positive value will increase damage
local balance_functions = {
    ['land-mine'] = function(force_name)
        -- landmines normally have a modifier of 0, so have them start at 25% of normal
        if force_name ~= nil then
            game.forces[force_name].set_ammo_damage_modifier('landmine', -0.75)
        end
    end,
    ['military-2'] = function(force_name)
        -- grenades normally have a modifier of 0, so have them start at 50% of normal
        if force_name ~= nil then
            game.forces[force_name].set_ammo_damage_modifier('grenade', -0.5)
        end
    end,
    ['military-4'] = function(force_name)
        -- cluster-grenades normally have a modifier of 0, so have them start at 50% of normal
        if force_name ~= nil then
            game.forces[force_name].set_ammo_damage_modifier('grenade', -0.5)
        end
    end,
    ['stronger-explosives'] = function(force_name)
        -- landmines should never increase in damage with stronger explosives
        if force_name ~= nil then
            game.forces[force_name].set_ammo_damage_modifier('landmine', -0.75)
            -- allow grenades to increase by 10%
            game.forces[force_name].set_ammo_damage_modifier('grenade', game.forces[force_name].get_ammo_damage_modifier('grenade') + 0.1)
        end
    end
}

local function on_research_finished(event)
    local research_name = event.research.name
    local force_name = event.research.force.name
    for b = 1, string_len(research_name), 1 do
        local key = string_sub(research_name, 0, b)
        if balance_functions[key] then
            balance_functions[key](force_name)
            return
        end
    end
end

local Event = require 'utils.event'
Event.add(defines.events.on_research_finished, on_research_finished)